Corneal sequestrum

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Your cat has been diagnosed with a corneal sequestrum. The following information will help you to understand what a corneal sequestrum is, why your cat has developed it – and what treatment options are available for you and your pet.

What is a corneal sequestrum?

The cornea is the clear window of the eye. Its clarity is essential for vision. A corneal sequestrum is a piece of cornea that has died off and is taking on a brownish discoloration. The corneal sequestrum is gradually being rejected by the surrounding healthy corneal tissue. The development of the sequestrum can initially be painless but with time, the affected eye will become sore as the sequestrum ‘erodes’ out of the surrounding healthy cornea. Blood vessels may grow towards the sequestrum in an attempt to reject it and heal the defect. This reaction together with the discoloration of the sequestrum can result in severe corneal opacification and visual impairment. Eyes with corneal sequestra are also prone to infection and may develop progressive ulceration with potential corneal perforation.

Why has my cat developed a corneal sequestrum?

We still do not know all the reasons why corneal sequestra develop and research on the problem is ongoing. However, the most common reason for the development of a corneal sequestrum appears breed-related as we most commonly see the condition in short-nosed cats such as in the Persian, the Burmese and the British Short-Hair. Another cause for the development of corneal sequestra is chronic corneal trauma – such as caused by rubbing of eyelid hair in patients with in-turned lids (‘entropion’). Finally, corneal sequestra can develop after an especially serious episode of cat flu due to the Feline Herpesvirus.

How are corneal sequestra treated?

Both medical treatment and surgical intervention are options. In some cases, where sequestra are small and where the affected eye is not too painful, it can be attempted to support the eye with  lubricating and antibiotic eye ointments and the sequestrum may eventually be ‘shed’ with the ingrowth of blood vessels. If the sequestrum is shed successfully, then the outcome can be very good. This treatment option is however to some degree unpredictable as it is not possible to know in which time frame the ‘shedding’ of the sequestrum can be achieved.

What are the risks of medical treatment for a corneal sequestrum?

In some patients, it may take weeks or months for a sequestrum to be shed – and it is possible that during this time, the lesion may ‘grow’ larger or deeper within the cornea.   There is also a risk that the sequestrum may become infected – with a risk of corneal perforation and loss of the eye. Emergency surgical intervention may be required in this case.

Surgical treatment of corneal sequestra

Surgical intervention instead is a much more predictable option to remove corneal sequestra as your ophthalmologist is ‘in the driving seat’. Under general anaesthesia and with the help of the operating microscope, the sequestrum will be excised with microsurgical knives. Depending on the depth to which the sequestrum extends into the corneal tissue, corneal defects of varying depth will be created. If the sequestrum was rather superficial and the remaining defect is shallow, a contact lens will usually be placed at the end of the operation to provide some protection and comfort. If a deep corneal defect ensues, then a ‘corneal grafting procedure’ will be performed to stabilise the defect. The most commonly used graft after removal of a corneal sequestrum is a ‘corneo-conjunctival transposition (CCT)’. This graft is especially strong and causes the least corneal scarring. Surgical intervention is especially indicated for corneal sequestra that cause pain, are large or deep or show signs of infection.

What are the risks of surgical treatment for a corneal sequestrum?

Surgical removal of a sequestrum does require a general anaesthetic – which of course has a small risk. Surgery to remove the sequestrum is a very straightforward procedure in the hands of a trained micro-surgeon, who will also be comfortable to apply a graft into the defect. In some patients, the defect may extend so deep into the cornea that it requires a ‘full thickness’ excision to remove all abnormal pigmented corneal tissue. A graft must be applied in this situation. Most grafts heal into the surrounding cornea quickly and uneventfully and graft failure is rare. However, in occasional cases, a graft can become infected or may not heal into the defect as expected. If this should occur, it may take a second operation to correct the problem but a good outcome can usually be achieved.

What is the aftercare following surgical removal of a sequestrum?

Patients will usually be discharged on the day of the operation and will have to wear a protective collar for approximately 10 days. Outdoors access should be restricted during this time and a litter tray provided. Most patients will require the application of an antibiotic eye drop or ointment and painkillers and antibiotics will be given by mouth for the same period. Most patients are pain-free and able to return to a normal life after two weeks.