KERATOCONUS (CONICAL CORNEA)

The eye is like a camera in which lenses focus the picture on a light sensitive film. In the human eye, the transparent cornea and lens focus light on the retina, which changes it into electrical signals, which are then transmitted to the brain by the optic nerve to be perceived as images.

The cornea is the front transparent window of the eye and forms the outermost one-sixth of the eyeball. It is lamellar in nature (like plywood) and is made up of 5 layers, each of which has a definite function. In order to be effective it must remain transparent. Freezing, heating, molding, lathing, tattooing, excising, incising and transplanting are all means by which the delicate and sensitive cornea has been altered for optical, therapeutic and cosmetic purposes. Due to absence of blood vessels in the cornea, much of its oxygen requirement comes from atmospheric oxygen dissolved in the tear film. When the eyelids are closed, oxygen enters the cornea from the superficial conjunctival vessels. Nutrients needed for the cornea pass into it by diffusion. Hence, carbon dioxide and waste products are also removed across the tear film. Hence, any deficiency of the tear film will directly or indirectly affect the cornea.

What is Keratoconus?

Keratoconus (from Greek: kerato- horn, cornea; and konos cone), is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its ial distortion of visinormal gradual curve.

Keratoconus can cause substanton, with multiple images, streaking andsensitivity to light all often reported by the patient. It is typically diagnosed in the patient’sadolescent years and attains its most severe state in the twenties and thirties. If afflicting both eyes, the deterioration in vision can affect the patient’s ability to drive a car or read normal print. In most cases, corrective lenses are effective enough to allow the patient to continue to drive legally and likewise function normally. Further progression of the disease may require surgery including intrastromal corneal ring segments, corneal collagen cross-linking, or corneal transplantation. However, despite the disease’s unpredictable course, keratoconus can often be successfully managed with little or no impairment to the patient’squality of life.

Keratoconus is the most common dystrophy of the cornea, affecting around one person in a thousand. It seems to occur in populations throughout the world, although it occurs more frequently in certain ethnic groups. The exact cause of keratoconus is uncertain, but has been associated with detrimental enzyme activity within the cornea. A genetic link seems likely, as the incidence rate is greater if a family member has been diagnosed. The progression of keratoconus is rapid in patients having Down syndrome.

Signs and symptoms

People with early keratoconus typically notice a minor blurring of their vision and come to their clinician seeking corrective lenses for reading or driving. At early stages, the symptoms of keratoconus may be no different from those of any other refractive defect of the eye. As the disease progresses, vision deteriorates, sometimes rapidly. Visual acuity becomes impaired at all distances, and night vision is often quite poor. Some individuals have vision in one eye that is markedly worse than that in the other eye. The disease is often bilateral, though asymmetrical in many patients. Some develop photophobia (sensitivity to bright light), eye strain from squinting in order to read, oritching in the eye, but there is normally little or no sensation of pain.

The classic symptom of keratoconus is the perception of multiple ‘ghost’ images, known asmonocular polyopia. This effect is most clearly seen with a high contrast field, such as a point of light on a dark background. Instead of seeing just one point, a person with keratoconus sees many images of the point, spread out in a chaotic pattern. This pattern does not typically change from day to day, but over time it often takes on new forms. Patients also commonly notice streaking andflaring distortion around light sources. Some even notice the images moving relative to one another in time with their heart beat.

The predominant optical aberration of the eye as an optical system in keratoconus is the so-called coma.

A NEW PERMANENT NON SURGICAL TREATMENT: CORNEAL COLLAGEN CROSSLINKING WITH RIBOFLAVIN (C3-R)

So far there has been not one successful way to stop the progression of keratoconus. With current methods using rigid contact lens or intra corneal ring segments, only the refractive error (spectacle numbers) can be corrected, but it has very little 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. A new non surgical, non invasive treatment, based on collagen cross linking with Ultraviolet A (UVA, 365nm) and riboflavin (Vitamin B 2), a photosensitizing agent is now available. This changes the intrinsic biomechanical properties of the cornea, increasing its strength by almost 300%. This increase in corneal strength has shown to arrest the progression of keratoconus in numerous studies all over the world.

What is collagen cross-linking?

A new treatment for keratoconus which has shown great success is Corneal Collagen Crosslinking with Riboflavin (C3-R), a one-time application of riboflavin eye drops to the eye. The riboflavin, when activated by approximately 30 minutes illumination with UV-A light, augments the collagen cross-links within the stroma and so recovers some of the cornea’s mechanical strength. C3-R, developed at the Technische Universität Dresden, Germany has been shown to slow or arrest the progression of keratoconus, and in some cases even reverse it, particularly when applied in combination with intracorneal ring segments.

How is the treatment done?

The treatment is performed in our operation theatre under complete sterile conditions. Usually, only one eye is treated in one sitting. The treatment is performed under topical anesthesia (using anesthetic eye drops). The surface of the eye (cornea) is treated with application of Riboflavin eye drops for 30 minutes. The eye is then exposed to UVA light for 30 minutes. Hence, the treatment takes about an hour per eye. After the treatment, antibiotic eye drops are applied; a bandage contact lens may be applied, which will be removed by our doctor during the follow up visit. Protective eye wear, such as sunglasses (also given by us) is to be worn for a few days until complete healing takes place.

[read more=”Read More” less=”Read Less”]

ADVANTAGES OF CROSS LINKING

• Permanent
• imple- Single- one hour treatment
• No follow up sittings required
• No need for admission
• Stops the progress and causes regression of disease
• Does not need eye donation as in corneal transplant
• No major precautions
• No injections or stitches
• No incisions as in Intacs or Corneal ring segments
• Quick recovery with short follow up

Who can benefit from this treatment?

Collagen cross-linking treatment is not a cure for keratoconus, rather, it aims to slow or even halt the progression of the condition. This is important to understand. Patients may need to continue to wear spectacles or contact lenses (although a change in the prescription may be required) following the cross-linking treatment but it is hoped that it could limit further deterioration in the patient’s vision and reduce the case for keratoplasty.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.

How does Cross Linking arrest keratoconus?

Until recently, there was no method to change the integrity and strength of the cornea itself for keratoconus patients. The non-invasive treatment C3-R (corneal collagen cross-linking riboflavin) treatment has been proven to strengthen the weak corneal structure in keratoconus. This method works by increasing collagen cross-linking, which are the natural “anchors” within the cornea. These anchors are responsible for preventing the cornea from bulging out and becoming steep and irregular (which is the cause of keratoconus).

What are the risks and consequences involved?

• Very few potential risks associated with this treatment have been reported so far. The Ultraviolet light dose used is designed to prevent damage to the cells that line the back of the cornea or the other structures within the eye.
• No lens opacities (cataracts) have been attributed to this treatment in European trials. The treatment involves the outer layer (epithelium) of the cornea. There is therefore discomfort and a short-term haze.
  Other lesser but more common risks include:
• Inability to wear contact lenses for several weeks after the treatment
  Changes in corneal shape necessitates fitting of a contact lens or a occasional change in spectacle correction.
• As is the case with any treatment, there may also be long-term risks that have not yet been identified.
• The increased corneal rigidity induced may wear off over time and further periodic treatments may be required

[/read]