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Penetrating Keratoplasty (PK) – full thickness transplantation

Penetrating Keratoplasty (PK) is a traditional full-thickness corneal transplant. This may be required in cases where the cornea is scarred, swollen or excessively thin (Keratoconus).

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Return of best vision after standard full thickness corneal transplantation may take up to a year or more after the operation. It is dependent on how long it takes for the grafted cornea to begin functioning as a lens; it must become transparent and it must have a regular surface curve. These important characteristics permit light to properly bend (refract) as it passes through the cornea, bending further as it passes through the crystalline lens and comes to focus on the retina.

The newly grafted cornea, if successful, only takes a few weeks to become thin and transparent but far more time is usually required until light is properly refracted through it.

The healthy cornea is transparent because it does not contain the fine blood vessels (capillaries) present in other tissues of the body. However, this lack of blood supply has a downside when cornea graft wound-healing is required. The cornea takes years to heal as compared to a superficial wound in the skin of your arm, which heals in only about a week! For this reason cornea graft sutures must be left in place for a year or more while the cornea graft-host interface heals. The tension generated by the sutures within the cornea often cause distortion of the curvature of the graft, causing the refraction of the eye to shift unpredictably. If the cornea surface is regular, and the prescription of the other eye is not too different, it is sometimes possible to prescribe glasses during this early rehabilitation period but the prescription lenses may need to be periodically changed as the cornea heals.

Some patients may need to wait until the sutures can be removed (1 to 1.5yrs) before the final surface topography is apparent and then glasses are prescribed. However, if after suture removal, significant cornea graft distortion or warpage (irregular astigmatism) remains, spectacles will not help. Instead, hard contact lenses may be suggested, but fitting can be challenging and is not always successful.

Other individuals require laser vision correction to reduce inadequate graft curvature or imbalances between the prescriptions of both eyes to maximize optical visual rehabilitation.

Of course, a good visual outcome is also dependent on general eye health and requires the absence of other visually limiting conditions such as cataract, glaucoma, or macular degeneration.