The ophthalmic health and refractive state of working dogs in South Brazil

Quantifying refractive error in companion dogs with and without nuclear sclerosis: 229 eyes from 118 dogs

OBJECTIVE

To evaluate the relationship between nuclear sclerosis (NS) and refractive error in companion dogs.

ANIMALS STUDIED

One hundred and eighteen companion dogs.

PROCEDURES

Dogs were examined and found to be free of significant ocular abnormalities aside from NS. NS was graded from 0 (absent) to 3 (severe) using a scale developed by the investigators. Manual refraction was performed. The effect of NS grade on refractive error was measured using a linear mixed effects analysis adjusted for age. The proportion of eyes with >1.5 D myopia in each NS grade was evaluated using a chi-square test. Visual impairment score (VIS) was obtained for a subset of dogs and compared against age, refractive error, and NS grade.

RESULTS

Age was strongly correlated with NS grade (p < .0001). Age-adjusted analysis of NS grade relative to refraction showed a mild but not statistically significant increase in myopia with increasing NS grade, with eyes with grade 3 NS averaging 0.58-0.88 D greater myopia than eyes without NS. However, the myopia of >1.5 D was documented in 4/58 (6.9%) eyes with grade 0 NS, 12/91 (13.2%) eyes with grade 1 NS, 13/57 (22.8%) eyes with grade 2 NS, and 7/23 (30.4%) eyes with grade 3 NS. Risk of myopia >1.5 D was significantly associated with increasing NS grade (p = .02). VIS was associated weakly with refractive error, moderately with age, and significantly with NS grade.

CONCLUSIONS

NS is associated with visual deficits in some dogs but is only weakly associated with myopia. More work is needed to characterize vision in aging dogs.

Refractive errors in mixed breed dogs of different ages

The purpose of the study was to evaluate the occurrence and range of refractive errors in dogs of different ages. A total of 99 clinically healthy, mixed-breed mesocephalic dogs were included in the study and divided into three different age groups according to the current human/pet analogy chart: 40 adults (23 males, 17 females, 1-8 years old, 3-70 kg), 21 seniors (14 males, 7 females, 6-11 years old, 7-42 kg), and 38 geriatrics (22 males, 16 females, 8-13 years old, 5-45 kg). All the dogs underwent an ophthalmic examination, including Schirmer tear test, tonometry, biomicroscopy, and ophthalmoscopy. Neither eye drops nor pharmacological sedatives were administered before the autorefractometry. The refractive states were assessed bilaterally using a hand-held Retinomax 3 (Righton) autorefractor. The results underwent statistical analysis using Statistica v12 software (ANOVA and t-test). A P-value < 0.05 was considered as significant. Emmetropia, defined as a refractive state > -0.5 D and < +0.5 D, was found in 36% of the adult, 43% of the senior, and 38% of the geriatric patients. Anisometropia was found in 1% of the adult, 9.5% of the senior and 5.5% of the geriatric dogs when the refractive power of the two eyes differed ≥ 1.0 myopia ≤ -0.5 D and hyperopia ≥ +0.5 D were found in 23% and 41% of the adult eye globes as well as 24% and 33% in the senior dogs and 15% and 47% in the geriatric dogs, respectively. The maximal values of the myopia in the adult and geriatric dogs were -2.5 D and -2.75 D, respectively. The maximal values of the hyperopia in the adult and geriatric dogs were 1.75 D and 2.5 D, respectively. No statistically significant correlation was found between the groups. Ametropia is a common refractive state for dogs of different ages. The most frequent refractive state in ametropic mixed-bed dogs in all age groups is hyperopia.