terminology and guidelines for glaucoma ii - Kwaliteitskoepel

1.3.2.c - Rim/disc ratio (RDR)
The fractional decimal value obtained dividing the rim thickness by the disc diameter. The closer the value is to 1,
the better the optic disc appearance. It can be calculated as vertical diameters as for the cup/disc ratio but obviously
with the opposite meaning, as rim area/disc area ratio (RDR or R/D). This latter can also be calculated for each degree
of the optic disc as a sector index of a healthy disc.
1.3.2.d - Retinal Nerve Fiber Layer Height (RNFLH)
The thickness of the RNFL depends on disc area, age, stage of the glaucomatous damage. It has been shown that vertical
polar sectors were thicker than nasal and temporal. It was also shown that RNFL height in normal was thicker
than in glaucomatous subjects 16,22 .
1.3.3 - RECORDING OF THE OPTIC NERVE HEAD (ONH) FEATURES
Colour disc photos are useful for patient documentation.
Colour photography with a 15° field gives optimal magnification.
Stereoscopic photographs are the preferred method. Pseudo-stereoscopic photos are also acceptable.
New systems for the ONH assessment, using alternative technologies, are being evaluated for reproducibility, specificity
and sensitivity, although very few are currently available to the general ophthalmologist due to their cost (see
Ch. 1.3.4).
Drawings are better than nothing if a fundus camera is not available.
Recording of the nerve fibre layer (NFL) features.
The photographic methods require specialized processing of film. Patients must have clear media and photography of
lightly coloured fundi are more difficult. The technique is available in some centres, though their use in routine clinical
work is limited.
New systems for NFL assessment, using alternative technologies, are being evaluated for reproducibility, specificity
and sensitivity, although currently very few are available to the general ophthalmologist due to their cost (see Ch.
1.3.4).
1.3.4 - IMAGING IN GLAUCOMA
Although clinical examination still remains the most important method of assessing the ONH for glaucomatous damage,
several imaging devices are now available, allowing quantitative measurements of nerve structure. This may aid
clinical management 23 .
These include confocal scanning laser ophthalmoscopy (e.g. Heidelberg Retina Tomograph (HRT)), scanning laser
polarimetry (e.g. GDx), optical coherence tomography (e.g. OCT) and retinal thickness analyzer (e.g. RTA). Other
methods of documentation of structure (e.g. stereo disc photography) are also widely used. In using these machines,
accuracy and reproducibility of measurement is important, as well as the ability to discriminate between healthy and
glaucomatous subjects, now very limited in early disease.
It must be emphasized that the process of categorising patients by means of imaging device measurements is not
the same as diagnosis. Diagnosis must also integrate all the other available information about the patient, including
clinical assessment of the ONH and RNFL, visual field and risk factors including IOP, age and family
history.
In the future, with greater clinical information being provided by optic disc measurement and with the cost of the
instruments declining, the clinical use of these devices is likely to expand.
1.3.4.1 - HRT
The Heidelberg Retina Tomograph is a confocal scanning laser which uses a 670nm light source and can assess the
optic nerve head by creating a threedimensional image 24-26 .
1.3.4.2 - GDX
The nerve fiber layer analyzer is a scanning laser polarimeter which uses a 780 nm polarized light source and can
quantify the retinal nerve fiber layer thickness by measuring the retardation of the reflected light 27-29 .
Ch. 1 - 20 EGS