Lensectomy and vitrectomy decrease the rate of photoreceptor loss in rhodopsin P347L transgenic pigs

Background: Photoreceptor degeneration in retinitis pigmentosa (RP) runs an inevitable, gradually progressive course. A wide variety of growth factors of different origins have been shown to slow the rate of degeneration in some rodent models of RP. Recently, lens-derived neurotrophic factors have been shown to rescue degenerating ganglion cells in crush models of the optic nerve. Our objective was to evaluate the potential rescue effect of lensectomy and vitrectomy (L&V) on photoreceptor degeneration in a large-animal model, the rhodopsin P347L transgenic pig. Methods: We operated on one eye of each of 49 3-week-old pigs - 15 vitrectomies and 34 L&V, 6 of which received steroids. Retinal paraffin sections were prepared for all eyes, in addition to immunohistochemistry in four eyes, 8 weeks after L&V. Results: At eight weeks after L&V, operated eyes showed significantly more nuclei in the outer nuclear layer (ONL) than the unoperated fellow eyes. The better preservation of the ONL persisted but was less prominent by 20 weeks after surgery. Steroid treatment did not markedly reduce the better preservation of the ONL seen at 8, 10, and 12 weeks after surgery. The significant difference in cell count between operated and unoperated eyes in the L&V group at 8 weeks was due to the difference in the number of rods, not the cones. Conclusion: Lensectomy and vitrectomy delay photoreceptor degeneration in rhodopsin P347L transgenic pigs. Lens-related rescue effect is a probable reason for the delayed degeneration.