3T high-resolution magnetic resonance imaging, conventional ultrasonography and ultrasound biomicroscopy of the normal canine eye.

BACKGROUND: Advances in MRI coil technology and increased availability of high-field MRI in veterinary medicine enable the acquisition of images of increasingly high spatial resolution while preserving signal-to-noise ratio.The purpose of the present study was to compare 3T high-resolution magnetic resonance imaging (HR-MRI) with ultrasound (US) and ultrasound biomicroscopy (UBM) in the normal canine eye, to assess its potential to depict normal ocular anatomy. RESULTS: HR-MRI was compared with US and UBM in 10 eyes from 10 healthy beagle dogs. Ocular structures (cornea, anterior chamber, iridocorneal angle, iris, lens, ciliary body, choroid, vitreous body, posterior wall of the eye, optic nerve and optic nerve sheath, extraocular muscles) were assessed subjectively and central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), anteroposterior, mediolateral and dorsoventral lens diameter (APLD, MLLD, DVLD), anteroposterior diameter of the globe including and excluding the scleroretinal rim (APDSRR, APD), vitreous chamber depth (VCD) and optic nerve sheath diameter (ONSD) were measured in HR-MRI and in US. Optic nerve diameter (OND) was measured in HR-MRI. HR-MRI and UBM appearance of the anterior segment were subjectively compared. Detailed reference high-resolution MRI images of normal eyes of Beagle dogs are provided. CONCLUSIONS: HR-MRI allowed assessment of all structures identified with US and UBM. The MRI examinations were performed under general anesthesia with the addition of a neuromuscular blocking agent, while US and UBM examinations were performed in conscious animals. Visibility of the entire ocular wall, the lens, the structures caudal to the ciliary body and the optic nerve and its sheath was superior with HR-MRI. HR-MRI allowed the distinction of retina, choroid and sclera, and the delineation of structures not previously identified in canine eyes with MRI, including Tenon's capsule and the sub-Tenon's space.Plane selection was more accurate with HR-MRI compared to US. In general, the range of measurements was narrower for MRI than for US. CCT, AQD, APLD, MLLD, APD, APDSRR and ONSD differed significantly between HR-MRI and US, respectively (p = 0.005-0.027).Micro-MRI may be useful for the assessment of ocular pathologies in the future.

Comparison of A-Scan ultrasonography and the Lenstar optical biometer in Guinea pig eyes.

OBJECTIVE: To compare the biometric parameters provided by A-scan ultrasonography and the Lenstar optical biometer in guinea pig eyes, including anterior segment depth (ASD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL), and differences of them between treated form deprivation (FD) eyes and untreated fellow eyes after 4 weeks of FD. METHODS: Three-week-old guinea pigs (N = 41) were subjected to biometric measurements before monocular FD (baseline) and after a 4-week FD. Statistical analyses including within-subject standard deviation (SDwithin), coefficient of variation (CV), and intraclass correlation coefficient (ICC), used to evaluate repeatability for both the A-scan ultrasonography and the Lenstar individually, and correlation and Bland-Altman analyses were used to assess agreement between the two methods. The absolute values of ASD, LT, VCD and AL as measured by the two devices were compared, and the differences of them between treated (T) and untreated fellow (F) eyes (ΔASD, ΔLT, ΔVCD and ΔAL) (Δ = T-F) were compared between the two devices after 4 weeks of FD. RESULTS: Measurements by the Lenstar (ICC: 0.923-0.994) were more repeatable than A-scan ultrasonography (ICC: 0.825-0.870). There was a high correlation for AL (r = 0.851, P < 0.001), a moderate correlation for VCD (r = 0.571, P < 0.001) and LT (r = 0.423, P < 0.001), and a low correlation for ASD (r = 0.230, P < 0.01) between the two devices. The values for ASD, VCD and AL measured by A-scan ultrasonography were larger than those measured by the Lenstar (all, P < 0.001), while LT provided by A-scan ultrasonography was much smaller than that of the Lenstar (P < 0.001). Bland-Altman plots showed poor agreement of absolute values of the four parameters between the two devices. Moreover, there was a high correlation between both methods for ΔAL (r = 0.704, P < 0.001), a moderate correlation for ΔVCD (r = 0.534, P < 0.001) and ΔASD (r = 0.574, P < 0.001), and no correlation for ΔLT (r = 0.303, P = 0.054). The ΔASD, ΔLT, and ΔAL measurements obtained by A-scan ultrasonography were greater than those obtained by the Lenstar (all, P < 0.001), while ΔVCD was mildly smaller using A-scan ultrasonography (P < 0.05). Bland-Altman plots illustrated there is good agreement of ΔAL, ΔVCD, ΔASD, and ΔLT between the two devices. CONCLUSIONS: The Lenstar exhibited better repeatability and provided smaller measurements for AL, VCD and ASD than A-scan ultrasonography. Furthermore, a high correlation and a good agreement for the ΔAL was observed between the two devices after a period of FD. In summary, the two devices cannot replace each other directly to obtain absolute values of ASD, LT, VCD and AL, but the Lenstar still can serve as an option in measuring ΔAL between eyes in guinea pig myopia model.

Visualization of different anatomical parts of the enucleated human eye using X-ray micro-CT imaging.

Micro-CT visualization allows reconstruction of eye structures with the resolution of light microscopy and estimation of tissue densities. Moreover, this method excludes damaging procedures and allows further histological staining due to the similar steps in the beginning. We have shown the feasibility of the lab-based micro-CT machine usage for visualization of clinically important compartments of human eye such as trabecular outflow pathway, retina, iris and ciliary body after pre-treatment with iodine in ethanol. We also identified the challenges of applying this contrasting technique to lens, cornea, and retina and proposed alternative staining methods for these tissues. Thereby this work provides a starting point for other studies for imaging of human eyes in normal and pathological conditions using lab-based micro-CT systems.

MULTIPLE INTRAVITREAL INJECTIONS DO NOT CAUSE ANTERIOR SCLERAL THINNING: An Ultrasound Biomicroscopy Study.

PURPOSE: To evaluate possible changes in anterior scleral thickness and structure and changes in the anterior segment in eyes receiving multiple intravitreal injections using ultrasound biomicroscopy imaging. METHODS: Prospective, interventional, nonrandomized, cross-sectional study. Both eyes from 33 patients previously treated at least by 15 intravitreal injections in one eye only for retinal diseases were included. Intravitreal injections were performed by ophthalmologists using an aseptic standardized procedure. Ultrasound biomicroscopy examination was performed in all eyes, and scleral thickness was measured at the pars plana in four quadrants. Anterior chamber depth and ciliary body size were measured. Scleral thickness in the study eye was compared with the fellow eye. Secondary outcome measures were 1) anterior chamber depth; 2) ciliary body size; 3) scleral qualitative changes in the study eye compared with the fellow eye and 4) risk factors for scleral thinning. RESULTS: There was no statistically significant difference in scleral thickness between the study and fellow eyes when comparing each quadrant between the two eyes (P = 0.86 superotemporal; P = 0.76 superonasal; P = 0.72 inferonasal; P = 0.55 inferotemporal). Scleral thickness was neither related to the number of injections nor to the duration of treatment in the treated eye. CONCLUSION: Multiple intravitreal injections do not impact scleral thickness in a clinical practice using different injection sites.

Anterior segment parameters measured in young healthy cats using a rotating Scheimpflug camera.

OBJECTIVE: The purpose of this study is to measure parameters of the anterior segment of normal feline eyes using a rotating Scheimpflug camera in young and adult cats. PROCEDURE: Sixteen domestic short-haired (DSH) healthy cats (seven castrated males and nine spayed females) with a mean age of 17 months (SD = 3.5) were anesthetized. Cats were considered immature and adults if they were < or ≥12 months of age, respectively. The keratometric values, the anterior chamber depth (ACD), and central corneal thickness (CCT) of the right eye of each animal were measured using a Pentacam Oculus topographer. The repeatability of the measures was assessed by calculating the coefficient of variation of the successive measures in cats (five repetitions per cat). We performed an ANOVA to test the effect of age on the parameters measures. RESULTS: The mean CCT and ACD were 601.97 ± 38 µm and 5.27 ± 0.04 mm, respectively. No significant differences were observed between adult and young cat's measures. The average keratometric value was 39.6 ± 0.3 D. The mean average cylindrical error was 2.48 ± 0.35 D (43.75% "against-the-rule" astigmatism and 43.75% "oblique" astigmatism). CONCLUSION: The Oculus Pentacam under clinical conditions give CCT and ACD values very similar to those reported in previous studies. Corneal astigmatism measures were markedly elevated (>2 D). Further studies with a larger population of cats of various breeds and ages are needed to confirm or refute these results, using a rotating Scheimpflug camera.

[Differences in anterior segment structure between Chinese Han people and American Caucasians].

Objective: To compare the difference of anterior segment structure between Chinese Han people and American Caucasians, and to explore the confounding factors of anterior chamber angle. Methods: Cross-sectional study. The study was designed to include two healthy groups of Chinese Han people (enrolled from Department of Ophthalmology, Peking University Third Hospital) and American Caucasians (enrolled from Department of Ophthalmology, University of California, San Francisco) from May 2008 to December 2010, each with approximately 120 participants, including 15 persons of each gender in each decade between 40 and 80 years of age. The parameters of the anterior segment were measured by the automatic refractive test, A-ultrasound and ultrasound biomicroscopy. Differences between the two groups were compared with the independent-sample t test or Wilcoxon two-sample test for continuous variable data and the χ(2) test for classified variable data. Multiple linear regression models were performed to analyze the associated factors of anterior chamber angle. Results: There were 118 subjects (118 eyes) and 117 subjects (117 eyes) enrolled in the Chinese and American Caucasians groups, respectively. Compared to Caucasians, Chinese had smaller A-ultrasound measured anterior chamber depth [(3.03±0.34) mm vs. (3.38±0.36) mm, t=-5.791, P<0.001], smaller relative lens position [0.227 (0.198, 0.256) vs. 0.235 (0.191, 0.262), Z=-3.063, P=0.002], smaller axial length [23.3 (20.9,28.3) mm vs. 24.2 (20.8,28.5) mm, Z=-5.510, P<0.001], smaller iris root distance [0.111 (0.000, 0.401) mm vs. 0.142 (0.000, 0.451) mm, Z=-3.188, P=0.001], smaller ciliary body thickness at 1 mm posterior to the scleral spur [0.661 (0.424, 0.892) mm vs. 0.716 (0.467, 0.942) mm, Z=-3.456, P=0.001], smaller trabecular ciliary process distance [0.780 (0.410, 1.400) mm vs. 0.930 (0.420, 1.470) mm, Z=-3.191, P=0.001], smaller trabecular ciliary process angle [73.4° (36.3°, 115.3°) vs. 81.1° (47.9°, 147.9°), Z=-3.407, P=0.001], smaller angle opening distance at 500 µm (AOD500) [0.181 (0.000, 0.703) mm vs. 0.264 (0.000, 0.806) mm, Z=-3.444, P=0.001], smaller angle recess area (ARA) [0.118 (0.011, 0.457) mm(2) vs. 0.179 (0.000, 0.626) mm(2), Z=-3.814, P<0.001], larger spherical equivalent [0.40 (-5.80, 4.00) D vs. -0.70 (-8.00, 4.00) D, Z=-5.454, P<0.001], larger lens thickness [(4.62±0.40) mm vs. (4.52±0.40) mm, t=2.077, P=0.039] and larger iris thickness [0.430 (0.280, 0.600) mm vs. 0.410 (0.240, 0.580) mm, Z=-2.263, P=0.024]. On average, with each decade of the increased age, Chinese had a greater decrease in the AOD500 than Caucasians (0.040 mm in Chinese vs. 0.030 mm in Caucasians), while the angle recess area decreased at the same rate (0.020 mm(2) in both groups). After adjusted for age, gender, spherical equivalent, axial length and other parameters of the anterior segment, the trabecular ciliary process angle [for AOD500, standardized regression coefficient (SRC)=0.487, R(2)=0.549, P<0.001; for ARA, SRC=0.372, R(2)=0.502, P<0.001] and anterior chamber depth (for AOD500, SRC=0.413, R(2)=0.476, P<0.001; for ARA, SRC=0.331, R(2)=0.403, P<0.001) were the main factors of anterior chamber angle parameters for Chinese and Caucasians, respectively. Conclusions: Compared with age and gender matched American Caucasians, Chinese Han people have more crowded anterior chambers and narrower anterior chamber angles. The more anteriorly positioned ciliary processes and shallower anterior chambers are the main factors that contributed to more crowded anterior chambers in Chinese Han people and American Caucasians, respectively. (Chin J Ophthalmol, 2018, 54: 820-826).

Schlemm's canal is a unique vessel with a combination of blood vascular and lymphatic phenotypes that forms by a novel developmental process.

Schlemm's canal (SC) plays central roles in ocular physiology. These roles depend on the molecular phenotypes of SC endothelial cells (SECs). Both the specific phenotype of SECs and development of SC remain poorly defined. To allow a modern and extensive analysis of SC and its origins, we developed a new whole-mount procedure to visualize its development in the context of surrounding tissues. We then applied genetic lineage tracing, specific-fluorescent reporter genes, immunofluorescence, high-resolution confocal microscopy, and three-dimensional (3D) rendering to study SC. Using these techniques, we show that SECs have a unique phenotype that is a blend of both blood and lymphatic endothelial cell phenotypes. By analyzing whole mounts of postnatal mouse eyes progressively to adulthood, we show that SC develops from blood vessels through a newly discovered process that we name "canalogenesis." Functional inhibition of KDR (VEGFR2), a critical receptor in initiating angiogenesis, shows that this receptor is required during canalogenesis. Unlike angiogenesis and similar to stages of vasculogenesis, during canalogenesis tip cells divide and form branched chains prior to vessel formation. Differing from both angiogenesis and vasculogenesis, during canalogenesis SECs express Prox1, a master regulator of lymphangiogenesis and lymphatic phenotypes. Thus, SC development resembles a blend of vascular developmental programs. These advances define SC as a unique vessel with a combination of blood vascular and lymphatic phenotypes. They are important for dissecting its functions that are essential for ocular health and normal vision.

Evaluation of the repeatability of a swept-source ocular biometer for measuring ocular biometric parameters.

PURPOSE: The purpose was to evaluate the repeatability of a new swept-source optical biometer for measuring ocular biometric parameters. METHODS: Thirty subjects with healthy and phakic eyes were included in this study, and only one eye per participant was analysed. Each eye was measured five times with the IOLMaster 700 swept-source optical biometer (Carl Zeiss Meditec, Jena, Germany). Axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), lens thickness (LT), white-to-white (WTW), and K1 and K2 keratometric readings were evaluated. The repeatability of swept-source biometry was evaluated on the basis of five measurements captured for each patient. RESULTS: The repeatability limits for the axial measurements AL, ACD, CCT, and LT were 0.03, 0.07, 0.004, and 0.11 mm, respectively. For the WTW distance and both keratometry readings, the repeatability limits were 0.20, 0.06, and 0.05 mm, respectively. The AL resulted in the lowest coefficient of variation, and the LT had the highest one. The spherical equivalent showed statistically significant negative correlations with the AL and ACD. CONCLUSION: Swept-source optical biometry showed high repeatability performance for all biometric parameters in healthy eyes, where the correlation between the spherical equivalent and AL showed the strongest value.

Effects of diurnal, lighting, and angle-of-incidence variation on anterior segment optical coherence tomography (AS-OCT) angle metrics.

BACKGROUND: First reported study to assess the effect of diurnal variation on anterior chamber angle measurements, as well as, to re-test the effects of lighting and angle-of-incidence variation on anterior chamber angle (ACA) measurements acquired by time-domain anterior segment optical coherence tomography (AS-OCT). METHODS: A total of 30 eyes from 15 healthy, normal subjects underwent anterior chamber imaging using a Visante time-domain AS-OCT according to an IRB-approved protocol. For each eye, the inferior angle was imaged twice in the morning (8 am - 10 am) and then again in the afternoon (3 pm - 5 pm), under light meter-controlled conditions with ambient room lighting 'ON' and lights 'OFF', and at 5° angle of incidence increments. The ACA metrics measured for each eye were: angle opening distance (AOD, measured 500 and 750 µm anterior from scleral spur), the trabecular-iris-space area (TISA, measured 500 and 750 µm anterior from scleral spur), and scleral spur angle. Measurements were performed by masked, certified Reading Center graders using the Visante's Internal Measurement Tool. Differences in measurements between morning and afternoon, lighting variations, and angle of incidence were compared. RESULTS: Mean age of the participants was 31.2 years (range 23-58). Anterior chamber angle metrics did not differ significantly from morning to afternoon imaging, or when the angle of incidence was offset by 5° in either direction away from the inferior angle 6 o'clock position. (p-value 0.13-0.93). Angle metrics at the inferior corneal limbus, 6 o'clock position (IC270), with room lighting 'OFF', showed a significant decrease (p < 0.05) compared to room lighting 'ON'. CONCLUSIONS: There does not appear to be significant diurnal variation in AS-OCT parameters in normal individuals, but lighting conditions need to be strictly controlled since variation in lighting led to significant variability in AS-OCT parameters. No changes in ACA parameters were noted by varying the angle-of-incidence, which gives confidence in being able to perform longitudinal studies in approximately the same area (plus/minus 5° of original scan location).

Wholemount imaging reveals abnormalities of the aqueous outflow pathway and corneal vascularity in Foxc1 and Bmp4 heterozygous mice.

Mutations in the FOXC1/Foxc1 gene in humans and mice and Bmp4 in mice are associated with congenital anterior segment dysgenesis (ASD) and the development of the aqueous outflow structures throughout the limbus. The aim of this study was to advance our understanding of anterior segment abnormalities in mouse models of ASD using a 3-D imaging approach. Holistic imaging information combined with quantitative measurements were carried out on PECAM-1 stained individual components of the aqueous outflow vessels and corneal vasculature of Foxc1(+/-) on the C57BL/6Jx129 and ICR backgrounds, Bmp4(+/-) ICR mice, and wildtype mice from each background. In both wildtype and heterozygotes, singular, bifurcated and plexus forms of Schlemm's canal were noted. Of note, missing portions of the canal were seen in the heterozygous groups but not in wildtype animals. In general, we found the number of collector channels to be reduced in both heterozygotes. Lastly, we found a significant increase in the complexity of the corneal arcades and their penetration into the cornea in heterozygotes as compared with wild types. In conclusion, our 3-D imaging studies have revealed a more complex arrangement of both the aqueous vessels and corneal arcades in Foxc1(+/-) and Bmp4(+/-) heterozygotes, and further advance our understanding of how such abnormalities could impact on IOP and the aetiology of glaucoma.

Estimation of axial curvature of anterior sclera: correlation between axial length and anterior scleral curvature as affected by angle kappa.

BACKGROUND: Though the development and fitting of scleral contact lenses are expanding steadily, there is no simple method to provide scleral metrics for scleral contact lens fitting yet. The aim of this study was to establish formulae for estimation of the axial radius of curvature (ARC) of the anterior sclera using ocular biometric parameters that can be easily obtained with conventional devices. METHODS: A semi-automated stitching method and a computational analysis tool for calculating ARC were developed by using the ImageJ and MATLAB software. The ARC of all the ocular surface points were analyzed from the composite horizontal cross-sectional images of the right eyes of 24 volunteers; these measurements were obtained using anterior segment optical coherence tomography for a previous study (AS-OCT; Visante). Ocular biometric parameters were obtained from the same volunteers with slit-scanning topography and partial coherence interferometry. Correlation analysis was performed between the ARC at 8 mm to the axis line (ARC[8]) and other ocular parameters (including age). With ARC obtained on several nasal and temporal points (7.0, 7.5, 8.0, 8.5, and 9.0 mm from the axis line), univariate and multivariate linear regression analyses were performed to develop a model for estimating ARC with the help of ocular biometric parameters. RESULTS: Axial length, spherical equivalent, and angle kappa showed correlations with temporal ARC[8] (tARC[8]; Pearson's r = 0.653, -0.579, and -0.341; P = 0.001, 0.015, and 0.015, respectively). White-to-white corneal diameter (WTW) and anterior chamber depth (ACD) showed correlation with nasal ARC[8] (nARC[8]; Pearson's r = -0.492 and -0.461; P = 0.015 and 0.023, respectively). The formulae for estimating scleral curvatures (tARC, nARC, and average ARC) were developed as a function of axial length, ACD, WTW, and distance from the axis line, with good determinant power (72 - 80 %; SPSS ver. 22.0). Angle kappa showed strong correlation with axial length (Pearson's r = -0.813, P <0.001), and the different correlation patterns of nasal and temporal ARC with axial length can be explained by the ocular surface deviation represented by angle kappa. CONCLUSIONS: Axial length, ACD, and WTW are useful parameters for estimating the ARC of the anterior sclera, which is important for the haptic design of scleral contact lenses. Angle kappa affects the discrepancies between the nasal and temporal scleral curvature.

Measurement of corneal and limbal epithelial thickness by anterior segment optical coherence tomography and in vivo confocal microscopy.

BACKGROUND: To compare corneal epithelial thickness (CET) and limbal epithelial thickness (LET) measured by anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscope (IVCM) in normal subjects, and evaluate the consistency between them. METHODS: Thirty-eight normal subjects (17 men and 21 women) were enrolled in this study. AS-OCT was performed at central cornea and the superior, inferior, nasal and temporal limbus. Then followed by IVCM examination performed at the same location. Agreement was analyzed by mean difference (AS-OCT minus IVCM), 95 % limits of agreement (LoA) (1.96 standard deviation of the difference), and Bland-Altman analysis. RESULTS: The average CET measured by AS-OCT and IVCM was 55.6 ± 4.0 µm and 51.9 ± 4.9 µm respectively. The value measured by IVCM was significantly lower than that measured by AS-OCT (P = 0.015). The average LET values tested by AS-OCT were 10.3 and 10.9 % less at nasal and temporal quadrant (nasal: P = 0.019, temporal: P = 0.003), and were similar as those measured by IVCM at superior and inferior quadrant. In subjects older than 40 years, CET and LET values measured by AS-OCT were significantly higher than those by IVCM. Such differences were not found in subjects ≤ 40 years old. CONCLUSIONS: CET values measured by IVCM are lower than those by AS-OCT, while LET values measured by two devices have good agreement. These two techniques have their own advantages in measuring epithelial thickness and are mutually complementary.

Real-Time Measurement of Dynamic Changes of Anterior Segment Biometry and Wavefront Aberrations During Accommodation.

OBJECTIVES: To analyze the dynamic relationship between ocular geometrical structure and high-order aberrations (HOAs) in teal-time during accommodation of human eye. METHODS: A custom-built spectral domain optical coherence tomography (OCT) system with high-speed and ultra-long scan depth was used to image the anterior segment, whereas a Shack-Hartmann wavefront sensor was used to detect the whole-eye aberration. A Badal optometer with switched visual targets was integrated with this system to induce 0 and 3.00 D accommodative stimuli. Three young adult subjects were measured and the structural parameters of anterior segment were measured from OCT images and accommodative response and HOAs were calculated and exponentially fitted in real time during the accommodation. RESULTS: The dynamic process from nonaccommodation to 3.00 D accommodation results in reduced pupil diameter, shallower anterior chamber depth, and increased crystalline lens thickness. After an accommodative active time, the RMS of the HOAs changes sharply when an accommodative stimulus is introduced and then tends to be stable. The accommodative response time and velocity are characterized by fitted parameters. The individual differences of changing in HOAs between subjects can be explained by the different sign and changing tendency of certain terms of aberration coefficients in form of Zernike polynomials during the accommodation. CONCLUSIONS: Based on the integrated ocular measurement platform including OCT system and wavefront sensor, our research demonstrated how the morphology of the human anterior segment affect the aberration in real time during accommodation. The dynamic relationship between them helps us to deeply understand the mechanism of accommodation.

Metrics of the normal anterior sclera: imaging with optical coherence tomography.

BACKGROUND: To investigate anterior scleral thickness in a cohort of healthy subjects using enhanced depth imaging anterior segment optical coherence tomography. METHODS: Observational case series. The mean scleral thickness in the inferonasal, inferotemporal, superotemporal, and superonasal quadrant was measured 2 mm from the scleral spur on optical coherence tomography in healthy volunteers. RESULTS: Fifty-three eyes of 53 Caucasian patients (25 male and 28 female) with an average age of 48.6 years (range: 18 to 92 years) were analysed. The mean scleral thickness was 571 µm (SD 84 µm) in the inferonasal quadrant, 511 µm (SD 80 µm) in the inferotemporal quadrant, 475 (SD 81 µm) in the superotemporal, and 463 (SD 64 µm) in the superonasal quadrant. The mean scleral thickness was significantly different between quadrants (p < 0.0001, repeated measures one-way ANOVA). The association between average scleral thickness and age was statistically significant (p < 0.0001, Pearson r = 0.704). CONCLUSIONS: Enhanced depth imaging optical coherence tomography revealed the detailed anatomy of the anterior sclera and enabled non-invasive measurements of scleral thickness in a non-contact approach. The anterior scleral thickness varies significantly between quadrants, resembling the spiral of Tillaux. An association of increasing scleral thickness with age was found.

Repeatability and intrasession reproducibility obtained by the Sirius anterior segment analysis system.

OBJECTIVE: To analyze repeatability and intrasession reproducibility of anterior segment measurements using the newly developed Sirius Scheimpflug system. METHODS: Three consecutive measurements on 100 eyes of 50 healthy subjects were performed on the same session by the same technician using the Sirius device at the Assuta Optic Laser Center, Tel-Aviv, Israel. For each eye, the following parameters were measured: anterior chamber angle (ACA), anterior chamber volume (ACV), and anterior chamber depth (ACD), thinnest corneal location, keratometry (anterior and posterior), cylinder, and axis. Repeatability was assessed using the coefficient of variation (CV). Intrasession reproducibility was assessed using intraclass correlation coefficient (ICC). RESULTS: Coefficient of variation of 2% and less was observed for ACA, ACD, thinnest corneal location, and anterior keratometry. Intraclass correlation coefficients were high for ACA, ACD, anterior keratometry measurements and moderate for anterior cylinder and axis. Higher CV with relatively low ICC values was noticed with ACV, posterior keratometry measurements, and posterior cylinder, and axis. The last 2 have the highest CV and lowest ICC: 48.79% (range: 37.64%-59.95%) and 0.38%, respectively. CONCLUSIONS: The Sirius Scheimpflug system has a very high repeatability and intrasessional reproducibility when measuring the ACD, ACA, anterior curvature parameters, and the thinnest corneal location. Thus, it can be used with confidence in clinical practice.

Anterior segment morphology and morphometry in selected reptile species using optical coherence tomography.

OBJECTIVE: To provide new and original images of the anterior segment (AS) of the eye of selected Ophidian, Chelonian, and Saurian species and to compare the AS architecture among and within these three groups. ANIMALS STUDIED: 17 Saurians, 14 Ophidians, and 11 Chelonians with no concurrent systemic or eye disease were included in the study. PROCEDURE: Age, weight, nose-cloaca distance (NCD), and pupil shape were collected for each animal. The AS was examined by optical coherence tomography (OCT). After gross description of the appearance of the AS, the central and peripheral corneal thickness (CCT, PCT) and anterior chamber depth (ACD) were measured using the software provided with the OCT device. The ratio CCT/ACD was then calculated for each animal. RESULTS: Pupil shape was a vertical slit in all the crepuscular or nocturnal animals (except for 1 chelonian and 1 ophidian). Each group had its own particular AS architecture. Saurians had a regularly thin cornea with a flat anterior lens capsule and a deep anterior chamber. Ophidians had a thick cornea with a narrow anterior chamber due to a very anteriorly anchored spherical lens. The spectacle was difficult to identify in all ophidians except in Python molurus bivitattus in which it was more obvious. Chelonians displayed an intermediate architecture which more closely resembled the Saurian type than the Ophidian type. CONCLUSION: Despite grossly similar AS architecture, the three groups of reptiles in the study demonstrated differences that are suggestive of a link between anatomical disparities and variations in environment and lifestyle.

Spectral domain optical coherence tomography imaging of spectacular ecdysis in the royal python (Python regius).

OBJECTIVE: To describe using spectral domain optical coherence tomography (SD-OCT), digital slit-lamp biomicroscopy, and external photography, changes in the ophidian cuticle, spectacle, and cornea during ecdysis. ANIMALS STUDIED: Four normal royal pythons (Python regius). PROCEDURES: Snakes were assessed once daily throughout a complete shed cycle using nasal, axial, and temporal SD-OCT images, digital slit-lamp biomicroscopy, and external photography. RESULTS: Spectral domain optical coherence tomography (SD-OCT) images reliably showed the spectacular cuticle and stroma, subcuticular space (SCS), cornea, anterior chamber, iris, and Schlemm's canal. When visible, the subspectacular space (SSS) was more distended peripherally than axially. Ocular surface changes throughout ecdysis were relatively conserved among snakes at all three regions imaged. From baseline (7 days following completion of a full cycle), the spectacle gradually thickened before separating into superficial cuticular and deep, hyper-reflective stromal components, thereby creating the SCS. During spectacular separation, the stroma regained original reflectivity, and multiple hyper-reflective foci (likely fragments from the cuticular-stromal interface) were noted within the SCS. The cornea was relatively unchanged in character or thickness throughout all stages of ecdysis. Slit-lamp images did not permit observation of these changes. CONCLUSIONS: Spectral domain optical coherence tomography (SD-OCT) provided excellent high-resolution images of the snake anterior segment, and especially the cuticle, spectacle, and cornea of manually restrained normal snakes at all stages of ecdysis and warrants investigation in snakes with anterior segment disease. The peripheral spectacle may be the preferred entry point for diagnostic or therapeutic injections into the SSS and for initiating spectacular surgery.

Anterior segment parameters of rabbits with rotating Scheimpflug camera.

BACKGROUND: Rabbit is one of the most commonly used experimental animals for corneal studies due to similarity of size to human cornea and ease of manipulation. In this study, we assessed anterior segment parameters of the healthy rabbit eyes with Pentacam HR (Oculus, Wetzlar, Germany). METHODS: Six-month-old, approximately 2.5-3 kg weighted, 30 female New Zealand rabbits were used in the study. Right eye of the each rabbit was imaged with Pentacam HR under intramuscular ketamine hydrochloride (Ketalar; Eczacibasi, Turkey) anesthesia (50 mg/kg). After the imaging, the rabbits with blinking errors, which results in low-quality images, were excluded from the study. Keratometric readings, central corneal thickness (CCT), anterior chamber depth (ACD), and anterior and posterior elevation values, and lens density were noted. RESULTS: In this study, the flattest and the steepest keratometric values were found as 43.34 ± 1.86, 42.7 ± 2.0, and 43.9 ± 1.9 diopters, respectively. The mean CCT and ACD of rabbits were found as 388 ± 39 µm and 2.08 ± 0.16 mm, respectively. Mean of the anterior and posterior elevation at thinnest point was found as 1.29 ± 4.28 and 3.91 ± 6.17 µm, respectively. CONCLUSIONS: Keratometric readings and anterior and posterior elevation values of rabbits were similar to human; however, corneal thickness and anterior chamber depth (ACD) values were lower than humans.

Scanning laser ophthalmoscopy and optical coherence tomography imaging of spectacular ecdysis in the corn snake (Pantherophis guttatus) and the California king snake (Lampropeltis getulus californiae).

PURPOSE: One of the singularities of the eyes of snakes is the presence of the spectacle, a transparent and vascularized integument covering the cornea. The spectacle is completely renewed during ecdysis. Combined scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and conventional macrophotography were used to image this phenomenon. MATERIAL AND METHODS: A spectral OCT/SLO examination and macrophotography were performed in four healthy adult corn snakes (Pantherophis guttatus) and one healthy adult California king snake (Lampropeltis getulus californiae) the day before the start of ecdysis and then daily during ecdysis. RESULTS: In all animals, ecdysis lasted 5 days. The spectacle was hardly visible at baseline, but became obvious at day one, while the subspectacular space became larger and the superficial cornea presented a hyperechoic band. At day two, eye surface became translucent, and at the same time, vascularization of the spectacle was visible using SLO. At day 3, the vascularization was no longer visible, while the subspectacular space increased and the eye surface remained translucent. At day 4, the eye surface was transparent and the superficial hyperechoic band started to become less bright. At day 5, the old spectacle was shed and all the parameters returned to baseline. CONCLUSION: We hypothesize that the echogenicity modifications of the anterior cornea correspond to major metabolic activity associated with new spectacle formation. This increased metabolic activity may contribute to the neovascularization and play an important role in the accumulation of fluid in the subspectacular space, facilitating the shedding of the old spectacle.

[Ocular surface system integrity].

The interplay of different structures belonging to either the anterior segment of the eye or its accessory visual apparatus, which all share common embryological, anatomical, functional, and physiological features, is discussed. Explanation of such terms, as ocular surface, lacrimal functional unit, and ocular surface system, is provided.