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In children with late childhood Batten disease, degeneration of a specific part of the eye’s retina called the parafovea occurs before other parts of the retina are affected, a study has found.

The study, “Automated retinal layer segmentation in CLN2-associated diseases: commercially available software characterizing progressive maculopathywas published in Translational vision Science and technology.

The retina is the area at the back of the eye that houses cells that detect light for vision. These cells are arranged in a particular pattern with distinct segments, in the shape of the “center of the target”: in the center is the fovea, the place where visual acuity is highest. Surrounding the fovea is the parafovea (“para” means “beside or near”), and outside the parafovea is the perifovea (“peri” means “around or surrounding”).

Late childhood Batten disease, also called CLN2 disease, is characterized by the death of nerve cells. Retinal cells are known to be particularly affected.

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Researchers from Weill Cornell Medical College looked at how the retina was affected in people with CLN2 disease at different ages. The team used data from a natural history clinical trial (NCT01035424); in total, they analyzed 27 eyes of 14 children with Batten disease.

“In CLN2-associated disease, loss of vision tends to occur late in the course of the disease after other symptoms have appeared; however, retinal structural changes may be noted on optical coherence tomography (OCT) in patients as young as 2 years old,” the researchers wrote.

Patients were an average of 42 months (about 3.5 years) at diagnosis and an average of 57.2 months (almost 5 years) when their eyes were assessed using OCT, a technique for imagery.

“This study includes patients aged 30 to over 97 months [about 8 years] …demonstrating imaging findings across a wide range of disease states,” the researchers wrote.

By analyzing the OCT measurements and comparing the measurements for these different ages, the researchers identified certain patterns of retinal changes. For example, comparing measurements of 39-month-old and 46-month-old patients, significant differences were found in the thickness of the parafovea, particularly in the outer nuclear layer.

No such differences were observed for fovea or perifovea at these time points. Significant differences in perifoveal thickness emerged in comparisons between patients aged 60-66 months and those older than 67 months.

« Parafoveal ONL [outer nuclear layer] thinning appears to be one of the first objective findings in CLN2-associated retinal degeneration,” the researchers concluded.

They added that this difference in the parafoveal outer nuclear layer was apparent “before the critical period identified by more conventional measures” based on OCT, such as central subfield (CST) thickness, which is essentially the thickness of the fovea.

“Unlike segmented thickness measurements, CST did not demonstrate a statistically significant difference in thickness between age cohorts,” the researchers wrote.

Measuring parafoveal outer nuclear layer thickness “may serve as a more sensitive biomarker for the onset of degeneration compared to other OCT measurements such as CST,” they added, noting that it could be useful in clinical trials testing experimental therapies for Batten disease.