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Describe the optic disc changes in glaucoma.

Ophthalmology · 3rd Professional

Normal Disc Anatomy

The optic disc consists of a central cup and a surrounding neuroretinal rim, the rim being the axons of the retinal ganglion cells turning to leave the eye. Glaucoma destroys axons, so it destroys rim, and the cup enlarges only because the rim has gone
The cup-disc ratio must be interpreted against disc size, which is the commonest error in disc assessment. A large disc has a large physiological cup and a small disc a small one; so a cup-disc ratio of 0.7 may be entirely normal in a large disc and grossly abnormal in a small one. Assess the rim, not the cup
The ISNT rule — in a normal disc the neuroretinal rim is thickest inferiorly, then superiorly, then nasally, and thinnest temporally. Violation of this order suggests glaucoma, and it is the single most useful rule for a non-specialist

Sign of glaucomatous damage	Description
Generalised enlargement of the cup	Concentric loss of rim; harder to detect without a baseline record
Focal notching of the rim	A localised excavation, characteristically at the inferotemporal then superotemporal pole, where the lamina cribrosa is thinnest. Highly specific for glaucoma
Vertical elongation of the cup	Because rim is lost at the upper and lower poles first, the cup becomes vertically oval — whereas a physiological cup is horizontally oval
Disc haemorrhage (DRANCE haemorrhage)	A flame-shaped or splinter haemorrhage crossing the disc margin, inferotemporal. It is a marker of active progression, is commoner in normal-tension glaucoma, is easily missed and resolves in weeks — so finding one should prompt a review of the target pressure
BARING of the circumlinear vessel	A vessel that normally hugs the rim is left with a gap between it and the cup edge as rim is lost
Bayonetting of vessels	A vessel makes a double right-angled bend as it dips into a deep, undermined cup and out again
Nasal shift of the vessel trunk	The central vessels are displaced nasally as the cup enlarges
Laminar dot sign	The pores of the lamina cribrosa become visible at the floor of an excavated cup
Peripapillary atrophy	Especially the beta zone of chorioretinal atrophy with visible sclera and choroidal vessels.
Retinal nerve fibre layer defects	Wedge-shaped dark defects radiating from the disc, best seen with red-free (green) light. They may precede the field defect by years and are visible with an ordinary ophthalmoscope with a green filter

Assessment and Applied Aspects

Examine the disc stereoscopically with a slit lamp and a 78 or 90 dioptre lens through a dilated pupil; a direct ophthalmoscope gives magnification but no depth perception, and depth is exactly what is being judged
Record the disc objectively — by stereo photography, or by drawing it in the notes.
Optical coherence tomography quantifies the retinal nerve fibre layer thickness and the ganglion cell complex, giving objective and reproducible measurement with comparison against a normative database and against the patient’s own baseline. It detects loss before perimetry does

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