CORNEAL ENDOTHELIAL DEGENERATION - CORNEAL OEDEMA

Corneal oedema is fluid retention in the cornea.

Clinical Signs

The appearance of corneal oedema is a blue or cloudy cornea.

Causes
1. inflammation of the cornea (keratitis)
2. corneal ulcers
3. age-related corneal endothelial degeneration
4. breed-related corneal endothelial degeneration

Breeds more commonly affected include
1. Welsh Springer Spaniel
2. Basset Hound
3. Chihuahua
4. Dachshund

Some may be affected in middle age eg 5-6 years of age.

The inner surface of the cornea is called the endothelium. In young dogs and cats there are in excess of 3000 cells, however this number reduces with age. These cells act as pumps whose role is to pump fluid out of the cornea to keep it in a dehydrated state. This lack of water results in the cornea being clear and transparent.

In some breeds and especially in older animals, these pumps may start to fail. The result is fluid retention in the cornea, or corneal oedema, and the cornea becomes cloudy.

In severe cases, the corneal oedema is so severe that vision may be affected. Furthermore, blisters may form just under the surface of the cornea (epithelium). If the surface is disrupted, superficial ulcers may result. These ulcers may be slow to heal.

Treatment

Treatment of corneal endothelial degeneration is the use of hypertonic saline drops. These drops work by drawing fluid out of the cornea, and they must be administered four times daily. In most cases the oedema can be reduced, and maintenance therapy is continued at a frequency of twice daily. The initial treatment of corneal ulceration is topical hypertonic saline drops four times daily.

Oral anti-inflammatory treatment, eg Rimadyl tablets, may also be commenced. If the ulceration fails to heal, surgery may be required to excise the non-healing ulcer. Following this surgery, the cornea is covered with a third eyelid flap. In severe cases when this surgery fails, thermal burns are used to encourage the ulcers to heal. This also works to control the fluid retention by forming a barrier layer of scar tissue. One complication following surgery is scarring, which can be unpredictable. However, in most cases if the ulceration and oedema are severe, vision has already been affected for some time. In these cases surgery is performed in order to reduce pain.

Topical treatment in most cases is life long, as this is a problem we can control rather than cure. If cloudiness reduces, increase the frequency of the drops back to four times daily. If an eye suddenly becomes sore, do the same and contact us as soon as convenient, as this suggests ulceration has occurred.

Surgical management

Some cases may benefit from surgery. There are (3) types of surgery - It is vital that these are performed using an OPERATING MICROSCOPE.

1. Keratectomy: The unhealthy cornea is removed with a corneal disc knife. The cornea then heals with scar tissue but this is stronger and is less prone to water bubbles. This scarring can result in reduced vision.

2. Thermokeratoplasty: The cornea is treated with multiple tiny pinpoint burns resulting in scarring. Once again this can result in reduced vision - and is sometimes considered an end stage procedure.

3. Gunderson Flap: An ultra-thin section of conjunctiva is sutured directly onto the cornea using an OPERATING MICROSCOPE. The conjunctiva is permanently left there and the sutures will dissolve out. This conjunctival graft will then act to "dehydrate" the cornea by providing another way out for the excess fluid. After 1 month the cornea normally goes clear. The benefit of surgery is reduced medication and over time and it may have a sparing effect on the remaining corneal endothelial cells.

Removal of the unhealthy cornea

Half circle shape where unhealthy cornea was removed

Gunderson flap place into position

Gunderson flap sutured into position

Gunderson Flap images supplied by Bron Williams

Gunderson Flap images supplied by Dr. Anu O'Reilly

Post Operative Care

The following concerns will be discussed with you at the time of the initial consult.

1. Visits following surgery

2. Antibiotic tablets or paste after surgery

3. Anti-inflammatory tablets or liquids after surgery

Please let us know at the time of the initial consult if your pet is currently taking any medications for any issue- not just their eyes (tablets, paste or liquid) or has any health issues.