Diagnostic Dilemmas in Neuro-ophthalmology

The European Neuro-Ophthalmology Society (EUNOS) and the North American Neuro-Ophthalmology Soci­ety (NANOS) presented a lively session on diagnostic dilemmas at the biannual European Society of Ophthalmolo­gy (SOE) meeting in Prague.

“In the time of COVID, we have missed a lot of neurologi­cal disease. We did not examine patients properly, and a mask is the neurologist’s enemy,” Professor Misha Pless explained.

He discussed double vision and his model for working through potential causes of double vision, which involves sys­tematically considering the potential cause from the cerebral cortex, through brainstem, to the cranial nerves, and onto the neuromuscular junction and the orbit.

“If you suspect myasthenia gravis in a patient,” he said, “test the saccades.”

Only testing pursuit movements can lead to false reas­surance; detecting abnormally slowed movements may only happen by testing fast eye movements.

“Another helpful test is the sleep test, the five-minute sleep test,” Prof Pless said, adding it is an alternative to the ice-pack test in myasthenia gravis. After measuring margin reflex distance and eye movements, the patient is asked to take a five-minute nap.

“You will see a difference in the examination,” Prof Pless said.

Ophthalmologists cannot miss two underlying diagnoses, he said, as they can be deadly. Subarachnoid haemorrhage typically presents with severe, sudden headaches patients de­scribe as “the worst of their life” and double vision resulting from an associated third nerve palsy. Pituitary apoplexy may present with double vision as a pituitary tumour expands rapidly due to a bleed.

Organic vs non-organic

Professor Karl Golnik had practical advice for differentiating organic from non-organic vision loss.

“My favourite trick for sure is the vertical prism test,” he said.

A patient reporting reduced vision in one eye is one such example of where the vertical prism test can be useful in differentiating organic from non-organic vision loss. The test involves holding a vertical four-dioptre prism, base down, in front of the better eye. If the patient reports vertical diplopia, seeing two letters of equal clarity, the test has shown equal vision in the symptomatic eye. However, if the patient reports seeing one image or vertical diplopia with a blurry lower letter, it reveals true monocular reduced vision.

“Bilateral visual acuity loss—this is a lot more difficult than unilateral,” Prof Golnik said. He recommended observing am­bulation and using the optokinetic nystagmus (OKN) drum. If the patient reports they cannot see the black and white stripes but then exhibits nystagmus on rotating the drum, their vision must be better than claimed.

Another potential non-organic presentation is a complaint of tunnel vision. Prof Golnik advised uncovering clinical find­ings that are not compatible with the optics of the visual field, whether that field is reduced or not.

“The further away you test the patient, no matter how small that visual field is, it expands,” he said.

When assessing a patient with a visual field deficit, non-ex­pansion of a narrowed field on greater testing distance, done quickly and easily on confrontation, can support a functional vision loss diagnosis.

Misha Pless MD is a Professor of Ophthalmology at the Mayo Clinic, Jackson­ville, Florida, US. pless.misha@mayo.edu Karl Golnik MD is Chairman of the Ophthalmology Department at the University of Cincinnati and the Cincinnati Eye Institute, Ohio, US. golnikkc@ucmail.uc.edu