A systematic approach to the fundus

Say which eye it is before you say anything else. On a photograph the disc is nasal, so a disc on the right side of the image is a right eye. Then say what the photograph covers: a standard posterior pole image is about forty five degrees across and includes the disc, the macula and the arcades; a widefield image reaches almost to the ora serrata and distorts the periphery. Then judge the media: a photograph that is hazy all over has a cataract or vitreous haemorrhage in the way, and subtle findings in a hazy image mean less than obvious ones in a clear one. Note the colour of the fundus: darker in a pigmented patient, and tigroid where the choroidal vessels show through a thin pigment layer, both normal.

At the ophthalmoscope the same step is the red reflex from arm's length, then coming in close on the temporal side, finding a vessel, and following its branches back to the disc.

The disc is examined in four parts, in order. The colour of the rim: pink in health, pale in atrophy, hyperaemic in swelling. The margin: sharp in health, blurred in swelling, and normally a little less sharp nasally. The cup: a pale central depression, its diameter compared with the disc's as a ratio, about 0.3 in most healthy discs and rarely above 0.5, and within about 0.2 of the other eye. The rim should follow the ISNT rule, thickest inferiorly, then superiorly, then nasally, then temporally; a rim that is notched at the top or bottom is losing fibres. Finally the vessels at the disc: they should emerge from the cup and cross the rim without bending sharply; bayoneting over a deep cup means glaucoma, new vessels on the disc mean proliferative retinopathy, and a splinter haemorrhage on the rim is a sign of progression in glaucoma.

A peripapillary crescent of bare sclera or pigment beside the disc is common in myopia and is not a finding. Myelinated nerve fibres, feathery white patches at the disc edge, are a normal variant.

Follow each of the four arcades out from the disc, artery and vein together, as far as the photograph goes. Arterioles are narrower and brighter with a central light reflex; venules are wider and darker, about half as wide again as the arteries beside them (an arteriole to venule ratio of about two to three). Look at calibre: narrowed, straightened arterioles with a broadened, coppery reflex are hypertension and arteriolosclerosis. Look at the crossings: where an artery crosses a vein it should not indent it; nicking of the vein at a crossing is arteriovenous nipping, and it is where branch vein occlusions start. Look for sheathing, a white line along a vessel, in old occlusion, inflammation and severe hypertension. Look for emboli, bright plaques at bifurcations. And look for new vessels away from the disc, fine tangles that do not obey the tree, which mean ischaemia.

Then look at what the vessels have left behind. Flame haemorrhages lie in the nerve fibre layer and follow its striations near the disc. Dot and blot haemorrhages are deeper and rounder. Cotton wool spots are fluffy white infarcts of the nerve fibre layer along the arcades. A wedge of haemorrhage confined to one vein's territory, fanning out from a crossing, is a branch vein occlusion; haemorrhage in all four quadrants with dilated tortuous veins and a swollen disc is a central vein occlusion.

The macula lies two disc diameters temporal to the disc, between the arcades, darker than the retina around it, with no vessels crossing its centre. In a young eye there is a bright pinpoint foveal reflex. Look for five things. Drusen: yellow round deposits, small and hard or large and soft, the sign of age-related degeneration. Exudate: waxy yellow deposits with sharp edges, in rings or a star around leaking vessels, the sign of macular oedema and of hypertension. Haemorrhage: red at the macula in diabetes, vein occlusion and wet degeneration, and a dark grey-green membrane beneath it in the last. Oedema: a loss of the reflex and a thickened, dull look, which the photograph shows poorly and OCT shows well. Pigment: clumping and atrophy in dry degeneration, a bull's eye in some toxic and inherited maculopathies.

A cherry red spot is the fovea looking red because the retina around it has turned pale: in a sudden painless loss of vision it is a central retinal artery occlusion, and in a child it is a storage disease.

Sweep the four quadrants beyond the arcades in turn: superotemporal, superonasal, inferonasal, inferotemporal. On a posterior pole photograph the periphery is mostly out of frame, so say so; on a widefield image it is where tears and detachments show. Look for a retinal break, a red horseshoe or round hole against the grey of the retina, and for detachment, a grey, wrinkled, elevated retina that has lost the choroidal pattern and whose vessels look dark. Look for lattice degeneration, spindle-shaped patches with white lines and pigment along the equator, the ground where breaks form. Look for bone spicule pigment in the mid periphery, the sign of retinitis pigmentosa. And look for haemorrhage and exudate out here too, because diabetic and hypertensive changes do not stop at the arcades.