Posted on December 8, 2017
Keratoconus (Greek: kerato: Cornea; konos: Cone) is a progressive disease of the eye in which the normally dome shaped cornea becomes thinner and begins to bulge into a cone-like shape. This conical shape results in an irregular refraction of light as it enters the, causing distortion of vision. Keratoconus usually affects both eyes, but can be asymmetrical. It often begins during the late teenage or early 20s.
The clinical spectrum of Keratoconus spans from very mild (subclinical) forme fruste keratoconus which has no symptoms, and is only picked up on screening, to very severe disease where the distortion of vision cannot be corrected by glasses or contact lenses.
Forme fruste is usually detected when a corneal topography is performed for these patients as part of a LASIK or refractive surgery work up. LASIK , PRK and SMILE are all contraindicated in these patients because these surgeries carry a high risk of converting the mild subclinical condition into full blown progressive ectasia/keratoconus.
ICL surgery is a safer and more effective option for these patients in case they want to avoid glasses or contact lenses, since ICL surgery does not involve removing a part of the corneal tissue to correct the refractive error unlike conventional laser surgery.
The Implantable Collamer Lenses, ICLs are very thin lenses that are placed inside the eye, between the iris and the natural lens of the eye, similar in function to contact lenses, since they are invisible to the naked eye, and allow perfect vision without glasses by correcting the refractive error. However, unlike a contact lens, ICL implantation is a permanent solution for refractive errors. ICL surgery, unlike LASIK, can be completely reversed by a simple surgical procedure, which makes the surgery ideal as any change in the refractive correction of the eye over time can be dealt with safely and effectively.
The toric implantable collamer lens (TICL) is conventionally indicated for the correction of myopia in adults aged 21-40 years with myopia ranging from −3.0 to 23.0 diopters (D) and up to 6 D of astigmatism at the spectacle plane, and can provide a better change of better vision without glasses or contact lenses to these patients.
The other subgroup of keratoconus patients who can benefit greatly from ICL surgery are those who obtain good vision with glasses, and in whom that disease is stable and has stopped progressing, Toric implantable lenses can reduce the need for glasses, and often eliminate the need for optical aids. Once the disease has stabilized, that is, there is no change in the refraction in the eye or the power of glasses, with no surgical intervention for 2 years, Toric ICLs can actually offer these patients a better quality of life.. Eyes having riboflavin-ultraviolet-A collagen cross linking (CXL or C3R) tend to have a fluctuation in refraction in the initial post treatment. After the refraction stabilizes, these patients may be offered ICL surgery. Similarly, in patients with an off centre cone, the surgeon may first offer the use of adjunct intracorneal ring segments (ICRS) to centralise the cone. Once the keratoconus is stabilized, better sight without glasses may be offered by the use of ICL.
However, there are three major caveats to this:
- The visual results obtained after ICL surgery in severe keratoconus are less predictable than in patients without keratoconus (that is, regular myopic astigmatism).
- The vision obtained with the use of Toric ICL in severe keratocnus is same as the best corrected vision with glasses or soft contact lenses. It is believed that keratoconus associated corneal aberrations would have an impact on the final visual quality.
- Before considering a keratoconus patient for ICL surgery, the surgeon must establish that the refractive status of the eye has been stable for atleast two years, In addition to that, the central cornea must be clear, with a keratometry reading of ≤52.00 D and a central or centralized cone.
The use of ICLs for correcting the refractive error in keratoconus is an off label use of the lens, even though it is widely practiced and accepted by both patients and ophthalmologists all over the world. Keratoconus patients unfit for corneal procedures and intolerant to refractive correction by spectacles or contact lenses have benefited greatly from toric ICL implantation alone or as an adjunct with other surgical procedures to correct the refractive errors associated with keratoconus after a special informed consent from the patients.