Reviewed by Robert C. Sergott, MD
According to Robert C. Sergott, MD, signs and symptoms of Alzheimer’s disease in the retina, optic nerve and posterior afferent visual system in the temporal and parietal lobes can alert physicians to an earlier diagnosis of Alzheimer’s disease than previously thought.
Sergott, director of the Neuro-Ophthalmology Service at Wills Eye Hospital and founding director and CEO of the Annesley EyeBrain Center at Thomas Jefferson University in Philadelphia, Pennsylvania, emphasized the importance of recognizing the often subtle signs and symptoms in patients over age 55 Years to be aware based on the possibility that treatments for Alzheimer’s disease could be available in the next few months.
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The availability of potential treatments to treat early illnesses may impair its current ability to destroy the brain and the function of the retina and optic nerve.
With diseases such as Alzheimer’s disease and Parkinson’s disease, patients may first present to an ophthalmologist rather than a neurologist because of the visual disturbances associated with them.
Beads from a case
Sergott described a 68-year-old man who presented with progressive visual field defect for 2 years and an inability to drive at night for approximately 1½ years. The patient described seeing oncoming lights while driving as starry bursts.
Restricted fields of vision can be a first indication of possible Alzheimer’s disease.
The differential diagnosis is extensive and includes retinal degeneration, quinine toxicity, central retinal artery occlusion, glaucoma or end-stage papilledema, confluent papillae glands, bilateral occipital lobe infarcts, nonphysiologic response, and cognitive impairment on automated perimetry.
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Sergott explained that visual field narrowing implies a visual field defect in the retina, optic nerve, or occipital lobe; photophobia in the retina; and night blindness and depth perception in a retinal or cortical problem.
Considering the 3 localizations suggests that there could be a retinal or a cortical problem or both.
“Alzheimer’s disease affects them all, meaning the retina, the optic nerve and the visual system behind the lateral knee joint,” he said.
The patient’s history was positive for prostate cancer and basal and squamous cell carcinomas, without metastases; Hypertension; and hyperlipidemia.
“A rule of life in neuroophthalmology is to determine whether the patient’s problem is caused by the recurrence of the cancer, especially breast cancer, or by the cancer therapy,” Sergott emphasized.
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The patient’s ocular examination was unremarkable with bilateral vision of 20/40. Interestingly, the patient could only see the test Ishihara plate despite having no history of color blindness.
Acquired color vision loss can occur in the cones, optic nerve, or cortical system.
“This provides a subtle clue to an afferent visual problem. Color vision measures contrast sensitivity,” he said. “With low-contrast visual acuity [VA]a deficit greater than 20/40 could be detected.”
Optical coherence tomography was unremarkable but showed a slight flattening with a slightly broadened fovea-macula contour.
Fundus autofluorescence also showed no prominent abnormality indicative of early Alzheimer’s disease.
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However, multifocal electroretinography (ERG) showed almost isoelectric recording in the right eye despite 20/40 vision. Multifocal ERG anomalies were present in the left eye, but not as pronounced as in the right eye.
The cranial MRI showed non-specific changes and that paraneoplastic autoantibodies and the CSF profile after lumbar puncture were negative.
Automated perimetry revealed a lower quadrantanopia in the left eye and a more subtle defect in the right eye. This localization pattern is in the right parietal temporal lobe.
“From these tests we know that this patient has brain disease in the right parietal temporal lobe,” Sergott explained. “The multifocal ERG results indicated the presence of retinal disease. This turned out to be an extensive process in the visual system.”
In addition to the limited visual fields, color blindness, and abnormal ERG, the patient’s history indicated dissatisfaction with the results of cataract surgery despite 20/40 bilateral VA and depth perception of only 40 arc seconds.
“One reason for postoperative dissatisfaction with a good Snellen VA can be Alzheimer’s disease,” he said. “The root of dissatisfaction may be subtle problems with reading and word-finding difficulties, as well as mild short-term memory loss.”
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Other clues are that the patient never showed up to appointments alone and often didn’t answer questions put to him, Sergott added.
Patients with predominantly visual symptoms may present with posterior cortical atrophy.
However, Sergott cautioned physicians against identifying patients with mildly impaired memory and impaired functioning, which could indicate other findings that may indicate a more global deficit in visual processing.
These can include a progressive decline in visuo-spatial abilities, visual perception, and literacy, occurring in patients averaging 50 to 65 years of age.
Experts disagree as to whether posterior cortical atrophy is a pure form of Alzheimer’s disease or a distinct entity. Lewy body dementia and prion disease can also share similar visual symptoms.
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Practical guidelines for ophthalmic presentations
Sergott prioritized the various ophthalmologic findings when ophthalmologists are confronted with patients similar to the patient under discussion.
The ophthalmic presentations of Alzheimer’s disease include the unfortunate patient with good visual acuity after cataract surgery and in patients without recent cataract surgery, loss of color vision, depth perception, and photoreceptor dysfunction manifesting as glare and night blindness.
Sergott said he believes the multifocal ERG may be the most sensitive test to identify retinal abnormalities in patients with dementia syndromes.
He also advised physicians to be alert to patients with visual field defects who have problems with the automated perimetry test, especially on repeat attempts.
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Patients with a homonymous hemianopsia may also have a normal MRI scan. This clinical presentation was intended to alert ophthalmologists and neurologists to the possibility of Alzheimer’s disease.
“Alzheimer’s disease should be suspected in such patients. Hopefully some treatments will become available later in 2021,” he said. “[As with] Most treatments work better the sooner they are started, before the disease destroys most of the brain and much of the retinal and optic nerve function. Ophthalmologists can be the key to kickstarting the diagnostic process.”
Robert C. Sergott, MD
This article is an adaptation of Sergott’s presentation at the Ohio Ophthalmological Society Virtual Annual Meeting in February. He has no financial interest in this matter.