What your surgery may have to do with it

It is both intuitive and well-established medically that cutting, or lasering, through nerves in your cornea is going to cause dry eyes at least temporarily. That is why all patients are advised to use artificial tears during the early healing period. That, however, does not explain why some patients have persistent tear film disorders. There are a number of explanations that have been suggested and may be worth more research if you are interested.

Nerves severed by laser and, where applicable, microkeratome: This is the obvious part, and nobody’s going to argue with you about the fact that it happens. In LASIK, the microkeratome cuts through a great deal of cornea to create a flap, and in doing so slices through a lot of nerves which don’t actually grow back. In both LASIK and PRK, the laser ablates (vaporises) tissue, including whatever nerves happened to be in that tissue. So obviously in LASIK where you’ve got more cutting/vaporising, more nerves are lost. PRK corrections for higher prescriptions (that is, where more tissue is being ablated) report higher incidences of dry eye. So what’s the problem? Those nerves that were cut are corneal sensory nerves whose job it is to tell the lacrimal glands (via the brain) "Hey! Getting kind of dry around here! Send more tears!" If the message doesn’t go, the tears don’t get produced, simple as that. Obviously there are still many more nerves out there (well, hopefully), sending this message, so it gets through some of the time, just not nearly as much as you need.

Neurotrophic keratitis? Sounds a lot fancier than it is. Honestly, I don’t really know anything about it, but there have been some very interesting articles on this and it’s definitely something to research, particularly for severe cases.

Cilia damaged by the microkeratome? Remember the all-important sticky part (mucin layer) of the tears, without which nothing will be wet therefore it will be dry? Well, the cilia help the sticky stuff stick to the outside of your eyes (epithelium). It is thought that the microkeratome (used to cut the LASIK flap) damages or destroys cilia.

Upper lids damaged by speculum? The speculum is the thing that holds your eye open (which is kind of important during an eye surgery). When they stretch your eyelids with this, it is thought it may damage your eyelids, causing them to blink less (which will result in moving tears around less and make fewer of them) and/or the big post LASIK complaint: sleeping with your eyes slightly open, which causes a great deal of surface evaporation.

Goblet cells disrupted? Goblet cells have a lot to do with the sticky stuff and are in fact critical to maintaining a stable tear film. It is believed that (a) placement of the suction ring, that really unpleasant part of the surgery when everything goes black, disrupts goblet cells at the limbus (where most of the goblet cells congregate) and in some patients it never returns to normal; and (b) compression by the microkeratome at the limbus when the flap is being created also disrupts them. Too much disruption & not enough mucins means dry eyes because the wetting stuff doesn’t work.

So, fortunately... they probably really can’t mess up our meibomian glands (which make the oily stuff) with the surgery, which is good, because they seem to have messed up everything else.

What other things may be contributing

There are many conditions you may have had before surgery, and probably still have for whatever reasons you had them before. These include:

• Meibomian gland dysfunction
• Blepharitis
• Low blink rate
• Low tear volume
• Poor tear quality

There are a number of potential underlying systemic contributors to dry eye which may have caused or exacerbated the conditions that existed before surgery and will be all that much more critical after surgery. These include:

• Medications, including those for eye problems, kidney problems, allergies, birth control, stomach and intestinal problems, diabetes, hypertension and more
• Lacrimal gland disorders or diseases
• Auto-immune diseases; Sjogren’s and other conditions
• Hormonal deficiencies (thyroid, menopause, etc)
• Decreased corneal sensation (causes range from ageing to long-term contact lens wear to herpes zoster) which lowers the blink rate, which results in fewer secretions from the lacrimal glands (tears)

You mean, it’s not just the surgery’s fault?

You didn’t have dry eyes before surgery (as far as you knew, anyway) and now you do. Ergo, the surgery caused your dry eyes. Fortunately and unfortunately, it’s not quite that simple. Fortunately, because if there are other explanations they may be things that you can do something about which will help your dry eyes. Unfortunately, because it can be so frustrating to be told calmly after surgery, when you are reporting persistent and painful dry eye symptoms, that you probably already had dry eyes, when nobody bothered telling you before surgery that you had dry eyes.

What seems to be happening is that people either have a condition minor enough that it wouldn’t have been diagnosed (called sub-clinical) — for example, their Schirmer’s or TBUT may have been borderline - or a condition that could and should have been diagnosed clinically but the patient wasn’t noticing symptoms so they weren’t tested. Surgery then disrupts their lacrimal function, i.e. reduces production of the watery part of the tears and probably disrupts the mucin layer (sticky part) too. This serves to knock them right over the edge into a state of severe, chronic dry eye.

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