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Purpose The aim of this study was to analyze the corneal morphology features and define mutations in the UbiA prenyltransferase domain-containing 1 (UBIAD1) gene in patients with Schnyder corneal dystrophy from a Polish population. Methods Five affected and 15 unaffected members originating from 3 families with Schnyder corneal dystrophy were included in the study. Phenotype analysis consisted of visual acuity, slit-lamp biomicroscopy with photography, time domain optical coherence tomography, spectral domain optical coherence tomography, and confocal microscopy. Three patients underwent a penetrating keratoplasty. Corneal buttons obtained from the penetrating keratoplasty were processed for light microscopy. Results A novel mutation I245N of the UBIAD1 gene was revealed in 1 proband and associated with the phenotype without central corneal opacities. The analysis of the other patients showed the N102S mutation. In vivo corneal morphology analysis using optical coherence tomography and confocal microscopy confirmed the presence of multiple crystalline corneal deposits in all affected corneas. The histological examination revealed multiple empty widenings of the corneal lamellae that could represent lipids removed from the specimen. Conclusions N102S may also be a mutation hotspot in the Polish population, as in other previously reported populations. Corneal crystals formed a characteristic pattern on optical coherence tomography scans.

The retinal pigment epithelium of Vertebrates was shown to be sensitive to cyclic oscillations of light and darkness. The morphological changes induced by prolonged darkness on the retinal epithelial cells of the freshwater turtle were studied, with particular regard to their localization and to their reversibility if animals are recovered under cyclic light. The eyes were processed for light and electron microscopy and a morphological and morphometric analysis was performed on the specimens. After 7 days of prolonged darkness, the vitreal extremity of some epithelial cells was partially detached; on the basal zone the infoldings were missing and vesicles and tubules, often arranged in rows, were observed. After 30 days of prolonged darkness, partial or complete double layers of epithelial cells were present: the superficial layer was connected, by means of the apical fringes, to the photoreceptors, whilst the deepest layer showed vesicles and tubules on its basal zone. After 7 days of recovery to L:D = 12:12, no cyclic activity was demonstrated and only occasional double layers of cells were present; on the basal surface isolated basal infoldings were present where two adjacent cells were joined together. It could be concluded that the detachment of the apical part of some cells, rapidly covered by the lateral sliding of the adjacent cells, and the substitution of the basal infoldings with vesicles and tubules could represent the morphological response of the retinal epithelium to the functional changes induced by prolonged darkness.

The Authors studied the postnatal development of the retinal pigment epithelium in the albino rat, in order to elucidate its morphological and functional evolution, correlated to the numerous functional roles played in Vertebrates (Scheme 1). At birth, epithelial cells show few cytoplasmic organules and the apical surface provided of small depressions. From the third to the fifth postnatal day the first apical microfolds surround the depressions. From the seventh to the ninth day inner segments develop, whilst the apical surface of the epithelial cells is covered by many finger-like microfolds. During the eleventh postnatal day the buds of the outer segments and many lamellar microfolds can be demonstrated. During the sixteenth day the retina reaches its adult morphology. It is therefore well-evident that birth, similarly to many other Vertebrates, is not the last step, but only a moment, in the development of the retina: this process is completed only during postnatal life, when environmental light is able to stimulate every ocular structure.

The Authors investigate the morphology and the behaviour of the synaptic ribbons (NS) in the outer plexiform layer of the retina of the turtle Pseudemys scripta elegans during the 24 hrs cycle; the animals were subjected to a light-dark cycle = 12:12 hours. New ultrastructural features are demonstrated in the rod arciform density and in the fibers connecting the central axis of the ribbon with the presynaptic membrane (Figs. 1 A-B). As to chronobiological data, the existence of different kinds of ribbons, each typical of a single period of the 24 hrs cycle is excluded: identical NS can likewise be observed at different hours of the day and under various environmental light stimulations (Figs. 2-3-4). Furthermore, it is also demonstrated that during the light period, every rod synapse in the outer plexiform layer has a typical ultrastructural topography of its own (Figs. 5 A-B-C). During the dark period, the ribbon with its neighbouring vesicles moves towards the nucleus, thus leaving the synaptic region (Figs. 6 A-B-C). From the analysis of our results, we are of the opinion that all previously demonstrated changes in number are only in part dependent on cyclic disruption and reconstruction. On the contrary, they can be the result of a different topographical arrangement of the organelles. When NS modify their relationship with the presynaptic membrane of the rods, they may behave as switch on the nervous circuits of the retina and play a facilitatory or inhibitory role on the discharge of synaptic vesicles during the different periods of the 24 hrs cycle.

Purpose: A morphological and morphometric study of the adult zebrafish ocular surface was performed to provide a comprehensive description of its parts and to evaluate its similarity to the human. Materials and Methods: The eyes of adult zebrafish were processed for light, transmission and scanning electron microscopy, and for immunohistochemical stain of corneal nerves; a morphometric analysis was also performed on several morphological parameters. Results: The corneal epithelium was formed by five layers of cells. No Bowman’s layer could be demonstrated. The stroma consisted of lamellae of different thickness with few keratocytes. The Descemet’s membrane was absent as the flat and polygonal endothelial cells directly adhered to the deepest corneal lamella. The immunohistochemical stain of neurofilaments failed to demonstrate corneal nerve fibers. The conjunctival epithelium was stratified, overlying the stroma formed by a subepithelial and a deep layer, this latter connected to the scleral cartilage. In the peripheral cornea and in the conjunctiva, many goblet and rodlet cells were observed. The morphometric analysis showed that the peripheral cornea epithelium was thicker when compared to the other parts of the ocular surface, with smaller superficial cells. Desmosomes and hemidesmosomes in the conjunctiva were significantly fewer in number than the other parts of the ocular surface. The stroma was thinner in the conjunctiva than in the cornea, while corneal lamellae were thicker in the intermediate stroma. Conclusions: The zebrafish ocular surface showed significant differences compared to the human, such as the absence of Bowman’s layer, Descemet’s membrane and corneal nerve fibers, the reduced stromal thickness, and the presence of rodlet cells. On the basis of these original findings, it is suggested that the use of the zebrafish as a model for studying normal or pathological human corneas should be undertaken with particular caution.