Photo Credit: FTiare

The presence of both the interdigitation and ellipsoid zones is associated with better visual acuity in patients with retinitis pigmentosa.

The presence of both the interdigitation zone (IZ) and ellipsoid zone (EZ) is associated with better visual acuity in patients with retinitis pigmentosa, according to findings published in Investigative Ophthalmology & Visual Science.

In a new study, James Taekyoon Kwan, MD, and colleagues aimed to further understand the structure-function relationship of the outer retina and the characteristics at presentation affecting visual function in patients with retinitis pigmentosa. This inherited retinal dystrophy is characterized by nyctalopia and classic examination findings, including peripheral bone spicules, arteriolar attenuation, and waxy optic disc pallor. For patients with this eye disease, visual function correlates with a degree of outer retinal loss, particularly of the IZ, EZ, and external limiting membrane.

The researchers conducted a retrospective chart review in patients with a clinical diagnosis of retinitis pigmentosa. The authors recorded the demographic and clinical variables of 80 eyes from 41 patients. Optical coherence tomography images were analyzed for the presence or absence of IZ, EZ, and cystoid macular edema. The primary endpoint was LogMAR visual acuity compared between patients younger than 20 years, aged 20 to 40 years, and older than 40 years. There were 13 eyes in the younger than 20 years group, 22 eyes in the aged 20-40 group, and 45 eyes in the older than 40 age group.

For the three groups, the LogMAR visual acuity was 0.47 ±0.36, 0.41 ±0.59, and 0.88 ±0.93, respectively, and there was no statistically significant difference in LogMAR visual acuity between the groups (Kruskal-Wallis, P=0.074). A significantly higher presence of the IZ was found in the aged 20-40 group versus those older than 40 group (χ², P=0.009). The presence of EZ and cystoid macular edema were not significantly different between the three groups. A comparison of visual acuity between eyes with presence of IZ and EZ (29 eyes) versus eyes with absence of IZ but presence of EZ (30 eyes) showed that those with IZ present had significantly better visual acuity (0.22 ±0.26 [Snellen equivalent 20/33] vs 0.42 ±0.45 [Snellen equivalent 20/53]; P=0.036).

“The oldest patients had lower frequencies of present IZ, possibly due to more progressed, late-stage disease in those over age 40 upon initial presentation,” the researchers concluded.