indirect causation? (desensitization and blink reflex)

[Rojzen]

Thank you, Dr. Gemoules, for the enormously valuable guidance you provide. . .

Regarding the absence of good science to prove a connection between prolonged contact lens wear and dry eye, I wonder if the following has been explored:

All the while corneal desensitization due to lens wear is likely to reverse after lens wear is discontinued, such that lens wear, and resulting desensitization are not logical DIRECT causes of ocular surface disease, is it possible that even a TEMPORARY period of corneal desensitization is enough to slow down blink reflex, in turn disturbing secretions triggered by the blink (i.e. meibomian and tear gland secretions), and also leading, in some cases, to gland atrophy?

I ask because a wonderful ophthalmologist I used to see had a number of post-LASIK patients, and he shared with me his strong belief that the temporary desensitization of the cornea caused by the nerve cutting performed in LASIK ruined people's blink patterns. He believed that if the blink was abnormal for long enough, meibomian glands could atrophy from lack of stimulation. . .It's my impression that someone has done research on the relationship between corneal desensitization and the blink reflex, but I don't know more about it.

I wore contacts for decades, forced by parents who were obsessed by appearance. The lenses always hurt, and I got corneal abrasions often. Ultimately, a few years after I stopped wearing the lenses completely, I developed endstage MGD (with gland dropout and Zero-second TBUT). I have to wonder whether I basically killed my meibomians by not blinking normally for many, many years.

[DrG]

Rojzen,

With a confocal microscope, one can readily see the damage created by LASIK. Quite simply, the nerves are cut. Some of those grow back, and some don't. And some don't grow back looking like "normal" nerves. To the best of my knowledge, there is no corresponding change in nerve density or morphology (appearance) associated with contact lens wear.

We do know there is a direct link between the nerves being cut and the resulting dry eye from LASIK, because the recovery of the dry eye seems to follow the regeneration of the nerves. This is why it is termed "neurotrophic." The temporary desensitization associated with contact lens wear is probably more a change in the resting potential of the nerves rather than their destruction.

I see lots of MGD in my patients, some of whom have never worn contact lenses. An interesting study might be to see if their blink rates are somehow different, but I somehow doubt it would show anything conclusive. Likewise, I see lots of dry eye patients who drop out of contact lens wear, and yet require nothing in the way of dry eye therapy following discontinuation of their contact lenses.

I just don't see the smoking gun. I wish I did so I could agree with you. But, I don't. I also see more LASIK problems than the average OD because that is my specialty. Therefore, my opinion of LASIK is rather skewed towards the negative. On the other hand, I feel that I see a large representative cross-section of contact lens wearers.