Keratoconus or conical cornea is a thinning and distortion of the central zone of the cornea, which is the clear dome front surface of the eye. Keratoconus usually becomes apparent between the ages of 10 and 25. It is often associated with allergies, infantile eczema and asthma. The initial symptoms of keratoconus are blurred vision and reduced night vision. This is caused by the cornea changing shape as it bulges forwards.
Keratoconus is an inherited disorder that occurs in about one in 3000 people. It is a recessive condition requiring genetic factors to be inherited from both parents, so the chances of the children of a person with keratoconus also having the condition are low at around one in 50. The cornea thins centrally and due to weak protein adherence, bulges forwards from the underlying internal eye pressure. This causes distortion and unevenness of the corneal surface which blurs light as it passes into the eye, resulting in blurred vision.
Your Envision Optical optometrist will usually detect keratoconus as part of our routine comprehensive examination. A decrease in vision will indicate performing digital corneal topography measurement, which maps the exact shape and curvature of the cornea. This will indicate the areas of steepening and distortion. These topography maps will be performed at each visit to accurately review for any progression of the keratoconus. No Medicare item currently exists for corneal topography so a private fee of $40 applies.
In its early stages, keratoconus manifests as astigmatism and myopia and the blurred vision is corrected with spectacles. As it progresses the corneal shape becomes irregular and spectacles will not give clear vision. At this point, your Envision optometrists will fit specialized rigid contact lenses which will provide clear vision. These specialized lenses sit over the distorted eye surface and provide a new, regular shaped smooth focusing surface at the front of the eye, eliminating the distortions caused by the keratoconus.
Regular visits will be required to ensure the lenses fit and perform optimally. Due to the progressive nature of keratoconus, regular six monthly checks are recommended to closely monitor the condition and to ensure the contact lenses are performing correctly and corneal health is optimized.
In about 85% of keratoconus, the condition gradually stabilizes by 35 years of age. In the remaining cases, the condition progresses and vision and tolerance to contact lenses may deteriorate.
For the progressive severe patient, modern treatment will indicate a referral to a corneal specialist for consideration of collagen cross-linking therapy. This treatment uses a combination of riboflavin drops and exposure to UV light to “set” the cornea and help prevent further deterioration. In severe progressive cases where vision deteriorates, a corneal graft operation may be required.
This operation is where the area of thinned cornea is removed and replaced by normal corneal tissue transplanted from a donor cornea. Corneal transplant is only done as a last resort to provide good vision. The success rate for corneal grafts is very high, and good vision can be restored in combination with glasses or specialised contact lenses.