Congenital eye diseases

From Cat
Microphthalmos in a kitten (mild case). Note prominence of nictitating membrane on the left side and visible sclera on the right side. Also note nuclear cataract, a frequent accompaniment to microphthalmos)[1]
Birman cat with early onset convergent strabismus[2]
Left eye microphthalmia in an adult Ragdoll female. This cat had no clinical signs attributable to the small left eye which was first diagnosed at 6 weeks of age.
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Agenesis (coloboma) of the upper lateral 2/3 of the eyelid is evident in this 6-month-old cat. Only the upper medial 1/3 of the lid is present. Trichiasis and fibrovascular keratitis are also present.
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Conjunctivitis neonatorum
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This cat was presented due to a swelling in the medial canthus and generalized conjunctivitis of the left eye. The white arrows point to the margins of the cartilage of the nictiating membrane that has a congenital defect causing an eversion of the nictitans.

There are a variety of congenital eye diseases in cats, of which the following are relatively common:

- Cases of advanced hereditary retinal degeneration in the Abyssinian cat have been examined over several years and the lens has always remained free of opacity. To date there are no proven reports of primary, hereditary, noncongenital cataract in the cat, apart from Hyperlipidemia. However, Rubin[3] reported three cases in related Himalayan cats in which the condition was bilateral and present as early as 12 weeks and with variable expression from posterior polar through posterior subcapsular to total; progression was recorded in one case. The relationship of the cats indicated simple autosomal recessive inheritance.
  • Anophthalmos

Anophthalmos, or the absence of the globe, has been reported together with absence of the optic nerve and optic tract but is rare (Barnett & Crispin, 2002). Anophthalmos and cyclopia are included with other congenital abnormalities as teratogenic anomalies following the use of griseofulvin in pregnant queens[4]

  • Strabismus, or squint, can be convergent (cross-eyed) or divergent and is a common feline ocular anomaly.
  • Buphthalmos

Buphthalmos, or a congenitally enlarged globe, is usually the result of congenital glaucoma and has been regularly reported in kittens (Barnett & Crispin, 2002). The eye is prominent, owing to its increased size, but the nictitating membrane may be retracted. In cases of exophthalmos, in which the eye is also prominent but of normal size, the nictitating membrane is also prominent.

  • Ankyloblepharon

Ankyloblepharon is adhesion of the eyelid margins to each other. Dogs and cats have physiologic ankyloblepharon until 10-14 days of age. If it persists past 15 days of age, infection of the conjunctival sac (ophthalmia neonatorum) may occur and is typified clinically by excessive swelling and/or discharge at the medial canthus. The eyelids should be separated using gentle (digital) traction. It is recommended to massage the fused lids toward the medial canthus with a warm, wet cotton ball to effect separation. Exudate should be submitted for bacterial culture. The palpebral fissure should be flushed with sterile saline and a broad-spectrum antibiotic ointment applied topically q 6 h. Untreated neonatal conjunctivitis can lead to severe corneal scarring or loss of the globe.

An ocular dermoid is a choristoma (normal tissue in an abnormal location). Dermoids may be present on the eyelid but most frequently they are located on the lateral conjunctiva or cornea. Treatment requires surgical excision and is curative.

  • Ophthalmia neonatorum

Ophthalmia neonatorum is associated with infection within the conjunctival sac prior to birth. Commonly caused by viral infections such as Herpes and calicivirus, the kittens are often born with pre-existing conjunctivitis, which often reveals itself as a bilateral purulent ocular discharge when the eyelid open at 7-9 days after birth (Barnett & Crispin, 2002).

Often a number of kittens in the litter are affected. Corneal ulceration, which can lead to corneal perforation and endophthalmitis and subsequent symblepharon may all occur as a consequence of viral infection.

Treatment involves opening/separating the eyelids with blunt scissors from the medial canthus along the line of fusion and frequent irrigation of the eyes with saline and antibiotic drops/ointment to keep the conjunctiva moist. Oral antibiotics/antiviral therapy may also be instigated.

  • Phthisis bulbi

Phthisis bulbi, a shrunken globe, is an acquired condition resulting from serious ocular insult such as trauma, endophthalmitis and severe uveitis. As with microphthalmos, the small globe is associated with endophthalmos and prominence of the nictitating membrane. Barnett & Crispin (2002) recommend removal of the eye if excesive discharge is present and persistent.

  • Exophthalmos

Exophthalmos, abnormal protrusion of the globe, is usually accompanied by prominence of the nictitating membrane and possibly chemosis and strabismus.

References

  1. Courtesy of Barnett, KC & Crispin, SM (2002) Feline Ophthalmology: An atlas & Text. p: 35 Elsevier Ltd
  2. Courtesy of Barnett, KC & Crispin, SM (2002) Feline Ophthalmology: An atlas & Text. p: 35 Elsevier Ltd
  3. Rubin, LF (1986) Hereditary cataract in Himalayan cats. Feline Practice. 16(1):14-15
  4. Scott, FW, LaHunta, A., Schultz, RD, Bistner, SI & Riis, RC (1975) Teratology 11:79-86