Keratoconus: Difference between being "predisposed" and showing "early signs"?

Factual Questions
1

I see an ophthalmologist every two years (I’ve worn glasses for myopia since I was a kid), and a few years ago when at one of these regular appointments, I was told I am “predisposed” to keratoconus. I was told this after they performed some type of scan of my cornea, which apparently revealed that my cornea is thin and not of a normal shape.

I thought, by “predisposed”, this meant I was just more likely to later develop keratoconus. The odds of developing keratoconus are pretty slim anyway (roughly 1 in a thousand), so due to the shape of my cornea the odds of me getting keratoconus might be 1 in 100 instead of 1 in 1000. Pretty slim still, which is why I wasn’t worried (and in fact, those were the exact figures my ophthalmologist originally gave me, if I remember correctly).

But I saw my ophthalmologist again yesterday, and again I had the scan of my cornea done. My ophthalmologist told me that the results were unchanged, which I figure is good news. But then, he started talking about how I was showing “early signs” of keratoconus.

This made no sense to me: if the scan of my eye hadn’t changed (and my vision hadn’t changed either), how can I now have “early signs” of keratoconus, while previously I was just merely “predisposed”? I of course asked him this question, and he told me that they were the same thing: being “predisposed” is no different to showing “early signs”.

This still didn’t make any sense to me, so again I questioned him on it, but again he just told me that there’s no difference between the two, and I left pretty confused and unsatisfied with his explanation.

I don’t suppose anyone would be able to offer an explanation from what I’ve described? I suppose the right answer is to phone him and ask again, but aside from the fact that getting him to speak to you on the phone is near enough impossible, his way of explaining things just doesn’t make much sense to me, so I thought I’d try the Straight Dope first.

Is there a difference between the two? Is keratoconus only diagnosed when the cornea actually starts changing shape, not if the shape is of a concern but is unchanged? Is having “early signs” of keratoconus the same as having keratoconus (even if there are no vision problems)?

Thank you.

2

It’s virtually impossible to say without seeing the scans, but you may show inferior steepening, irregular steepening, or some other keratoconic-type “trait” on the corneal topography that’s borderline. With those findings, if you’re still correctable to 20/20 with glasses and without symptoms (haloes, blur, distortion, etc) you’re either borderline, or predisposed, depending on how the doctor chooses to express it.

In some clinical conditions (such as hypertension) the terms “borderline” have a specific and numerically quantifiable meaning. Keratoconus isn’t one of them, so I think the doctor is just expressing himself in a way that’s a bit unclear (and terrifying you in the process, unfortunately.)

May I ask how old you are? Keratoconus that shows up at an older age (late twenties and beyond) tends to progress to a lesser extent than keratoconus that first shows up at an earlier age.

Caveats are: I’m not your doctor, haven’t seen your eyes, and have no idea what your particular eyes look like. I’m an optometrist who has worked with quite a few keratoconus patients.

3

Thank you cromulent. I’m 33.

Yes, I’m still correctable to 20/20 without symptoms. And my prescription is, I believe, fairly weak: the SPH numbers are -2.75 and -1.75.

So from what you’ve written, it sounds like “predisposed” is a bad choice of words, and “borderline” / “early signs” are more accurate. Any idea how often “borderline” / “early signs” cases turn into full-blown keratoconus? Of course you’re not familiar with my case, but is it possible to put a percentage on it for the population in general?

And I still don’t understand at what point a keratoconus diagnosis is made. Keratoconus is a “degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than the more normal gradual curve”, according to Wikipedia. So if my cornea is thin and a conical shape (which it is), but if my eyes have not changed in a number of years (and change seems to be a requirement according to the definition that I’ve quoted), is that still keratoconus? Is it shape of the cornea that defines keratoconus, or is the degenerative/structural changes/thinning part that defines keratoconus?

4

Having a cone shaped cornea, isn’t that just astigmatism? According to Wikipedia, “Astigmatism is an optical defect in which vision is blurred due to the inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or toric curvature of the cornea or lens.”

So if the shape of the cornea is what causes my astigmatism, and if my eyes are not changing, then why would I have keratoconus and not just astigmatism?

5

Most doctors would call the disease entity “keratoconus” only when it affects the patients vision in some way (i.e. the patient is no longer correctable with glasses to 20/20, or suffers from haloes, distortion or glare) regardless of the corneal scan.

I think it’s impossible to say what percentage of “borderline” cases progress because there isn’t a specific, numerical definition of “borderline” in this situation. Having said that, if you’re 33 and your vision in unaffected, my gut feeling (and I’m not your doctor, as you know!) is that you don’t have much to worry about. Even if you did develop keratoconus, it would be more likely to be of the mild and slowly progressing type. Having said that, the best way to monitor this is to continue following up with your doctor at regular intervals so that you and he will know if anything starts to change. The corneal topographic scans are generally sensitive to even small changes in corneal curvature.

6

I have keratoconus, now basically a non-issue after cornea transplants, though vision is still nowhere near where it was when I was 18.

One thing I learned is that many doctors know less about KC than they admit to their patients. I’m sure they’re well-meaning, but they just don’t know. I didn’t even realize the extent of this until after my fourth doctor (most of the changes of doctors due to moving) and realized that many of them had advice that completely contradicted each other.

So I would strongly urge you to get a second opinion and to bounce off the second doctor some of what the first is saying. There is a national foundation (NKCF) that lists doctors who are familiar with KC.

To be more specific about the original post, I’ve never heard of pre-disposed as a diagnostic term… but by the time anyone realized I had KC, I was in the “How can you see that well with your eyes so screwed up?” stage. (And I wasn’t seeing well, so I take that to mean my eyes were *really *screwed up. My doctor’s depth perception test had 15 levels of difficulty and I couldn’t get the second one right.)