SD-OCT reveals choroidal anatomy, variability

Choroidal thickness, which was found to vary among individuals, tends to decrease with age, according to a study.

Gabriel Coscas

PARIS — Better knowledge of choroidal anatomy, now made possible by spectral-domain optical coherence tomography, could help shed light on the pathophysiology of a variety of chorioretinal afflictions, according to an expert.

“OCT has driven us beyond the limits of the [retinal pigment epithelium] to explore the choroid, the nourishing tissue underneath the retina,” Gabriel Coscas, MD, said in an interview with Ocular Surgery News during the meeting of the French Society of Ophthalmology. “These in vivo images can be correlated to histology, and we have a sufficient resolution to be able to measure choroidal thickness in different areas. The new software enables the system to compensate for the weaker signal behind the [retinal pigment epithelium].”

Study

In a study, Dr. Coscas found that choroidal thickness varies among individuals and tends to decrease with age. Significant differences were also found when comparing the choroid of normal eyes and myopic eyes with and without choroidal neovascularization.

A total of 82 eyes of 82 patients were enrolled and examined. Images with sufficient contrast to demarcate the choroidal-scleral border were obtained in 58 eyes (71%), which were divided into four groups: normal eyes (23), myopic eyes (seven), highly myopic eyes (19) and myopic eyes with CNV (nine). Mean ages for the four groups were 42, 53, 55 and 57 years, respectively.

Choroidal thickness, from the external limiting membrane to the choroidal-scleral junction, was measured at different distances from the fovea on a horizontal section between 1.5 mm temporal to 1.5 mm nasal. Other measurements were taken at predefined intervals in the retrofoveal area.

“We found a mean choroidal thickness of 333 µm in normal eyes and a considerably lower thickness in myopic eyes. Even low myopic eyes had a significant decrease, down to 248 µm, and high myopic eyes with and without CNV were respectively 113 µm and 88 µm,” Dr. Coscas said.

After adjusting the data for age, a statistically significant mean difference of 200 µm in favor of the normal eye group was found at all locations, with a slight, gradual decrease from the center to the periphery.

In normal eyes, choroidal thickness was found to decrease progressively from the center of the fovea toward the temporal and nasal sector, while in myopic eyes there was less variation.

“The diagram curve was much flatter, showing a similar thickness at all locations. In eyes with CNV, there was progressive thinning, but not uniform, in the nasal and temporal areas,” Dr. Coscas said.

There were, however, many interindividual variations. In one case, a normal eye had a thicker choroid in the temporal area, and the retrofoveal thickness was only 131 µm, thinner than the average not only for normal eyes but also for the low myopic group.

On the other hand, in all myopic groups, there were individuals with a choroid thinner than average in the retrofoveal area.

Meaningful correlations

Interesting data emerged from the analysis with respect to age, according to Dr. Coscas. In the group of normal eyes, a significant thinning of the choroid was observed in relation to age at all locations. In the highly myopic group, there was a large interindividual variation and a less pronounced decrease in thickness, but results may not be as accurate because the group was relatively small.

“This tendency of the choroid to become thinner with age may partly explain why we have degenerative diseases related to age. The choroid provides oxygen and nourishment to the retina, but a thinner choroid may signify that less nutrients are available,” Dr. Coscas said.

It is also possible that the correlation of high myopia with a thinner choroid might be the consequence of abnormal stretching caused by the elongated shape of myopic globes, he said. – by Michela Cimberle

• Gabriel Coscas, MD, can be reached at Université Paris Est Créteil, 40 Ave. de Verdun, 94010 Creteil, France; +33-1-45175225; fax: +33-1-45175227; email: gabriel.coscas@gmail.com.
• Disclosure: Dr. Coscas has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.