and ranges from mild to profound. The non-organic nature of the visual loss is most easily demonstrated when one eye is severely affected, typically by using techniques that “fog” the fellow eye, as in the case under discussion. In the crossed cylinder method, minus and plus cylinders of equal magnitudes are aligned in a trial frame over the “good” eye so that they cancel out optically. The patient is asked to read the Snellen chart with both eyes open, starting from the largest letters and reading down to the smallest. As the patient proceeds, the examiner turns one of the cylinders until the good eye is sufficiently blurred that the patient could only be reading with the eye that has the unexplained visual loss. Similar fogging can be achieved with increasing plus lenses in the phoropter, but with that technique the examiner loses the opportunity to observe the patient during the test and, in addition, the movement of the lenses is less subtle than the motion of the crossed cylinders. Red-green duochrome lenses can provide similar information, but in most cases the best acuity one can obtain with this method is around 20/40. Measurement of stereo-acuity can be a helpful adjunct for determining intact near vision. In cases involving both eyes or in those with visual loss in an only good eye, fogging techniques are not applicable. In such cases it is often possible to demonstrate better vision by working from the smallest letters on the Snellen chart up, using encouragement and the power of suggestion.

In cases of non-organic visual loss, the ideal test is one that demonstrates normal vision, but sometimes we must settle instead for showing gross inconsistencies. Examples of this include the ability to navigate about the room or reach for objects despite claimed blindness, intact central visual field in the face of severe loss of acuity, and apparent total monocular blindness with an intact pupillary response.

Diagnosis: Non-organic visual loss

Tip: In most cases of non-organic visual loss, specific examination techniques can disclose the

nature of the disorder and thereby obviate the need for extensive and costly evaluation.

FURTHER READING

Adie’s tonic pupil

D. M. Jacobson, Pupillary responses to dilute pilocarpine in preganglionic 3rd nerve disorders. Neurology, 40 (1990), 804–8.

R.H. Kardon, J. J. Corbett, H. S. Thompson, Segmental denervation and reinnervation of the iris sphincter as shown by infrared videographic transillumination. Ophthamo-

logy, 105 (1998), 313–21.

A. Kawasaki, Disorders of pupillary function, accommodation and lacrimation. In N. R. Miller, N. J. Newman, V. Biousse, J. B. Kerrison, eds., Walsh and Hoyt’s Clinical Neuro-Ophthalmology, 6th edn. Philadelphia: Lippincott Williams and Wilkins, 2005, Vol. 1, Chapter 16, pp. 739– 805.

Non-arteritic anterior ischemic optic neuropathy

A.C. Arnold, Pathogenesis of nonarteritic anterior ischemic optic neuropathy. Ophthalmol Clin N Am, 14 (2001),

83–98.

S.Lessell, Nonarteritic anterior ischemic optic neuropathy: enigma variations. Arch Ophthalmol, 117 (1999), 386–8.

V. Purvin, Ischemic optic neuropathy. Semin Cerebrovasc Dis Stroke, 4 (2004), 2–17.

Vasculopathic cranial mononeuropathy

K.L. Chou, S. L. Galetta, G. T. Liu et al., Acute ocular motor mononeuropathies: prospective study of the roles of

neuroimaging and clinical assessment. J Neurol Sci, 219 (2004), 35–9.

D. M. Jacobson, Progressive ophthalmoplegia with acute ischemic abducens nerve palsies. Am J Ophthalmol, 122 (1996), 278–9.

D. M. Jacobson, T. D. McCanna, P. M. Layde, Risk factors for ischemic ocular motor palsies. Arch Ophthalmol, 112 (1994), 961–6.

J. T. Kissel, R. M. Burde, T. G. Klingele, H. E. Zeiger, Pupil-sparing oculomotor palsies with internal carotidposterior communicating artery aneurysms. Ann Neurol, 13 (1983), 149–54.

S.K. Sanders, A. Kawasaki, V. Purvin, Long-term prognosis in patients with vasculopathic sixth nerve palsy. Am

J Ophthalmol, 134 (2002), 81–4.

J.D. Trobe, Third nerve palsy and the pupil: footnotes to the rule. Arch Ophthalmol, 106 (1988), 601–2.

Migraine

R.A. Davidoff. Migraine. Manifestations, Pathogenesis, and Management, 2nd edn. Oxford: Oxford University Press, 2002.

S.L. Hupp, L. B. Kline, J. J. Corbett, Visual disturbances of migraine. Surv Ophthalmol, 33 (1989), 221–36.

Non-organic visual loss

K. K. Kramer, F. G. La Piana, B. Appleton, Ocular malingering and hysteria: diagnosis and management. Surv Ophthalmol, 24 (1979), 89–96.

B. W. Miller, A review of practical tests for ocular malingering and hysteria. Surv Ophthamol, 17 (1973), 241–6.

H. S. Thompson, Functional visual loss. Am J Ophthalmol, 100 (1985), 209–13.