> Seems like it would be quite an unusual patient not to be able to
> "see" if he had either dry eye or blephartis. Like doc, is my eye
> red?
I think there's a lot about dry eye that you don't understand.
The precorneal tear film layer HAS a refractive index of its own.
Optimal visual acuity depends on the tear film layer being intact.
People with dry eye syndrome have blurred, and variable, vision very
frequently. This causes eyestrain, tension around the eyes, "foreign
body" sensation, headaches, fatigue, light sensitivity, and a host of
other symptoms.
Don W - 28 May 2007 16:18 GMT
> I think there's a lot about dry eye that you don't understand.
That is probably true.
> The precorneal tear film layer HAS a refractive index of its own.
> Optimal visual acuity depends on the tear film layer being intact.
[quoted text clipped - 3 lines]
> body" sensation, headaches, fatigue, light sensitivity, and a host of
> other symptoms.
The above two I understand.
"HAS" ???
Don W.
Jan - 28 May 2007 21:00 GMT
Neil Brooks schreef:
> The precorneal tear film layer HAS a refractive index of its own.
> Optimal visual acuity depends on the tear film layer being intact.
Neil, the refraction index of the tearlayer is nearly the same as is the
cornea and so not that important optically speaking.
However you are quite right in mentioning the importance of this layer
when it comes to vision acuity.
It 'smooths' the optical surface of the cornea epitheliumlayer and keeps
it transparent (among other important things)
Jan (normally Dutch spoken)
Don W - 28 May 2007 22:29 GMT
> > The precorneal tear film layer HAS a refractive index of its own.
> > Optimal visual acuity depends on the tear film layer being intact.
>
> Neil, the refraction index of the tearlayer is nearly the same as is the
> cornea and so not that important optically speaking.
Well, the tear film has a thickness several orders of magnitude less
than the cornea, so the refractive index difference would not matter
too much, it seems. No eye model incorporates it, that I have seen.
Don W.
Jan - 28 May 2007 23:42 GMT
Don W schreef:
> Well, the tear film has a thickness several orders of magnitude less
> than the cornea, so the refractive index difference would not matter
> too much, it seems. No eye model incorporates it, that I have seen.
>
> Don W.
The thickness of this tear layer is of no importance Don and forget what
I said about the difference in indices between the tearlayer and the
cornea....
tearlayer 1.336
cornea 1.376
The fact the curvature of the front and back of the tearlayer (plano)
are the same as the frontcurvature of the cornea counts.
Jan (normally Dutch spoken)
BTW, a very slim lens is still a lens.