terminology and guidelines for glaucoma ii - Kwaliteitskoepel

Fig. 5
A) Cirumlinear vessel,
B) Bared circumlinear
vessel
ground. The initial abnormality in glaucoma may be either diffuse thinning or localized defects. Since the prevalence
of true NFL defects is < 3% in the normal population, their presence is very likely to be pathological 13-18 .
1.3.2.a - Optic disc size (vertical disc diameter)
The thickness of the rim and, conversely, the size of the cup varies physiologically with the overall size of the disc 19 .
The size of optic discs varies greatly in the population.
Disc size is related to refractive error, being usually smaller in hyperopes than in myopes. Discs in highly myopic eyes
above 7 diopters are harder to interpret.
The vertical diameter of the optic disc can be measured at the slit lamp using a contact or a condensing lens. The slit
beam should be coaxial with the observation axis; a narrow beam is used to measure the disc height using the white
scleral ring as a reference landmark. The magnification corrections needed vary with the optical dimensions of the
eye and with the lens used for measurement. The measured or estimated ONH size should be written in the chart.
Magnification correction factors
Type of lens Lim CS et al 20 Manufacturer’s data
Volk 60 D 0.88 0.92
78 D 1.11 1.15
90 D 1.33 1.39
Nikon 60 D 1.03 1.02
90 D 1.63 1.54
Haag-Streit Goldmann - 1.14
1.3.2.b - Cup/disc ratio (CDR)
The decimal value obtained by dividing the cup diameter with the disc diameter. The closer the value is to 1, the
worse the damage. The vertical cup/disc ratio is a better measure of deviation from normal than the horizontal ratio,
because early neuroretinal rim loss occurs preferentially at the upper and lower poles of the disc 21 .
A difference in cup/disc ratio between eyes with equal overall optic disc size is suggestive of tissue loss and therefore is
highly suspicious of acquired damage. Expressing the size of a cup as a cup/disc ratio (C/D or CDR) is of limited value
unless the actual size of the disc is known. A CDR > 0.65 is found in less than 5% of the normal population (Fig. 2a).
Ch. 1 - 19 EGS