Lower risk of diabetic retinopathy, macular edema associated with longer axial length

Issue: February 2013

A longer axial length may be linked to a lower risk of diabetic retinopathy and diabetic macular edema in patients with diabetes, according to a study.

Current treatment for diabetic retinopathy focuses on controlling the effects of the disease once it occurs but not on preventing disease development, Ecosse L. Lamoureux, PhD, said.

“With recent studies implicating a neurovascular component in diabetic retinopathy, it is becoming much more important for researchers to prevent this condition from developing or progressing in the first place, as neuronal damage is irreversible,” he told Ocular Surgery News.

Lamoureux said he hopes the study results will spur further investigation into the development of prophylactic therapies for diabetic retinopathy.

In the clinic-based study, 630 eyes of 367 patients were examined; 306 eyes were hyperopic, 188 were emmetropic, 104 were mildly myopic, and 32 were at least moderately myopic. Mean axial length was 23.4 ± 1.4 mm, mean anterior chamber depth was 3.4 ± 0.7 mm, and mean corneal curvature was 7.7 ± 0.3 mm. Diabetic retinopathy was found in 208 eyes and diabetic macular edema in 148 eyes.

A longer axial length was the only variable that was independently associated with lower odds of having any diabetic retinopathy (P < .001 per 1 mm increase in axial length). This association was found in mild (P = .006), moderate (P = .002) and severe cases (P = .01).

A lower risk of diabetic macular edema was also associated with a longer axial length (P < .001). This association was found in patients with mild (P < .001) and moderate cases (P = .002) but not severe cases.

Study data showed that contrary to previous research, myopia as a whole was not associated with a lower risk of diabetic retinopathy.

“Coupled with the lack of a correlation of [corneal curvature] and hyperopia with diabetic retinopathy, our results suggest that refractive myopia is likely a surrogate for longer [axial length] that influences diabetic retinopathy risk,” the study authors said.

The current standard of treatment for diabetic retinopathy is laser therapy, and although this treatment is effective, it can create debilitating side effects such as vision loss, Lamoureux said.

The study authors speculated that a longer vitreous chamber, rather than a deeper anterior chamber, leads to stretching and thinning of retinal tissues and blood vessels. This, in turn, reduces blood flow, which has been hypothesized to reduce the risk of diabetic retinopathy, the study said.

Lamoureux and first author Ryan E.K. Man said they hope to eventually confirm that a reduction in blood flow and/or retinal oxygen consumption contributes to the relationship between axial length and a lower risk and severity of diabetic retinopathy.

“Previous studies have shown the reduction in retinal blood flow with a longer axial length in healthy eyes. We are now in the process of investigating the changes in retinal blood flow and oxygen saturation levels with axial length in both normal and diabetic eyes,” Man said. – by Ashley Biro

Reference:

Man RE, et al. Ophthalmology. 2012;doi:10.1016/j.ophtha.2012.03.021.

For more information:

Ecosse L. Lamoureux, PhD, can be reached at Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, 32 Gisborne St., East Melbourne, Victoria 3002, Australia; 61-3-9929-8371; fax: 61-3-9662-3859; email: ecosse@unimelb.edu.au.
Ryan E.K. Man can be reached at Centre for Eye Research Australia, Department of Ophthalmology, University of Melbourne, 32 Gisborne St., East Melbourne, Victoria 3002, Australia; 61-3-9929-8352; email: spectr4m@gmail.com.
Disclosures: Lamoureux and Man have no relevant financial disclosures.