Overview and Clinical Importance
Cataracts are opacities of the lens or lens capsule that interfere with light transmission to the retina, leading to visual impairment and potentially blindness. They are one of the most common causes of vision loss in dogs and a high-yield NAVLE topic. The lens is a transparent, biconvex, avascular structure composed of lens fibers (crystallin proteins) surrounded by the lens capsule.
| Etiology |
Key Features |
| Hereditary/Genetic |
Most common cause. Bilateral, symmetrical. HSF4 gene mutations. Juvenile onset (1-5 years). Affected dogs should not be bred. |
| Diabetic |
Second most common. Rapid onset (75-80% within 1 year of diagnosis). Bilateral. Sorbitol accumulation via aldose reductase. Risk of capsule rupture. |
| Senile/Age-Related |
Third most common. Dogs greater than 7-8 years. Slow progression. Must differentiate from nuclear sclerosis. |
| Secondary to Uveitis |
Chronic inflammation alters aqueous. Inflammatory mediators damage lens epithelium. Usually begins in cortex. |
| Traumatic |
Penetrating injuries (cat claw most common). Capsule rupture causes phacoclastic uveitis. Usually unilateral. Emergency. |
| Secondary to PRA |
Toxic dialdehydes from degenerating retina. Posterior cortical location. Surgery NOT indicated (non-functional retina). |
| Congenital |
Present at birth. May be hereditary or in utero insults. Nuclear location. May associate with other anomalies. |
| Nutritional |
Rare. Arginine deficiency in orphan puppies. Usually reversible if corrected early. |
Lens Anatomy and Physiology
The lens is embryologically derived from surface ectoderm, while other ocular structures form from mesoderm. This is clinically significant because lens proteins are immunologically sequestered, leading to potential immune-mediated inflammation when exposed (lens-induced uveitis).
Key Anatomical Components
- Lens Capsule: Elastic basement membrane encasing the lens; thicker anteriorly
- Lens Epithelium: Single layer of cuboidal cells beneath anterior capsule; divides into lens fibers
- Cortex: Outer, younger lens fibers; softer consistency
- Nucleus: Central, older lens fibers; firmer, denser
- Zonules: Suspensory ligaments attaching lens to ciliary body
High-YieldThe lens is avascular and receives nutrients from aqueous humor via diffusion. Changes in aqueous composition (uveitis, glaucoma) can affect lens metabolism and contribute to cataract formation.
| Breed |
Age of Onset |
Notes |
| Boston Terrier |
Juvenile to adult |
High prevalence (11.1%); increased glaucoma risk post-op |
| Cocker Spaniel |
1-5 years |
American and English; increased glaucoma risk |
| Miniature/Toy Poodle |
1-5 years |
High prevalence; also predisposed to PRA |
| Labrador Retriever |
Variable |
Also predisposed to PRA; increased retinal detachment risk |
| Siberian Husky |
Juvenile |
Posterior subcapsular location common |
| Bichon Frise |
Adult |
High prevalence; increased retinal detachment risk |
Etiology of Canine Cataracts
Breed Predispositions
NAVLE TipBoston Terriers and Cocker Spaniels have increased risk of post-operative glaucoma. Labrador Retrievers, Bichon Frises, and Poodles have increased risk of post-operative retinal detachment.
| Stage |
Lens Involvement |
Tapetal Reflection |
Vision/Significance |
| Incipient |
Less than 15% |
Fully visible |
No visual deficit; monitor |
| Immature |
15-99% |
Partially visible |
Variable impairment; best surgical prognosis |
| Mature |
100% |
Not visible (blocked) |
Blind; PLR intact if retina functional |
| Hypermature |
100% with resorption |
Partially visible (resorption) |
Wrinkled capsule; high LIU risk; poorer prognosis |
Pathophysiology of Diabetic Cataracts
Approximately 75-80% of diabetic dogs develop cataracts within the first year of diagnosis, regardless of glycemic control.