Q. What is Keratoconus? (Kconus)
A. Keratoconus is that condition of the cornea, in which the cross section of the cornea assumes a more conical shape, compared to the near spherical cross section of the normal cornea. The cornea, incidentally, is the clear transparent structure which sits like a dome over the coloured portion of the eye, much like the glass in front of a wrist-watch.
Q. Is Kconus present from birth?
A. No, it usually manifests during the late teens or in the twenties, though it is thought to be due to genetic causes.
Q. How is it suspected by a patient, in the early stages?
A. If the patient is unhappy with the quality of vision with his spectacles, but feels he sees better with a hard contact lens, he needs to be tested for Keratoconus.
Q. What are the tests for Kconus?
A. Until recently, clinical suspicion by the ophthalmologist was the most important. After all, the eye does not see what the mind does not know! He then did a Retinoscopy, or reflected a beam of light into the patient’s eye from a distance of one meter. In Kconus, he often found a characteristic “scissors” image being reflected back. You do not need to know more details of this test! He then subjected the patient’s cornea to slit lamp bio microscopy, where he examined the cornea under high magnification, where early change of shape could be picked up.
However, in modern times, there are machines called corneal topographers which document precisely the contour of the cornea, much like terrain mapping tests in geography. They even issue a warning, telling the eye surgeon that the patient being tested is a “Kconus suspect”. In late cases, the cornea thins near the steepest part of the cone. We now have instruments called pachymeters, which measure the thickness of the cornea at various zones of the cornea. An area of unusual thinning would arouse suspicion of Keratoconus.
Q. Are all Kconus cases progressive?
A. Good question. No, only around a quarter (25% for those who are mathematically challenged!) of cases will progress. The progress is usually very slow, over years. In those who also suffer from allergic conjunctivitis (a common association) or frequent “eye rubbers” the rate of progression may be faster.
Q. What is the worst case scenario? Can my cornea “burst’?
A. In a small percentage of progressive cases, the inner layers of the cornea can give way – a condition called “hydrops”. The cornea becomes steamy, opaque as it accumulates water. This condition is usually self-limiting – the imbibed water disappears and the vision can even improve over time.
Q. I have been diagnosed as Kconus am unhappy with my spectacles. What next?
A. The answer, in 2 words, is contact lenses. There are several options in contact lens wear for Kconus. Let your doctor decide which is best for you, after trials. You may wear ‘hard’ contact lenses, which are the smallest contact lenses, sitting only on the cornea. The other lenses are the RGP (rigid-gas permeable) or ‘semi-soft’ contact lenses, which allow oxygen to enter the cornea through the lens. These are larger in size. Sometimes, your doctor may prescribe ‘piggy-back’ lenses, i.e. a soft contact lens, which is large and sits snugly over the conical cornea and is comfortable, over which you wear a hard or RGP lens, to improve vision. There are special large lenses designed for Keratoconus, called “Rose K2 lenses” after their inventor, Dr. Rose (nothing to do with the flower by the same name!)The last option, which is horrendously expensive (around Rs.90, 000/- for a single lens and Rs.140, 000/- for a pair, in 2010) is the Scleral Lens. The technical name for these is Scleral Lens Prosthetic Device or SLPD; the measurements for each patient are taken and the lenses are custom made and dispensed. These lenses are very large, sit over the white portion of the eye, and are shaped somewhat like tea saucers. In the deepest part the lens, a fluid is filled. The lens then sits on the eyeball, without touching the cone. The cone is always bathed in fluid, so there is both comfort and excellent vision. These lenses are long lasting and do not need frequent replacements.
Q. What is the C3R procedure for Keratoconus?
A. You are remarkably well informed. About a decade ago, in Germany, eye surgeons began experimenting with a procedure called “Collagen Cross linking of Cornea, using Riboflavin (hence the term C3R…get it?) and a special ultraviolet light. The cornea is largely composed of fibres called collagen, which are interlinked with one other to give the cornea strength and allow it to retain its shape. In Kconus, the cross linking between groups of collagen fibres is reduced, causing the cornea to stretch forward in response to the normal pressure from within the eye – (Intra-ocular pressure), thus worsening the cone. It was discovered that a combination of Ultraviolet-A light and Riboflavin (a component of B complex vitamin) could cause the collagen fibres to bond to each other tighter, thus preventing the cone form progressing. The actual procedure is simple. Riboflavin drops are instilled onto the cornea surface, at intervals of every few minutes for 20 to 30 minutes, usually after scraping off the top layer, called the epithelium. Then, the ultraviolet rays are focussed onto the cornea, using a special lamp for about 30 minutes. The eye can be bandaged or a bandage contact lens inserted for a few days till the epithelium grows back. This procedure has a caveat however; the corneal thickness has to be a minimum of 400 microns, to prevent UV damage to the innermost layer of the cornea, the endothelium. Hence it cannot be done in advanced Kconus, where the cornea is already considerably thinned. The remarkable thing about this procedure, which has completed 5 years in patient treatment, is there have been hardly any cases showing progression of Kconus after the treatment and in some cases, there has been actual reversal with reduction in the spectacle number and astigmatism! Incidentally this procedure is also called CXL (short for collagen cross linking)
Q. I do not wish to wear CL/cannot tolerate any CL/cannot afford the SLPD. My cornea is too thin to do C3R.Are there no surgical remedies? What about INTACS?
A. Yes, there are a host of surgical remedies. A few centres in India are using tiny plastic bands inserted into the periphery of the cornea, through a minor surgery. This causes the periphery of the cornea to stretch outward, thus flattening the cone. These plastic pieces are known as INTACS (Intra-stromal corneal segments). The upside is that it is a reversible procedure; the segments can always be removed. The downside is that it is not a very predictable procedure – one cannot estimate exactly how much correction will ensue, though there are some formulae which work as guidelines. The INTACS pieces are also currently not exactly cheap!
Q. Can we not do a corneal transplant?
A. We most certainly can. Corneal transplant or keratoplasty done for Kconus is very successful, with over 90% grafts remaining clear at 5 years. The traditional transplant is still penetrating keratoplasty or PK, where the entire thickness of the cornea (in the central 7-8mm zone), i.e. all its layers are transplanted i.e. replaced by a similar or slightly larger disc of donor cornea which also contains all the layers. In India, this is how a vast majority of corneal transplants are done for Kconus. However, increasingly, Indian eye surgeons are doing a procedure called DALK or deep anterior lamellar keratoplasty. The innermost layer or endothelium of the patient’s cornea is quite healthy in Kconus and need not be sacrificed. Hence, in DALK, this layer is left behind. The donor cornea minus the donor corneal endothelium is transplanted. The procedure does have a learning curve, being technically a little more demanding. However, DALK leads to even less chances of graft rejection than PK and the recovery period is often reduced. Visual results are almost at par with PK.
For more details on corneal transplants, readers are invited to read the chapter on the subject elsewhere in the book.