OCULUS Keratograph - Special Reprint [2981 KB]

Development and realization of a new 

non-invasive method for tear film assessment 

using a corneal topographer 

Validation of new non-invasive 

methods for tear film assessment 

using a Keratograph

Imprint 

Publisher: 

OCULUS Optikgeräte GmbH 

Postfach • 35549 Wetzlar • GERMANY 

Tel. ++49-641-2005-0 • Fax +49-641-2005-295 

E-Mail: export@oculus.de • www.oculus.de 

Print: 

Bernecker Mediagruppe, Melsungen 

Layout: 

Grips Design GmbH, Wetzlar



using a corneal topographer* 

B. Sc. Doreen Wiedemann [1],[2] 

A particularly suitable approach to tear film examination is found in methods that non-invasively analyze the optical 

radiation reflected by the tear film [2]. For this purpose a grid is projected onto the cornea and the precorneal tear 

film, respectively. The only non-invasive commercial device to date that is suitable for this, the Tearscope (Keeler), 

is currently neither available nor being produced. Alternative methods will therefore gain significance in future. The 

Keratograph is based on the same type of projection, qualifying it as as a non-contact, non-invasive method of inquiry. 

To date the Keratograph has primarily been used for measuring corneal topography. The purpose of the present 

study was to clarify to what extent it is also suited for tear film assessment and what modifications would be needed 

in order to make both qualitative and quantitative tear film measurements. The device chosen for this purpose was 

the Keratograph (Oculus), a modern, well-established model that is widely used in optometric and ophthalmic practices 

in Germany. After suitable modification the device was used in a clinical trial for determining tear meniscus 

height as well as non-invasive tear film break-up time. The newly developed method was also compared with selected 

well-established tests of high practical relevance. These tests involved use of the Tearscope 

(Keeler) for determining non-invasive tear film break-up time and a biomicroscope 

equipped with a measuring eyepiece for determining the height of the tear meniscus. 



using a Keratograph* 

B. Sc. Doreen Wiedemann [1],[2] ; Dipl.-Ing. (FH) Martina Michel [1],[2] ; 

Prof. Dipl.-Ing. (FH) Wolfgang Sickenberger, MS. Optom. (USA) [1],[2] ; 

Dipl.-Ing. (FH) Sebastian Marx [1],[2] 

The majority of established tear film examination methods to date are based on observation of induced tear film 

reflections. Examples are the determination of tear meniscus height, assessment of interference phenomena, and 

the observation of non-invasive tear film break-up time. One limitation common to all these methods is the 

subjective nature of the observations made [1]. The fact that tear film data thus obtained contain indeterminable 

distortions that limit comparability poses a serious obstacle to their interpretation. Standardisation may serve to 

solve some such problems, but not to exclude them. In 2007 the Report of the Diagnostic Methodology Subcom- 

mittee of the International Dry Eye Workshop (RDEWS) was published, containing recommendations for standardisation 

in established tear film examination methods and clinical studies on dry eye disorders with a view to im- 

proving comparability [2]. The members of the subcommittee are nonetheless agreed that it would be of great 

importance to develop objective analysis methods that might supplement recommended test combinations for 

examining the precorneal tear film. [3]. Such was the situation that motivated the 

development of an automated, examinerindependent technique for detection of 

non-invasive tear film break-up time. 

[1] Fachhochschule Jena; [2] JENVIS Research Institute 

* First publication in “Die Kontaktlinse”, issue 7 and 8/2010 

weiterlesen auf 

Seite 4 

weiterlesen auf 

Seite 16



using a corneal topographer 


radiation reflected by the tear film [2]. For this purpose a grid is projected onto the cornea and the precorneal tearfilm, 

respectively. The only non-invasive commercial device to date that is suitable for this, the Tearscope (Keeler), is 

currently neither available nor being produced. Alternative methods will therefore gain significance in future. The 

Keratograph is based on the same type of projection, qualifying it as as a non-contact, non-invasive method of inquiry. 

To date the Keratograph has primarily been used for measuring corneal topography. The purpose of the present study 

was to clarify to what extent it is also suited for tear film assessment and what modifications would be needed in 

order to make both qualitative and quantitative tear film measurements. The device chosen for this purpose was the 

Keratograph (Oculus), a modern, well-established model that is widely used in optometric and ophthalmic practices 

in Germany. After suitable modification the device was used in a clinical trial for determining tear meniscus height 

as well as non-invasive tear film break-up time. The newly developed method was also compared with selected 

well-established tests of high practical relevance. These tests involved use of the Tearscope (Keeler) for determining 

non-invasive tear film break-up time and a biomicroscope equipped with a measuring eyepiece for determining the 

height of the tear meniscus. 

1 Introduction 


radiation reflected by the tear film [2]. For this purpose a grid is projected onto the cornea and the precorneal tear film, 

respectively. The only non-invasive commercial device to date that is suitable for this, the Tearscope (Keeler), is currently 

neither available nor being produced. Alternative methods will therefore gain significance in future. The Keratograph is 

based on the same type of projection, qualifying it as as a non-contact, non-invasive method of inquiry. To date the 

Keratograph has primarily been used for measuring corneal topography. The purpose of the present study was to clarify 

to what extent it is also suited for tear film assessment and what modifications would be needed in order to make both 

qualitative and quantitative tear film measurements. The device chosen for this purpose was the Keratograph (Oculus), 

a modern, well-established model that is widely used in optometric and ophthalmic practices in Germany. After suitable 

modification the device was used in a clinical trial for determining tear meniscus height as well as non-invasive tear film 

break-up time. The newly developed method was also compared with selected well-established tests of high practical 

relevance. These tests involved use of the Tearscope (Keeler) for determining non-invasive tear film break-up time and 

a biomicroscope equipped with a measuring eyepiece for determining the height of the tear meniscus. 

2 Tear Film Analysis Methods 

Tear film analysis methods can be classified as either quantitative or qualitative or as either invasive or non-invasive. 

Quantitative methods yield information on the amount of tear fluid produced per unit of time as well as on the tear 

volume contained in the anterior eye segment. Tear film quantity depends on the production rate, distribution and drainage 

of tear fluid. Qualitative methods of tear film analysis yield information on the stability and composition of the tear 

film. These methods also give insights into the properties of the different tear fluid layers [3]. 

Optometric examination methods are termed invasive when they injure the integrity of the eye. These include, for example, 

the application of fluorescein or the use of test strips which can come into direct contact with or irritate the eye [4]. The 

following table gives an overview of the most important methods of tear film analysis. 

– 4 –

Development and realization of a new non-invasive method for tear film assessment using a corneal topographer 

Invasive Minimally Invasive Non-Invasive 

Quantitative Schirmer‘s test I, 

Schirmer‘s test II (Jones test), 

dilution test 

Qualitative BUT 

(Break-Up Time) 

Further Tests LWE 

(Lid Wiper Epitheliopathy) 

ULMS 

(Upper Lid Margin Staining) 

Table 1: Overview of the most important tear film analysis methods 

Phenol red thread test 

according to Kurihashi, 

tear meniscus examination 

with slit lamp 

Tear meniscus examination 

with Tearscope (Keeler) 

Flow behavior NIBUT 

(non-invasive break-up time), 

interference test 

LIPCOF 

(lid parallel conjunctival folds) 

DEQ 

(dry eye questionnaire) 

The present study was dedicated to the examination of the tear meniscus and tear-film break-up time by means of the 

Keratograph. These methods are classified as non-invasive because the Keratograph neither comes into contact with the 

eye nor impairs its physiology in the process [5]. However, caution should also be exercised with non-invasive methods 

because swelling of the tear meniscus has been observed even under stable test conditions. These techniques therefore 

merit classification in the grey area between non-invasive and minimally invasive [2]. 

3 Methods 

3.1 Reference Methods 

3.1.1 Tear meniscus height (TMH) 

The tear meniscus was assessed using a slit lamp with weak diffuse illumination or reduced direct focal illumination. For 

the latter a vertically or horizontally oriented light band of 0.5 to 1 mm width was used. Height measurements were performed 

using a monocular adjustable measuring eyepiece (see Figure 1) calibrated for 10x magnification. The eyepiece was 

equipped with a 10 mm graticule plate with 0.2 mm divisions. For larger magnification an appropriate scale factor must be 

used, since the magnification scale in the focal plane is then no longer 1.0 [6]. Table 2 shows the scale divisions for different 

magnifications and measuring eyepieces and the calculation of the scale factor. 

Figure 1 

1 graticule 

2 length scale 

3 Tabo angle scale 

4 cover glass 

5 measuring sphere 

6 insertion connecting piece 

– 5 –


interval (target) x magnification (target) = interval 

magnification (actual) (actual) 

– 6 – 

Measuring eyepiece 

10x 

magnification (actual) interval (actual) 

in mm 


10x 

interval (actual) 

in mm 


12x 

interval (actual) 

in mm 

8x 0.125 0.250 0.300 

10x 0.100* 0.200* 0.240 

12x 0.083 0.167 0.200* 

16x 0.063 0.125 0.150 

20x 0.050 0.100 0.120 

24x 0.041 0.083 0.100 

32x 0.031 0.062 0.075 

40x 0.025 0.050 0.060 

* This value gives the scale division appropriate to the calibration of the magnification used. This is a necessary condition 

in order for measuring scale and measured object to be of the same scale. The values take no account of devicespecific 

measurement errors. [6] 

Table 2: Relationship between scale division and magnification used 

Disregard of the relationship between scale gradation and magnification can lead to significant errors in measuring the 

tear meniscus. 

3.1.2 Non-invasive tear film break-up time (NIBUT) 

It is generally known and has been variously demonstrated that tear film break-up consists in a destabilization or loss 

of integrity of the precorneal tear film. Non-invasive tear film break-up time was defined by Mengher et al. in 1985 as 

follows: NIBUT is defined as the time in seconds between the last complete blink and the first perturbation of a grid 

projected onto the surface of the cornea [7]. NIBUT is measured non-invasively and without application of fluorescein. 

NIBUT measurement methods thus differ significantly from the invasive BUT method. 

3.1.3 NIBUT measured with the Tearscope (Keeler) 

The Tearscope (Keeler) is the only commercial device available for non-invasive tear film analysis. A cold light source is 

used in general, the corneal microscope only serving for magnification. After 3 to 4 blinks the subject is asked to keep 

his or her eyes open. From this moment on the reflected projection surface is observed closely. Irregularities in the 

reflected image indicate places on the cornea where the tear film is losing stability or breaking up. If no grid is used, 

the full Tearscope (Keeler) illumination source is employed, producing a white reflection surface. This method permits 

continuous observation and identification of the type of tear film break-up, which may, for example, show as an areal 

expanse or as stripes or spots. 

Figure 2: Reflection image generated with the Tearscope (Keeler)


Due to the high contrast of the reflected image, distortions and disturbances can be observed very well in a dark-coloured 

iris. Not so in the case of a light-coloured iris, where determination of tear film break-up time becomes more difficult and 

less accurate. Similar difficulties can occur when the tear film has a thin or low-reflecting lipid layer [8]. Figure 3 shows 

the poor contrast that results when these two factors coincide, illustrating the difference compared with the image obtained 

of the dark-coloured eyes (Figure 2, centre). 

Figure 3: Low-contrast reflection image resulting from a light-coloured iris in association with a low-reflecting lipid layer 

3.2 Tear Film Analysis Using the Keratograph 

3.2.1 Tear meniscus height (NIK TMH) 

For the newly developed tear meniscus measurement method presented in this study, illumination was effected by means 

of four IR diodes. These IR diodes were mounted on the Keratograph in vertical orientation and arranged in two pairs located 

one above the other. The automatic red ring illumination otherwise used for corneal topography was deactivated. 

This ensured a dark background for the examination. The diodes were covered up in turn to determine the influence of 

each diode pair on the appearance of the reflected image and hence on measured tear meniscus height and the results 

obtained were compared with each other. The following combinations were tested: 

a) 3 images with both diode pairs; 

b) 3 images with the upper diode pair; 

c) 3 images with the lower diode pair. 

Figure 4: Illumination conditions obtained with the Keratograph 

The measurement was performed over a predefined width centered 2 mm nasally from the pupil center, since the height 

of the tear meniscus varies along the length of the lower eyelid. Figure 5 shows the reflections occurring with NIK TMH 

as compared with the reference method. The yellow arrows show the meniscus height. 

– 7 –


Figure 5: TMH (top); NIK TMH (bottom) 

3.2.2 Non-invasive tear film break-up time (NIK BUT). 

An illuminated ring pattern was projected onto the cornea using the Keratograph. In this case the Placido disk consisted 

of 22 rings. After three blinks the projected ring pattern was examined for signs of tear film break-up as described above. 

Attention was given in particular to distortions and gaps in individual rings and the time such deviations from the original 

ring pattern took to occur was measured. 

Figure 6: Graphic representation of wave-like distortions; these were also interpreted as a tear film destabilization, i.e. break-up. 

Figure 7: left: Ideal ring pattern; right: ring pattern with wave-like distortions 

– 8 –

Development and realization of a new non-invasive method for tear fi lm assessment using a corneal topographer 

Examinations were recorded on video. At the start of the recording the subject was asked to blink his or her eyes three 

times and then to keep them open. The recording was discontinued at the next eye blink. This procedure was repeated 

three times. Tear fi lm break-up time was measured according to the defi nition by Mengher et al. [7] both for the reference 

method and for the newly developed method. Figure 8 summarizes the measurement procedure. 

1. tear meniscus 

measurement 

1. tear meniscus 

measurement 

Figure 8: Overview of test procedure 

General preparations 

Information and informed consent 

2. NIBUT 

measurement 

Examination using a slit lamp 

30 minutes break 

3. Examination of 

anterior eye segment 

Examination using the Keratograph 

2. NIBUT 

measurement 

Statistical evaluation 

3. Examination of 

anterior eye segment 

4. Documentation 

of results 


of results 

– 9 –


3.3 Modifications on the Keratograph 

Two software modifications were developed for the Keratograph to realize the measurements described above: 

 

 

tear meniscus measurement program 

tear film measurement program. 

Figure 9: Menu of the new measurement program incorporated in the Keratograph (OCULUS) software 

In single-shot mode the new software provides a measuring scale for determining tear meniscus height and a magnification 

function to facilitate measurement of reflection height. The accuracy of the measurement depends on the magnification 

function, being greater at higher than at lower magnification. A running digital clock is displayed in the top left-hand 

corner during the video recording. The time was measured manually with a stopwatch, since an automatic eye blink trigger 

function was not yet available at the time of the study. 

Figure 10: Single-shot mode with measuring scale, magnification function and saving option 

3.4 Subjects 

– 10 – 

Measuring scale 

Magnification function 

Save (including measured value) 

A total of 34 subjects participated in the study, 16 (47%) female and 18 (53%) male. The subjects’ age ranged from 19 

to 53 years with a mean value of 28.3 ± 7.2 years. 

The newly developed method is designed for use in contact lens fitting as well as for detection of pathological alterations 

of the eye in clinical screenings. The inclusion and exclusion criteria were determined on the basis of these designated 

application areas, with no resulting exclusions. The only inclusion criterion was that test persons had to be of age. The 

only exclusion criterion was the wearing of contact lenses within the last 24 hours preceding the examination. This was 

to minimize short-term contact-lens-induced fluctuations in tear film parameters.

4. Results 


4.1 Tear Meniscus Height 

4.1.1 Tear meniscus height measurements using a slit lamp 

In 22 out of the total of 34 subjects tear meniscus height was found to be lower, in four equal to and in eight greater than 

0.2 mm. The Shapiro-Wilk Test showed the measured data to be normally distributed within each series of measurements. 

(p=0.096). Figure 11 shows the frequency distribution within the classifi cation groups. 

4.1.2 Tear meniscus height measurement using the Keratograph 

Measurements of tear meniscus height using the Keratograph were considered separately for each of the three illumination 

setups in order to determine the infl uence of each individual diode pair on refl ection height. As with the reference 

measurements, all measurement series performed with the Keratograph were found to have produced normally distributed 

data according to the Shapiro-Wilk test. Figure 11 shows the frequency distributions, along with the reference methods 

(shown grey) for comparison. 

Corneal microscope with measuring eyepiece 

Keratograph (upper diode pair) 

65% 

71% 

82% 

76% 

Figure 11: Percent distribution of results 

Frequency distribution of tear meniscus height 

n = 34 

12% 

6% 

3% 

Keratograph (both diode pairs) 

Keratograph (lower diode pair) 

9% 

24% 

24% 

15% 

TM < 0.20 mm TM = 0.20 mm TM > 0.20 mm 

The differences between means were analyzed using the t-test for paired samples. The null hypothesis was that the differences 

between means were entirely the product of chance. 

T Test pair 1* pair 2** pair 3*** 

Paired differences (mean) 0.0035 0.0088 0.0144 

Standard deviation 0.0372 0.365 0.0404 

T value 0.553 1.410 2.081 

p value (signifi cance, 2-tailed 0.584 0.168 0.045 

Table 3: Differences between means and correlations (n=34) 

*pair 1: Corneal microscope with measuring eyepiece vs. 

Keratograph (both diode pairs) 

**pair 2: Corneal microscope with measuring eyepiece vs. 

Keratograph (upper diode pair) 

***pair 3: Corneal microscope with measuring eyepiece vs. 

Keratograph (lower diode pair) 

15% 

– 11 –


On considering the differences between the mean obtained with the reference method and the mean obtained with each 

of the three Keratograph versions (Table 10), it becomes clear that the smallest deviation from the reference method 

is achieved when both IR diode pairs are used. The p value for method pairs one and two indicates a signifi cance level 

higher than α = 0.05. Therefore the null hypothesis cannot be rejected, meaning that the difference between the means 

is possibly due to chance. For method pair three the null hypothesis is rejected, since the difference between the means is 

signifi cant. The results show that using only the lower diode pair for illumination is not a suitable setup for tear meniscus 

measurement. 

4.2 Non-invasive tear fi lm break-up time 

Not all of the 34 subjects showed tear fi lm break-up during measurement. Measurements that were terminated not by tear 

fi lm break-up but by a blink were excluded, in keeping with the defi nition of Mengher et al. [7]. 

4.2.1 NIBUT measured using the Tearscope (Keeler) 

This sample had a median of 8.2 seconds and a range from 4.5 seconds to 29.9. seconds. The Shapiro-Wilk test showed no 

normal distribution (p=0.000). A statistical analysis was also performed of the horizontal width of the observed measurement 

range. Tearscope (Keeler) measurements showed the width to range from 3.5 to 4.9 mm with a mean value of 4.2 

±0.3 mm. 

4.2.2 NIK BUT measured with the Keratograph 

In 17 of 34 subjects, measurements were in compliance with the defi nition of Mengher et al.. In fi ve out of these 17 subjects 

NIK BUT was shorter than 10 seconds, in 10 it ranged between 10 and 20 seconds and in two it was greater than 20 

seconds. Neither of the two methods indicated a normal distribution of this sample. The median of the results obtained with 

the Keratograph was 11.33 s, with a range from 5.70 s to 25.07 s. 

The horizontal width of the measurement range was analyzed as with the reference method, giving a range from 8.25 to 

10.46 mm and a mean of 9.37 ± 0.46 mm. The mean was rounded to 9.4 mm to facilitate a comparison of the two methods. 

– 12 – 

76% 

29% 

Figure 12: Distribution of results in per cent 

Frequency distribution of tear fi lm break-up time 

n = 17 

Tearscope Keratograph 

18% 

59% 

6% 

12% 

NIBUT < 10 10ss 10 10 ss ≤ < NIBUT < 20 20 ss NIBUT > ≥ 20 20s s


The median of the two methods differed by 2.5 s and the mean by 2.8 s. There was little deviation between the extremes 

obtained with the two methods. The standard deviation was 5.0 s for the results obtained with the reference method and 

5.24 s for those obtained with the Keratograph. Wilcoxon’s test was used to determine whether the differences found between 

the two methods might be attributable to chance. This yielded a p-value of 0.049, indicating a significant difference 

for α = 0.050 and hence rejection of the null hypothesis. Moreover, Spearman’s rank correlation coefficient was calculated 

as 0.088, indicating no appreciable correlation between the measurement results of the two methods. 

5 Discussion 

5.1 Tear Meniscus Height 

The reference method was performed with a measuring eyepiece mounted on the slit lamp. As already mentioned, this 

method requires appropriate magnification for accurate results. Since it is not being applied to an inanimate object, it also 

requires a certain degree of experience on the part of the examiner. The longer it takes the examiner to perform the measurement, 

the greater the influence of reflex secretion provoked by the examination and hence the probability of obtaining 

distorted results. This is where the advantage of the newly developed method lies. The use of IR diodes avoids exposure of 

the subject to glare, thus markedly reducing the risk of reflex secretion. Moreover, the examination takes less time, since 

only one shot of the tear meniscus is taken. When the measurement has been completed, the examiner can then take all 

the time he needs for the evaluation. For this purpose the software of the Keratograph was modified to include a segment 

magnification function and a measuring scale calibrated to the magnification being used. These modifications reduce the 

influence of measurement errors that have caused problems in the past. In addition, the picture material can be automatically 

incorporated in the patient file for later use in follow-up examinations. 

5.2 Non-invasive Tear Film Break-Up Time 

The illumination system of the Keratograph consists of 200 red LEDs with a wavelength of 653 nm. LEDs have the 

advantage of emitting very little heat radiation, minimizing the danger of thermally induced alterations of the tear film. 

The method of area illumination and projection differs from that of the Tearscope (Keeler) in the use of an additional grid. 

However, the Tearscope (Keeler) provides only poor contrast in the case of light-coloured eyes associated with a low- 

reflecting lipid layer, making it difficult to obtain accurate NIK-BUT measurements. Compared with the Tearscope (Keeler) 

the newly developed method permits very good observation of tear film break-up phenomena under constant contrast 

conditions, independent of eye colour or of interference effects related to the lipid layer. This provides ideal conditions 

for discriminating between disorders of the tear film, caused for example by air bubbles or mucin threads, and tear film 

break-up. The Keratograph provides a markedly larger field of observation so that peripheral tear break-ups are also 

considered. 

– 13 –


6 Conclusion and Outlook 

Modern contact lens fitting as it is practised today would be unthinkable without the Keratograph. With around one in 

three contact lens wearers complaining of dryness problems or dry eye symptoms there is a practical interest in obtaining 

information on a person’s tear film quality and quantity when they have their corneal geometry measured in preparation 

of contact lens fitting. The present newly developed method is suited for non-invasive assessment of tear meniscus height 

as well as determination of non-invasive tear film break-up time. All results obtained with the method can be directly 

incorporated in the patient file. The highest priority of future development work should be to facilitate the generation of 

reproducible, objective data in the area of non-invasive tear film analysis. One important step towards this end will be to 

develop automatic examiner-independent methods. The results obtained in this study, and the modifications performed 

by the Oculus company on the Keratograph for this purpose - implemented in its TF Scan module - constitute important 

steps in this direction. This new objective method has in the meantime been validated by the JENVIS Research Institute. 

The validation included a comparison of NIK BUT with classical analysis methods, e.g. BUT, Schirmer‘s test, tear meniscus 

height and the results of a personal dry eye questionnaire. 

Figure 13: NIK-BUT validation study 

Current plans to continue development work on the Keratograph will open the field for numerous follow-on studies. Future 

development work on the TF Scan module could be aimed at an assessment of NIK DUT, i.e. non-invasive drying-up time. 

The present study has prepared the ground for this new avenue of research. 

– 14 – 

Follow-on study 

(n=101) 

Validation 

 

Classification 

Tear film & 

dry eye

Literature 


[1] MARQUARDT, R.; LEMP, M. A.: Das trockene Auge in Klinik und Praxis.- 1. Aufl. - Heidelberg: Springer Verlag, 1991 

[2] The Ocular Surface, Report of the International Dry Eye WorkShop (DEWS): 

Methodologies to Diagnose and Monitor Dry Eye Disease: Report of the Diagnostic 

Methodology Subcommittee of the International Dry Eye WorkShop, 2007 

[3] SICKENBERGER, W.: Klassifikation von Spaltlampenbefunden. Großostheim: 

Bezug über Ciba Vision Vertriebs GmbH, 2001 

[4] MASTERS,B. R.: Noninvasive Diagnostic Techniques in Ophthalmology,Springer Verlag, 1990 

[5] KLYCE, S. D.; DINGELDEIN, S.A.: Corneal Topography, aus: Noninvasive Diagnostic Techniques in Ophthalmology, 

Springer Verlag, S. 61-77, 1990 

[6] Augenuntersuchungen mit der Spaltlampe. Ophthalmologische Geräte von Carl Zeiss, 

http://www.zeiss.com/C12567A10053133C/allBySubject/576876A46968B68AC125718600422005 (Stand 1.11.09) 

[7] MENGHER, L. S.; PANDHER, K. S.; BRON, A. J.: Non-invasive tear film break-up time: sensitivity and specificity. 

Acta Ophthalmologica, Vol.: 64: 441-444, 1986 

[8] GUILLON, J.P.: Non-invasive tearscope plus routine for contact lens fitting. Contact Lens and Anterior Eye, 

(Supplement) Vol.: 21: 31-40, 1998 Validation of new non-invasive methods for tear film assessment using 

a Keratograph 

Author: 

Doreen Wiedemann, BSc, student of the Master Program in Optometry /Vision Science / Jena University of Applied Science, 

collaborator of the JENVIS Research Institute, Jena 

Email: wiedemann@jenvis-research.com 

Advisor: 

Prof. Dipl.-Ing. (FH) W. Sickenberger, MS. Optom. (USA), FH Jena 

Dipl.-Ing. (FH) M. Michel, JENVIS Research Institute, Jena 

– 15 –



using a Keratograph* 

B. Sc. Doreen Wiedemann [1],[2] ; Dipl.-Ing. (FH) Martina Michel [1],[2] ; 

Prof. Dipl.-Ing. (FH) Wolfgang Sickenberger, MS. Optom. (USA) [1],[2] ; 

Dipl.-Ing. (FH) Sebastian Marx [1],[2] 

[1] [2] Fachhochschule Jena; JENVIS Research Institute 

* First – 16 publication – in “Die Kontaktlinse”, issue 8-2010



using a Keratograph 

The majority of established tear film examination methods to date are based on observation of induced tear film 

reflections. Examples are the determination of tear meniscus height, assessment of interference phenomena, and 

the observation of non-invasive tear film break-up time. One limitation common to all these methods is the sub- 

jective nature of the observations made [1]. The fact that tear film data thus obtained contain indeterminable distortions 

that limit comparability poses a serious obstacle to their interpretation. Standardisation may serve to solve 

some such problems, but not to exclude them. In 2007 the Report of the Diagnostic Methodology Subcommittee 

of the International Dry Eye Workshop (RDEWS) was published, containing recommendations for standardisation 

in established tear film examination methods and clinical studies on dry eye disorders with a view to improving 

comparability [2]. The members of the subcommittee are nonetheless agreed that it would be of great importance 

to develop objective analysis methods that might supplement recommended test combinations for examining the 

precorneal tear film. [3]. Such was the situation that motivated the development of an automated, examiner- 

independent technique for detection of non-invasive tear film break-up time. 

1 Introduction 

This study is based on the results of a development study entitled “Development and realization of a new non-invasive 

method for tear film assessment using a corneal topographer” which was published in the 7-8/2010 issue of this journal. 

The present follow-on study was dedicated to a validation of objective Non-Invasive Keratograph Break-Up Time 

(NIK-BUT), the aim being to delimitate normal from critical values. For this purpose a test battery was set up conforming 

to the RDEWS recommendations and covering the more established qualitative, quantitative and subjective tear film 

analysis methods. A further aim, motivated by substantial controversy over the correlation of results, was to determine 

comparability between the individual examination methods. 

Follow-on study 

(n=101) 

Validation 

Classification 

Figure 1: Overview of methods considered in the present validation study 

Tear film & 

dry eye 

– 17 –

Validation of new non-invasive methods for tear film assessment using a Keratograph 

2 Materials and Methods 


2.1.1 Tear meniscus height (TMH and NIK-TMH) 

Tear meniscus height (TMH) was determined at reduced room lighting using a measuring eyepiece (10x, 0.2 mm scale division) 

mounted on a slit lamp. A horizontal light band was projected onto the test subject’s face such that it approached 

the lower eyelid from below, and the tear meniscus was measured three times over a defined central measuring range. 

Tear meniscus height (NIK-TMH) was measured with the Keratograph using the same two measurement tools described in 

the preceding article [5]. These were incorporated unchanged in the TF-Scan software, the only modification being the use 

of horizontally arranged white diodes in place of the previous red ring illumination. This modification was made purely for 

technical reasons related to the equipment. NIK-TMH was thus determined three times and the results were entered in a 

documentation form. 

2.1.2 Break-up time (BUT) 

BUT was measured at mid-range magnification. Measurements were performed in a darkened room under direct focal illumination 

with the blue and yellow filters interposed. The Dry Eye Test (DET) was performed for better reproducibility of the 

amount of fluorescein applied. Subjects were asked to blink three times after receiving fluorescein and then keep their eyes 

open. The time from the last blink until the first appearance of dark areas on the cornea was measured with a stopwatch. 

This was done three times and the resulting arithmetic mean was calculated. Table 1 gives a classification of invasive tear 

film break-up time. 

Classification BUT (in s) Interpretation 

Grade 0 ≥10 stable tear film 

Grade 1 6-9 tear film stability critical 

Grade 2 ≤ 5 dry eye disorder 

Table 1: Classification of BUT 

2.1.3 McMonnies DEQ 

Test subjects completed the McMonnies’ Dry Eye Questionnaire (McMonnies DEQ) for a subjective assessment of tear film. 

Answers were classified according to a scoring system with a total score range from 0 to 45 defining three grades of dryness. 

Classification Total score Interpretation 

Grade 0 0-9 no dry eye; asymptomatic 

Grade 1 10-20 slightly dry; critical 

Grade 2 >20 dry eye 

Table 2: Classification according to the McMonnies DEQ 

– 18 –


2.1.4 Schirmer test (without anaesthetic) 

For the Schirmer test (without anaesthetic), a standardised 5 mm wide strip of filter paper was placed in the temporal 

third of the lower fornix as an indicator and left there for five minutes with the test subject’s eyes open. After this time 

the test strip was removed and the moistened length of strip was read in mm and entered in the documentation form. 

Figure 2: Schirmer test in progress 

Classification length (mm/5 min) Interpretation 

Grade 0 ≥ 15 normal 

Grade 1 6-14 slightly dry eye 

Grade 2 ≤ 5 dry eye 

Table 3: Classification according to the Schirmer test (without anaesthetic) [3][4] 

2.2 NIK-BUT method 

2.2.1 Technical modifications on the Keratograph 

The TF-Scan software (Oculus) was reviewed in preparation of the validation study and modified in cooperation with the 

Oculus company. This software permits automatic determination of tear film break-up time, providing a graphic representation 

referred to as a Tear-Map, which shows the location and size the regions in question. The colour coding of the 

Tear-Map was modified (see Figure 3). In addition to the “first break-up time” (NIKf-BUT) the software now also gives the 

“average break-up time” (NIKav-BUT), i.e. the average of all tear film break-ups occurring over the entire cornea. 

Figure 3: Modified colour scale of the tear map 

red below 6s 

orange / yellow from 6s (previously 9s) on 

green from 12s (previously 16.5s) on 

The time reading shown against white background below the colour scale in Figure 3 gives the time between the first 

blink, which triggers the measurement, and the second blink, which terminates it. 

– 19 –


2.2.2 NIK-BUT 

After creating a test subject in the patient file the option „New measurement (NIBUT)“ was selected from the control bar 

of the Keratograph. After the operator had centered the test subject’s eye a window appeared in the screen prompting 

the operator to have the test subject blink twice. The second blink automatically triggered the video recording and measurement. 

The measurement was terminated by either of two events: another blink or excessive blur or distortion of the 

reflected image of the Placido rings, making continued detection impossible. After measurement completion the following 

information was available for documentation: a video recording, a representation of tear film break-up over time including 

its graphic depiction in a tear map, the first break-up time (NIKf-BUT) and the average break-up time (NIKav-BUT) 

(see Figure 4). 

Figure 4: Output after a NIK-BUT measurement: left: video; top right: progress of tear film break-up over time; bottom 

right: Tear-Map and display of NIKf-BUT and NIKav-BUT. 

– 20 –

Validation of new non-invasive methods for tear fi lm assessment using a Keratograph 

Results for NIKf-BUT and NIKav-BUT were entered in the documentation form. This measurement was performed three 

times per test subject. Figure 5 gives an overview of the test procedure. 

1. NIK-TMH 

measurement 

1. TMH 

measurement 

General preparations 

Information and informed consent 

Examination using the Keratograph 

2. NIK-BUT 

measurement 

2. BUT 

measurement 

Figure 5: Schematic overview of test procedure 

Break 

Examination using a slit lamp 

McMonnies DEQ 

3. Subjective assessment 

of examination 

3. Subjective assessment 


Schirmer test (without anaesthetic) 

1. Measurement (mm / 5 min) 2. Subjective assessment 


Statistical evaluation 


of results 


of results 

3. Documentation of results 

– 21 –


2.3 Subjects 

101 subjects participated in the validation study. Their age and sex distribution is shown in Table 4. 

N 101 

Mean age 41 ± 16 years 

Min. age 18 years 

Max. age 75 years 

Mean age of females (n=57) 40 ± 16 years 

Mean age of males (n=44) 40 ± 17 years 

Table 4: Demographics 

2.4 Statistical methods 

The results obtained with the various methods were first analysed descriptively and tested for normal distribution using 

the Shapiro-Wilk test. This led to rejection of the null hypothesis in each case, indicating absence of normal distribution 

for every method used. 

A cut-off value was determined for the boundary between normal and critical tear film quality in preparation of a classification 

of Non-Invasive Keratograph Break-Up Time (first break-up time and average break-up time). This was done by 

comparing the results of TMH, BUT, the McMonnies DEQ and Schirmer test with the corresponding NIK-BUT values using 

ROC (receiver operating characteristic) curves. This analysis method is used for gaining information on the sensitivity 

and specificity of diagnostic tests. It involves plotting sensitivity on the y-axis and 1 - specificity on the x-axis of a twodimensional 

coordinate system. Significant deviation of the resulting curve from the diagonal reference line indicates 

good discrimination by the test under consideration. The performance of the test is represented by the area under the 

ROC curve, also referred to as AUC (Area Under Curve). AUC can range between ca. 0.5 and ca. 1.0, with high values 

indicating a powerful test and low absolute values a test of low discriminatory power. 

Discriminatory power AUC 

Unacceptable 0.5 – 0.7 

Acceptable 0.7 – 0.8 

Very good 0.8 – 0.9 

Excellent 0.9 – 1.0 

Table 5: Interpretation of AUC values 

For this type of statistical evaluation it is first necessary to map all objective and subjective results to either of two test 

outcome levels. In the present study this information was obtained from the classification keys of the individual reference 

tests (Table 6). 

Discriminatory power Grade 0 Grade 1 Grade 2 

0 (normal) x 

1 (critical) x x 

Table 6: Definition of the two test outcome levels 

To determine the discriminatory power of the present newly developed method we analysed it firstly in comparison with 

all the other tests and secondly in comparison with the tests with the highest sensitivity and specificity for dry eye, namely 

with BUT and the McMonnies DEQ [1]. This appeared all the more appropriate as it is meaningful to combine objective and 

subjective methods [6]. 

– 22 –

3 Measurement data and results 


The purpose of the validation study was to establish a distinction between normal and critical NIK-BUT values. This is the 

primary focus in the following presentation of results, which gives the results obtained with the individual methods only in 

a brief overview. 

3.1 Reference methods 

3.1.1 Tear meniscus (TMH and NIK-TMH) 

In 15 of the 101 test subjects NIK-TMH measurement yielded values below 0.2 mm, in 16 equal to and in 70 greater than 

0.2 mm. TMH measurements deviated only slightly from this distribution. 

69% 62% 

Frequency distribution 

n = 101 

Grade 0 Grade 1 Grade 3 

Figure 6: Frequency distribution of NIK-TMH and TMH across the three groups 

Analysis of the relationship between the two methods yielded a correlation coefficient of 0.722 and a coefficient of determination 

of 0.568. This is confirmation of our finding in the development study that NIK-TMH and TMH produce comparable 

results, justifying their combined use for the present classification. 

3.1.2 Break-up time 

The results of invasive tear film break-up time (BUT) were likewise classified into three levels (see Figure 8). The entire 

sample had an arithmetic mean of 7.53 ± 3.73 s, a median of 6.90 s, and a range from 2.10 s to 19.40 s. 

26% 

NIK-TMH TMH 

16% 23% 


n = 101 

Figure 7: Frequency distribution of BUT across the three groups 

BUT 

15% 15% 

37% 37% 


– 23 –


3.1.3 McMonnies DEQ 

In the McMonnies questionnaire the test subjects produced a mean overall score of 10.36 ± 6.83 and a median of 9.00. The 

lowest overall score was 1 point and the highest was 28. 

Figure 8: Frequency distribution for the McMonnies DEQ across the three groups 

3.1.4 Schirmer test (without anaesthetic) 

The results of the Schirmer test gave a mean of 18.58 ± 7.36 mm/5 min and a median of 22.00 mm/5 min for the entire 

sample (n=101). The maximum, limited by the length of the test strip, was 25 mm/5 min and the minimum in this study 

was 3 mm/5 min. 

Figure 9: Frequency distribution of the results of the Schirmer test across the three groups 

– 24 – 

58% 


n = 101 

McMonnies DEQ 

30% 

12% 


70% 


n = 101 

Schimer I - Test 

19% 

11% 

Grade 0 Grade 1 Grade 3

3.2 Comparison of methods and statistical data 


3.2.1 Frequency distributions for each of the reference methods 

The results obtained for the 101 subjects with the five reference methods were in each case classified into three groups. 

69% 62% 

Figure 10: Synopsis of frequency distributions of results across the three groups 

No confirmation of normal distribution was obtained when the results of all the reference methods were considered 

together. 

3.2.2 Correlation and comparability of reference methods 

The outcomes obtained with the individual reference methods were examined for correlations using Spearman’s rank correlation 

test. Strong and significant correlations were only found between NIK-TMH and TMH and between NIKf-BUT and NIKav- 

BUT. Weak correlations were found between BUT and NIKf-BUT and between BUT and NIKav-BUT. No correlations were found 

between any of the established reference methods. Table 7 gives the correlation coefficients for each method pair. 

NIK-TMH NIKf-BUT NIKav-BUT TMH BUT McMonnies Schirmer test I 

NIK-TMH 1,000 ,065 ,081 ,722(**) ,087 -,198(*) ,078 

NIKf-BUT ,065 1,000 ,868(**) ,062 ,505(**) -,280(**) ,132 

NIKav-BUT ,081 ,868(**) 1,000 ,070 ,454(**) -,246(*) ,090 

TMH ,722(**) ,062 ,070 1,000 ,127 -,207(*) ,056 

BUT ,087 ,505(**) ,454(**) ,127 1,000 -,182 ,258(**) 

McMonnies -,198(*) -,280(**) -,246(*) -,207(*) -,182 1,000 -,182 

Schirmer test I ,078 ,132 ,090 ,056 ,258(**) -,182 1,000 

** The correlation is significant at a level of 0.01 (two-tailed) 

* The correlation is significant at a level of 0.05 (two-tailed) 


n = 101 

NIK-TMH TMH BUT McMonnies DEQ Schimer I - Test 

26% 

58% 

70% 

16% 23% 

37% 30% 

19% 

15% 15% 


Table 7: Spearman’s nonparametric rank correlation coefficients for all reference methods studied (n = 101) 

37% 

12% 11% 

– 25 –


The following diagrams illustrate the high degree of scatter and hence poor comparability of the results obtained with the 

various reference methods. Each diagram shows the results obtained for the entire sample (n=101). 

Figure 11: Representation of value pairs: Comparison of NIKav-BUT and NIKf-BUT with BUT and McMonnies DEQ (n=101) 

The diagrams in Figure 11 show that there is no linear relationship or indeed any correlation between the results of the 

method pairs chosen. The diagrams in Figure 12 show there to be a particularly large scatter among the data obtained for 

BUT vs. Schirmer test. 

Figure 12: Representation of value pairs: Comparison between BUT and TMH and between BUT and Schirmer test (n=101) 

3.2.3 ROC curves 

As already described, the output range of each tear film test was divided into an asymptomatic and a symptomatic subrange. 

This was done to facilitate a comparison of NIK-BUT with a combination of subjective and objective tear film tests, 

the McMonnies DEQ serving as a subjective and TMH, BUT and the Schirmer test as objective tests. Test subjects were 

classified as symptomatic if altogether at least three out of four tear film tests yielded results classified as critical or dry 

eye disorder (Grade 1 or 2). According to this combination of objective and subjective criteria, 82 of the total of 101 test 

subjects were asymptomatic and 19 were assessed as symptomatic. The predictive values of NIKf-BUT and NIKav-BUT were 

found to be significant (NIKf-BUT: AUC=0.679; p=0.016; NIKav-BUT: AUC=0.646; p=0.048). 

Figure 13: ROC curves for NIKf-BUT and NIKav-BUT (n=101; reference methods: TMH, BUT, Schirmer test and McMonnies DEQ) 

– 26 – 

NIKav-BUT 

TMH 

25,0 

20,0 

15,0 

10,0 

5,0 

0,0 

BUT/NIKav-BUT 

0,0 5,0 10,0 15,0 20,0 25,0 

0,50 

0,45 

0,40 

0,35 

0,30 

0,25 

0,20 

0,15 

0,10 

0,05 

BUT 

BUT/TMH 

0,00 

0,0 5,0 10,0 15,0 20,0 25,0 

BUT 

Sensitivity 

1,0 

,8 

,5 

,3 

0,0 

NIKav-BUT 

Schimer-Test I 

-5 

25 

20 

15 

10 

0,0 ,3 ,5 ,8 1,0 

1 - Specifity 

5 

McM. DEQ/NIKav-BUT 

5 15 25 35 15 

McMonnies DEQ 

BUT/Schimer-Test I 

0 

0,0 5,0 10,0 15,0 

BUT 

20,0 25,0 

Source of curve 

Reference line 

NIKav-BUT-MW 

NIKf-BUT-MW


The value with the smallest difference between sensitivity and specificity represents the cut-off value. The smallest 

difference between the two for NIKf-BUT was 0.01, giving a cut-off value of 9s, and for NIKav-BUT the smallest difference 

was again 0.01, giving a cut-off value of 14s. Test subjects with lower NIK-BUT values should be considered as critical or 

symptomatic. 

Assessment of NIK-BUT on the basis of BUT and the McMonnies DEQ 

NIK-BUT was then assessed on the basis of one objective and one subjective test, both of which were selected for having 

the highest discriminatory power and performance with regard to dry eye within their class (BUT test and McMonnies DEQ 

[1]), and the results of these two tear film tests were considered anew. Test subjects were classified as symptomatic when 

the BUT test and the McMonnies DEQ both yielded values classifiable as critical or dry eye disorder (Grade 1 or 2). According 

to this classification 61 of the 101 test subjects were asymptomatic and 40 were symptomatic, i.e. seen as critical or as 

having dry eye disorder. When interpreted on the basis of these two tests NIK-BUT shows good and significant predictive 

power (NIKf-BUT: AUC=0.750; p=0.000; NIKav-BUT: AUC=0.735; p=0.000). 

Figure 14: ROC curves for NIKf-BUT and NIKav-BUT (n=101; reference methods: BUT and McMonnies DEQ) 

Again the cut-off value was determined by finding the value giving the smallest difference between sensitivity and specificity. 

The smallest difference was found to be 0.01, giving cut-off values of 14s for NIKav-BUT and 10s for NIKf-BUT. NIK- 

BUT values below the cut-off value merit interpretation as critical. 

Using the same two reference methods as an assessment basis an attempt was then made to distinguish between critical 

and dry eye tear film. This time test subjects were classified as symptomatic if both the BUT test and the McMonnies DEQ 

were indicative of Grade 2 dry eye disorder. 84 of 101 test subjects were found to be asymptomatic and 17 symptomatic 

under this interpretation. With AUC values of 0.763 and 0.751, respectively, this test has good discriminatory power, but 

our findings on it should be viewed as tentative because of the low number symptomatic cases (NIKf-BUT: AUC=0.763; 

p=0.001; NIKav-BUT: AUC=0.751; p=0.001). 

Sensitivity 

Sensitivity 

1,0 

,8 

,5 

,3 

0,0 

1,0 

,8 

,5 

,3 

0,0 

0,0 ,3 ,5 ,8 1,0 

1 - Specifity 

0,0 ,3 ,5 ,8 1,0 



NIKav-BUT-MW 

NIKf-BUT-MW 



NIKav-BUT-MW 

NIKf-BUT-MW 

Figure 15: ROC curves for classification as Grade 2 dry eye disorder according to NIKf-BUT and NIKav-BUT (n=101; 

reference methods: BUT and McMonnies DEQ) 

– 27 –


The cut-off values for this test can be defined as 5s (NIKf-BUT) and 7s (NIKav-BUT). This gives the following three-level 

classification for NIKf-BUT and NIKav-BUT: 

Table 8: Classification of NIK-BUT results 

Classification NIKf-BUT (in s) NIKav-BUT (in s) Interpretation 

Grade 0 ≥10 ≥14 stable tear film 

Grade 1 6-9 8-13 critical tear film 

stability 

Grade 2 ≤ 5 ≤ 7 dry eye disorder 

Figure 16 gives the frequency distribution for this classification. Those for the reference methods have been calculated and 

are shown on the basis of the established classification keys. 

Figure 16: Frequency distribution for NIK-BUT, BUT and the McMonnies DEQ across the three groups 

4 Discussion 


The present study showed no correlation between established dry eye tests. For example, Spearman’s rank correlation coefficient 

between the Schirmer test and the BUT test was 0.258. On the other hand, there have been studies showing a good and 

significant correlation between these two tests when a local anaesthetic was used prior to the Schirmer test (n=44; Pearson’s 

correlation coefficient 0.653; p=0.000 [7]. Findings on the reliability of the Schirmer test in terms of its ability to classify tear 

film quantity have been contradictory and highly varied [8] whether performed with or without the use of an anaesthetic. By 

comparison, the correlations of NIK-BUT with other established methods such as TMH or BUT are markedly higher. 

Due to inconsistent findings on the relationships between different examination methods it has not been possible to date 

to a define generally applicable gold standard for tear film analysis and classification. For a classification of tear film quality 

and quantity it is therefore advisable to use not just one or two tests with an additional subjective questionnaire such 

as the McMonnies DEQ. Numerous studies have sought to find optimal test combinations, some comprising both objective 

and subjective tests. 

– 28 – 

60% 58% 

NIK-BUTav 

26% 

58% 


n = 101 

NIK-BUTf BUT McMonnies 

37% 

33% 

28% 30% 

12% 9% 

37% 


12%


A further source of controversy is that the more established methods are operator-dependent, making it difficult to judge 

their objectivity. With NIK-BUT, by contrast, non-invasive tear film break-up time is measured automatically and thus 

objectively, without the operator influencing the outcome. Thus NIK-BUT circumvents two error sources involved in the 

BUT method. The latter requires fluorescein application, which can distort outcomes by affecting the composition of the 

tear film as well as through the difficulty of reproducible dosage. Mc Monnies DEQ and BUT have been suggested as a test 

combination for diagnosis of dry eye disorder, having together the highest sensitivity and specificity. This was the motivation 

for using these two methods for the determination of NIK-BUT cut-off values. The resulting classification is recommended 

by the authors for assessing tear film quality by NIK-BUT. 

4.2 NIK-BUT method 

In the present study NIK-BUT was no longer determined manually as in the development study but automatically. This 

eliminates any influence of the operator on individual measurement results, including the operator response time previously 

contained in time measurements. Detection occurs with computer assistance, capturing even the smallest tear film 

break-up. These factors have led to shorter break-up times than are measured manually. This was the reason for measuring 

both the first and the average break-up time in the present validation study. The results thus obtained show that both are 

suitable for assessing tear film quality and provide good and significant discriminatory power for distinguishing between 

normal and critical tear film break-up times. The present study was performed on a modified version of the TF-Scan software 

(Oculus) used in the development study. The modified version has lower rates of error resulting from pupillary response, 

shadowing from the nose or eyelashes or additional reflections at the upper tear meniscus. Further improvements 

relate to the colours used on the tear map and the adjusted classification of break-up times according to the cut-off values 

found. 

Some imprecision appears to remain in the central region. This can be seen in Figure 4 for example, which shows no breakup 

time, or rather no tear film break-up, in the central region. This occurred several times, leading us to assume that the 

altered contrast conditions have made detection against the dark pupil more difficult. 

5 Conclusion and preview 

The present validation study on NIK-BUT was successful in identifying significant cut-off values which permit discrimination 

between normal and critical NIK-BUT values. 

Measurement of NIK-BUT offers numerous advantages over conventional methods for both the examiner and the person 

being examined. The procedure can be learnt quickly and easily, making it suitable both as a screening method and as an 

objective, examiner-independent diagnostic test. The test outcome is presented in the form of an intuitively colour-coded 

tear map, making communication easier and facilitating the customer’s or patient’s understanding, i.e. whether in a clinical 

setting or in preparation of contact lens fitting. No auxiliary equipment is required, lowering the risk of skewed results 

as well as costs. 

The highest priority of further development work should be on extending the classification of NIK-BUT to permit a reliable 

diagnosis of dry eye disorder. To this end the authors have already carried out a study in which patients with a diagnosis 

of dry eye were examined with NIK-BUT. The tear map generated in the process allows to locate the break-up zones. This 

can now serve as a basis to examine whether the location and size of the break-up zones can contribute to the diagnosis. 

Another aspect of potential clinical interest might lie in using the method for examining the tear film after LASIK. 

– 29 –


Literature 

[1] The Ocular Surface, Report of the International Dry Eye WorkShop (DEWS): 

Methodologies to Diagnose and Monitor Dry Eye Disease: Report of the Diagnostic 

Methodology Subcommittee of the International Dry Eye WorkShop, 2007 

[2] The Ocular Surface, Report of the International Dry Eye WorkShop (DEWS): Design and Conduct of Clinical Trials.: 

Report of the Diagnostic Methodology Subcommittee of the International Dry Eye WorkShop, 2007 

[3] The Ocular Surface, Report of the International Dry Eye WorkShop (DEWS): The Definition and Classification of 

Dry Eye Disease, Report of the Diagnostic Methodology Subcommittee of the International Dry Eye WorkShop, 2007 

[4] SICKENBERGER, W.: Klassifikation von Spaltlampenbefunden.3.Auflage, Großostheim: Ciba Vision Vertriebs GmbH, 2010 

[5] Wiedemann, D.: Entwicklung und Erprobung neuer nichtinvasiver Untersuchungsmethoden des Tränenfilms mittels 

Videokeratographen. Die Kontaktlinse, Nr.: 7-8, 2010 

[6] Michel, M.: Diplomarbeit: Bestimmung des kontaktlinsenrelevanten okulären Trockenheitsgrades anhand validierter 

und optimierter Patienten-Fragebögen und objektiven Tests.. Fachhochschule Jena, Fachbereich SciTec, Studiengang 

Augenoptik, Erscheinungsjahr 2008 

[7] ISREB, M.A.; GREINER, J.V.; KORB, D.R; GLONEK, T.; MODY, S.S; FINNEMORE, V.M.; REDDY, C.V.: Correlation of lipid layer 

thickness measurements with fluorescein tear film break-up time and Schirmer’s test; Nature Publishing Group: Eye 

(2003) Vol: 17: 79–83, 2003 

[8] CHO P.; YAP M.: Schirmer-Test I – A Rewiev. Optometry and Vision Science, Vol. 70 No. 2, 152-156, 1993 

Author: 

Doreen Wiedemann, student of the master program in optometry and vision science at FH Jena 

associate at the JENVIS Research Institute, Jena 

Email: wiedemann@jenvis-research.com 

– 30 –


– 31 –

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