Macular thickness varies with age-related macular degeneration genetic risk variants in the UK Biobank cohort.

To evaluate the influence AMD risk genomic variants have on macular thickness in the normal population. UK Biobank participants with no significant ocular history were included using the UK Biobank Resource (project 2112). Spectral-domain optical coherence tomography (SD-OCT) images were taken and segmented to define retinal layers. The influence of AMD risk single-nucleotide polymorphisms (SNP) on retinal layer thickness was analysed. AMD risk associated SNPs were strongly associated with outer-retinal layer thickness. The inner-segment outer segment (ISOS)-retinal pigment epithelium (RPE) thickness measurement, representing photoreceptor outer segments was most significantly associated with the cumulative polygenic risk score, composed of 33 AMD-associated variants, resulting in a decreased thickness (p = 1.37 × 10-67). Gene-gene interactions involving the NPLOC4-TSPAN10 SNP rs6565597 were associated with significant changes in outer retinal thickness. Thickness of outer retinal layers is highly associated with the presence of risk AMD SNPs. Specifically, the ISOS-RPE measurement. Changes to ISOS-RPE thickness are seen in clinically normal individuals with AMD risk SNPs suggesting structural changes occur at the macula prior to the onset of disease symptoms or overt clinical signs.

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

BACKGROUND: To assess the normal retina of the pigeon eye using spectral domain optical coherence tomography (SD-OCT) and establish a normative reference. METHODS: Twelve 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. RESULTS: The 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). CONCLUSIONS: Measured data could be used as normative references for diagnosing pigeon retinopathies and further research on avian fundus structure.

Interpretation of anatomic correlates of outer retinal bands in optical coherence tomography.

By providing the sectioning capability to differentiate individual retinal layers, optical coherence tomography (OCT) is revolutionizing eye disease diagnosis and treatment evaluation. A better understanding of the hyper- and hypo-reflective bands in retinal OCT is essential for accurate interpretation of clinical outcomes. In this article, we summarize the interpretations of clinical OCT and adaptive optics (AO) OCT (AO-OCT) of the outer retina in the human eye, and briefly review OCT investigation of the outer retina in animal models. Quantitative analysis of outer retinal OCT bands is compared to established parameters of retinal histology. The literature review and comparative analysis support that both inner/outer segment (IS/OS) junction and IS ellipsoid zone nonexclusively contribute to the second band; and OS, OS tips, and retinal pigment epithelium apical processes contribute to the third band in conventional OCT. In contrast, AO-OCT might predominantly detect the IS/OS junction and OS tip signals at the second and third bands due to its improved sectioning capability and possible AO effect on the sensitivities for recording ballistic and diffusive photons from different regions of the outer retina.

3D-Reconstructed Retinal Pigment Epithelial Cells Provide Insights into the Anatomy of the Outer Retina.

The retinal pigment epithelium (RPE) is located between the neuroretina and the choroid, and plays a critical role in vision. RPE cells internalise outer segments (OS) from overlying photoreceptors in the daily photoreceptor renewal. Changes to RPE structure are linked with age and retinopathy, which has been described in the past by conventional 2D electron microscopy. We used serial block face scanning electron microscopy (SBF-SEM) to reconstruct RPE cells from the central mouse retina. Three-dimensional-reconstructed OS revealed the RPE to support large numbers of photoreceptors (90-216 per RPE cell). Larger bi-nucleate RPE maintained more photoreceptors, although their cytoplasmic volume was comparable to smaller mono-nucleate RPE supporting fewer photoreceptors. Scrutiny of RPE microvilli and interdigitating OS revealed the angle and surface area of contact between RPE and photoreceptors. Bi-nucleate RPE contained more mitochondria compared to mono-nucleate RPE. Furthermore, bi-nucleate cells contained larger sub-RPE spaces, supporting a likely association with disease. Use of perfusion-fixed tissues ensured the highest possible standard of preservation, providing novel insights into the 3D RPE architecture and changes linked with retinopathy. This study serves as a benchmark for comparing retinal tissues from donor eyes with age-related macular degeneration (AMD) and other retinopathies.

Dual roles of the retinal pigment epithelium and lens in cavefish eye degeneration.

Astyanax mexicanus consists of two forms, a sighted surface dwelling form (surface fish) and a blind cave-dwelling form (cavefish). Embryonic eyes are initially formed in cavefish but they are subsequently arrested in growth and degenerate during larval development. Previous lens transplantation studies have shown that the lens plays a central role in cavefish eye loss. However, several lines of evidence suggest that additional factors, such as the retinal pigment epithelium (RPE), which is morphologically altered in cavefish, could also be involved in the eye regression process. To explore the role of the RPE in cavefish eye degeneration, we generated an albino eyed (AE) strain by artificial selection for hybrid individuals with large eyes and a depigmented RPE. The AE strain exhibited an RPE lacking pigment granules and showed reduced expression of the RPE specific enzyme retinol isomerase, allowing eye development to be studied by lens ablation in an RPE background resembling cavefish. We found that lens ablation in the AE strain had stronger negative effects on eye growth than in surface fish, suggesting that an intact RPE is required for normal eye development. We also found that the AE strain develops a cartilaginous sclera lacking boney ossicles, a trait similar to cavefish. Extrapolation of the results to cavefish suggests that the RPE and lens have dual roles in eye degeneration, and that deficiencies in the RPE may be associated with evolutionary changes in scleral ossification.

Associations with photoreceptor thickness measures in the UK Biobank.

Spectral-domain OCT (SD-OCT) provides high resolution images enabling identification of individual retinal layers. We included 32,923 participants aged 40-69 years old from UK Biobank. Questionnaires, physical examination, and eye examination including SD-OCT imaging were performed. SD OCT measured photoreceptor layer thickness includes photoreceptor layer thickness: inner nuclear layer-retinal pigment epithelium (INL-RPE) and the specific sublayers of the photoreceptor: inner nuclear layer-external limiting membrane (INL-ELM); external limiting membrane-inner segment outer segment (ELM-ISOS); and inner segment outer segment-retinal pigment epithelium (ISOS-RPE). In multivariate regression models, the total average INL-RPE was observed to be thinner in older aged, females, Black ethnicity, smokers, participants with higher systolic blood pressure, more negative refractive error, lower IOPcc and lower corneal hysteresis. The overall INL-ELM, ELM-ISOS and ISOS-RPE thickness was significantly associated with sex and race. Total average of INL-ELM thickness was additionally associated with age and refractive error, while ELM-ISOS was additionally associated with age, smoking status, SBP and refractive error; and ISOS-RPE was additionally associated with smoking status, IOPcc and corneal hysteresis. Hence, we found novel associations of ethnicity, smoking, systolic blood pressure, refraction, IOPcc and corneal hysteresis with photoreceptor thickness.

Automatic choroidal segmentation in OCT images using supervised deep learning methods.

The analysis of the choroid in the eye is crucial for our understanding of a range of ocular diseases and physiological processes. Optical coherence tomography (OCT) imaging provides the ability to capture highly detailed cross-sectional images of the choroid yet only a very limited number of commercial OCT instruments provide methods for automatic segmentation of choroidal tissue. Manual annotation of the choroidal boundaries is often performed but this is impractical due to the lengthy time taken to analyse large volumes of images. Therefore, there is a pressing need for reliable and accurate methods to automatically segment choroidal tissue boundaries in OCT images. In this work, a variety of patch-based and fully-convolutional deep learning methods are proposed to accurately determine the location of the choroidal boundaries of interest. The effect of network architecture, patch-size and contrast enhancement methods was tested to better understand the optimal architecture and approach to maximize performance. The results are compared with manual boundary segmentation used as a ground-truth, as well as with a standard image analysis technique. Results of total retinal layer segmentation are also presented for comparison purposes. The findings presented here demonstrate the benefit of deep learning methods for segmentation of the chorio-retinal boundary analysis in OCT images.

Normative pattern and determinants of outer retinal thickness in an Asian population: the Singapore Epidemiology of Eye Diseases Study.

BACKGROUND/AIMS: To evaluate the distribution and determinants of outer retinal thickness in eyes without retinal diseases, using spectral-domain optical coherence tomography (SD-OCT). METHODS: Participants were recruited from the Singapore Epidemiology of Eye Diseases Study, a population-based study among Chinese, Malays and Indians in Singapore. A total of 5333 participants underwent SD-OCT imaging in which a 6×6 mm2 measurement area centred at the fovea. Outer retinal thickness was defined as the distance from the outer plexiform layer to the retinal pigment epithelium layer boundary. RESULTS: 7444 eyes from 4454 participants were included in final analysis. Of them, mean age was 58.4 years (SD 8.3), and 2294 (51.5%) were women. Women (121.0±8.1 µm) had thinner average outer retinal thickness than men (125.6±8.2 µm) (p<0.001). Malays (121.4±8.7 µm) had thinner average outer retinal thickness than Indians (124.3±8.6 µm) and Chinese (123.7±7.9 µm) (both p<0.001). In multivariable models, thinner average outer retinal thickness was associated with older age (per decade, ß=-1.02, p<0.001), hypertension (ß=-0.59, p=0.029), diabetes (ß=-0.73, p=0.013), chronic kidney disease (ß=-1.25, p=0.017), longer axial length (per mm, ß=-0.76, p<0.001), flatter corneal curvature (per mm, ß=-2.00, p<0.001) and higher signal strength (ß=-1.46, p<0.001). CONCLUSION: In this large sample of Asian population, we provided normative SD-OCT data on outer retinal thickness in eyes without retinal diseases. Women had thinner outer retina than men. For the first time, these findings provide fundamental knowledge on normative profile of outer retinal thickness in Asians.

Bruch´s membrane thickness in relationship to axial length.

PURPOSE: To assess a potential role of Bruch´s membrane (BM) in the biomechanics of the eye, we measured its thickness and the density of retinal pigment epithelium (RPE) cells in various ocular regions in eyes of varying axial length. METHODS: Human globes, enucleated because of an ocular tumor or end-stage glaucoma were prepared for histological examination. Using light microscopy, the histological slides were histomorphometrically examined applying a digitized image analysis system. RESULTS: The study included 104 eyes with a mean axial length of 27.9±3.2 mm (range:22.6mm-36.5mm). In eyes without congenital glaucoma, BM was significantly thickest (P<0.001) at the ora serrata, followed by the posterior pole, the midpoint between equator and posterior pole (MBEPP), and finally the equator. BM thickness was not significantly correlated with axial length (ora serrata: P = 0.93; equator:P = 0.31; MBEPP:P = 0.15; posterior pole:P = 0.35). RPE cell density in the pre-equatorial region (P = 0.02; regression coefficient r = -0.24) and in the retro-equatorial region (P = 0.03; r = -0.22) decreased with longer axial length, while RPE cell density at the ora serrata (P = 0.35), the MBEPP (P = 0.06; r = -0.19) and the posterior pole (P = 0.38) was not significantly correlated with axial length. Highly myopic eyes with congenital glaucoma showed a tendency towards lower BM thickness and lower RPE cell density at all locations. CONCLUSIONS: BM thickness, in contrast to scleral and choroidal thickness, was independent of axial length in eyes without congenital glaucoma. In association with an axial elongation associated decrease in the RPE cell density in the midperiphery, the findings support the notion of a biomechanical role BM may play in the process of emmetropization/myopization.

CHANGES OF OUTER RETINAL THICKNESS WITH INCREASING AGE IN NORMAL EYES AND IN NORMAL FELLOW EYES OF PATIENTS WITH UNILATERAL AGE-RELATED MACULAR DEGENERATION.

PURPOSE: To test the hypothesis that the thickness of outer retinal layers will change with increasing age in normal eyes and in the normal fellow eyes of patients with unilateral age-related macular degeneration. METHODS: Spectral domain optical coherence tomography images of 127 normal eyes of 127 subjects and 58 normal fellow eyes of 58 patients with unilateral age-related macular degeneration were studied. The thickness between the retinal pigment epithelium line and the cone outer segment tips line, between the cone outer segment tips line and the photoreceptor inner segment/outer segment line, and between the inner segment/outer segment line and the external limiting membrane line were measured at the fovea in both groups. RESULTS: The thickness between retinal pigment epithelium line and the cone outer segment tips line, and between inner segment/outer segment line and the external limiting membrane line were significantly and negatively associated with age in the normal group. Cone outer segment tips line and the photoreceptor inner segment/outer segment thickness was not significantly associated with age. Retinal pigment epithelium line and the cone outer segment tips line was thinner in the fellow eyes of patients with unilateral age-related macular degeneration than in the age-matched normal eyes. Cone outer segment tips line and the photoreceptor inner segment/outer segment and inner segment/outer segment line and the external limiting membrane line thicknesses in the fellow eyes were not significantly different from that of normal eyes. CONCLUSION: The tissue between the retinal pigment epithelium line and the cone outer segment tips line may become atrophic in older eyes and in the normal fellow eyes of patients with unilateral age-related macular degeneration.

Associations with Retinal Pigment Epithelium Thickness Measures in a Large Cohort: Results from the UK Biobank.

PURPOSE: To describe associations of ocular and systemic factors with retinal pigment epithelium (RPE)-Bruch's membrane (BM) complex thickness as measured by spectral-domain (SD) optical coherence tomography (OCT). DESIGN: Multisite community-based study. This research has been conducted using the UK Biobank Resource. PARTICIPANTS: Sixty-seven thousand three hundred eighteen people 40 to 69 years old received questionnaires, physical examination, and eye examination, including macular SD OCT. Systematic selection process identified 34 652 eyes with high-quality SD OCT images from normal individuals for analysis. METHODS: We included people with no self-reported ocular disease, diabetes, or neurologic disorders; visual acuity of ≥20/25; refraction between -6 diopters (D) to 6 D, and IOP of 6 to 21 mmHg. Only high-quality, well-centered SD OCT images with central, stable fixation were included. Descriptive statistics, t tests, and regression analyses were performed. Multivariate regression modeling was used to adjust for covariates and to identify relationships between RPE-BM thickness and ocular and systemic features. MAIN OUTCOME MEASURES: Retinal pigment epithelium-BM thickness, as measured by SD OCT segmentation using Topcon Advanced Boundary Segmentation at 9 Early Treatment of Diabetic Retinopathy Study subfields. RESULTS: Mean RPE-BM thickness was 26.3 µm (standard deviation, 4.8 µm) at central subfield. Multivariate regression with age stratification showed that RPE thinning became apparent after age 45. Among those aged ≤45, RPE-BM was significantly thicker among those of black or mixed/other race (+3.61 and +1.77 µm vs. white, respectively; P < 0.001) and higher hyperopia (+0.4 µm/D; P < 0.001), but not for other variables considered. Among those age >45, RPE-BM was significantly thinner with older age (-0.10 µm/year; P < 0.001), Asian ethnicity (-0.45 µm vs. white; P = 0.02), taller height (-0.02 µm/cm; P < 0.001), higher IOP (-0.03 µm/mmHg; P < 0.001), and regular smoking (-0.27 µm vs. nonsmokers; P = 0.02). In contrast, RPE-BM was significantly thicker among black or mixed/other race (+3.29 µm and +0.81 µm vs. white, respectively; P < 0.001) and higher hyperopia (+0.28 µm/D; P < 0.001). There was no significant association with sex or Chinese ethnicity. CONCLUSIONS: We describe novel findings of RPE-BM thickness in normal individuals, a structure that varies with age, ethnicity, refraction, IOP, and smoking. The significant association with IOP is especially interesting and may have relevance for the etiology of glaucoma, while the association between age and smoking may have relevance for the etiology of age-related macular degeneration.

OPTICAL COHERENCE TOMOGRAPHY EVIDENCE ON THE CORRELATION OF CHOROIDAL THICKNESS AND AGE WITH VASCULARIZED RETINAL LAYERS IN NORMAL EYES.

PURPOSE: To correlate choroidal thickness (CT) and age with vascularized retinal layer and outer retinal layer thickness in normal eyes. METHODS: This was a prospective, cross-sectional study. Complete ophthalmological examination, biometry, and enhanced depth imaging spectral domain optical coherence tomography were performed. Choroidal and individual retinal layer thickness measurements were obtained. Thickness maps for all layers were evaluated using the 1 mm, 3 mm, and 6 mm early treatment diabetic retinopathy study (ETDRS) macular grid areas. RESULTS: One hundred and twenty eyes were included. Choroidal thickness correlated negatively with age in all ETDRS areas. The ganglion cell layer (GCL) in the 1 mm; the GCL and inner plexiform layer (IPL) in the 3 mm and 6 mm; and the GCL, IPL, and inner nuclear layer in the 6 mm areas correlated negatively with age and positively with CT. Retinal nerve fiber layer thickness in the 6 mm area correlated negatively with age. The retinal pigment epithelium-photoreceptor layer in all areas correlated negatively with age and positively with CT. CONCLUSION: In normal subjects, vascularized retinal layer thicknesses and outer retinal layer thickness correlate positively with CT and negatively with age. The role of neuronal versus vascular components should be considered when evaluating individual retinal layer thicknesses.

CHOROIDAL THICKNESS IN RELATION TO ETHNICITY MEASURED USING ENHANCED DEPTH IMAGING OPTICAL COHERENCE TOMOGRAPHY.

PURPOSE: To investigate the posterior choroidal thickness in healthy subjects of three different ethnicities. METHODS: In this prospective cross-sectional study, the choroidal thickness of 88 individuals (176 eyes) was measured using enhanced depth imaging-spectral domain optical coherence tomography. Subfoveal choroidal thickness was measured between the retinal pigment epithelium-Bruch membrane complex and chorioscleral interface. Nasal, temporal, superior, and inferior choroidal thicknesses at 0.5, 1.5, and 3.0 mm locations from the fovea were evaluated as well. RESULTS: Males and females were perfectly matched by number in all groups. The mean age of the entire study population was 27.43 ± 1 years. Mean subfoveal choroidal thicknesses of whites, Africans, Asians, and entire study population were 403.62 ± 37.4 µm, 372.47 ± 31.4 µm, 383.64 ± 40 µm, 386.64 ± 10.5 µm, respectively. Mean spherical error of the entire study population was -1.2685 diopter. Whites had the longest eyes on average 24.17 mm > 24.08 mm (Africans) > 23.86 mm (Asians), with the statistical mean of 24.04 mm for the entire study population. Subfoveal choroidal thickness was not significantly correlated with ethnicity in either ethnic group (P > 0.05). Subfoveal choroid thinned by 2.51 µm per 1 year increase in age (P = 0.282). Subfoveal choroidal thickness and sex were not significantly correlated to (P = 0.402). Subfoveal choroidal thickness was in strong negative correlation only with refractive error (P = 0.01) and axial length (P = 0.008). The intereye difference in subfoveal choroidal thickness was not statistically significant (P = 0.845). CONCLUSION: Enhanced depth imaging-spectral domain optical coherence tomography is a productive imaging method to study the choroidal thickness. Subfoveal choroidal thickness is not significantly correlated with ethnicity. The study reproduced previously found relations between thinner choroids and longer axial lengths, and increasing myopic refraction and showed no significant associations between subfoveal choroidal thickness and age and sex. Either the right or left eye can be used in future studies.

Conditional Ablation of Retinol Dehydrogenase 10 in the Retinal Pigmented Epithelium Causes Delayed Dark Adaption in Mice.

Regeneration of the visual chromophore, 11-cis-retinal, is a crucial step in the visual cycle required to sustain vision. This cycle consists of sequential biochemical reactions that occur in photoreceptor cells and the retinal pigmented epithelium (RPE). Oxidation of 11-cis-retinol to 11-cis-retinal is accomplished by a family of enzymes termed 11-cis-retinol dehydrogenases, including RDH5 and RDH11. Double deletion of Rdh5 and Rdh11 does not limit the production of 11-cis-retinal in mice. Here we describe a third retinol dehydrogenase in the RPE, RDH10, which can produce 11-cis-retinal. Mice with a conditional knock-out of Rdh10 in RPE cells (Rdh10 cKO) displayed delayed 11-cis-retinal regeneration and dark adaption after bright light illumination. Retinal function measured by electroretinogram after light exposure was also delayed in Rdh10 cKO mice as compared with controls. Double deletion of Rdh5 and Rdh10 (cDKO) in mice caused elevated 11/13-cis-retinyl ester content also seen in Rdh5(-/-)Rdh11(-/-) mice as compared with Rdh5(-/-) mice. Normal retinal morphology was observed in 6-month-old Rdh10 cKO and cDKO mice, suggesting that loss of Rdh10 in the RPE does not negatively affect the health of the retina. Compensatory expression of other retinol dehydrogenases was observed in both Rdh5(-/-) and Rdh10 cKO mice. These results indicate that RDH10 acts in cooperation with other RDH isoforms to produce the 11-cis-retinal chromophore needed for vision.

Characterization of Choroidal Layers in Normal Aging Eyes Using Enface Swept-Source Optical Coherence Tomography.

PURPOSE: To characterize qualitative and quantitative features of the choroid in normal eyes using enface swept-source optical coherence tomography (SS-OCT). METHODS: Fifty-two eyes of 26 consecutive normal subjects were prospectively recruited to obtain multiple three-dimensional 12 x 12 mm volumetric scans using a long-wavelength high-speed SS-OCT prototype. A motion-correction algorithm merged multiple SS-OCT volumes to improve signal. Retinal pigment epithelium (RPE) was segmented as the reference and enface images were extracted at varying depths every 4.13 µm intervals. Systematic analysis of the choroid at different depths was performed to qualitatively assess the morphology of the choroid and quantify the absolute thicknesses as well as the relative thicknesses of the choroidal vascular layers including the choroidal microvasculature (choriocapillaris, terminal arterioles and venules; CC) and choroidal vessels (CV) with respect to the subfoveal total choroidal thickness (TC). Subjects were divided into two age groups: younger (<40 years) and older (≥ 40 years). RESULTS: Mean age of subjects was 41.92 (24-66) years. Enface images at the level of the RPE, CC, CV, and choroidal-scleral interface were used to assess specific qualitative features. In the younger age group, the mean absolute thicknesses were: TC 379.4 µm (SD ± 75.7 µm), CC 81.3 µm (SD ± 21.2 µm) and CV 298.1 µm (SD ± 63.7 µm). In the older group, the mean absolute thicknesses were: TC 305.0 µm (SD ± 50.9 µm), CC 56.4µm (SD ± 12.1 µm) and CV 248.6µm (SD ± 49.7 µm). In the younger group, the relative thicknesses of the individual choroidal layers were: CC 21.5% (SD ± 4.0%) and CV 78.4% (SD ± 4.0%). In the older group, the relative thicknesses were: CC 18.9% (SD ± 4.5%) and CV 81.1% (SD ± 4.5%). The absolute thicknesses were smaller in the older age group for all choroidal layers (TC p=0.006, CC p=0.0003, CV p=0.03) while the relative thickness was smaller only for the CC (p=0.04). CONCLUSIONS: Enface SS-OCT at 1050 nm enables a precise qualitative and quantitative characterization of the individual choroidal layers in normal eyes. Only the CC is relatively thinner in the older eyes. In-vivo evaluation of the choroid at variable depths may be potentially valuable in understanding the natural history of age-related posterior segment disease.

Third harmonic generation microscopy of a mouse retina.

PURPOSE: To demonstrate lipid-specific imaging of the retina through the use of third harmonic generation (THG), a multiphoton microscopic technique in which tissue contrast is generated from optical inhomogeneities. METHODS: A custom fiber laser and multiphoton microscope was constructed and optimized for simultaneous two-photon autofluorescence (TPAF) and THG retinal imaging. Imaging was performed using fixed-frozen sections of mouse eyes without the use of exogenous fluorescent dyes. In parallel experiments, a fluorescent nuclear stain was used to verify the location of the retinal cell nuclei. RESULTS: Simultaneous THG and TPAF images revealed all retinal layers with subcellular resolution. In BALB/c strains, the THG signal stems from the lipidic organelles of the cellular and nuclear membranes. In the C57BL/6 strain, the THG signal from the RPE cells originates from the pigmented granules. CONCLUSIONS: THG microscopy can be used to image structures of the mouse retina using contrast inherent to the tissue and without the use of a fluorescent dye or exogenously expressed recombinant protein.

Circumpapillary course of retinal pigment epithelium can be fit to sine wave and amplitude of sine wave is significantly correlated with ovality ratio of optic disc.

The purpose of this study was to develop a method of quantifying the degree of optic disc tilt in normal eyes. This was a prospective, observational cross sectional study of 126 right eyes of 126 healthy volunteers. The optic disc tilt was determined from the circular peripapillary optical coherence tomographic (OCT) scan images. The course of the retinal pigment epithelium (RPE) layer in the peripapillary cross sectional scan images was fit to a sine wave curve, and the amplitude of the sine curve was used to reflect the degree of the optic disc tilt in the optical axis. The repeatability of the amplitude determinations was calculated. The correlation between the amplitude and the ovality ratio of the optic disc was determined. The correlation between the amplitude and the body height was also calculated. The mean amplitude was 36.6 ± 17.5 pixels, which was significantly and inversely correlated with the ovality ratio of the optic disc (R = -0.59, P < 0.001). The intra-rater and inter-rater correlation coefficients of the amplitude were significant high (P < 0.001, both). The amplitude was significantly and inversely correlated with the body height (R = -0.38, P < 0.001), but not with the axial length. In conclusion, a sine wave function can be used to describe the course of the RPE in the circumpapillary OCT images. The results indicate that the amplitude of the sine wave can be used to represent the degree of optic disc tilt. Thus, the sine wave analyses can be used as a quantifiable and repeatable method to determine the optic disc tilt.

Altered fundus appearance resulting from autofluorescence imaging with the confocal scanning laser ophthalmoscope (cSLO) in cats.

PURPOSE: This paper is to report that imaging the tapetal fundus of cats with the 488 nm laser of the Spectralis(®) HRA+OCT (Heidelberg Engineering Inc., Heidelberg, Germany) can result in a pale appearance of the imaged area. ANIMALS STUDIED AND PROCEDURES: Wild-type and Rdy kittens (CRX mutant heterozygotes-CRX(Rdy+/-) ) (8-20 weeks of age) and adult cats (1-4 years of age) were imaged by confocal scanning laser ophthalmoscope (cSLO) and spectral domain optical coherence tomography (SD-OCT) using the Spectralis(®) HRA+OCT. Color fundus photography (RetCam II(®) , Clarity Medical Systems, Inc., Pleasanton, CA) was performed after imaging using the Spectralis(®) HRA+OCT. RESULTS: Following retinal cSLO imaging using the 488 nm laser (autofluorescence imaging) in both wild-type kittens and adult cats, the imaged region appeared paler than the adjacent retina that had not been imaged. This change was probably due to retinal bleaching and was fully reversible. Imaging CRX(Rdy+/-) kittens or adults, which had very reduced levels of visual pigments, did not induce the altered fundus appearance. CONCLUSIONS: Those using autofluorescence imaging by cSLO should be aware that it can induce a characteristic pale appearance of the tapetal fundus in the imaged area of normal cats.

Macroscopic and histological variations in the cellular tapetum in dogs.

We aimed to document macroscopic variations in the cellular tapetum in the dog, to provide a histologic description of the macroscopic results and to evaluate the correlation between the macroscopic appearance and aging. Fifty three dogs including 5 beagles, 1 Chihuahua and 47 mixed breeds of each gender were used. For a macroscopic study, the fresh tapetal fundi were photographed using digital camera. For a histological study, the glutaraldehyde-formalin fixed eyes were embedded in nitrocellulose and stained with hematoxylin-eosin or thionine. The normal tapetum was triangular with the rounded angles and the smooth contour. The atypical tapetum was smaller and more variable in shape, contour and color than the normal one. In severe cases, the fundus was devoid of the tapetum. The atypical tapetum tended to increase in frequency with aging. Retinal pigment epithelial cells on the normal tapetum were unpigmented. In the eye with the atypical tapetum, regardless of tapetal size and shape, unpigmented retinal pigment epithelial cells showed a similar distribution to that on the normal tapetum, even in a dog without a tapetum. Although there is a congenitally hypoplastic tapetum, the atypical tapetum tends to increase in incidence and severity with aging.

The fibrous tapetum of the horse eye.

The tapetum lucidum is a light-reflective tissue in the eyes of many animals. Many ungulates have a fibrous tapetum. The horse has one of the largest eyes of any living animal and also has excellent vision in low-light environments. This study aimed to clarify the macroscopic tapetal shape, relationship between the tapetal thickness and the degree of pigmentation of the retinal pigment epithelium (RPE), spatial relationship between the visual streak and the tapetum, and wavelength of the light reflected from the tapetum in the horse. Macroscopically, weak light revealed the tapetum as a horizontal band located dorsal to and away from the optic disc. The tapetum expanded dorsally as the illumination increased. The tapetal tissue consisted of lamellae of collagen fibrils running parallel to the retinal surface; these spread over almost the entire ocular fundus and were thicker in the horizontal band dorsal to the disc. Only the horizontal band of the tapetum was covered by unpigmented RPE, suggesting that this band reflects light and is responsible for mesopic and scotopic vision. The visual streak was located in the ventral part of the horizontal band, ventral to the thickest part of the tapetum. The wavelength of the light reflected from the horizontal band of the tapetum was estimated from the diameter and interfibrous distance of the collagen fibrils to be approximately 468 nm. Therefore, the light reflected from the tapetum should be more effectively absorbed by rods than by cones, and should not interfere with photopic vision.