Introduction
Cataracts are a significant cause of vision impairment and blindness in dogs, affecting a substantial portion of the aging canine population. While cataract surgery offers a definitive solution, the potential for preventing cataract formation or slowing its progression is a valuable area of research for improving canine eye health. Senile cataracts in dogs are thought to be influenced by oxidative stress, a process implicated in the development of cataracts in both dogs and humans. Consequently, commercially available oral antioxidant supplements and eye drops are often marketed with claims of preventing or delaying cataract progression.
Several antioxidants, including vitamins C and E, beta-carotene, alpha-lipoic acid, and grape seed extract, have been suggested to slow cataract progression. In veterinary ophthalmology, Ocu-GLO and Meni-One Eye R/C are common oral antioxidant supplements. However, there has been a lack of clinical studies evaluating the efficacy of these specific supplements in delaying the progression of senile cataracts in dogs. This retrospective study aimed to investigate whether dogs administered Ocu-GLO or Meni-One Eye R/C exhibited a delayed progression of senile cataracts compared to a control group.
Materials and Methods
Antioxidant Products
The study included dogs diagnosed with incipient or immature cataracts that were administered either Ocu-GLO (Animal HealthQuest, USA) or Meni-One Eye R/C (Meni-One, Japan) as oral antioxidant supplements. Both supplements contain a blend of antioxidants, including grape seed extract and vitamin E. Ocu-GLO also contains alpha-lipoic acid and vitamin C, while Meni-One Eye R/C includes astaxanthin and curcuminoids. All dogs received supplements at the manufacturer’s recommended dosage.
Animals and Data Collection
Medical records of dogs aged 8 years or older presenting with incipient or immature cataracts at the Veterinary Medical Teaching Hospital of Seoul National University between January 1, 2015, and July 10, 2020, were retrospectively reviewed. Dogs with congenital cataracts or concurrent ocular or systemic diseases that could contribute to cataract formation (such as uveitis, diabetes mellitus, or retinal detachment) were excluded. Comprehensive ophthalmic examinations, including menace response, dazzle reflex, tear volume measurement (Schirmer tear test 1), intraocular pressure (IOP) estimation, and slit lamp biomicroscopy, were performed. Cataract stages were classified as incipient (less than 15% lens opacity), immature (greater than 15% opacity, with tapetal reflection visible), mature (tapetal reflection obscured), and hypermature (lens material resorption evident).
Cataract Progression Analysis
For incipient cataracts, dogs were divided into three groups: a control group (C1) receiving no supplements, a group receiving Ocu-GLO (O1), and a group receiving Meni-One Eye R/C (M1). The time from diagnosis of incipient cataract to diagnosis of immature cataract was recorded. For immature cataracts, a similar grouping was used (C2, O2, M2), and the time from diagnosis of immature cataract to diagnosis of mature cataract was recorded. Follow-up periods were established up to a maximum of 800 days.
Statistical Analysis
The Kruskal-Wallis test and Chi-squared test were employed to compare age, sex, and breed distributions among the groups. Kaplan-Meier survival analysis and log-rank tests were used to assess cataract progression rates. Cox proportional hazards models were utilized to correct for potential confounding factors, such as breed distribution, and to calculate hazard ratios (HR) for cataract progression. Statistical significance was defined as p < 0.05.
Results
Incipient Cataract Progression
A total of 112 dogs (156 eyes) with incipient cataracts were included. No significant differences in mean age or sex distribution were found among the control, Ocu-GLO, and Meni-One groups. However, a significant difference in breed distribution was observed (p = 0.006). Kaplan-Meier survival analysis indicated no significant delaying effect of either Ocu-GLO or Meni-One on the progression of incipient cataracts compared to the control group (log-rank test, p > 0.05 for all comparisons). Similarly, Cox proportional hazards models, after adjusting for breed differences, did not reveal a significant delaying effect of the supplements on incipient cataract progression (HR = 0.460, p = 0.143 for O1 vs. C1; HR = 0.320, p = 0.133 for M1 vs. C1).
Immature Cataract Progression
A total of 60 dogs (77 eyes) with immature cataracts were analyzed. While age and sex distributions were comparable across groups, a significant difference in breed distribution was noted (p = 0.002). Kaplan-Meier survival analysis showed that the progression of immature cataracts in dogs treated with Ocu-GLO (O2 group) was significantly slower than in the control group (C2 group) (p = 0.032). The Meni-One group (M2) also showed a trend towards slower progression, though it did not reach statistical significance compared to the control group (p = 0.067).
Crucially, Cox proportional hazards models, after accounting for breed distribution, demonstrated a significant delaying effect of both Ocu-GLO and Meni-One on immature cataract progression. The hazard ratio for progression was significantly lower in the O2 group (HR = 0.265, p = 0.026) and the M2 group (HR = 0.246, p = 0.005) compared to the control C2 group.
Discussion
This study represents a significant contribution to understanding the role of oral antioxidants in managing canine cataracts. While a previous study suggested that half of dogs develop cataracts by approximately 9.4 years of age, this research focused on older dogs (8 years and above) to specifically investigate senile cataracts and minimize the likelihood of hereditary factors. The mean age of cataract onset in this study aligned with existing literature, reinforcing the focus on age-related changes.
The findings suggest that antioxidants may not effectively halt the early stages of cataract development (incipient cataracts). This aligns with observations in human clinical trials where antioxidants have shown conflicting or no significant effects on incipient age-related cataracts. The slow progression rate of incipient cataracts in many dogs might make it difficult to detect a statistically significant delaying effect from supplements within typical study durations. Future research could benefit from longer follow-up periods or more sophisticated methods for quantifying subtle changes in lens opacity.
However, the study provides compelling evidence that oral antioxidants, specifically Ocu-GLO and Meni-One Eye R/C, can significantly delay the progression of immature canine cataracts. This is a critical finding, as immature cataracts tend to progress more rapidly and can lead to complications like lens-induced uveitis. The significant reduction in the hazard ratio for cataract progression in supplemented groups highlights the potential benefit of these antioxidants in this stage. The combination of multiple antioxidants in these supplements, compared to single-ingredient studies in humans, might contribute to their efficacy.
The study acknowledges several limitations inherent in its retrospective design, including variations in re-evaluation intervals and the challenges of quantifying subtle cataract changes, especially in dogs due to the presence of the tapetum. Factors such as diet and environmental exposure were also difficult to control. Nevertheless, the consistent results from both Kaplan-Meier survival analysis and Cox proportional hazards modeling, even after accounting for breed variations, lend considerable weight to the findings regarding immature cataracts.
Conclusion
This retrospective study indicates that while oral antioxidant supplements like Ocu-GLO and Meni-One Eye R/C may not significantly delay the progression of incipient senile cataracts in dogs, they show promise in slowing the advancement of immature senile cataracts. These findings suggest that antioxidant supplementation could be a valuable therapeutic option for delaying cataract progression in dogs, particularly for those that are not candidates for surgery or where delaying the need for surgery is desirable. Further prospective, controlled clinical trials are warranted to confirm these results and explore optimal antioxidant formulations and dosages for canine cataract management.
References
[(#B1)] Gelatt KN, Macklin KS. Canine cataracts. Vet Clin North Am Small Anim Pract. 1986;16:553–565.[(#B2)] Hendrix DV, Meunier SF. Cataracts. In: Slatter D, editor. Fundamentals of Veterinary Ophthalmology. 3rd ed. Philadelphia: WB Saunders; 1997. pp. 260–271.
[(#B3)] Babizhayev MA, Deykin A, Nosyrev V. N-acetylcarnosine (NAC) as a robust antioxidant and pro-longevity agent for the prevention of eye lens opacity and lens clouding. Drug Exp Clin Res. 2007;33(Suppl):31–60.
[(#B4)] Varma SD. Oxidative stress and cataract. Am J Clin Nutr. 1999;69:578S–585S.
[(#B5)] Spector A. Theiopredictive factors in cataract formation. Prog Retin Eye Res. 1999;18:303–331.
[(#B6)] Giblin FJ, Jacobus CH, Seeger PG. The role of glutathione and related enzymes in the protection of the lens against oxidative stress. Free Radic Biol Med. 1996;21:807–815.
[(#B7)] Varma SD, Srivastava SK, Ramakrishnan R. Antioxidant role of Vitamin E and C in selenite-induced cataracts. Ophthalmic Res. 1987;19:126–131.
[(#B8)] Miyoshi H, Kadosawa T, Fuji A, et al. Effects of grape seed extract on canine lens epithelial cells treated with hydrogen peroxide. J Vet Med Sci. 2012;74:1183–1187.
[(#B9)] Varma SD, Mikuni I, Noda Y, et al. Inhibition of lens opacity by alpha-lipoic acid. Ophthalmic Res. 1991;23:110–116.
[(#B10)] Varshney UK, Sharma K, Jain GK. Effect of grape seed extract and Zincovit tablet on selenite-induced cataract in rats. J Pharm Pharmacol. 2011;63:1130–1135.
[(#B11)] Alden ME. Cataract: a review of nutritional relevance and prevention. J Am Diet Assoc. 1990;90:946–952.
[(#B12)] Spector A. The antioxidant system in the lens. Lens Res. 1991;8:233–241.
[(#B13)] Lerman S. Ocular effects of ultraviolet radiation. Int Ophthalmol Clin. 1986;26:101–117.
[(#B14)] Anonymous. Beta-carotene and vitamin E supplementation and cataract. The AREDS and the OPTIC studies. Arch Ophthalmol. 1998;116:437–445.
[(#B15)] Zatón G, Bartov E, Eisenberg S. Prevention of experimental
