Deletion of histone demethylase Lsd1 (Kdm1a) during retinal development leads to defects in retinal function and structure.

Purpose: The purpose of this study was to investigate the role of Lysine specific demethylase 1 (Lsd1) in murine retinal development. LSD1 is a histone demethylase that can demethylate mono- and di-methyl groups on H3K4 and H3K9. Using Chx10-Cre and Rho-iCre75 driver lines, we generated novel transgenic mouse lines to delete Lsd1 in most retinal progenitor cells or specifically in rod photoreceptors. We hypothesize that Lsd1 deletion will cause global morphological and functional defects due to its importance in neuronal development. Methods: We tested the retinal function of young adult mice by electroretinogram (ERG) and assessed retinal morphology by in vivo imaging by fundus photography and SD-OCT. Afterward, eyes were enucleated, fixed, and sectioned for subsequent hematoxylin and eosin (H&E) or immunofluorescence staining. Other eyes were plastic fixed and sectioned for electron microscopy. Results: In adult Chx10-Cre Lsd1fl/fl mice, we observed a marked reduction in a-, b-, and c-wave amplitudes in scotopic conditions compared to age-matched control mice. Photopic and flicker ERG waveforms were even more sharply reduced. Modest reductions in total retinal thickness and outer nuclear layer (ONL) thickness were observed in SD-OCT and H&E images. Lastly, electron microscopy revealed significantly shorter inner and outer segments and immunofluorescence showed modest reductions in specific cell type populations. We did not observe any obvious functional or morphological defects in the adult Rho-iCre75 Lsd1fl/fl animals. Conclusion: Lsd1 is necessary for neuronal development in the retina. Adult Chx10-Cre Lsd1fl/fl mice show impaired retinal function and morphology. These effects were fully manifested in young adults (P30), suggesting that Lsd1 affects early retinal development in mice.

Pathologic findings in postmortem corneas after successful laser in situ keratomileusis.

PURPOSE: To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK). METHODS: Corneas from 48 eyes of 25 postmortem patients were processed for histology and transmission electron microscopy (TEM). The 25 patients had LASIK between 3 months and 7 years prior to death. Evaluation of all 5 layers of the cornea and the LASIK flap interface region was done using routine histology, periodic acid-Schiff (PAS)-stained specimens, toluidine blue-stained thick sections, and TEM. RESULTS: In patients for whom visual acuity was known, the first postoperative day uncorrected visual acuity was 20/15 to 20/30. In patients for whom clinical records were available, the postoperative corneal topography was normal and clinical examination showed a semicircular ring of haze at the wound margin of the LASIK flap. Histologically, the LASIK flap measured, on average, 142.7 microm (range, 100-200). A spectrum of abnormal histopathologic and ultrastructural findings was present in all corneas. Findings at the flap surface included elongated basal epithelial cells, epithelial hyperplasia, thickening and undulations of the epithelial basement membrane (EBM), and undulations of Bowman's layer. Findings in or adjacent to the wound included collagen lamellar disarray; activated keratocytes; quiescent keratocytes with small vacuoles; epithelial ingrowth; eosinophilic deposits; PAS-positive, electron-dense granular material interspersed with randomly ordered collagen fibrils; increased spacing between collagen fibrils; and widely spaced banded collagen. There was no observable correlation between postoperative intervals and the severity or type of pathologic change except for the accumulation the electron-dense granular material. CONCLUSIONS: Permanent pathologic changes were present in all post-LASIK corneas. These changes were most prevalent in the lamellar interface wound. These changes along with other pathologic alterations in post-LASIK corneas may change the functionality of the cornea after LASIK.

Histologic and ultrastructural findings in human corneas after successful laser in situ keratomileusis.

OBJECTIVE: To examine the histologic and ultrastructural features of human corneas after successful laser in situ keratomileusis (LASIK) in 2 patients post mortem. METHODS: Portions of 4 corneas were processed for histology, transmission electron microscopy, and scanning electron microscopy. RESULTS: Case 1 had undergone LASIK 3 months prior to death and case 2 had undergone LASIK 20 months prior to death. A Hansatome (Bausch & Lomb Surgical Inc, Clarement, Calif) microkeratome with a 180-microm plate had been used for case 1 and an Automated Corneal Shaper (Chiron Corporation, Munich, Germany) with a 160-microm plate had been used for case 2. Histologically, the LASIK flap measured 160 microm and 150 microm in thickness in case 1 and case 2, respectively. Corneas from both cases exhibited minor epithelial ingrowth into the wound, reactive keratocytes at the wound margin, irregular collagen fibrils in the wound bed, and severed collagen bundles at the flap hinge. These findings were more pronounced in case 1 than in case 2, and the wound interface was virtually imperceptible in case 2. Additionally, the corneas from case 1 contained periodic acid-Schiff--positive electron dense material and wide-spaced collagen at the wound interface, and there was an absence of corneal nerves. CONCLUSIONS: These findings show that changes caused by wound repair that are present at 3 months are minor 20 months after LASIK.