Keratoconus

What Is Keratoconus?

Keratoconus is a disease of the cornea. The cornea is the transparent 'front window' of the eye. A normal cornea has a smooth curved surface analogous to the shape of a tennis ball. The cornea is important because it is the main focusing structure of the eye and so any change in its shape will reduce vision. In keratoconus the surface of the cornea is distorted by the presence of a protrusion shaped somewhat like a volcano. The protrusion is microscopic being only fractions of a mm high. It cannot be felt and can only occasionally be seen by the naked eye.

Normal cornea (left) is smoothly curved Keratoconus cornea (right) is distorted by a volcano-like bulge

Symptoms

Keratoconus usually begins in young patients ie from the late teens to the 30s. It affects men and women equally. One or both eyes may be affected. It may begin in one eye and later involve the other. The main symptom is reduced vision. If the distortion of the cornea's shape worsens with time so will the vision. This happens in some patients although in many the condition stabilises. It is not possible to predict whether keratoconus will be progressive or at what rate it will worsen.

A few patients also have glare when driving at night or on a sunny day. In advanced cases 'hydrops' can occur. This is the sudden onset of discomfort, redness and reduced vision caused by the formation of small split in the cornea. This usually clears up after a few weeks but can cause permanent cornea scarring. A 'proud nebula' is a small white scar located at the tip of the keratoconus protrusion. It may cause additional reduced vision and glare and also discomfort when wearing contact lenses (see treatment below).

Scar has formed on this keratoconus
cornea due to 'hydrops' (arrow)

Cause

The cause is unknown. It is not usually a familial condition. A few patients with severe asthma or excema develop keratoconus. Keratoconus is not caused by anything the patient has done and will not be improved by any change in lifestyle or diet.

Diagnosis

This requires specialist equipment. The slit lamp microscope used by an ophthalmologist shows up the protrusion on the cornea surface. The corneal topographer makes a map of the cornea surface and accurately identifies the keratoconic protrusion. Retinoscopes and keratometers are devices used to measure the eyes when prescribing glasses and contact lenses. In keratoconus they both show abnormal readings.

Topography of normal cornea (left) shows
green and yellow colour in the centre
Contrast with the keratoconus cornea (right) where
the volcano-like protrusion shows a red colour

Treatment

Below is my treatment schedule for keratoconus. It looks complicated but is in fact straightforward. The steps are explained below.

KERATOCONUS TREATMENT
Keratoconus mild and not getting worse Contact Lenses	Keratoconus advanced and / or getting worse. Contact lenses not wearable. Cornea not scarred INTACS implants	'Proud Nebula' on cornea Remove	Keratoconus extremely advanced. Cornea scarred and / or shape grossly distorted Cornea Transplant
	Vision still not clear enough.
	Phakic Intraolocular Lens implant and / or Lasek (Excimer laser)

LIFESTYLE. Remember that keratoconus is not caused by anything that you have done and will not be improved by any change in lifestyle or diet.

CONTACT LENSES. The main treatment for keratoconus is to wear a contact lens on the keratoconic eye. This does not change the keratoconus at all, it simply covers the protrusion on the cornea so neutralising it. Normal vision is restored to all except advanced cases by wearing a contact lens. It is usually necessary to wear a rigid gas permeable (hard) contact lens although it is sometimes possible to wear special types of soft lenses (eg: Softperm) instead.

INTACS IMPLANTS. This is an exciting new treatment for keratoconus. Intacs implants have been used for about a decade to treat eyes that are myopic (short sighted) but otherwise normal. A few years ago it was realised that, by modifying the technique they could also be used to treat keratoconus.

In 2000 I became one of the first eye surgeons in the United Kingdom to use intacs, initially for patients who were myopic but whose eyes were otherwise normal. I have been using it to treat patients with keratoconus since 2002.

Intacs consist of two tiny pieces of plastic which are inserted into a channel created within the cornea. They cannot be felt, are permanent (unless you choose to have them removed – see below) and require no care or maintenance at all. They are normally invisible except on very close inspection when they look like a contact lens on the eye.

The implants work by gently stretching the cornea, so reducing the abnormal protrusion on its surface. This in turn improves the patient’s vision. Improvement varies between patients. Some see perfectly and no longer need glasses or contact lenses, some see well with glasses and can abandon contact lens wear, some continue to depend on contact lenses but see better than before whilst wearing them and a minority get no improvement. Some patients who have improved vision after intacs implants but who still are dependent on glasses or contact lenses can be improved by further surgery (see ‘Phakic Intraocular Lenses and Lasek’ below).

Recently, great interest has been generated by the realisation that intacs inserts can sometimes prevent the progression of keratoconus. Our understanding of this exciting possibility is still early, but should it turn out to be correct, intacs may offer the possibility of a cure for keratoconus.

Another advantage of this technique is that it is reversible ie: the implants can be removed (by the doctor – this requires a minor procedure) and the eye then returns to its previous state. No part of the cornea is removed during insertion ie: the technique is ‘additive’ rather than
‘subtractive’. Although it is unlikely that this will be necessary there are occasions when reversibility might be helpful, for example if the patient’s vision correction needs change with age or if new technologies for treating keratoconus become available.

The two tiny Intacs implants rest on a fingertip

Photo of Intacs after insertion

PROUD NEBULAE. These can be removed surgically. This is well worth doing as it often improves vision and contact lens comfort.

A 'proud nebula' is seen as a white scar on this keratoconus cornea (left) The same image at high magnification is on the right
Keratoconus cornea after removal of proud nebula Only a faint impression of the scar remains (arrow)

PHAKIC INTRAOCULAR LENSES AND LASEK (EXCIMER LASER SURGERY). Further surgery may be helpful after intacs implantation has reduced the abnormality in cornea shape. For example there may be residual myopia (short sightedness) and/or astigmatism. These focusing abnormalities can be corrected by a Phakic Intraocular Lens such as the Artisan. This is a tiny focusing lens which is inserted into the eye through a keyhole incision. Once inserted it is held permanently in place on the iris (coloured part) of the eye by special attachments. It works together with the eye’s natural lens which is not removed. It is capable of correcting even the most severe short sight/astigmatism. However it will not work in keratoconus until intacs have been implanted into the cornea. Lasek (Excimer laser surgery), is a commonly performed procedure to treat short and long sight. Unfortunately only very small corrections can be made by this technique on a keratoconic cornea, but these can be useful to put the ‘finishing touches’ to any residual focusing error after intacs and phakic intraocular lenses. In particular Wavefront Lasek, which removes only very small quantities of corneal tissue, can be helpful in sharpening the patient’s vision.

CORNEA TRANSPLANTATION. Traditionally this has meant the complete removal of a circular disc of tissue from the centre of the patient’s own cornea and its replacement by a transplant, obtained from a deceased person, which is sutured (stitched) into place. In essence the patient’s diseased cornea is removed and replaced by a normal cornea.

This technique is usually successful but complications can occur. These include rejection of the foreign tissue by the patient’s immune system, wearing out of the transplant after many years and astigmatism (a highly uneven corneal shape, post-operatively) which necessitates the wearing of gas permeable contact lenses to see clearly.

N.B. These illustrations of full thickness replacement/transplantation of the cornea (‘penetrating keratoplasty’) should be taken as a general guide to the surgery, rather than an exact description

in health, the cornea is perfectly clear

this technique is suitable when disease extends through the full thickness of the cornea

a circular cut is made into the diseased cornea

the diseased cornea is removed

a healthy cornea is transplanted into the space created by removal of the patient’s diseased cornea

the cornea transplant is held in place with ultra-fine sutures.
These are not visible to the naked eye.
The transplant bonds slowly to the patient’s cornea and the sutures are then removed

I performed this full thickness cornea transplant
for a patient with keratoconus
(The patient is looking slightly sideways)

Recently a major step forward in cornea transplantation for keratoconus has occurred. This is the advent of a form of partial transplantation called deep anterior lamellar keratoplasty. In this technique a circular disc of tissue from the centre of the patient’s own cornea is removed, but crucially the innermost layer of the patient’s cornea, called the endothelium, is left behind. The transplanted donor cornea has its own endothelium removed before it is sutured in place.

This technique is appropriate in keratoconus because in this disease it is the middle layer of the cornea (called the ‘stroma’) which is abnormal whilst the endothelium is healthy. Preserving the patient’s healthy endothelium has major advantages because in this form of cornea transplantation rejection of the transplant almost never occurs.

I always perform partial or deep anterior lamellar keratoplasty in keratoconus when it is possible to do so. However if the keratoconus is too advanced, for example the cornea is severely scarred, this surgery may not be possible and penetrating keratoplasty will be done instead.

N.B. These illustrations of partial thickness transplantation of the front/anterior/stromal region of the cornea (deep anterior lamellar keratoplasty) should be understood as a general guide to the surgery, rather than an exact description.

in health, the cornea is perfectly clear

diseased corneas may be scarred and/or abnormally shaped

the surgeon will remove the diseased front/anterior/stromal region of the cornea

air is injected into the cornea to separate the abnormal front/anterior/stromal region from the normal endothelial (back/innermost/posterior) region

the abnormal front/anterior/stromal region is then completely removed

a healthy cornea is transplanted into the patient’s cornea to replace the diseased front/anterior/stromal region.
The cornea transplant consists only of the front/anterior/stromal region of healthy cornea
– the endothelial (back/posterior/innermost) region has been removed so that the new cornea fits exactly into the patient

the cornea transplant is secured with ultra-fine sutures

For more information read Masterclass on Keratoconus