Keratoconus and Spectacles
By Ralph Goldsmith
If you have Keratoconus then you may rely on contact lenses to correct your vision. If you do, and you have any problems wearing them, you may wonder how to explain to people why glasses aren’t an alternative. Well here’s the answer.
First a quick reminder of what the disease is.
Keratoconus is a disease that effects the cornea, which is the front clear part of the eye. The disease causes the cornea to thin and bulge outward resulting in distorted vision.
Most people have never heard of Keratoconus, unless that is they either have it, or know someone that has it.
I’ve been a contact lens wearer for many years. Most of the time I have managed to get good useable vision with them.
But, I have had bad days when the contact lenses irritate, or even become too painful to wear. When I can’t wear my lenses I often get asked why I don’t put on a pair of glasses.
Actually it’s not accurate to say that glasses don’t work with Keratoconus. For early stages or very mild conditons they work just fine.
Once the disease progresses however they are pretty much useless and here’s why.
To understand the limitations of glasses let’s first take a quick look at how your eye works.
The retina, which is right at the back of the eye, is a layer of highly specialised cells. The special cells generate nerve impulses in response to light. These impulses are what your brain recognises as vision.
Because your eye is a sphere the Retina is curved.
For all this to work three things need to happen
The image must be reduced in size to fit onto the retina.
The scattered light must come together — that is, it must focus — at the surface of the retina.
The image must be curved to match the curve of the retina.
Spectacles are used for correction of vision issues like:
Myopia (nearsightedness) which occurs when a distant object looks blurred because the image comes into focus before it reaches the retina.
Farsightedness, for which the technical term is Hyperopia, which is when an object that is close to you looks blurred because your eye is focusing the object at a point further back than your retina..
Astigmatism which is caused by a distortion that results in a second focal point. Keratoconus often results in a very extreme and irregular Astigmatism
Glasses work very well with a normally shaped eye.
The lenses of the glasses are shaped to refract or bend light so that the focal point changes. In other words making sure that the image comes into focus just as it gets to the Retina.
It is possible to correct regular astigmatism with glasses
This is because there is a limited amount of distortion and it is still just a matter of shifting the second focal point to the correct position so that it aligns with the first focal point. Early stages or mild Keratoconus will often result in a regular Astigmatism so glasses can be quite effective.
However, once the Keratoconus progresses the Astigmatism becomes very irregular and the cornea can often have multiple curves (giving multiple focuses). Once this happens it becomes impossible for glasses to address all of the focal points that this creates.
The practical upshot of this is that the light doesn’t get focused properly on the back of the eye, which results in the retina getting an image that is blurred, and often consists of many images overlapping (what I refer to as “Ghosting”).
That;s the reason why sticking on a pair of spectacles is not an alternative to wearing contact lenses.
Vision Life is an organisation devoted to raising awareness of the eye condition Keratoconus and to helping people who’s lives have been impacted by the disease. Get a free information pack and newsletter at
http://whatiskeratoconus.com
