Friday, January 13, 2012


What is Keratoconus ?
A clinical condition characterized by thinning and forward protrusion of the cornea 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

Why does is occur ?
Etiology of this condition is still not clear. Eye rubbing, hormonal variations, genetic predisposition have been proposed to be causative factors in the disease. It is possible that this condition could be secondary to increased breakdown of the stromal collagen lamellae by the lysosomal enzymes released by the basal epithelium in these eyes. The substance of the cornea consists of hundreds of layers that are linked to each other by a substance called collagen. If these collagen cross-links between layers are lost due to keratoconus, there is a progressive corneal thinning and stretching which gradually progresses, often in both eyes. Normal pressure within the eye causes the cornea to bulge forward into an irregular cone shape. When light enters the eye, it first passes through the cornea. If the cornea has turned conical, there is distortion of the image. The eye develops astigmatism (cylindrical errors) and myopia [shortsightedness] and the vision may become severely blurred

Clinical features
Clinical presentation is usually with progressive visual symptoms secondary to corneal changes. Irregular astigmatism results in blurred vision, glare, and diplopia. Glasses do not help improve vision, and rigid contact lens wear is required for improving eyesight

Contact lenses
Semisoft or RGP contact lens, can help in cases with mild to moderate keratoconus. However advanced cases require fitting with Rose- K lenses or Scleral lenses. Both these advanced lenses are now available at AJEH.

Collagen crosslinking or  C3R
Current methods such as rigid contact lens, & intracorneal ring segments correct only the refractive error without any effect on the progression of keratoconus. It is estimated that eventually 21% of the keratoconus patients require surgical intervention to restore corneal anatomy and eyesight.
C3R is a new 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 30 minutes. This results in cross linking of the collagen fibres of the cornea, thereby increasing its physical strength by upto 300%. This treatment is now available at AJEH. 

What is collagen cross-linking?
Collagen cross-linking is a new treatment for keratoconus, that uses a photosensitizing agent, riboflavin (vitamin B2) & ultraviolet light (UVA, 365nm) exposure. In extensive experimental studies (including biomechanical stress & strain measurements) researchers have demonstrated a significant increase in corneal rigidity / stiffness after collagen cross-linking using this riboflavin/UVA treatment. The 3 & 5 year results of Dresden clinical study in human eyes has shown arrest of progression of keratoconus in all treated eyes. (Wollensak G. Crosslinking treatment of progressive keratoconus: New Hope. Current Opinion in Ophthalmology 2006; 17: 356 – 360)

How is the treatment done?
The treatment is performed under topical anesthesia. The skin (epithelium) of the surface of the cornea is partially scratched, followed by application of Riboflavin eye drops for 30 minutes. The eye is then exposed to UVA light for 30 minutes. After the treatment, antibiotic ointment is applied and an eye-pad is worn overnight until the next day when the surface of the eye has healed. Oral analgesics are required for the first 1 -2 days

Who can benefit from this treatment?
Collagen cross-linking treatment is not a cure for keratoconus, Rather, it aims to  halt the progression of the condition. This is important to understand. Patients will continue to wear spectacles or contact lenses (although a change in the prescription may be required) following the cross-linking treatment. The main aim of this treatment is to arrest progression of keratoconus, and thereby prevent further deterioration in vision and the need for corneal transplantation. However in advanced keratoconus, wherein the corneal thickness is below 350 microns, this  treatment may not be possible. In such a situation other alternatives such as deep anterior lamellar keratoplasty  (DALK) should be considered

Surgical treatment
Surgical intervention is often necessary in advanced Keratoconus to restore corneal anatomy 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, the transplanted donor cornea is at risk for endothelial rejection .

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 . 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.

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