What is the critical finding here?

The first year resident correctly identified the white cataract of the right eye, but she missed a critical finding. As soon as I walked into the exam room, from 10 feet away, I knew that a critical finding was missed — something that would cause a serious visual issue even if a perfect cataract surgery was performed. What is the critical finding here?(Full video below)

sensory XT

This patient has a dense white cataract in her right eye resulting in hand-motion vision. Her left eye is normal and sees 20/20. There is a history of trauma to the right eye 5 years ago and the patient reports by history that she lost vision within a year of this trauma. She never sought medical treatment due to lack of access to care and financial considerations. She presents to our charity eye clinic in Los Angeles for treatment.

The first year resident diagnoses a white cataract in the right eye and does an ultrasound B-scan which shows a normal posterior segment. But one critical diagnosis is missed. This patient has a large angle sensory exotropia due to not having useful vision from the eye for about the past four years. This will likely pose some issues with diplopia in the post-operative period. Cataract surgeons need to still understand the full spectrum of ophthalmology and this includes strabismus.

The patient has no history of strabismus prior to the traumatic cataract and when we look at a photo of her face from her California driver’s license, her eyes are aligned normally (ortho). Since the B-scan shows a normal posterior segment we can be reasonably sure that the visual potential of the eye is quite good and likely normal. When we restore vision to the right eye with a cataract surgery she will be happy with the vision out of that right eye. But when she has both eyes open together she will certainly experience diplopia.

When we look at a photo of her face from the initial consultation we can see that she has about 30 prism diopters of right exotropia by Hirschberg light-reflex testing.

 

XT light reflex

Since the diplopia is not longstanding and there is no history of amblyopia, there will be no suppression of the image from the right eye. There is a chance that the patient will initially have diplopia which will then slowly resolve over the course of the few weeks in the post-op period. However there is also a reasonable chance that a second surgery to address the strabismus will be needed.

The patient must be warned about this during the pre-operative consultation. Remember this wise adage from one of my mentors:

The surgeon who warns of a potential post-op issue ahead of time is a genius for predicting it; the surgeon who tells a patient of a complication after it has already happened may be blamed as having caused it.

Our patient did experience diplopia in the post-op period. We gave it a few months to see if it would resolve, but to no avail. She ended up needing a secondary strabismus surgery to align her eyes. Now she is doing fine with great vision and no diplopia.

unilateral white cataract small
Figure: Another patient has a white cataract in the left eye and just a small degree of sensory exotropia of under 10 prism diopters. He will likely have only mild transient diplopia which should resolve over the course of a few weeks.

Here is the video of the cataract surgery:

 

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