• 6 Pearls for Identifying Occult Disease in Patients With Unexplained Vision Loss

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    The vast majority of ophthalmic diseases have manifestations that are readily apparent on a clinical exam. 

    As a result, eye care providers are often perplexed when visual complaints do not correlate with their exam findings. Resolving such visual complaints can be difficult, but are essential for reducing diagnostic errors, a leading type of error in paid ophthalmology malpractice claims.

    Here are six clinical pearls to help you identify occult disease in patients with a seemingly normal exam. 

    1. Beware of “red flag” symptoms

    In the absence of obvious exam findings, a critical appraisal of the patient’s symptomatology can help with localization. Symptoms such as nyctalopia, hemeralopia and photopsias have fairly high specificity and should increase index of suspicion for sensory retinal disease. 

    Similarly, occult cerebral diseases can result in specific visual symptoms associated with higher cortical function such as alexia (inability to read), prosopagnosia (impaired facial perception), and palinopsia (persistence of a visual image after stimulus is removed). Amaurosis will rarely have exam findings but must be worked up urgently to exclude stroke or giant cell arteritis (GCA).

    2. Consider the common culprits

    Diseases of the outer retina and optic nerve disproportionately present with minimal exam findings in the early stages. An initial differential diagnosis should be wide and include inherited retinal dystrophies, Leber’s hereditary optic neuropathy (LHON), cancer associated retinopathy (CAR) and acute zonal outer occult retinopathy (AZOOR). 

    Optic nerve sheath meningiomas are frequently missed due to failure of appropriate neuroimaging acquisition and interpretation. Keratoconus can also present with subtle findings in the initial stages and is a common cause of diagnostic error.

    3. Thoroughly assess visual function

    Relying on Snellen visual acuity and confrontation visual fields as being wholly representative of visual function is a common pitfall. Color vision testing, static and kinetic perimetry, contrast sensitivity, and stereoacuity measures can all reveal subtle features of occult disease that would be otherwise missed in a standard patient work up.

    Dyschromatopsia is often present before other identifiable clinical changes and can be readily tested in clinic. Don’t forget to refract the patient — you can learn a lot about visual function through the phoropter.

    4. Personally evaluate pupillary function

    Pupillary reactivity is a general reflection of the integrity of the afferent visual system. Though a relative afferent pupillary defect may be absent in causes of symmetric vision loss from occult disease, bilateral reduction of pupillary response can be an objective finding that supports organic disease. 

    Don’t forget about the phenomenon of paradoxical pupillary reaction which can be seen in a number of optic nerve and retinal disorders.

    5. Utilize targeted ancillary testing

    Streak retinoscopy can reveal oil droplet cataracts or irregular astigmatism which could prompt topographic evaluation. Fine stippling of the retinal pigmented epithelium should be investigated with autofluorescence and ocular coherence tomography. Subtle arteriolar attenuation can be the first sign of degenerative neuroretinal disease. 

    It’s important to remember that form and function do not always correlate. When the exam and imaging fail to reveal structural changes, electroretinography (ERG) is a vital tool to evaluate photoreceptor function.

    6. Everything must add up 

    Beware of dismissing evidence that refutes your provisional diagnosis. A patient with progressive unilateral vision loss, anisometropia, and “amblyopia” in their more hyperopic eye doesn’t add up. Confirmation bias and anchoring are among the most common cognitive biases which lead to misdiagnosis.

    Objective findings in your assessment must be taken into account. Subjective abnormalities should be retested or assessed in a different manner to either confirm or refute the diagnosis. Near vision and distance vision should be equal and compatible with stereopsis findings. Remember that truly functional vision loss is not a diagnosis of exclusion and requires demonstration of normal visual function. 

    When history and clinical assessment show unresolvable concerns, consider a broader differential, attain more information, and develop a habit of asking yourself, “What else might this be?”

    Andrew Melson, MD

     

    About the author: Andrew Melson, MD, is a neuro-ophthalmologist and assistant professor of ophthalmology at the Dean McGee Eye Institute in Oklahoma City, Okla.

    The Academy’s YO Info Editorial Board collaborates with the Young Neuro-Ophthalmologist Committee (YONO) of the North American Neuro-Ophthalmology Society (NANOS) on information of interest to young ophthalmologists. Thanks to YONO for recommending Dr. Melson as a contributor to YO Info.