Eye Care

Fitting Keratoconus

Keratoconus is a bilateral non-inflammatory corneal ectasia with an incidence of approximately 1 per 2,000 in the general population (1). The treatment of Keratoconus can be implemented by the use of spectacle lenses, contact lenses of various kinds and surgery.

In more advance Keratoconus cases where severe irregular astigmatism with resultant higher order aberrations are present, the use of Rigid Gas Permeable (RGP) lenses are indicated to restore the patients vision.  Unfortunately in some Keratoconus cases, contact lens intolerance develops and many patients consider Penetrating Keratoplasty (cornel graft). Lim, et al found that 83% of patients opting for Penetrating Keratoplasty was due to intolerance to contact lens wear (2).

However, Smiddy, et al found that 87% of the Keratoconus cases referred for Penetrating Keratoplasty to the Wilmer Institute at the Johns Hopkins Medical Institution could be successfully refitted with contact lenses.  Of the successfully fitted cases ultimately 31% needed keratoplasty after an average of 38.4 months of lens wear and 69% did not require Keratoplasty over an average follow-up interval of 63 months of wearing contact lenses.

Of the postoperative penetrating Keratoplasty eyes 60% had to wear contact lenses for best vision. Their conclusion was that Penetrating Keratoplasty can be delayed or avoided in many Keratoconus patients by using proper fitting contact lenses and further that Keratoconus eyes often need contact lenses after Keratoplasty (3).

Piggyback system

One option to improving the comfort of RGP lenses on Keratoconic and irregular corneas is to use a piggyback system. A piggyback system comprises of a soft contact lens first placed on the cornea and then followed by a RGP lens fitted on top of the soft lens.  With the birth of Silicone Hydrogel soft lenses and hyper DK RGP materials, piggyback systems have become a safe and viable option for vision correction of the compromised cornea. Tsubota, et al found that the oxygen pressure under piggybacked oxygen-permeable hard contact lenses was 95 +/- 14 mmHg after 5 minutes wear which was almost three times higher than the 34 +/- 14 mmHg when PMMA and low water-content lenses were used (4). Clare O'Donnell first reported on the fitting of a hyper-Dk piggyback contact lens system in Keratoconus and other irregular corneas in 2004 (5).

“Don’t rub your eyes!” your mother used to say. “It’s not good for you”. But then who ever listened to their mother? It seems that in recent years, science have caught up with our mothers’ wisdom and a number of research papers are now clearly proving that rubbing your eyes can in fact damage your eye’s corneal health.

In our own practice we have seen many cases of keratoconus and healthy corneas distorted due to vigorous rubbing of the eye. The picture below shows the topography of an otherwise normal cornea that is chronically rubbed at the 6 o’clock position. The patient had best corrected vision of about 6/75 (20/25) at the time. Once her allergies were managed and she stopped rubbing the cornea her vision returned back to a normal 6/6 (20/20) after about 2 months.

Back in 1976, Karseras and Ruben wrote in their paper on the aetiology of Keratoconus that most keratoconus patients rub their eyes excessively. Eye-rubbing is considered the dominant aetiological factor in two-thirds of patients with keratoconus who progress to contact lens wear. Charles McMonnies in 2007 seemed to agree that abnormal rubbing may increase the likelihood of the development of some forms of keratoconus. He postulated that when vigorous knuckle-rubbing forces are located on the normal peripheral cornea, the thinner or weakened cone apex may be exposed to high intraocular pressure distending forces that may tend to promote ectasia.

Most recently Dr Alan Carlson wrote a comprehensive article on the dangers of rubbing the eye in patients with Keratoconus and post-LASIK:

Eye care has seen a massive explosion of new diagnostic instruments and treatment procedures in the last number of years.  From instruments like the front and back chamber OCTs, Oculus Pentacam and Zeiss GDx to procedures like Intra ocular injections to halt the progression of previously untreatable wet macular degeneration, 30 days continues wear silicone soft contact lenses, Orthokeratology and also Corneal Collagen Cross-linking (CxL).

People who have Keratoconus are particular excited about the possibility of having Corneal Cross-linking done to their eyes in the hope of improving their sight.  It is however very important to stress that CxL is not a cure for keratoconus.  The main function of the procedure is only to halt the progression of the ectasia (bulge or cone on the cornea).  A couple of months after the procedure some flattening of the cone can occur, but this is not significant enough for the keratoconus patient to have normal sight without the use of other optical devices like Rigid Gas Permeable contact lenses.

For this reason it is not a necessity for all Keratoconus patients to have the Corneal Collagen Cross-linking procedure.  The keratoconus group that will benefit the most from CxL is the ones who develop keratoconus at a young age, normally between the ages of 16 to 28, and show quick thinning and progression of the keratoconus cone. 

Corneal collagen Cross-linking has been available in South Africa for a while but has only recently become available in the United States and Drs James Owen and William Tullo wrote a comprehensive article about CxL for the August edition of the US based Contact Lens Spectrum titled:

A Closer Look at Corneal Cross-Linking

The first treatment to halt the progression of corneal ectasia may soon be available in the United States. Although corneal collagen cross-linking (CXL) is currently available in most countries around the world, the majority of patients in the United States who have keratoconus must wait to access this technology. This procedure is exciting because it will allow for successful contact lens fitting of patients who might otherwise become contact lens intolerant.

At the end of the month I'm flying to Orlando, USA to lecture at the Vision by Design Congress 2011 on the use of Orthokeratology to rehabilitate Post LASIK and Keratoconic corneas. 

My two boys are now at the age where all of their questions contain the words 'Why' or 'How' and so the conversation came to "Why am I going" and "How am I going to get there?”  The second question got us on to the topic of Airplanes and after many, many more Why's and How's my available reserve of answers ran out long before there were any visible sign of their never ending barrage of questions slowing down.  This forced me to do what any self-respecting parent will do under these circumstances. Stall.  Easily achieved by telling them to go clean their rooms and secretly dashing off to consult the guru of all knowledge. 

The Google Search Box.

After many "Go clean your Rooms!" I finally managed to compile some really interesting facts about Aviation which I thought will be interesting enough to share with everyone.  So if there is still a 4 or 5 year old lurking inside you dying to ask the question 'Why' or 'How', this is for you:

Intrastromal rings or Intacs broke into the ophthalmic market with a big bang and was hailed as a savior surgical procedure for Keratoconus patients.  The idea is to implant two semi circular rings into the tissue of the cornea on opposite sides of the keratoconus ectasia (protrusion of corneal tissue).  The mechanical effect of the Intact rings is to stretch the corneal tissue and in the process flatten the ectasia point of the Keratoconus.

Unfortunately the surgery outcome of the Intrastromal rings hasn't been as good as expected and very few patients achieve normal functional sight after the procedure.  Another complication is post op infections of the procedure as highlighted on this case study.

A 20-year-old woman presented with photophobia, decreased vision, and pain 11 days after uncomplicated implantation of intrastromal corneal ring segments (ICRSs) for keratoconus in both eyes. Bilateral corneal stromal infiltrates were noted at the site of ICRSs implantation. The patient was started on frequent topical fortified antibiotics in both eyes. Despite aggressive medical management, stromal infiltrates progressed, necessitating removal of ICRSs from both corneas to control infectious keratitis and melting of cornea.

Cultures obtained at the time of initial presentation yielded Streptococcus viridans. Patient responded well to the treatment and was left with stromal scars in both corneas.