In the case of using colored lenses, the patient will only be able to see red letters through the red lens and green letters through the green lens. Using specially designed eye charts with alternating green and red letters, in the former case, or with polarized letters, in the latter case, can allow the examiner to test the vision in each eye separately without the patient's knowledge ( Levy and Glick, 1974 Bruce and Newman, 2010 Newman and Biousse, 2014). Similarly, using glasses with colored lenses (one green lens and one red lens) or glasses with lenses which are polarized in different directions can help unmask the NOVL patient. A mismatch between visual acuity and stereopsis, i.e., worse visual acuity than would be suggested by the corresponding Titmus test score, is suggestive of nonorganic visual loss.Īdapted from Biousse and Newman (2009), pp. The corresponding minimum Snellen visual acuity necessary to obtain a given score on Titmus testing is listed in the right-hand column. * Stereopsis, measured in arc seconds from a standard Titmus test, is listed in the left-hand column. The success of many of the tests that will be presented in the rest of this chapter depends, in part, on the ability of the examiner to use sleight of hand, appropriate banter, and misdirection, much in the same way an illusionist misdirects an audience with hand or body motions or distracts the audience with skillfully engaging banter ( Bruce and Newman, 2010 Newman and Biousse, 2014). Patching the good eye (with a taped patch) of a patient with presumed profound monocular visual loss and observing the patient's behavior during the interview can be helpful.

For example, these patients may attempt to close one eye during examination to simulate their complaint of monocular vision loss ( Bruce and Newman, 2010 Newman and Biousse, 2014). However, observation does have a role in the NOVL patient who complains of monocular vision loss. Truly monocular patients can still navigate a new environment with ease as long as there is useful vision in the unaffected eye. Monocular vision loss represents the ideal testing situation, since it is difficult for the patient to separate out what each eye sees individually ( Bruce and Newman, 2010 Newman and Biousse, 2014). Newman, in Handbook of Clinical Neurology, 2016 Monocular vision loss Postgeniculate visual loss can be differentiated from pregeniculate visual loss by (1) a normal funduscopic appearance, (2) intact pupillary light reactions, and (3) appropriate lesions on brain imaging. Lesions of the geniculate nuclei, optic radiations, or visual cortex produce congruent hemianopic field defects that may go unrecognized unless the hemianopia intrudes on macular vision. The fibers serving identical points in the homonymous half fields do not fully commingle in the optic tract, so lesions damaging this structure produce incongruous homonymous hemianopia. Optic tract abnormalities are comparatively rare but produce characteristic visual changes.

Lesions involving the optic chiasm produce nonhomonymous visual abnormalities (e.g., the bitemporal hemianopia illustrated by lesion 3 in Fig. Binocular visual loss, on the other hand, can result from disease located anywhere in the visual pathways from the corneas to the occipital poles. Monocular vision loss is due to a lesion in one eye or optic nerve. Baloh, Joanna Jen, in Goldman's Cecil Medicine (Twenty Fourth Edition), 2012 Localization of Lesions within Visual Pathways

Monocular vs binocular vision