Diagnosing KC

[Fordy]

Guys,

What is the difference beetween having KC and a severe astigmatism?

I wondered this because many of the symptoms appear the same.

Over to you wise people.

Fordy

[Andrew MacLean]

From the point of view of the patient the major difference is that KC is a progressive condition that is often associated with other ophthalmological conditions like corneal hydrops.

If left untreated KC can lead to the loss of useful sight to the extent that the person with KC would, in most jurisdictions, be registered as blind.

[GarethB]

Regular astigmatism is in one plane so easy to correct. In KC the astigmatism is in multiple planes due to the variety of high points and flat regions caused by a thinning cornea.

Regular astigmatism can be corrected with glasses where as the iregularities can not. There is a diagram accesable from the home page, I think it is the page that says what KC is?

[Lynn White]

Fordy

You are right in a way... there are times when I have referred patients I feel may be keratoconic and the diagnosis has been "High Astigmatism". However, a fair guide is that keratoconus can be sustepcted when:

Astigmatism is increasing when usually it should be stable - (most astigmatism is fairly stable by the time you are a teenager)
Astigmatism is not "regular" i.e. not symmetrical
Best corrected vision is glasses is becoming worse but vision can be improved by contact lenses.

Lynn

[Lynn White]

Actually this is entirely spooky! I wrote the last post while in practice (a normal, non keratoconus day in practice). I logged off and the next patient came in, a young woman, a nurse, in her mid twenties, who complained she was getting headaches and felt her eyes had got worse.

She is quite a low prescription with low levels of astigmatism and I found the astigmatism had gone up by 0.50 - 0.75 D each eye respectively and in the left eye had changed axis. Her vision came up nicely with this but I wasn't happy, as really, this should not be changing at her age. I knew she had allergies, asked if she had dry eyes - she said yes. Did she rub her eyes? Oh definitely. I observed she was casually sitting with one leg over the other but almost in the lotus position, so asked if she was by any chance "bendy". "Oh yes, I have been diagnosed as hypermobile", demonstrating her bendy fingers.

Checking her cornea, her curvatures had steepened slightly but there was no distortion, although on ophthalmoscopy, there was distinct shadowing inferiorly on the left eye. Unfortunately this practice does not have topography, so I could not check this.

Now this to me shouts possible risk for keratoconus. The risk factors are all there - allergies, dry eyes, hypermobility (which suggests a problem with collagen in the ligaments and many people with this condition also have keratoconus). She also mentioned that although her vision was poor in glasses, it was great in contacts (even though they are soft disposable).

I discussed the eye rubbing issue and gave dry eye therapy (drops and hot compresses) and arranged regular monitoring. As she is at the moment, a diagnosis of KC is not possible, as she does not meet the "criteria". If dry eye therapy works and she stops eye rubbing, she may not develop KC - but then she may not have anyway. We don't have the luxury of viewing parallel universes (like the film "Sliding Doors") to see what would happen if she carried on as she was without addressing the eye rubbing issues etc.

Working with older people, who most usually have some dry eye issues, I know their refractions (and corneas) can change markedly if their eyes get very dry and can go back to normal when we treat it. So these changes do go hand in hand with dry eye but they do not develop into KC in this older group.

So you can see, it is very hard to identify what is KC and what is, say, a corneal change that might lead to KC but doesn't quite.

Lynn