Eye drop-based treatment may replace surgery
Eyes are amazing structures. They have adapted in different ways to suit individual species. For example, because horses are a prey species, their eyes are on the sides of their head, which enables them to achieve a visual field of 350 degrees—almost all the way around them. On the other hand owls, which are nocturnal predators, can see great distances to find their prey with minimal light due to their large eyes, which have comparatively more photoreceptor cells on their retinas. It would take just one birthday candle’s light for an owl to be able to see across a football field!For all species, loss of vision can be very problematic, making normal life difficult. That is why Dr. Bianca da Costa Martins, a clinical professor of ophthalmology at the University of Illinois Veterinary Teaching Hospital in Urbana, is seeking new approaches to treating corneal ulcers, a condition that frequently leads to loss of eyesight in all species.
Corneal Ulcers Cause Concerns
“The cornea is the outer windshield of the eye. It is a clear, transparent structure that is responsible for transmission and refraction of light. The cornea and the sclera, which is the white part of the eye, protect the inner eye structures from injury and disease,” explains Dr. Martins.
A corneal ulcer develops when the cornea is damaged. “The most common cause of corneal ulcers is trauma, such as from a fight with an animal, eyelid and eyelash abnormalities, and self-trauma,” explains Dr. Martins. “In some cases, a corneal ulcer starts superficially, with only some cell layers missing. In other cases, such as from a dog bite or cat scratch, a full corneal laceration occurs.”
More superficial ulcers are easier to treat and heal, but deep, complicated, or infected ulcers generally need more help. They are often painful, and patients respond to the pain by rubbing their eyes, ultimately making the ulcer larger and deeper.
Left untreated, an ulcer may get infected and progress to complete perforation of the cornea. This can result in complications including iris prolapse, where the colored part of the eye starts to come out of the eye surface; inner eye inflammation and infection; retinal detachment, which causes blindness; and vision loss. In severe cases the entire eye may need to be removed.
New Treatment Shows Promise
Superficial ulcers are routinely treated with topical drops and ointments. Deeper ulcers and ulcers that have complications may need surgical treatment. Recently, Dr. Martins has been investigating the use of amniotic tissue in the healing of ulcers.
“The amniotic membrane is the inner layer of the placenta, the one in contact with the fetus. It has several properties and compounds that are beneficial in the healing process: it decreases the inflammatory process, fights collagen degradation, and decreases scar formation,” notes Dr. Martins.
This membrane can be safely taken after the normal delivery of a foal from tissue that is usually discarded. The amniotic tissue is used in the surgical treatment of corneal ulcers.
“We surgically suture the amniotic membrane on the cornea after removing infected and damaged tissue,” says Dr. Martins. “In some cases, this works better than conjunctival grafts, since the amniotic tissue graft results in much less scarring and a more transparent cornea.”
The conjunctiva is the membrane that covers the eye and the inside of the eyelid. Traditionally a portion of the conjunctiva would be used to cover the corneal defect, but this often results in a large scar that can cause loss of vision. The use of amniotic tissue increases the likelihood that vision will be preserved.
Dr. Martin’s newest research involves a liquefied amniotic tissue called amniotic membrane homogenate.
“The amniotic membrane homogenate is meant to be used topically as an eye drop and is showing promising results,” reports Dr. Martins. An eye drop-based treatment may allow for a less invasive way of healing the cornea and could eliminate the need for surgery in some instances.
With these advances in ulcer treatment, animals with a corneal ulcer have a better chance of retaining their vision.
By Melissa Giese