Glaucoma and small optic discs: a diagnosis challenge

The Science behind the Tip

Diagnosis and follow-up of glaucoma is challenging in eyes with small optic discs (height < 1.2 mm or surface area < 1.15 mm2, as measured with a slit lamp beam or imaging device, respectively)(1,2). In healthy eyes, these discs either have no detectable cups, or very small ones due to crowding of the optic nerve fibres in a small scleral canal. Typical glaucomatous disc changes such as thinning of the neuroretinal rim and an abnormally high cup-to-disc ratio, are late and mild(1). Small optic discs thus can have misleadingly low cup-to-disc ratios and visual field loss often occurs despite a normal disc appearance. Parapapillary chorioretinal atrophy can be more apparent than changes at the disc itself and may thus be a more sensitive indicator of structural glaucomatous damage(1).

Glaucomatous small optic discs have to be differentiated from buried optic nerve drusen in the presence of subtle visual field defects, especially when intraocular pressure is normal(3).

Careful follow-up may be all the more important as small optic discs may have less reserve capacity as compared to normal size discs. Optic nerve fibres may be fewer in number, possibly making these discs more vulnerable to glaucomatous insults(4).

Contributor: Michèle Detry, Brussels
Co-editors: John Thygesen and Ann Hoste
Peer reviewers: Roger Hitchings and Anders Heijl

References

1. Jonas JB, Fernandez MC, Naumann GO. Glaucomatous optic nerve atrophy in small discs with low cup-todisc ratios. Ophthalmology. 1990;97:1211-5.

2. Jonas JB, Gusek GC, Guggenmoos-Holzmann, Naumann GO. Size of the optic nerve scleral canal and comparison with intravitreal determination of optic disc dimensions. Graefes Arch Clin Exp Ophthalmol. 1988;226:213-5.

3. Katz BJ, Pomeranz HD. Visual field defects and retinal nerve fiber layer defects in eyes with buried optic nerve drusen. Am J Ophthalmol. 2006;141:248-53.

4. Panda-Jonas S, Jonas JB, Jakobczyk M, et al. Retinal photoreceptor count, retinal surface area, and optic disc size in normal human eyes. Ophthalmology. 1994; 101:519-23.

Tip Reviewer: Roger Hitchings
Tip Editors: Ann Hoste, John Salmon and John Thygesen