10/03/2026
Would you describe this fundus photograph as showing total cupping, or would you grade the cupping differently?
Bayonetting of retinal vessels is a characteristic fundus finding seen in deepening of the optic cup, particularly in advanced glaucomatous optic neuropathy. It refers to the sharp angulation or apparent bending of retinal vessels as they pass over the wall of a deeply excavated optic cup.
Normally, retinal vessels emerge from the optic disc and pass smoothly over the relatively shallow surface of the optic nerve head. With progressive loss of the neuroretinal rim, the optic cup becomes deeper and larger. The vessels are consequently displaced towards the edge and wall of the cup, producing the characteristic bayonet-like appearance.
Bayonetting is usually associated with advanced glaucomatous cupping, but it should not be considered diagnostic of glaucoma on its own. The optic disc must be assessed as a whole, including the size and shape of the disc, cup-to-disc ratio, neuroretinal rim, vessel displacement and the retinal nerve fibre layer.
In glaucoma, progressive loss of retinal ganglion cells produces thinning of the neuroretinal rim, particularly at the superior and inferior poles. This results in vertical enlargement of the cup and may lead to violation of the normal ISNT rule. As cupping becomes more pronounced, other signs such as nasal displacement of vessels, baring of circumlinear vessels, increased visibility of the lamina cribrosa and peripapillary retinal nerve fibre layer defects may become evident.
The cup-to-disc ratio should always be interpreted in relation to the disc size. A large cup is not necessarily pathological because a patient with a large optic disc may naturally have a large physiological cup. Similarly, asymmetry between the two eyes becomes more significant when it is associated with corresponding changes in the neuroretinal rim, retinal nerve fibre layer or visual field.
Therefore, while examining a suspicious optic disc, the clinician should not simply record the C/D ratio. The depth and configuration of the cup, integrity of the neuroretinal rim, course of the retinal vessels, presence of disc haemorrhage, retinal nerve fibre layer appearance and comparison with the fellow eye should all be carefully assessed.
In summary, bayonetting of retinal vessels is a sign of marked optic-disc excavation, classically encountered in advanced glaucomatous optic neuropathy. Its presence should prompt a careful evaluation for other structural and functional evidence of glaucoma rather than being interpreted in isolation.
