Diabetics who are nearsighted may be less susceptible to diabetic retinopathy

Two studies are of particular note in today's Scientific Program of the 2009 Joint Meeting of the American Academy of Ophthalmology (AAO) and the Pan-American Association of Ophthalmology (PAAO): a report by Swiss neuro-ophthalmic researchers about vision exam clues that should make ophthalmologists suspect an atypical variant of Alzheimer's disease; and new evidence from a Singapore National Eye Center study that diabetics who are nearsighted may be less susceptible to diabetic retinopathy.

The AAO-PAAO meeting is in session October 24 through 27 at the Moscone Center, San Francisco, CA. As the largest, most comprehensive ophthalmic education conference in the world, it offers United States and international Eye M.D.s more than 2,000 scientifically-based, peer-reviewed presentations, including instruction courses, skills transfer labs, "Breakfast with the Experts" roundtables and 900 research papers and posters.

Is it a Visual Problem or Alzheimer's? New Data Helps Doctors Make the Diagnosis

Sometimes when a patient tells his ophthalmologist that he "can't see," what he really means is "I can see, but I can no longer read or write." In a minority of Alzheimer's patients the disease shows up first as problems with vision rather than memory or other cognitive functions. But diagnosis can be difficult because standard eye exams are often inconclusive for these patients. Neuro-ophthalmologists Pierre-Francois Kaeser, MD, and Francois-Xavier Borruat, MD, Jules Gonin Eye Hospital, Switzerland, examined and followed 10 patients with unexplained vision loss who were ultimately diagnosed with the visual variant of Alzheimer's disease (VVAD). Their study describes clinical clues that may improve ophthalmologists' ability to detect VVAD and refer patients for further tests. When patients receive neurological assessment, treatment and family counseling early in the disease, outcomes may be better for all concerned.

VVAD patients differ from typical Alzheimer's patients in a number of ways. At the time they report visual problems, many are younger than those for whom memory loss is the tell-tale sign. In Dr. Kaeser's study the median patient age was 65, and only 3 of 10 reported memory loss. In comprehensive neuro-ophthalmic exams, even though most patients' visual acuity was adequate, all but one had difficulty with reading, 8 of 10 with writing, and 6 of 10 with basic calculations. The visual field was altered in 8 of 10 patients. All had trouble identifying colored numbers despite being able to name colors correctly, and, importantly, 8 of 10 patients had difficulty recognizing and interpreting components of a complex image (simultagnosia). This is an early indicator of the brain damage that prevents later-stage Alzheimer's patients from recognizing people they know and navigating familiar surroundings. MRI and PET scans revealed neurological changes consistent with VVAD in all study patients. Though VVAD patients' first symptoms are visual, Alzheimer's memory and personality impairments eventually occur in most.

"Ophthalmologists should be aware of the possibility of VVAD in patients with unexplained vision problems, particularly difficulty with reading," said Dr. Kaeser. "Suspect VVAD when a patient tests well for visual acuity, but has vision complaints that are unusual or severe for late middle age. Refer him for neurological evaluation."

Does Nearsightedness Reduce the Risk of Diabetic Retinopathy?

To learn more about factors that may reduce diabetic retinopathy (DR) risk, Laurence Shen Lim, MRCS, and colleagues at the Singapore National Eye Centre, studied how refractive error (vision worse than 20/20, without glasses) relates to the presence and severity of DR. Earlier, smaller studies had suggested a protective effect for nearsightedness (myopia), but were inconclusive. Dr. Lim's study is the first to include axial length (AL, measured from the front to back of the eye) in an analysis of the myopia-DR relationship. About 10 percent of people with diabetes develop DR, which damages the eye's retina, the specialized tissue where images are focused for relay to the brain's visual cortex. DR is a major cause of vision loss worldwide.

Reduced risk of DR, especially severe DR, was found in patients whose myopia resulted from two anatomical characteristics: longer axial length and deeper anterior eye chamber (anterior chamber depth, ACD). The findings held true for all degrees of refractive error in these patients. The 675 diabetics evaluated by Dr. Lim's team were drawn from the Singapore Malay Eye Study, a population based study of adults aged 40 to 80.

"This DR-protective effect may result from conditions often found in myopia, including atrophy of the retina, choroid, or vitreous," Dr. Lim said. Though these conditions can cause vision problems in other circumstances, they may lower DR risk by reducing retinal metabolic needs and/or improving oxygen circulation in the back of the eye. "Our findings add to our understanding of how DR develops and the assessment of DR risk in nearsighted patients," Dr. Lim added.