We recently met Mila who is an 18mth old, female guinea pig. She was born with a congenital malformation known as an ocular dermoid. Dermoids are normal areas of skin in abnormal locations. Dermoids are congenital, meaning that they form before birth while the foetus is developing. However, they are not thought to be hereditary (i.e. they are not passed from parent to child). Ocular dermoids are usually haired skin and they can occur anywhere on the eye. The hair rubbing on the eye can cause problems such as irritation and corneal ulcerations.
Mila’s dermoid was on her left eye and was causing excessive lacrimation (excessive tear production) in that eye, hyperaemia (increase in blood vessels), pain and irritation. The dermoid originated from the conjunctiva on the underside of the upper lid but extended to the cornea at the limbus (the junction between the cornea and the sclera, white of the eye). Mila is a long haired guinea pig which meant the hair growing from the dermoid was also long, this contributed to the discomfort it was causing her.
Mila’s dermoid was surgically removed under a general anaesthetic, she is recovering well following her surgery and her eye is returning to normal.
Depending on the location, size and length of hair on the dermoid other treatment options may include plucking the hair from the surface (although it will always grow back) or using electrolysis or cryosurgery to permanently remove the hairs. Removal of the hairs will prevent irritation but sight may still be affected by the presence of skin on the eye, dependent on the location.
There are a few other conditions of the eye lids that guinea pigs can suffer from. A relative common presentation seen is ‘fatty eye,’ also know as ‘pea eye.’ In this condition a drooping of the lower lid is seen, with a protrusion of the conjunctival fat. There are a number of potential causes of this condition, including a genetic component, age, obesity and previous infection. Treatment is usually not necessary as it rarely causes any clinical problem.
Occasionally guinea pigs can develop ectropian. This is rolling inwards of the eye lid which results in the haired skin then rubbing on the cornea of the eye causing pain and irritation. The ectropian may be congenital defect but will also occur due to the eyelids being swollen and inflamed for any other reason. Treatment would involve resolving any underling cause for eye inflammation or surgery.
Finally, in rare cases, guinea pigs can develop ectopic cilia. These are eyelashes growing from the inside aspect of the eyelid margin. Again this causes irritation to the eye. Correction can be to remove the hairs through plucking, electrolysis or cryosurgery or surgical removal of that section of eyelid margin, provided the area affected is less than a third of the length of the eyelid.