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    Reactivating cones possibility in addressing RP

    Take-home: Glucose entrapment in the retinal pigment epithelium is responsible for central vision loss in retinitis pigmentosa. Injecting wild-type rods into the eye to restore glucose transportation or injecting glucose into the subretinal space can facilitate cone regeneration.

    Dr. KaplanReactivating lost cone photoreceptor vision might be a breakthrough in addressing retinitis pigmentosa (RP). This important finding is based on the results observed in an autosomal dominant pig model of RP (P23H), the most common autosomal-dominant mutation in RP in the United States. The key to the breakthrough was restoration of glucose trapped in the retinal pigment epithelium (RPE) that ultimately reactivated the dormant cones.

    “Patients with RP go blind regardless of the gene mutation ultimately because of loss of cone vision resulting from cone dormancy,” Henry Kaplan, MD, reported. 

    While most RP mutations occur in rod-specific photoreceptor genes, there is progressive rod destruction, loss of peripheral vision, and dark adaptation. The subsequent loss of cone function, or cone dormancy, results in functional blindness.

    Cone dormancy in RP results in viable cone nuclei for many years after outer segment/inner segment degeneration. (A) Glucose transport to the subretinal extracellular space and cone inner segment is essential to provide energy for regeneration of cone outer segment. (B) Degeneration of rod outer segment and loss of contact with apical microvilli results in entrapment of glucose in the RPE. Ensuing glucose starvation of cone photoreceptors results in outer segment degeneration (C) and inner segment disassembly but with maintenance of viable cone nuclei (D). Courtesy of Henry Kaplan, MD.

    This important functional loss (i.e., cone dormancy) is defined as the deterioration of central vision that follows rod degeneration in RP because of cone degeneration, Dr. Kaplan explained. He is the Evans Professor of Ophthalmology, chairman, Department of Ophthalmology and Visual Sciences, and director, Kentucky Lions Eye Center, University of Louisville, Louisville, KY.

    Stages of cone degeneration

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