terminology and guidelines for glaucoma ii - Kwaliteitskoepel

1.3 - OPTIC NERVE HEAD AND RETINAL NERVE FIBER LAYER
The identification of structural, contour and color changes is best done stereoscopically. The pupil should be dilated
whenever possible to facilitate the exam. Two methods allow for time-efficient and inexpensive stereoscopic examination
of the posterior pole:
• indirect fundus lens (78D or 90D) at the slit-lamp
• direct fundus lens (central part of Goldmann and Zeiss 4-mirror, Hruby) at the slit-lamp
Fig. 1
Different optic nerve head contours: A) normal ONH,
B) glaucomatous ONH, C) tilted ONH.
The direct ophthalmoscope can give three-dimensional
information using parallax movements. It is essential to
select a spot size with a diameter smaller than the diameter
of the disc. This is to avoid light spreading from the peripapillary
retina altering the colour appearance of the rim.
The evaluation of the optic nerve head (ONH) and retinal
nerve fiber layer (RNFL) may be divided into 2 parts:
1.3.1 - Qualitative
a) contour of the neuroretinal rim
b) optic disc hemorrhages
c) parapapillary atrophy
d) bared circumlinear vessels
e) appearance of the retinal nerve fibre layer
1.3.2 - Quantitative
a) optic disc size (vertical disc diameter)
b) cup/disc ratio (vertical)
c) rim/disc ratio
d) retinal nerve fiber layer height (RNFLH)
1.3.1.a - Contour of the neuroretinal rim
With intact nerve fibers the contour of the rim depends on
the shape of the optic disc canal (Fig. 1).
The disc is usually slightly vertically oval. Black subjects
often have larger discs as a result of a greater vertical disc diameter 1 .
In normal discs with small cups the neuroretinal rim is at least as thick at the 12 and 6 o’clock positions as elsewhere
and usually thickest (83% of eyes) in the infero-temporal sector, followed by the supero-temporal, nasal and then
temporal sectors (I.S.N.T.) 2 . This pattern is less marked in larger discs, in which the rim is distributed more evenly
around the edge of the disc (Fig. 2a, 2b).
Optic cups are on average horizontally oval. However, large physiological cups in large discs tend to be more round
than horizontally oval and the more vertically oval discs tend toward having a more vertically oval cup.
Cupping tends to be symmetrical between the two eyes, the comparative vertical cup/disc ratio being within 0.2 in
over 96% of normal subjects.
Glaucoma is characterized by progressive thinning of the neuroretinal rim. The pattern of loss of rim varies and may
take the form of diffuse thinning, localized notching, or both in combination (fig. 2b). Thinning of the rim, while occuring
in all disc sectors, is generally greatest at the inferior and superior poles, leading to a loss of the physiological rim
shape so that the infero-temporal rim is no longer the thickest 3-7 .
The optic cup often enlarges in all directions, but usually the enlargement occurs predominantly in the vertical direction,
as a result of rim loss at the poles (Fig. 2b).
Ch. 1 - 16 EGS