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Corneal Sequestration is a necrosis (cell death) of the middle of the cornea (the stroma). It can be conformational (genetic) or sometimes of infectious origin (e.g., set off by the herpes virus.) Persian and Himalayan cats are particularly predisposed to corneal sequestration. The necrotic area is dark in color and prevents vision through this area. Progression to complete blindness is rare though partial loss of the visual field is not uncommon in advanced cases.

To treat this condition, a corneal allograft is sometimes used as a transplant graft when the lesion is very deep into the cornea. The central layer, or stroma, from the donor cornea is actually what is transplanted. The procedure is known as a partial thickness corneal transplant (lamellar keratoplasty). Lamellar Keratoplasty affords complete removal of the diseased cornea, restoration of the anatomic thickness of the cornea and corneal clarity which preserves vision.

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  Figure 1.

  A patient with a very large sequestrum. It is the large dark kidney bean-shaped area in the lower right hand portion of the cornea.…

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  Figure 2.

  A sample ultrasound picture of a sequestrum. The white hyperechoic area shows exactly the thickness and location of the sequestrum within the cornea. This allows for a more accurate excision of the lesion to the exact depth needed.…

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  Figure 3.

  The recipient at a check-up 2 weeks following surgery. Fluorescein dye has been placed in the eye to visualize the intactness of the corneal epithelium.…

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  Figure 4.

  Our patient “Chopper” at 3 months follow up. He is doing well and has a clear, healthy cornea.…

Description of the Procedure:

• Figure 1 shows a patient with a very large sequestrum. It is the large dark kidney bean-shaped area in the lower right hand portion of the cornea.
• The surgeon used Ultrasound Biomicroscopy (UBM) to see the internal anatomy of the cornea. This equipment has a 50 MHz probe that is extremely sensitive and can determine very precisely the depth of the lesion within the middle layer of the cornea. Figure 2 shows a sample ultrasound picture of a sequestrum. The white hyperechoic area shows exactly the thickness and location of the sequestrum within the cornea. This allows for a more accurate excision of the lesion to the exact depth needed.
• A special vacuum trephine is used to make a precise and delicate cut of the required diameter partially through the thin cornea. Its control is so fine that 1/4 turn moves the cutting edge 65 microns (0.065 millimeter) deeper into the cornea. The concept is to remove the surface layers containing the sequestrum but leave the important endothelial lining cells in place.
• The allograft is cut in a similar location using a special donor trephine that makes a slightly larger diameter full thickness cut through the cornea. The surgeon then removes the outer and inner layers of the donor cornea. This leaves just the stroma to be transplanted.
• Sutures smaller than a human hair (9-0 suture) are carefully placed around the edges of the graft and the donor cornea is secured with 16 to 20 sutures using microsurgical techniques and an operating microscope.

Post Operative Follow Up:

• Figure 3 shows the recipient at a check-up 2 weeks following surgery. Fluorescein dye has been placed in the eye to visualize the intactness of the corneal epithelium. The donor cornea is healing into place as expected and the cornea remains clear, which is a good sign of overall health of the endothelial cells and the transplanted donor corneal stroma.
• Figure 4 shows our patient “Chopper” at 3 months follow up. He is doing well and has a clear, healthy cornea.

Dr. Silverman is not affiliated with Veterinary Transplant Services. He has kindly supplied the photographs and information for this presentation, with the consent of his patient’s owners, to illustrate a representative case that benefited from transplant of a corneal allograft from VTS. For more information about VTS allografts, please contact Dr. Newman.