ABOUT KERATOCONUS - Diagnosis

Keratoconus is described as the cornea becoming thinner and cone shaped. Medium to advanced keratoconus is fairly obvious to diagnose, as by this time the cornea is so irregular, vision is affected and cannot be corrected with spectacles. Often, the cone itself can be seen (Munsen’s sign, where the patient looks down and you can see the cone distorting the shape of the lower lid).

Detecting it in the early stages is more difficult and this often confuses patients – why was their keratoconus not picked up earlier?

When keratoconus starts to develop, the only thing you may notice is that your glasses need changing more often. If you move between practices for each test, this may not be noticed by your professional, or if it is, may not be acted upon if you go somewhere else next time. The most significant symptom at this point is that astigmatism increases quite a bit.

As it develops further, the optometrist may notice distortions in the pupil reflex. This is the “red eye” effect you see in photographs – the red of the retina shining through the pupil. Any distortions show up as shadows, typically an inferior triangular shadow may be seen, caused by a steepening of the lower cornea.

Also, optometrists often use a retinoscope which relies on this reflex to detect your prescription. In keratoconus, this reflex is strangely split and distorted – something we call “scissoring” – see below

Someone who is experienced in keratoconus will pick that up immediately but unfortunately, due to its rarity, many high street optometrists are not that familiar with these signs as they do not see many keratoconics. Some may never ever see one. Some eyes can show these shadowing signs and yet not develop KC.

For many years, keratoconus has required the following to merit a full diagnosis:

Fleischers Ring; Stress lines of Vogt; corneal thinning; scarring; increased visibility of corneal nerves and finally corneal hydrops.

	Fleischers ring Formed by hemosiderin (iron) pigment deposited around base of cone. Generally present in around 50% of cases.
	Stress lines of vogt Small, mainly vertical lines in the cornea that disappear on applying gentle pressure to the globe.
	Corneal thinning In keratoconus, the central (apex) of the cornea is usually the thinnest. Often the apex can be displaced downwards.
	Corneal scarring Scarring such as this is seen in more advanced keratoconus. It can sometimes be caused by rigid lenses if they are fitted too flat.

Some ophthalmologists will not confirm a diagnosis of keratoconus unless some of these signs are present – even if other signs such as rapidly changing prescription are present. The point at which diagnosis is made may vary a good deal between countries, depending on what treatment options are available.

Topography

This is a new technology which many practices will not have available to them. It is based on the simple placido disc. This projects rings of light and dark onto your cornea. Compare the two images below.

The left is a normal cornea, the right has keratoconus. In corneal topography, these images are processed and “mapped”.

The left is a normal spherical eye, the middle a normal astigmatic eye and the end a keratoconic eye. You can see here the characteristic inferior steepening that causes the distortion that makes it difficult to for the keratoconic to see clearly.

In the early stages, the topographs may appear like this:

This case was picked up only because the astigmatism was increasing in mid life – when it should be stable. Spectacles give perfectly normal vision and there is no significant shadowing with either ophthalmoscope or retinoscope. It is unlikely to have been picked up without using a topography machine and is termed sub-clinical keratoconus, as it is causing no symptoms.

Such cases are now discovered regularly in laser clinics. People with sub-clinical keratoconus often attend such clinics because they are not satisfied with their spectacle vision or they are changing their glasses a lot for no apparent reason. When the topography is performed prior to surgery, the pattern is then picked up. It is inadvisable for anyone with this kind of pattern to undergo laser surgery as the process itself can trigger keratoconic progression.

The obvious answer may seem that every optometrist’s should have a corneal topography machine. However, these machines are currently expensive and although extremely useful in contact lens fitting, they are not yet seen as an essential item.

It is also fair to say, as topographs do detect more mild/sub-clinical cases of keratoconus, diagnosis will become more subtle and the condition will be more understood.