What is Keratoconus ?

A clinical condition characterised by thinning & forward protrusion of the cornea ie the clear front part of the eye, resulting in conical shape. This disorder is usually bilateral, with onset at the age of 10 -14 years. Affects both sexes, with a slight female preponderance. Although it has been reported in families, the risk of inheritance is reasonably low.

Why does is occur ?

Etiology of this condition is still not clear.  It is possible that this condition could be secondary to increased breakdown of the stromal collagen fibers by the enzymes released by the surface layer of cells in these eyes.

Clinical features

Clinical presentation is usually with progressive decrease in quality  of vision secondary to corneal changes. Irregular astigmatism results in blurred vision, glare, and double vision. Glasses do not help much in improving vision, and rigid contact lens wear is usually required for improving eyesight.

Management

Glasses can be prescribed to correct the induced astigmatism in early keratoconus.  Once the cylindrical power increases beyond 4.0 diopters, patients find it difficult to tolerate such high power in glasses. Semisoft or RGP contact lens, can help in cases with mild to moderate keratoconus. The front surface of the contact lens behaves like the front surface of the eye with a regular shape. This provides reasonably clear vision for normal daily activities. However, fitting of contact lens in eyes with keratoconus requires expertise in CL fitting and a special set of trial lenses. With increasing progression of keratoconus, patients may find it difficult to wear the contact lens, and at times the lens keeps falling out of the eye. In such situations, piggy back lens ie RGP lens mounted on a soft contact lens can be tried.

Collagen cross linking

This is a newer modality of treatment for keratoconus, where in Riboflavin eye drops are applied followed by exposure of the cornea to ultraviolet radiation for a duration of 25 -30 minutes. This results in increased cross linking of the collagen fibres of the cornea, thereby increasing its physical strength. This therapy helps in preventing further progression of keratoconus, and thereby helpful to stabilize the disease. (Approx cost 25,000 rupees for both eyes)

Intacs implants

This is a newer surgical treatment for mild to moderate keratoconus. In this surgery, fine plastic implants are placed in the peripheral cornea, which helps flatten the central cornea, thereby improving the unaided vision. Patients are able to return back to normal glass wear or comfortable contact lens wear post treatment. This procedure is painless and simple to perform. The surgery is performed under topical anesthesia, and takes only 5 -10 minutes per eye. (Approx cost 45,000 rupees per eye)

Surgical treatment

Surgical intervention is often necessary in advanced Keratoconus to restore corneal shape and thereby improve quality of vision. Traditionally full thickness corneal transplantation procedures have been commonly performed for advanced keratoconus. Although this procedure has successful outcome in a large number of cases, it sacrifices the healthy
endothelium of the host cornea. The transplanted donor cornea is at risk for rejection, and requires steroid therapy for a long duration to prevent rejection. This predisposes the eye to steroid induced complications such as cataract  and glaucoma.

Deep Anterior Lamellar Keratoplasty (DALK)

With advancement in corneal surgical techniques, it is now possible to selectively remove the anterior layers from the cornea and replace it  with donor tissue to restore its anatomy and function. Deep anterior lamellar keratoplasty (DALK) is one such procedure wherein the
host corneal endothelium is retained, and anterior corneal tissue is replaced with normal thickness donor tissue. As the host endothelium is retained there is no risk of rejection, and steroids have to be  given only for a short duration of time. However DALK surgery requires
more surgical expertise compared to the traditional full thickness keratoplasty, and hence performed by only well trained corneal surgeons all over the world.

In  advanced stages of Keratoconus, due to extreme thinning, the inner layer of the cornea can rupture, leading to increased leakage of fluid into the cornea. This results in whitening of the cornea, with sudden decrease in vision. This condition is called acute hydrops. In this situation, topical medications have to be applied for symptomatic relief. It takes 3 - 4 months for the corneal oedema to resolve, following which a standard full thickness keratoplasty is required to restore corneal clarity and visual improvement. It this situation lamellar surgery is not recommended, and hence one should not wait for this complication to occur, and take advantage of lamellar procedures at an early stage.

Standard full thickness corneal transplantation procedure, is very successful in restoring corneal structure and function. However one needs to use topical steroids for a longer duration than lamellar procedures. Full thickness corneal grafts in keratoconus have the best clinical outcome, when compared with other indication of corneal transplantation surgery.