Cornea is the first coat of eye which is transparent circular structure. Functionally it acts as a lens responsible for focusing rays inside the eye. It is an important optical structure through which rays of light enter the eye. Any damage or injury to this delicate structure can lead to permanent loss of corneal transparency or in other words cause clouding and opacification.
Loss of corneal transparency prevents the entry of light rays into the eye and reduces vision. In cases of severe of damage, this can cause total loss of vision making the person visually handicapped. There are other conditions also such as malnutrition, Vitamin A deficiency, infection, certain corneal diseases such as ‘keratoconus’ and ‘corneal degeneration’, which can cause corneal blindness.
Corneal disease is third largest cause of blindness or low vision in Indian population. Corneal disorders encompass a wide spectrum of diseases most common of these are pterygium, Keratoconus, corneal dystrophy, corneal tears, corneal oedema, infective keratitis, contact lens related keratitis, allergic keratoconjunctivitis, each of these diseases need methodical approach and specialized care.
Pterygium
Pterygium is a veil like lesion that usually occurs in exposed part of white of the eye. This grows slowly over the cornea (the central black portion) and can obstruct vision or deteriorate vision by inducing cylindrical power.
Symptoms of pterygium may include:
Burning
Gritty feeling
Itching
Sensation of a foreign body in the eye
Blurred vision
Causes of Pterygium : significant risk factors include:
Prolonged exposure to ultraviolet light
Dry eye
Irritants such as dust and wind
Treatment of Pterygium
Pterygium is not only cosmetically disfiguring but can affect the vision also. In view of this it is advisable to surgically excise it at the earliest. Surgical excision of pterygium is a simple day care procedure with no adverse effects.
Latest surgery method involves removing the pterygium tissue and placing a healthy tissue on bare area which prevents recurrence and is cosmetically very rewarding.
Surgery for pterygium is minimally invasive, sutureless and is very safe.
Pterygium does not respond to medical treatment of any kind be it in form of eye drops or ointment and surgical excision is the treatment of choice.
Keratoconus
It is a progressive disease of the outer transparent layer of the eyeball (cornea) affecting young adults mostly in their twenties. It is characterized by progressive thinning of the normally round cornea causing it to bulge forward & assume a cone like shape. This irregularity in the cornea results in the formation of a distorted image of objects on the retina & gives rise to blurred vision.
Symptoms & signs of Keratoconus
Keratoconus causes myopia or nearsightedness & astigmatism.
Frequent change in glasses prescription with fluctuation in vision.
Glare & sensitivity to light especially during night.
In advanced stage of Keratoconus corrective prescription glasses do not help patient to see clearly & they have to switch to using hard or semi-soft contact lenses.
Keratoconus can be diagnosed at an early stage with detailed eye examination which includes Retinoscopy,
Slit lamp examination & sophisticated tests like Topography to check the shape & curvature of cornea & Pachymetry to determine the thickness of the cornea.
Causes
Exact causes of Keratoconus is not known but latest research suggests that the cornea becomes weakened due to an imbalance of enzymes within the corneal tissue. Young patients produce high levels of free radicals which cause oxidative damage to the cornea in absence of protective enzymes causing thinning & bulging of the cornea.
Keratoconus also shows some genetic predisposition. It may transmit from parent to children & affect more than one family member. It is also associated with excessive rubbing as it is more common in allergic conjunctivitis patients who have itching & tend to rub their eyes more frequently.
Other risk factors are overexposure to ultra violet rays, chronic eye irritation & improperly fitting contact lenses.
Treatment Options
In early stages, when the cornea is still regular, corrective prescription glasses or soft contact lenses can help the patient. As keratoconus advances, the corneal surface becomes increasingly irregular & these options do not help adequately. In intermediate & advanced stage, various other treatment options & different types of contact lenses are available.
Rigid Gas permeable contact lenses : provide a smooth refractive surface replacing the irregular cone like surface of the cornea, thus enabling the patient to see clearly. Lens fitting in Keratoconus can be demanding & time consuming process. RGP lenses are not as comfortable as soft contact lenses.
Piggybacking Contact Lenses : a soft contact lens is first placed on cornea to give it a cushion like effect & RGP lens is fitted over it. Best features of both lenses are combined – makes the wearer comfortable & at the same time gives crisp & clear vision. The fitting should be perfect to ensure good oxygen permeability to the cornea as the patient will be wearing two lenses. However, with newer high oxygen permeable lenses this is not a problem.
Hybrid Contact lenses : uniquely designed wherein the central visual portion is made up of high oxygen permeable rigid material & peripheral anchoring portion is of soft hydrogel material. Maximizes the best features of both lenses & improves wearers comfort as well as visual performance in keratoconic eyes.
