Keratometry in normal cats: a cross-sectional study in Japan using an automated handheld keratometer.

Keratometry was performed in 73 domestic cats of varied signalment in Japan using an automated handheld keratometer. The mean corneal curvature radius was significantly lower for cats younger than 1 year than for those older than 2 years (8.04 mm vs. 8.80-8.99 mm, P<0.01). The radius was significantly greater in males than in females among the cats older than 11 years (9.22 mm vs. 8.84 mm, P=0.01), while the age distributions of the males and females were similar. Corneal astigmatism did not significantly differ across the gender and age groups. The predictability of the corneal curvature and astigmatism was approximately 41-43% and less than 3%, respectively, as a function of age and bodyweight. The results highlighted some age- and sex-related keratometric variations in domestic cats in Japan.

Characterising keratometry in different dog breeds using an automatic handheld keratometer.

BACKGROUND: Keratometry is clinically important and is routinely performed as part of human ophthalmic examination. In veterinary ophthalmology, little is known about keratometry in dogs, and its practical application has been limited. The present study aimed to describe keratometry in some dog breeds popular in Japan using a handheld keratometer. METHODS: Client-owned dogs of various signalment were enrolled prospectively in the keratometry examination. Interbreed variations in mean corneal curvatures (R1R2avg) and corneal astigmatism (Δ(R1-R2)) were evaluated statistically with respect to their bodyweight based on the data which fulfilled the predetermined inclusion criteria. P<0.05 was considered statistically significant. RESULTS: On examination of 237 dogs from 16 different breeds, R1R2avg (mean±sd) ranged from 7.54±0.30 mm in Pomeranians to 9.28±0.19 mm in golden retrievers. Δ(R1-R2) (mean±sd) ranged from 0.22±0.11 mm in miniature schnauzers to 0.57±0.30 mm in French bulldogs. CONCLUSION: The present study successfully described keratometry in 16 dog breeds. The study revealed considerable interbreed variations in both R1R2avg and Δ(R1-R2), which did not necessarily correlate with bodyweight. These results are useful both clinically in fitting contact lenses in the management of corneal diseases and non-clinically in optometric studies in dogs.

Surgically induced astigmatism in canines following sutured dorsonasal vs dorsotemporal clear corneal incisions.

OBJECTIVES: To investigate use of the Pentacam® HR for evaluation of surgically induced corneal astigmatism (SIA) in canines undergoing bilateral phacoemulsification and determine differences between dorsonasal and dorsotemporal clear corneal incisions. ANIMALS: Client-owned canines undergoing bilateral phacoemulsification. PROCEDURES: Patients received anterior segment imaging pre-operatively, immediately post-operatively, and 2-4 months post-operatively (follow-up). Total corneal refractive power was used to determine SIA. Surgically induced astigmatism was compared between right and left eyes, representing dorsotemporal and dorsonasal incisions, respectively. Repeated measures analyses were used between time points and paired t test compared SIA between eyes. RESULTS: Complete imaging series were obtained for seven patients. Follow-up imaging occurred at a median of 112 days (range 60-132 days) post-operatively. For repeated measures analyses, significant differences were found between pre- and immediate post-operative values (P < 0.01), and between immediate post-operative and follow-up values (P < 0.01). There was no significant difference between pre-operative and follow-up values. Surgically induced astigmatism was significantly different between right and left eyes, with values of 2.01 ± 1.24 D and 3.05 ± 1.58 D at 3 mm radius (P < 0.05), and 2.04 ± 1.18 D and 3.06 ± 1.27 D at 4 mm radius (P < 0.05) for dorsotemporal and dorsonasal incisions, respectively. CONCLUSIONS: Preliminary investigation revealed improvement of corneal SIA 2-4 months post-operatively, but development of significantly more SIA in dorsonasal vs dorsotemporal incisions. This prompts consideration of patient or microscope rotation to create a more dorsotemporal incision when possible.

Correction of refractive errors in rhesus macaques (Macaca mulatta) involved in visual research.

Macaques are the most common animal model for studies in vision research, and due to their high value as research subjects, often continue to participate in studies well into old age. As is true in humans, visual acuity in macaques is susceptible to refractive errors. Here we report a case study in which an aged macaque demonstrated clear impairment in visual acuity according to performance on a demanding behavioral task. Refraction demonstrated bilateral myopia that significantly affected behavioral and visual tasks. Using corrective lenses, we were able to restore visual acuity. After correction of myopia, the macaque's performance on behavioral tasks was comparable to that of a healthy control. We screened 20 other male macaques to assess the incidence of refractive errors and ocular pathologies in a larger population. Hyperopia was the most frequent ametropia but was mild in all cases. A second macaque had mild myopia and astigmatism in one eye. There were no other pathologies observed on ocular examination. We developed a simple behavioral task that visual research laboratories could use to test visual acuity in macaques. The test was reliable and easily learned by the animals in 1 d. This case study stresses the importance of screening macaques involved in visual science for refractive errors and ocular pathologies to ensure the quality of research; we also provide simple methodology for screening visual acuity in these animals.

Lens aberrations and their relationship with lens sutures for species with Y-suture branches.

Work remains to be done to understand the origins of ocular aberrations. We analyze lens aberrations of several species with Y-suture branches (bovine, ovine, and porcine) and their relationship with suture distribution. Aberrations are measured in vitro with a point diffraction interferometer in 10 different eyes of each species. The minimum number of Zernike polynomials minimizing the root mean square error of the wavefront is estimated by processing the interferograms. Through this we find significant amounts of astigmatism, coma, spherical aberration, and trefoil in the lenses of the three species. Moreover, we observe a high degree of correlation between the orientation of the lens sutures and the axis of nonrotationally symmetric aberrations. Our results point to lens sutures as the histological origin of the most significant lens aberrations: astigmatism, coma, and trefoil, but we are unable to find a major suture governing all the axes.

Refractive state of the Spanish Thoroughbred horse: a comparison with the Crossbred horse.

OBJECTIVE: To assess the refractive state of the equine eye utilizing retinoscopy. To compare the refractive state of Spanish Thoroughbred horses with the refractive state of Crossbred horses. PROCEDURES: The refractive state of 135 horses (264 eyes) was assessed utilizing streak retinoscopy. Two perpendicular meridians were examined in order to assess astigmatism at a working distance of approximately 67 cm. A group of 81 Spanish Thoroughbred horses was compared with a group of 54 Crossbred horses. Cyclopentolate ophthalmic solution was instilled in the eyes of a group of 18 horses to determine if accommodation has any influence on the assessment of the refractive state. RESULTS: Mean ± SE refractive state of all horses examined was -0.17 ± 0.04 D. The mean refractive state of the Spanish Thoroughbred was -0.28 ± 0.06 D while that of the Crossbred was -0.01 ± 0.05 D. The refractive state of the Spanish Thoroughbred was found to be statistically different to that of the Crossbred. The most prevalent refractive state was emmetropia in all cases, followed by hyperopia for the Crossbred, and myopia for the Spanish Thoroughbred. Astigmatism ≥0.50 D present in both eyes from the same individual was found in 21.7% of all horses examined. Anisometropia ≥1.00 D was diagnosed in 4 out of 129 horses with both visual eyes. Cycloplegia did not statistically affect the refractive state of the evaluated eyes. CONCLUSIONS: The equine eye has a refractive state close to emmetropia. Myopia is higher among Spanish Thoroughbred horses than among Crossbred horses.

Relationship between wave aberrations and histological features in ex vivo porcine crystalline lenses.

Wave aberrations of isolated ex vivo porcine crystalline lenses were measured by using a point-diffraction interferometer. This method allowed us to gain greater insight into the detailed aberration structure of eye lenses showing systematic presence of some dominant aberrations. In order of significance, astigmatism together with spherical aberration, coma, and trefoil are the main aberrations present in all lenses. We found a high correlation between the axis of both astigmatism and trefoil with the Y-shaped suture planes of the lens, revealing a subtle relationship between the induced aberrations and the histological features.

Astigmatism in infant monkeys reared with cylindrical lenses.

To determine whether developing primate eyes are capable of growing in a manner that eliminates astigmatism, we reared infant monkeys with cylindrical spectacle lenses in front of one or both eyes that optically simulated with-the-rule, against-the-rule, or oblique astigmatism (+1.50-3.00x90, x180, x45 or x135). Refractive development was assessed by retinoscopy, keratometry and A-scan ultrasonography. In contrast to control monkeys, the cylinder-lens-reared monkeys developed significant amounts of astigmatism. The astigmatism was corneal in nature, bilaterally mirror symmetric and oblique in axis, and reversible. The ocular astigmatism appeared to be due to a reduction in the rate of corneal flattening along the steeper meridian while the other principal meridian appeared to flatten at a more normal rate. However, regardless of the orientation of the optically imposed astigmatism, the axis of the ocular astigmatism was not appropriate to compensate for the astigmatic error imposed by the treatment lenses. Our results indicate that visual experience can alter corneal shape, but there was no evidence that primates have an active, visually regulated "sphericalization" mechanism.

Prevalence of astigmatism in infant monkeys.

PURPOSE: Human infants exhibit a high prevalence of astigmatism. Although macaque monkeys are commonly used as animal models in experiments on early ocular growth and emmetropization, the prevalence of astigmatism in infant monkeys is unexplored. In this study we examine the prevalence and nature of astigmatism in infant monkeys. METHODS: Refractive and corneal astigmatism were measured in 132, 2-5-week-old rhesus monkeys (Macaca mulatta) using cycloplegic retinoscopy and keratometry, respectively. Longitudinal measures of refractive development were obtained from 16 normal infants over the first 6 months of life. RESULTS: Infant monkeys exhibited a low prevalence of astigmatism. Approximately 90% of the 2-5-week-old infants had <1.00 D of either refractive or corneal astigmatism. When refractive astigmatism was observed, it was well correlated with the direction and magnitude of corneal astigmatism. When corneal astigmatism was >1.00 D (n=20), it was predominantly against-the-rule in nature (70.0%). The infant monkeys that were followed longitudinally rarely showed significant astigmatic errors at any time during the observation period. When these infant monkeys exhibited significant astigmatism, it was usually transient and not present on subsequent measurements. CONCLUSIONS: Unlike human infants, infant monkeys exhibit relatively little astigmatism. The low prevalence of astigmatism during early development suggests that astigmatism does not provide an essential cue for vision-dependent eye growth in infant primates.