Congenital Ocular Anomalies in Dogs
Congenital anomalies affecting the eyeball or its surrounding tissues typically manifest shortly after a puppy’s birth, though they may emerge within the first six to eight weeks of life. Many of these defects stem from genetic inheritance. For instance, persistent pupillary membrane (PPM), characterized by strands of fetal tissue remaining on the eye post-birth, is more prevalent among Basenjis, Pembroke and Cardigan Welsh Corgis, Chow Chows, and Mastiffs.
On the other hand, persistent hyperplastic tunica vasculosa lentis (PHTVL) and persistent hyperplastic primary vitreous (PHPV) are commonly inherited in Doberman Pinschers. Multifocal retinal dysplasia, entailing the malformation of the retina, is observed in English Springer Spaniels. Collie Eye Anomaly affects Collies, Shetland Sheepdogs, and Australian Shepherds, while retinal dystrophy is found in Briards and photoreceptor dysplasia, which affects the cells responsible for perceiving light and color, is prevalent in Collies, Irish Setters, Miniature Schnauzers, and Norwegian Elkhounds.
Ocular abnormalities may also arise spontaneously, such as colobomas of the anterior, or occur in utero. Additionally, exposure to toxic compounds, inadequate nutrient intake, and systemic infections and inflammations during pregnancy, such as panleukopenia, pose potential risk factors for ocular abnormalities.
Symptoms and Types
Dogs can experience various abnormalities affecting their eyes or surrounding tissues. Here are some common issues and their associated signs:
Colobomas of the lid:
- Notch in the eyelid or missing eyelid tissue may be visible.
- Variable eyelid twitching and watery eyes.
Colobomas of the iris:
- Iris may appear misshapen.
- Sensitivity to bright light.
- Typically does not affect vision.
- Most common in herding dogs like Basenjis, Collies, and Australian Shepherds.
Persistent pupillary membranes (PPM):
- Fetal tissue remains on the eye after birth.
- Variable iris defects, cataracts, and colobomas of the uvea.
- Common in Basenjis.
Dermoids:
- Tumor-like cysts may develop on the eyelids, conjunctiva, or cornea.
- Variable eyelid twitching and watery eyes.
Iris cysts:
- Cysts may not be visible as they are located behind the iris.
- Symptoms may include slight bulging of the iris unless the cyst affects vision.
Congenital glaucoma (high eye pressure) with buphthalmos (abnormal eye enlargement):
- Tearing
- Enlarged, red, and painful eyes.
Congenital cataracts:
- Cloudiness in the eyes.
- Often inherited, such as in Cavalier King Charles Spaniels.
Congenital keratoconjunctivitis sicca (KCS) or dry eye:
- Common in Yorkshire Terriers.
Other congenital issues:
- Lack of pupils or abnormally shaped pupils.
- Lack of tear duct openings in Cocker Spaniels.
- Lack of iris.
Persistent hyperplastic tunica vasculosa lentis (PHTVL) and persistent hyperplastic primary vitreous (PHPV):
- Begins in utero, with progressive atrophy of the vascular system supporting the eye lens.
- Common in Briards, Cocker Spaniels, Beagles, and Rottweilers.
Retinal dysplasia:
- Appears as folds or rosette shapes on the retina.
- Common in Briards.
Retinal detachment:
- Retina detaches from the back of the eye, leading to blindness.
- Common in Labrador Retrievers, Bedlington Terriers, and Sealyham Terriers.
Photoreceptor dysplasia:
- Night blindness (if rods are affected).
- Day blindness (if cones are affected).
- Slow or absent pupillary reflex to light.
- Involuntary eye movement.
Optic nerve underdevelopment:
- Often results in blindness.
- Common in Miniature and Toy Poodles.
Rod-cone malformation:
- Common in Irish Setters and Collies (rod and cone malformation).
- Common in Norwegian Elkhounds (rod malformation).
- Common in Alaskan Malamutes (cone malformation).
Furthermore, hereditary defects like corneal opacities, PPM, cataracts, retinal detachment, and dysplasia are often associated with factors such as abnormally small eyes, missing eyeballs, or hidden eyeballs due to other eye deformities.
Causes
- Genetic factors
- Spontaneous malformations
- Uterine conditions (e.g., infections and inflammations during pregnancy)
- Toxic exposure during pregnancy
- Nutritional deficiencies during pregnancy
Diagnosis
To diagnose your dog’s eye condition, it’s important to provide as much of its medical history as possible, including any in utero conditions, the mother’s health status, diet during pregnancy, and the dog’s post-birth development and environment. Following a comprehensive history, your veterinarian will conduct tests to assess the eye’s health.
A Schirmer tear test may be conducted to evaluate tear production in your dog’s eyes. If glaucoma is suspected, a tonometer will be used to measure the internal eye pressure. Abnormalities within the eye will be examined using an indirect ophthalmoscope and/or a slitlamp biomicroscope.
Ultrasound imaging of the eyes can reveal issues with the lens, vitreous humor, retina, or other problems in the posterior segment of the eye. In cases of iris cysts, ultrasound helps determine whether the mass behind the iris is a cyst or tumor. Cysts may vary in behavior, some growing while others shrink. Typically, follow-up appointments are scheduled to monitor cyst progress unless further intervention is necessary.
Angiography is another diagnostic method used to assess posterior eye problems such as retinal detachment and abnormal blood vessels. A radiopaque substance visible on X-ray is injected into the area requiring visualization, enabling examination of the blood vessels for irregularities.
Treatment
The treatment plan for your dog will vary depending on the specific type of eye abnormality present. Your veterinarian may recommend referral to a veterinary ophthalmologist for further expertise in eye diseases. Surgery may be an option for repairing certain congenital birth defects, while medications can help alleviate symptoms associated with some abnormalities.
For conditions like congenital keratoconjunctivitis sicca (dry eye), treatment typically involves the use of tear substitutes alongside antibiotics. Mydriatics, another type of medication, may be prescribed to improve vision in cases where congenital cataracts affect the center of the dog’s eye lenses.
Photoreceptor dysplasia, unfortunately, does not have a medical treatment to halt its progression. However, dogs with this condition often do not experience additional physical abnormalities and can adapt well to their environment, provided it remains stable and safe for them.
Living and Management
For dogs with congenital keratoconjunctivitis sicca (KCS), regular checkups with a veterinarian are necessary to monitor tear production and the condition of the external eye structures. Dogs with abnormalities like congenital cataracts, PHTVL, and PHPV should undergo checkups twice a year to track the progression of their condition.
Furthermore, considering that most congenital ocular anomalies have a hereditary basis, it’s important to refrain from breeding dogs diagnosed with any of these disorders. This helps prevent the transmission of genetic predispositions to future generations.