Cognitive Visual Disturbances in Chiasmal Disorders: A Review on Exceptional Visual Disabilities as Based on 30 Years’ Clinical Experience

A combined delay by the patient and the doctor is a common feature of chiasmal disorders. For the patient, the main reason seems to be unawareness of visual loss as being associated primarily with slow growth of the basic lesion (typically pituitary adenoma, craniopharyngioma, or skull base meningioma). Delay can also arise due to the insidious and asymmetric nature of the initial visual field drop-outs, the defects of one eye being compensated for by the other when binocular. Complaints, when acknowledged, are usually vague.

When seen in the clinic, however, a minority of patients may present more specific features that include cognitive elements, the most frequent being a lateralizing ignorance under customary testing for single eye visual acuity.Usually this manifests as varying degrees of nasal preference on the board, or a temporally located ignorance (NP/TI). Some patients experience an inability to read print, despite apparently normal or fair visual acuity data. A few also describe mis-interpretation of moving events in visual space. The following is suggested as a kind of collective definition: a cognitive ignorance or mis-interpretation in visual space, probably related to conductive loss of information to supratentorial connections and not readily compensated for by relevant eye movements.

Over 3 decades, varying degrees of this aberrant visual behaviour have been acknowledged in a total of 64 adult patients, in one eye or in both, and often with a side difference when of binocular occurrence.It may be associated with visual acuity loss, but has also occurred in patients with a decimal best corrected visual acuity of 1.0 in both eyes. One such patient with full monocular acuities presented 4-5ᵒ paracentral heteronymous scotomas as the only visual field manifestation; both eyes were strictly nasal on the chart, and reading books had become impossible. In cases with markedly reduced visual acuity (e.g. 0.16–0.05), single eye testing may even add the most central nasal 10–20° to the hemianopic temporal visual field loss . Paradoxically, fixation usually appears stable in such cases despite the apparent inclusion of the central target for fixation in the functional scotoma.