Spectral domain optical coherence tomography (SD-OCT) assessment of the healthy female canine retina and optic nerve

Objective To provide normative data for canine whole retinal thickness (WRT), nerve fiber layer thickness (NFL), photoreceptor layer thickness (PR), and outer nuclear layer thickness (ONL) using spectral domain optical coherence tomography. Animal studied: Twelve healthy adult intact female beagles. Procedure Horizontal volume scans through the area dorso‐temporal from the optic nerve (superior retina), and the area ventro‐temporal from the optic nerve (inferior retina) were used to evaluate the thickness of retinal NFL, PR, ONL, and WRT. Peripapillary circular scans were used to evaluate NFL thickness. Statistical analyses were performed to compare the thickness of the individual layers between the superior and inferior retina (paired t‐test). One‐way analysis of variance (ANOVA) was used to compare the thickness of peripapillary NFL between the superior, inferior, temporal and nasal quadrants of the circle scan. Results The WRT, PR, and NFL thickness were greater in the superior than in the inferior retina (198.7 ± 9.6 μm vs. 164.4 ± 6.4 μm, P < 0.0001; 95.5 ± 6.5 μm vs. 78.8 ± 7.4 μm, P < 0.0001; and 26.4 ± 1.6 μm vs. 25.0 ± 1.9 μm, P = 0.0236, respectively). No statistical difference was found between the ONL thickness of the superior and inferior retina (50.1 ± 6.4 μm vs. 44.3 ± 3.6, P = 0.0578). Peripapillary NFL thickness showed a similar tendency as the linear scans, with the superior quadrant having the greatest thickness (91.26 ± 7.0 μm) and the inferior quadrant being the thinnest (76.42 ± 9.2 μm) (P < 0.001). Conclusions Results of our in vivo studies showed significant differences between thickness values for the superior (tapetal) and inferior (nontapetal) retinal regions.     

Distinctive histopathologic features of canine optic nerve hypoplasia and aplasia: a retrospective review of 13 cases

Canine optic nerve hypoplasia (ONH) and aplasia (ONA) are significant neuro-ophthalmologic disorders that have been reported in several species. The purpose of this study was to describe the distinctive histopathologic features of ONH and ONA in canine patients identified from a collection of 20 000 ocular submissions at the comparative ocular pathology laboratory of Wisconsin from 1989 to 2006. The following information about ONH and ONA cases was collected: signalment, and clinical and gross findings, including unilateral vs. bilateral involvement. Microscopic evaluation was performed, with attention to optic nerve malformation, retinal ganglion cell (RGC) and nerve fiber layer (NFL) loss, and retinal disorganization. The distribution of retinal vasculature was recorded and a search for unusual findings of ONH and ONA was performed. Information and histologic documentation was available for 13 cases. Eight cases of ONH and five cases of ONA were identified. The average group age was 20.2 months and 16.1 months, respectively. The most common breed was the Shih Tzu (3/13). ONH usually presented bilaterally (7/8); all ONA cases presented as a unilateral disease (5/5). The morphologic findings in the optic nerve (ON) in ONH included variable degrees of ON hypoplasia and gliosis, as well as ectopic vestigial ON remnants within orbital nerves and connective tissues. The NFL was detected in the majority of the ONH cases; however, RGCs were rare or absent. Mild retinal disorganization was seen occasionally. Most cases of ONH were associated with regional peripheral retinal blood vessel extension into the vitreous, leaving the peripheral retina avascular. In ONA cases the retinal blood vessels, NFL and RGCs were totally absent and retinal disorganization was severe. Distinctive microscopic features encountered in ONA included anterior segment dysgenesis in some cases. The retina in these cases was stretched across the posterior lens capsule, never making contact with the posterior pole of the globe. The current study reviews the human and veterinary literature pertaining to ONH and ONA, compares ONH and ONA in dogs, and presents related ophthalmic histopathologic findings that have not been reported previously.     

In vitro measurement of rabbit corneal epithelial thickness using ultrahigh resolution optical coherence tomography

The objective of this study was to reproducibly measure corneal epithelial thickness centrally and at the limbus in the rabbit cornea using ultrahigh resolution optical coherence tomography (OCT). Twelve freshly enucleated New Zealand white rabbit eyes were kept in a moist chamber at 4 degrees C. An ultrahigh resolution OCT system with a spatial resolution of 1.3 microm was used to image the cornea and its component layers. The central and peripheral (limbal) regions of all the samples were scanned within 6 h of harvest in order to minimize the post-mortem degradation of the corneal epithelium. The thickness of the corneal epithelium was determined by measuring the pixel equivalents of the obtained image. Unpaired Student's t-test was used to evaluate differences. The epithelial thickness centrally was found to be 45.8 +/- 2.2 microm, and 37.6 +/- 1.4 microm at the limbus (P < 0.001). Rabbit corneal epithelium is thicker centrally than at the limbus when measured by ultrahigh resolution OCT. This technique will aid in delineating the pathophysiology of diseases of the anterior cornea.     

Assessment of the pigeon (Columba livia) retina with spectral domain optical coherence tomography

BackgroundTo assess the normal retina of the pigeon eye using spectral domain optical coherence tomography (SD-OCT) and establish a normative reference.MethodsTwelve eyes of six ophthalmologically normal pigeons (Columba livia) were included. SD-OCT images were taken with dilated pupils under sedation. Four meridians, including the fovea, optic disc, red field, and yellow field, were obtained in each eye. The layers, including full thickness (FT), ganglion cell complex (GCC), thickness from the retinal pigmented epithelium to the outer nuclear layer (RPE-ONL), and from the retinal pigmented epithelium to the inner nuclear layer (RPE-INL), were manually measured.ResultsThe average FT values were significantly different among the four meridians (p < 0.05), with the optic disc meridian being the thickest (294.0 ± 13.9 µm). The average GCC was thickest in the optic disc (105.3 ± 27.1 µm) and thinnest in the fovea meridian (42.8 ± 15.3 µm). The average RPE-INL of the fovea meridian (165.5 ± 18.3 µm) was significantly thicker than that of the other meridians (p < 0.05). The average RPE-ONL of the fovea, optic disc, yellow field, and red field were 91.2 ± 5.2 µm, 87.7 ± 5.3 µm, 87.6 ± 6.5 µm, and 91.4 ± 3.9 µm, respectively. RPE-INL and RPE-ONL thickness of the red field meridian did not change significantly with measurement location (p > 0.05).ConclusionsMeasured data could be used as normative references for diagnosing pigeon retinopathies and further research on avian fundus structure.     

Assessment of the posterior segment of the cat eye by optical coherence tomography (OCT)

OBJECTIVES: To assess the feasibility of optical coherence tomography (OCT) for examining the cat ocular fundus, to provide normative data on retinal thickness in different fundus regions, and to demonstrate selected surgically induced vitreoretinal pathologies in the cat. ANIMAL STUDIED: Forty-five eyes of 28 healthy domestic cats and two eyes of domestic cats that had undergone subretinal implantation surgery for a visual prosthesis were examined. PROCEDURES: An optical coherence tomograph (Zeiss-Humphrey) was used to examine the anesthetized animals. At least five vertical and five horizontal scans in regular distribution were recorded for each cat including (1) the peripapillary region, (2) the area centralis, and (3) the peripheral retina. Thickness was measured manually at five locations in each scan. Retinal thickness was compared in the three above-mentioned fundus regions, between eyes and between vertical and horizontal scans. OCT was additionally performed in animals with retinal detachment and a subretinal visual prosthesis. RESULTS: OCT measurements required only minimal adjustments of human settings and yielded high quality images. In comparison to humans intraretinal layers were more difficult to differentiate. Retinal thickness was highest in the peripapillary region (245 +/- 21 microm), followed by the peripheral retina (204 +/- 11 microm) and the area centralis (182 +/- 11 microm; all P < 0.0001). There was no statistically significant difference between right and left eye or between vertical and horizontal scans. OCT demonstrated retinal detachment, an iatrogenic break and a subretinal prosthetic device in high detail. CONCLUSIONS: Retinal thickness was measurable with high precision; values compare well to older histologic studies. OCT bears significant advantages over histology in enabling one to repeat measurements in living animals and thus allowing longitudinal studies. Various vitreoretinal pathologies common in feline eyes are detectable and quantifiable by OCT.