Interpret / Visual fields

Pattern to pathway

A field defect is an address. One eye or both, the vertical midline or the horizontal, homonymous or not, how congruous, whether the macula is spared: answer those and the pattern tells you where the lesion sits, from the retina to the occipital cortex. The fields here are schematic diagrams of each pattern, drawn as the patient sees them, not perimeter printouts.

Where is the lesion?

Field 01 of 9

Left eye

Right eye

Schematic fields, as the patient sees them; dark is lost.

Where is the lesion?

The pathway

The rules

One eye or both? One eye: the problem is in front of the chiasm, in the retina or the nerve. Both eyes: the chiasm or behind it, unless there are two separate problems.
Does it respect the vertical midline? Yes: the chiasm or behind it, where the fibres are sorted into left and right worlds. The retina and nerve do not know where the vertical meridian is.
Does it respect the horizontal midline? Yes: the optic nerve head, whose fibres and blood supply are divided into upper and lower halves. Arcuate, altitudinal and nasal step defects are nerve head patterns.
Homonymous or heteronymous? The same side in both eyes (homonymous) is behind the chiasm, on the opposite side of the brain. Opposite sides (bitemporal) is the chiasm.
How congruous? The more alike the two eyes' defects, the further back the lesion: tract lesions are incongruous, occipital lesions almost identical.

The rules

One eye or both?: One eye: the problem is in front of the chiasm, in the retina or the nerve. Both eyes: the chiasm or behind it, unless there are two separate problems.
Does it respect the vertical midline?: Yes: the chiasm or behind it, where the fibres are sorted into left and right worlds. The retina and nerve do not know where the vertical meridian is.
Does it respect the horizontal midline?: Yes: the optic nerve head, whose fibres and blood supply are divided into upper and lower halves. Arcuate, altitudinal and nasal step defects are nerve head patterns.
Homonymous or heteronymous?: The same side in both eyes (homonymous) is behind the chiasm, on the opposite side of the brain. Opposite sides (bitemporal) is the chiasm.
How congruous?: The more alike the two eyes' defects, the further back the lesion: tract lesions are incongruous, occipital lesions almost identical.
Is the macula spared?: Sparing of the central few degrees in a homonymous hemianopia points to the occipital pole with its double blood supply.
Reliability first: Fixation losses, false positives and false negatives on the printout decide whether the field can be believed at all.

Every pattern

Left eye
Right eye
Normal. Schematic fields, as the patient sees them; dark is lost.
Retina. Nothing is lost. Each eye's field extends about 60 degrees nasally and 90 degrees temporally, with the blind spot 15 degrees temporal to fixation where the disc has no photoreceptors.
Left eye
Right eye
Central scotoma, right eye. Schematic fields, as the patient sees them; dark is lost.
Optic nerve. One eye and the centre: the papillomacular bundle, the fibres from the macula, or the macula itself. In a young adult with pain on eye movement this is optic neuritis; in an older smoker, a toxic or nutritional neuropathy; with distortion, a macular disease.
Left eye
Right eye
Bitemporal hemianopia. Schematic fields, as the patient sees them; dark is lost.
Optic chiasm. The temporal field of each eye is seen by the nasal retina, and nasal fibres cross in the chiasm. A lesion there, classically a pituitary adenoma pressing from below, takes both temporal fields and respects the vertical midline in each eye.
Left eye
Right eye
Right homonymous hemianopia. Schematic fields, as the patient sees them; dark is lost.
Occipital cortex. The same side of both fields: behind the chiasm, on the opposite side of the brain (the left hemisphere sees the right world). When it is complete and congruous, the whole retrochiasmal pathway is possible; the occipital cortex is the most common site, from a posterior cerebral artery stroke.
Left eye
Right eye
Left homonymous hemianopia with macular sparing. Schematic fields, as the patient sees them; dark is lost.
Occipital cortex. Sparing of the central few degrees on the affected side points to the occipital pole, which has a dual supply from the posterior and middle cerebral arteries: a posterior cerebral artery occlusion leaves the pole alive.
Left eye
Right eye
Right superior quadrantanopia. Schematic fields, as the patient sees them; dark is lost.
Temporal lobe radiations. A pie in the sky: the fibres from the inferior retina, which sees the superior field, loop forward around the temporal horn as Meyer's loop before turning back. A left temporal lobe lesion takes the right upper quadrants of both eyes.
Left eye
Right eye
Left inferior quadrantanopia. Schematic fields, as the patient sees them; dark is lost.
Parietal lobe radiations. A pie on the floor: the superior retinal fibres run straight back through the parietal lobe. A right parietal lesion takes the left lower quadrants.
Left eye
Right eye
Inferior altitudinal defect, left eye. Schematic fields, as the patient sees them; dark is lost.
Optic nerve. One eye, and the horizontal midline respected: the optic nerve head, whose blood supply is divided into an upper and a lower half. This is the field of non-arteritic anterior ischaemic optic neuropathy, sudden and painless, with a swollen disc.
Left eye
Right eye
Superior arcuate scotoma with a nasal step, right eye. Schematic fields, as the patient sees them; dark is lost.
Optic nerve. The nerve fibres arch around the macula from the disc, and those from the inferior disc rim serve the superior field. Glaucoma damages the rim in bundles, so the loss is an arc that stops at the horizontal midline nasally: the nasal step.
Left eye
Right eye
Generalised constriction, both eyes. Schematic fields, as the patient sees them; dark is lost.
Retina. The periphery goes in from all sides. In the retina this is retinitis pigmentosa, with night blindness first; in the nerve, end-stage glaucoma or papilloedema of long standing. A field that stays the same size at two testing distances is functional (tunnel), a true one widens with distance (funnel).

Reading a perimetry printout

24-2 and 30-2: The standard Humphrey programmes: a grid of points across the central 24 or 30 degrees, each tested to threshold.
Greyscale: The picture: darker means less sensitive. It is the map, not the evidence.
Total and pattern deviation: Total deviation compares with an age-matched normal; pattern deviation removes a general depression (cataract, a small pupil) to reveal the focal defect.
Reliability indices: Fixation losses, false positives, false negatives. High false positives make a field look better than it is.
Mean deviation: One number for the whole field's depression, used to stage glaucoma and follow it.
Progression: One field is a photograph; the trend across several is the diagnosis. Glaucoma is followed by the series, never by a single test.

A verified, openly licensed perimetry printout has not yet been found for the atlas, so none is shown; the patterns above are diagrams.

The bedside test is confrontation: how to do it. The pathway continues in neuro-ophthalmology.