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Summer 2006 newsletter

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Inside this Issue

Summary of talk by Stephen Tuft, Consultant Opthalmologist, Moorfields’ 25 March 2006

Keratoconus: Treatment, Complications and Genetics

KC is the commonest corneal dystrophy (abnormality of the cornea) affecting around 1 in 2000 of the population in the UK. It is thought to be genetically determined, but there may be environmental factors as well, such as allergies and eye rubbing. Prevalence of KC is 4 times higher in Asian populations.

KC results in thinning of the cornea and ectasia (a change in the curvature) although some people get thinning without ectasia. KC has different forms including central cones, saggy cones, thinning at the edge of the cornea for which scleral lenses are usually used, and keratoglobus, where the whole cornea is affected, and again scleral lenses are usually used. KC affects the alignment of collagen fibres. Enzymes cause breakages in the links between fibres, which slip apart.

There are some newer treatments for KC. Intacs may be useful for people with early KC and not appropriate for moderate or advanced KC. Collagen cross-linking (C3-R) involves locking the collagen fibrils together with riboflavin and using UV light as a bonding agent. Early results of this treatment look promising, and Moorfields has applied for ethical approval to begin trials of C3-R.

Complications

  • Hydrops (rupturing of the back surface of the cornea) affects about 2% of eyes in contact lens clinics. The resulting waterlogging affects the natural defences of the eye so there is a higher risk of infection. Hydrops can also stimulate growth of blood vessels into the cornea. But, it can also sometimes improve the shape of the cornea when it shrinks as the waterlogging goes down.
Corneal scarring – a study is currently being done to
  • investigate whether fitting contact lenses with a ‘3 point touch’ (edges and centre), has any effect on corneal scarring. However, scarring occurs in people with KC who have never worn contact lenses, so scarring looks like a natural feature of KC
  • Corneal ‘pips’ – laser can be used to smooth these out.

A review of 2600 patients with KC over 25yrs showed 675 out of 52000 eyes needing transplant surgery (13%). Progression of KC varied between different racial groups – Afro-Caribbeans were most likely to need transplant surgery, followed by Asians and West Africans, with Caucasians having the lowest rate.

8% of patients know an affected relative (but this varies in different parts of the world eg 19% in Finland). Random testing of siblings and parents showed ‘forme fruste’ KC (extremely mild, subclinical KC) in around 50%.

The Moorfield’s genetic study involves 169 families identified so far with inherited KC and 10 pairs of twins. Within that, only a few families have a number of affected members. And in most families, KC appears in one or two generations and then peters out.

Genetic studies around the world have so far all identified different chromosomes. So unlike single gene disorders, such as cystic fibrosis, it looks as though KC is a multi-gene disorder, so that it will only occur if all the relevant genes are present. The Moorfields study is ongoing and new micro-array analysis (which splits a person’s DNA into 10,000 sites of activity) will enable the investigations to be refined.

Mr Tuft is still looking for more families where several members have KC and is especially interested in pairs of siblings. More funding is also needed for the study.

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