KERATOCONUS

What is keratoconus?

It is a developmental anomaly in which the central portion
of the cornea becomes thinner and bulges forward
in a cone-shaped fashion.
Two types of cones are commonly described:
a round cone and an oval (or sagging) cone.

It usually starts around puberty, is noninflammatory, progressive, bilateral, although one eye may be involved long before the other. 

The main symptom is a loss of visual acuity due to irregular astigmatism and myopia. 
Optimal corneal optics require a smooth regular surface.
This disease is encountered in about 1 person out of 2000.
The origin is still unknown but is hereditary.

The condition is one of abnormal elasticity: this condition is being measured by the ORA the instrument in our consultation. 

Frequent eye rubbers as in allergy are more prone to develop keratoconus.  Apart from instructing patients to avoid eye rubbing, there is little to influence its natural progression.The disease consists in a weakening of the rigidity of the cornea which leads to diminished vision.


What can be done?

Eyeglasses - Contact lenses - CCL - Intracorneal ring segments - Lamellar or penetrating keratoplasty

Contact lenses
Keratoconus is managed by many different contact lens designs.  No one design is best for every type of keratoconus. Since each lens design has its own unique characteristics, the ophthalmologist carefully evaluates the needs of the individual situation to find the lens that offers the best combination of visual acuity, comfort and corneal health.

A diagnostic instrument for contact lens fitting is rapidly gaining popularity: the corneal topographer. This is the machine where you are asked to place your chin in a chinrest, forehead against a headrest, and calmly stare at a red light while a whorl of illuminated concentric rings is brought very close to your eye. A reflection is formed in the cornea as if it were a mirror. If the corneal surface is smooth and regular, the reflected lines are circular and equally spaced. When the corneal surface has abrupt changes in elevation and curvature, as in keratoconus, the lines become irregular and distorted.

The keratometer, which for years has been used to measure the central corneal curvature, uses the same reflecting principle but has only one illuminated ring. Corneal topographers use numerous rings, supplying information about the corneal surface from center to edge. This expanded information is especially useful in keratoconus, because the cone is often displaced from the center of the eye.

Computers can simulate how the back surface of the contact lens might follow the front surface of the cornea, but many more variables affect how a lens actually fits. Patients have different blink rates, lid tension, tear composition, and lens powers. Skilled contact lens technicians know lenses must position properly between blinks, move just the right amount during blinks, provide crisp vision and be comfortable to boot. To achieve success in all these categories, fitters must ultimately watch the lens perform in its dynamic natural environment - on the eye, not on a computer monitor.

Intracorneal ring segments ICRS

These ring segments regularize the front surface of the cornea by building tissue in the midperiphery and maintaining the biomechanical condition within the underlying stroma. 

In studies and our own experience on ICRS implantation have shown more than two line of improvement in visual acuity on average. The inhibiting effect of ICRS on keratoconus progression is still unclear, however, the addition of CCL minimizes the progression.


Procedure:

under topical anesthesia a curved glide creates a channel in the periphery of the cornea by gently separating the tissue layers. One or two tiny plastic segments  are placed in the channel much like placing a pencil in between the pages of a book.

Lamellar or penetrating keratoplasty
In keratoconus, a corneal transplant is warranted when the cornea becomes dangerously thin or when sufficient visual acuity to meet the individual’s needs can no longer be achieved by contact lenses due to steepening of the cornea, scaring or lens intolerance.

Lens intolerance occurs when the steepened, irregular cornea can no longer be fitted with a contact lens, or the patient cannot tolerate the lens.