Apr 2016

More documents

Recommendations

Info

with Prof Charles McGhee & A/Prof Dipika Patel Series Editors The ABCs of OCT in glaucoma Background BY HANNAH KERSTEN* AND PROFESSOR HELEN DANESH-MEYER Glaucoma is a multifactorial optic neuropathy characterised by slowly progressive degeneration of the retinal ganglion cells and their axons. Unfortunately, there is not yet one single test that can discriminate glaucomatous eyes from normal eyes; the diagnosis of glaucoma is made based on a specific pattern of structural and functional changes. In the past, the retinal nerve fibre layer (RNFL) was only able to be assessed subjectively by slit-lamp examination and retinal photography, providing qualitative data. Optical coherence tomography (OCT) was first described by Huang and colleagues in 1991 1 . OCT, as used to acquire high resolution, crosssectional images of the ocular structures, utilises low-coherence near infrared light (800-1400 nm) generated by a super-luminescent diode, which passes through the pupil to the posterior structures of the eye 1 . It is analogous to B-scan ultrasound except that it uses light instead of sound. Over the past 10 to 15 years, OCT has become an invaluable tool and is in widespread use in both optometry and ophthalmology. OCT is used in the diagnosis and longitudinal analysis of a multitude of ophthalmic disorders that affect the optic nerve and macula, including glaucoma. Newer spectral-domain OCT has increased resolution (approximately 3 – 5 µm) and faster scan acquisition time than older time-domain OCT technology. Common spectral-domain OCT models include the Zeiss Cirrus and the Heidelberg Spectralis. Peripapillary Retinal Nerve Fibre Layer Measurements Measurement of the peripapillary RNFL thickness using OCT is now a routine component of the comprehensive glaucoma assessment. In healthy eyes, the RNFL is generally thickest in the in the inferior quadrant, followed by the superior, nasal and temporal quadrants (the “ISNT” rule). There is, however, a large degree of RNFL variability in “normal” eyes, and there is some overlap in the structural characteristics of normal eyes and eyes with early optic nerve damage due to glaucoma 2 . Many patients will have anomalous structural features that may confound the interpretation of OCT measurements, and the eye may be incorrectly classified as “abnormal”. In patients with perimetric glaucoma, the location of the RNFL thinning should correlate with the visual field defect. In those with pre-perimetric disease, it is important to compare the peripapillary RNFL thickness in the individual quadrants with the appearance of the optic nerve head on clinical examination. The ability to detect and measure structural change is essential in the diagnosis and management of glaucoma. Progression analysis software, included with some OCT models, is able to track the progression of RNFL thinning over time (figures 1 and 2). It is necessary to review the RNFL overview at each visit, as well as the progression scans, as these overview scans will give more comprehensive information regarding RNFL thickness in each eye (as well as the differences between the two eyes). It is important to discriminate true disease-related changes from measurement variability and normal age-related change. When a scan is accurate and well-centred, the 95% tolerance for average RNFL thickness is approximately 4 µm 2 . Spectral-domain OCT is more sensitive at detecting glaucoma progression than time-domain OCT 3 . Fig 1. Guided progression analysis on Zeiss Cirrus OCT. This shows progression of left RNFL thinning. The first two exams are used as baseline measurements, with subsequent scans compared to baseline. The signal strength is good in all scans however the first baseline shows an area nasal to the optic disc with an incomplete scan, hence the reason for the lower average RNFL thickness in Baseline 1 compared with Baseline 2. Over time, there has been a significant reduction in RNFL thickness in both the superior and inferior quadrants. Fig 2. Guided progression analysis on Zeiss Cirrus OCT. This shows stable RNFL thickness over six consecutive OCT scans. There is marked RNFL thinning, particularly in the superior and inferior quadrants. The fluctuation in average RNFL thickness between exams is within the 95% confidence limits for scan repeatability. Signal strength is adequate in all scans. Macular OCT Scans in Glaucoma Although the use of OCT in glaucoma has been primarily focused on the assessment of peripapillary RNFL thickness, in recent years the macular region has emerged as an area of interest; glaucomatous macular damage can occur early in the disease process. Although the macular region represents less than 2% of the retinal area, it contains 30% of the retinal ganglion cells 4 . One of the main advantages of 12 NEW ZEALAND OPTICS April 2016 macular assessment in glaucoma is that a significant portion of retinal thickness at the macula is composed of the RNFL, ganglion cell layer and the inner plexiform layer. Spectral-domain retinal layer segmentation algorithms have allowed for the quantification of individual layers in the macular region, and the measurement of ganglion cell complex thickness (the combined thickness of the RNFL, ganglion cell layer and the inner plexiform layer, although macular analysis in some OCT models includes only the ganglion cell and inner plexiform layers) 3 . The GCC thins as the glaucomatous damage progresses, with lower thickness values associated with poorer mean deviation scores on visual field testing 2,5 . Ganglion cell complex thickness in glaucoma can correlate well with RNFL thinning and visual field loss (figure 3). Repeatability of ganglion cell complex measurements may be reduced in more advanced glaucoma 6 . Fig 3. Structure-function correlation. The top left image shows a glaucomatous right optic nerve with vertical elongation of the optic cup and thinning of the superior and inferior neuroretinal rim. The rim thinning is most pronounced inferiorly. This correlates with functional changes on visual field testing, with almost complete loss of the superior visual field, and greatly reduced sensitivity in the inferior visual field. The lower images show diffuse thinning of the ganglion cell complex (measured with the Zeiss Cirrus OCT), with more extensive thinning in the inferior region. This correlates with the optic nerve and visual field appearance. Consider Other Ocular and Systemic Pathology Glaucoma is not the only condition that can cause thinning of the retinal layers. A vast number of ocular and systemic disorders can lead to peripapillary RNFL and macular thickness changes on OCT and it is always important to consider these conditions as part of the examination process. A comprehensive history and complete eye examination is essential. The patterns of RNFL loss can vary greatly between conditions. For example, patients with optic neuritis are more likely to have temporal RNFL thinning (figure 4) and the degree of RNFL loss may be out of proportion to visual field results. Multiple sclerosis is associated with thinning of the RNFL and macula (including the ganglion cell complex), even in patients with no history of optic neuritis 7 . Patients with compressive optic neuropathies can present with thinning of the RNFL. These patients are likely to have reduced RNFL thickness in the nasal and temporal quadrants compared with glaucoma patients 8 . A tilted disc, particularly in myopic patients, can cause a localised RNFL defect in the superior or inferior quadrants, similar to glaucomatous RNFL loss 9 . Longitudinal follow-up is necessary to determine whether the RNFL thinning is glaucomatous or due to the tilting of the optic nerve head 10 . Fig 4. RNFL thinning in a patient with a history of optic neuritis. This patient had a single episode of right optic neuritis (confirmed by MRI examination). Note the dramatic reduction in RNFL thickness, particularly in the temporal quadrant (less likely to be affected in glaucoma). The average RNFL thickness was 55 µm. The visual field was normal. Factors Affecting OCT Measurements A number of factors influence the quality and accuracy of retinal measurements acquired with OCT: •• Image resolution is affected by eye movement. The degradation of the image is a function of the frequency and size of saccadic eye movements, compared with the image acquisition time and the transverse resolution of the OCT 11 . Newer OCT technology attempts to counter this with the use of eye-tracking systems incorporated into the software 12 . •• Scans should be well-centred: macular scans should be centred at the fovea and accurate measurement of the peripapillary RNFL requires the reference to be centred precisely at the optic nerve head 13 . •• The signal strength of the scan needs to be adequate. Recommended minimum signal strength varies by manufacturer. Even scans with adequate signal strength may show software segmentation failure, where the automatic segmentation of the retinal layers is incorrect. If possible, these scans should be re-taken. •• Scans can be acquired effectively over a range of pupil sizes, however if the pupil size is less than 3 mm this can affect thickness measurements and scan quality 14 . •• Opacities of the lens generally give rise to lower thickness values (affecting results by up to 12%), with more advanced lens opacities leading to a greater decrease in thickness 14 . Image repeatability significantly improves following cataract extraction •• OCT measurements are affected by axial length and, subsequently, refractive error 15 , and measurements are most accurate within the range of +5 to -5 dioptres 14,16 . Longer, more myopic eyes tend to have thinner RNFL thickness values 15 . •• RNFL values for people of different ethnicities vary modestly, although it has been found that all ethnicities examined had 95% confidence limits that overlapped 15 . •• RNFL thickness decreases with age - by approximately 2 µm per decade, with loss of about 5000 axons per year 15 . Anterior Segment OCT in Glaucoma It is worth briefly mentioning the role of OCT in the examination of the anterior segment of glaucoma patients. Anterior segment OCT imaging, using a 1310 nm light source, permits the visualisation of the angle structures and provides quantitative data that can be useful in the identification of the mechanism of IOP elevation and the diagnosis of angle closure glaucoma (figure 5) 17,18 . OCT of the AC angle is a tool that is a useful addition to gonioscopy, but it should not replace gonioscopic examination. It can be used to measure the actual size of the angle, and is also particularly helpful for visualising structural changes to the angle following YAG peripheral iridotomy. Anterior segment OCT can also be used to as a noninvasive measure of central corneal thickness, a useful measure in initial glaucoma assessment. Fig 5. Anterior segment OCT scan showing narrow anterior chamber angles Conclusion There have been significant developments in glaucoma imaging over the last decade, and these imaging modalities, particularly OCT scans of the peripapillary RNFL and macula, are now used routinely in glaucoma diagnosis and on-going management. There are continuous advances in spectral-domain OCT technology, with increased resolution, reduced scan acquisition time, progression analysis software updates, en face imaging and eye movement tracking allowing for more accurate and reproducible scans, and more in-depth analysis of the ocular structures. Although OCT examination is an important component of the modern glaucoma assessment, it is not a diagnostic tool 3 ; it is a useful test in the armamentarium of the ophthalmologist and optometrist, and it should be used in conjunction with other measures of optic nerve structure and function. ▀ References 1. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991;254:1178-1181. 2. Grewal DS, Tanna AP. Diagnosis of glaucoma and detection of glaucoma progression using spectral domain optical coherence tomography. Curr Opin Ophthalmol 2013;24:150-161. 3. Bussel, II, Wollstein G, Schuman JS. OCT for glaucoma diagnosis, screening and detection of glaucoma progression. British Journal of Ophthalmology 2014;98 Suppl 2:ii15-19. 4. Curcio CA, Allen KA. Topography of ganglion cells in human retina. Journal of Comparative Neurology 1990;300:5-25. 5. Hood DC, Raza AS, de Moraes CG, Liebmann JM, Ritch R. Glaucomatous damage of the macula. Prog Retin Eye Res 2013;32:1-21. 6. Sung MS, Kang BW, Kim HG, Heo H, Park SW. Clinical validity of macular ganglion cell complex by spectral domain-optical coherence tomography in advanced glaucoma. Journal of Glaucoma 2014;23:341-346. 7. Petzold A, de Boer JF, Schippling S, et al. Optical coherence tomography in multiple sclerosis: a systematic review and meta-analysis. Lancet neurol 2010;9:921-932. 8. Danesh-Meyer HV, Yap J, Frampton C, Savino PJ. Differentiation of Compressive from Glaucomatous Optic Neuropathy with Spectral-Domain Optical Coherence Tomography. Ophthalmology 2014; 121: 1516-1523 9. Hwang YH, Yoo C, Kim YY. Characteristics of peripapillary retinal nerve fiber layer thickness in eyes with myopic optic disc tilt and rotation. Journal of Glaucoma 2012;21:394-400. 10. Chang RT, Singh K. Myopia and glaucoma: diagnostic and therapeutic challenges. Curr Opin Ophthalmol 2013;24:96-101. 11. Hee MR, Izatt JA, Swanson EA, et al. Optical coherence tomography of the human retina. Arch Ophthalmol 1995;113:325-332. 12. Serbecic N, Beutelspacher SC, Aboul-Enein FC, Kircher K, Reitner A, Schmidt-Erfurth U. Reproducibility of high-resolution optical coherence tomography measurements of the nerve fibre layer with the new Heidelberg Spectralis optical coherence tomography. British Journal of Ophthalmology 2011;95:804-810. 13. Cheung CYL, Yiu CKF, Weinreb RN, et al. Effects of scan circle displacement in optical coherence tomography retinal nerve fibre layer thickness measurement: a RNFL modelling study. Eye 2009;23:1436-1441. 14. Savini G, Zanini M, Barboni P. Influence of pupil size and cataract on retinal nerve fiber layer thickness measurements by Stratus OCT. Journal of Glaucoma 2006;15:336-340. 15. Budenz DL, Anderson DR, Varma R, et al. Determinants of normal retinal nerve fiber layer thickness measured by Stratus OCT.[Erratum appears in Ophthalmology. 2008 Mar;115(3):472]. Ophthalmology 2007;114:1046-1052. 16. Menke MN, Knecht P, Sturm V, Dabov S, Funk J. Reproducibility of nerve fiber layer thickness measurements using 3D fourier-domain OCT. Invest Ophthalmol Vis Sci 2008;49:5386-5391. 17. Sharma R, Sharma A, Arora T, et al. Application of anterior segment optical coherence tomography in glaucoma. Survey of Ophthalmology 2014;59:311-327. 18. Smith SD, Singh K, Lin SC, et al. Evaluation of the anterior chamber angle in glaucoma: a report by the american academy of ophthalmology. Ophthalmology 2013;120:1985-1997. * Hannah Kersten is a therapeutically qualified optometrist with glaucoma prescriber accreditation. She has recently completed her doctoral studies in the Department of Ophthalmology at the University of Auckland, under the supervision of Professor Helen Danesh-Meyer, and Dr Richard Roxburgh of the Department of Neurology. The topic of her thesis was optical coherence tomography in neurodegenerative disease. Hannah is currently working as a post-doctoral research fellow in the Department of Ophthalmology and she is also involved in glaucoma co-management with Professor Danesh-Meyer at Eye Institute in Auckland.
Colour vision test ends Routine, school-based check-ups of 11 and 12-year-old students will no longer include testing for colour vision deficiency as of July 1. The Ministry of Health announced it would eliminate the test in February to allow more time for technicians to identify hearing and vision problems among children at an earlier age when intervention makes a bigger difference. Colour blindness is relatively unusual, especially among girls. The condition is found in 0.5% of the female population, whereas colour vision deficiency affects about 10% of the 26,000 boys screened annually as part of the standard Year 7 checks. The Ministry’s decision was influenced by a summer research project, which reviewed the medical literature on the efficacy of colour vision testing, and was overseen by ophthalmologist Dr Graham Wilson, in his role as clinical senior lecturer at the University of Otago, and his brother Nick Wilson, a professor at Otago’s Department of Public Health. “We found there was no evidence to support screening for colour blindness,” says Dr Wilson. “We screen for things like breast cancer and cervical cancer, things that can kill you, and colour blindness doesn’t rise to that level.” Ministry Chief Advisor, Child and Youth Health, Dr Pat Tuohy explained the policy change to medical technicians who conduct the school checks at a conference in late February. “They feel it will free up their time to do other things,” says Dr Wilson, who attended the conference. “I think people see the common sense in it.” Dr Wilson, his brother and Nishanthan Ramachandran, a health policy student, published their paper Is screening for congenital colour vision deficiency in school students worthwhile? A review in the November 2014 edition of Clinical and Experimental Optometry. The review analysed the literature on screening for congenital colour vision deficiency in school students, which predominantly uses the Ishihara test, and found no association between congenital colour vision deficiency and the level of educational achievement; only a rare association between the condition and other health and lifestyle impacts; and limited interventions. “Given this picture, the weight of evidence appears to be in favour of not adopting (or discontinuing) routine colour vision screening programmes for school students; however, it may be worthwhile for a career advisor to refer school students to an optometrist or ophthalmologist for colour vision screening, upon expression of interest in an occupation where normal colour vision is either particularly desirable or is a regulatory requirement,” concluded their paper. ▀ Donations for ship-clinic The Tauranga Rotary club is raising funds and looking for equipment donations for a humanitarian group to bring an ophthalmic clinic to remote Pacific islands. The club has launched a campaign to raise $95,000 for Marine Reach, a humanitarian organisation that delivers health services to isolated populations from its vessel, the MV Pacific Hope. The total money raised—likely to include a matching grant from a Rotary international fund—will be used to purchase items on an ophthalmic clinic “wish list”, including a Sonamed Portable AB Scanner, Nidek hand held keratometer, a slit lamp, an instrument sterilising container, portable microscope and an operating bed. The plan is for the ship-board clinic to be dedicated and named The Rotary Foundation Ophthalmology Clinic, with contributors of over $500 recognised by inscription on a special plaque displayed in the Clinic. Other donors will be invited to sponsor a specific piece of equipment and have their name inscribed on an appropriate plaque fixed to the item. The club is also open to surplus equipment donations or discounted price offerings. Marine Reach purchased the Pacific Hope and refit the vessel in 2013. It undertook its first clinical voyage, with a dental and general medical outreach programme in Fiji and Vanuatu, from late June to early October 2015. The next voyage is likely to begin in June 2016. Anyone interested in making a financial or equipment contribution should contact project coordinator David Garland on 07 543 2012. You can also make a direct financial contribution through Give a Little at https://givealittle.co.nz/ org/tgarotary. For more information on Marine Reach, visit www.marinereach.com. ▀ ZEISS launches DriveSafe Zeiss has launched new DriveSafe lenses to provide better vision in challenging driving conditions. Calling them “probably the most exciting safety feature in your car,” Zeiss says the new lenses are designed to maximise safety and comfort for spectacle wearers through a new premium coating and state-of-the art lens design. According to Zeiss’ research, 83% of drivers wear glasses and the majority (72%) of these prefer a single pair for everyday use that can also assist with the visual challenges of driving. Spectacle wearers report feeling discomfort when driving in rain (94%), at dusk (88%), at night (76%) and in fog (74%). While the majority of traffic accidents occur at dusk or after nightfall. “DriveSafe lenses address the major challenges facing spectacle wearers while driving in difficult light and weather conditions,” the company said. To better understand the requirements for dynamic vision while driving, ZEISS commissioned a study by the Research Institute of Automotive Engineering and Vehicle Engines in Stuttgart (FKFS) using a modified car on a real-world course. The setup included head and eye tracking systems to observe drivers’ visual behaviour. The study found that drivers focus on the road ahead and distant moving objects about 97% of the time, look at the dashboard 2% of the time and alternate viewing between the mirrors 1% of the time. Progressive lens wearers move their heads more than single vision wearers in order to avoid lens zones of incorrect power or that have high levels of aberration. FKFS also found that the closest object viewed on the dashboard is approximately 50-75 cm away from the driver’s eye, implying the near zone of a progressive lens, designed for a much closer distance, is virtually unused. “Drivers must contend with a rapidly alternating set of circumstances that require constant attention and dynamic vision. The DriveSafe lens is optimised to provide uncompromised distance vision, with a large intermediate zone that supports quick and comfortable focus when switching between the dashboard and mirrors.” The new lenses incorporate ZEISS DuraVision DriveSafe antireflective coating to mitigate the uncomfortable blue-light glare from Xenon/HID and LED headlights and Zeiss’ Luminance Design Technology that takes into account pupil size in different light conditions to assist drivers in detecting objects in conditions where they are more likely to feel stressed or insecure, such as twilight, rain or at night. European wearer trials revealed very high satisfaction levels for ZEISS DriveSafe lenses, the company reported, with 97% of test subjects satisfied with the new lenses when driving, including in challenging situations such as in the dark and twilight. Respondents reported good dynamic vision in near, intermediate and distant zones, good perception of colours and reduced dazzle/glare from headlights. In addition, 94% of respondents found the new lenses suitable for doing everyday tasks. “Drivers require the best technology for their vision needs today,” says Hilke Fitzsimons, managing director for ZEISS Australia and New Zealand. “Surveys show over two-thirds of adults have difficulty in driving in low light or adverse weather conditions. Our new DriveSafe lenses address problems of glare, depth perception, and vision acuity at all distances.” ZEISS DriveSafe will be available in New Zealand from April 4 in both progressive and single vision designs. The launch will be supported by an extensive digital promotion where consumers will be invited to become “test drivers” and win a pair of ZEISS DriveSafe Lenses at www.zeiss.com.au/DriveSafe. ▀ Get to the main cause of dry, irritated eyes* Optrex ActiMist – clinically proven to work How does Optrex ActiMist work? Optrex ActiMist contains liposomes (tiny bubbles fi lled with moisture) that migrate across the surface of the eyelid and collect at the edges of the eye. Hygienic. Can be used by multiple people Lasts 6 months after opening These liposomes mix with natural lipids on the eyelid. Won’t smudge make-up ActiMist liposomes Convenient and portable 4UP TO HOURS RELIEF 2 CLINICALLY PROVEN Natural lipids ActiMist liposomes When the eyes are open the new lipid mixture spreads over the whole tear fi lm, and helps fi ll the gaps to restore the damaged lipid layer. Suitable for use with contact lenses Order stock for your practice today FREE CALL 0800 393 564 EYELOGIC www.optrex.co.nz optrex@eyelogic.com.au Always read the label. Use only as directed. If symptoms persist, see your healthcare professional. †When wearing make-up, it is recommended to apply from 20cm. *Due to disturbed lipid layer of the tear fi lm. References: 1. Lee S et al. Klin Monatsbl Augenheilkd 2004; 221:1–12. 2. Khaireddin R, Schmidt KG. Klin Monatsbl Augenheilkd. 2010; 227: 128-134. 3. Pult H et al. Contact Lens Anterior Eye 2012, 35:203-207. Reckitt Benckiser, Auckland. TAPS DA1541 April 2016 NEW ZEALAND OPTICS 13
Page 1 and 2: THE MAGAZINE FOR NEW ZEALAND’S OP
Page 3 and 4: OTs tackle low vision Collaboration
Page 5 and 6: IT’S TIME TO PLAY... $..‘000’
Page 7 and 8: Making the revolutionary, routine.
Page 9 and 10: A NEW LOOK FOR AUCKLAND EYE After n
Page 11: oDocs goes commercial, seeks invest
Page 15 and 16: Summer Student Symposium 2016 A div

Apr 2016

Create successful ePaper yourself

Delete template?

Save as template?