By now, we're all aware that some patients who've undergone laser-assisted in situ keratomileusis (LASIK) develop eye irritation that can be challenging to treat. The good news is that with the correct diagnosis, we can successfully treat most of these patients and bring them back to comfort.

To diagnose correctly, we need to keep in mind the most common causes of eye irritation under these circumstances, and the specific symptoms associated with them. When we're armed with a precise diagnosis, our treatment protocol of choice is more effective, usually in a shorter amount of time.

I handle my cases of post-LASIK eye irritation using what I call the "divide and conquer" method. Here, I'll explain how I divide patients into appropriate treatment groups according to the results of history and exam.

Let's begin by examining the two primary causes of post-LASIK irritation.

Irritant #1: dry eye

Dry eye is a primary cause of irritation following LASIK, and for good reason. The surgery itself contributes directly to the problem, in two ways:

�         As the surgeon cuts the LASIK flap, corneal nerves are cut, denervating the overlying corneal tissue. (Hyperopic flaps are larger than myopic flaps, so the former denervates more tissue than the latter.) Because intact corneal sensation partially drives tear production, decreased corneal sensation decreases tear secretion. (Just as irritated eyes tear more, eyes that have lost sensation tear less.)

�         In cases where surgery was bilateral, followed by a bilateral decrease in corneal sensation, blink rate also decreases. This results in less tear delivery to the ocular surface.

The combination of decreased tear production and decreased blink rate causes an increase in tear film osmolarity. As with any sustained increase in tear film osmolarity, conjunctival goblet cell density on the ocular surface decreases. This is important because these mucus-containing goblet cells help provide natural lubrication for the eye surface.

The end result of this chain of events is dry eye symptoms.

Recognizing symptoms specific to dry eye

Patients with dry eye most often complain of a sandy, gritty feeling in their eyes that gets worse as the day progresses. This is because at night the closed eyelids form a watertight barrier that blocks evaporation, giving the eye surface a chance to recover. However, once the eye is open, evaporation begins. As the day progresses, evaporation pulls further and further ahead of tear production, so symptoms increase.

Dry eye symptoms are insidious in onset, but may start more precipitously after LASIK. Symptoms often follow a course such as the following:

�         Initially, patients may only complain of an increased awareness of their eyes.

�         As symptoms increase, LASIK patients may compare the symptoms to the feeling of a "dry contact lens" in the eye.

�         As ocular surface changes develop, patients may complain of sandy, gritty irritation in the eye.

�         As the cornea becomes involved, patients can develop sensitivity to light.

Irritant #2: anterior or posterior blepharitis

As you know, blepharitis isn't caused by LASIK. However, it is common, and it can contribute significantly to eye irritation following surgery.

Blepharitis can be divided into two major types: anterior and posterior.

�         Posterior blepharitis (or meibomitis) is the most common type of blepharitis. It involves an inflammatory process centered around the meibomian glands, which can spread throughout the lid margin and spill over to involve the ocular surface as well. Ultimately, inflammation involving the meibomian gland leads to fibrosis. This causes increasing disorganization and dysfunction of the meibomian glands.

�         Anterior blepharitis is less common. It's usually characterized by a dandruff-like process that occurs at the base of the lashes. (An even more uncommon type of anterior blepharitis, caused by Staphylococcus aureus, causes purulent drainage and crusting on the eyelashes.)

Symptoms of meibomitis

Like dry-eye patients, patients with meibomitis complain of chronic sandy, gritty irritation or burning in their eyes. However, in these patients the symptoms are worse on awakening in the morning. That's because their inflamed eyelids are up against the cornea at night; tear secretion decreases, and inflammatory mediators have all night to act on the surface of the eye. (They may complain about the redness of their eyes in the morning.) A few patients may have discovered that hot compresses provide some relief.

Other hallmarks of meibomian gland problems:

�         Some patients experience a second peak in their symptoms late in the day. This occurs because, over time, meibomian gland inflammation causes gland damage and gland dysfunction develops. As a result, these patients have meibomitis symptoms in the morning and dry eye symptoms late in the day because of increased tear film evaporation.

�         Patients who've had the problem for a long time may experience a resolution of their early morning symptoms, but an intensification of their symptoms late in the day. (As gland architecture is destroyed and heals with fibrosis, meibomian gland inflammation resolves.)

�         Occasionally, patients with meibomian gland dysfunction and orifice closure report that it feels as if their eyes are tearing -- yet these patients don't complain of tear overflow.
This occurs because of the loss of the lipid layer. The lipid layer, in addition to decreasing tear film evaporation, decreases the surface tension of the tear film, holding it tight to the globe. When this lipid layer is lost, tears splash around more. As a result, and with the concomitant loss of lipid from the lid margin, the aqueous layer from the tear film can begin to touch the mucocutaneous junction of the lid.
When this happens it feels to the patient as if his eye is tearing. (If tear overflow actually does occur you'll need to consider making a diagnosis of nasolacrimal drainage dysfunction.)

�         As in the case of dry eye, meibomitis symptoms are insidious in onset.
In addition to dry eye and meibomitis, frequent use of artificial tears can also be a cause of irritation. (Most preserved and non-preserved solutions are capable of causing irritation.) Indications that this may be the problem include:

o       The patient uses artificial tears more than four times a day.

o       The patient reports a history of regular or escalating eye drop use, which provides only temporary relief.

o       The patient complains about the eye drops stinging.

o       The patient describes symptoms as being equivalent throughout the day. (The damage is being promoted at regular intervals by continued overuse of the topical medication. The patient may not make the connection because use of the medication may temporarily mask symptoms by increasing the lubrication of the ocular surface.)

Divide before conquering

A diagnosis of dry eye can usually be made from the history; the examination will permit you to determine the cause (or causes) of the dry eye. When other causes are responsible for the irritation, the history and a careful examination will narrow the differential diagnosis and enable a definitive diagnosis.

The following seven categories of questions should be used to extract the information you need when taking the patient's history. Once you've collected this information you'll have a constellation of symptoms that will match those associated with one or more of the conditions detailed above.

1.      Character of the irritation. What does it feel like?

a.      Is it a sandy, gritty feeling?

b.      Do your eyes itch?

c.      Do they burn?

d.      Do you have a foreign body sensation?

e.      Do you feel increased "awareness" of your eyes?

2.      Location. Where is the irritation?

a.      on the surface of the eye?

b.      in the eye?

c.      on the lid margin?

d.      on the skin?

3.      Diurnal variation. Are the symptoms worse at any particular time of day? Patients typically have difficulty with this question. It helps to ask what the symptoms are like upon awakening, at the breakfast table, at lunch and after dinner in the evening.
Also, be sure to ask these two questions:

a.      A Are the symptoms worse on awakening or late in the day?

b.      A Do you experience two symptoms peaks -- on awakening in the morning and then late in the day?

4.      Onset. Did the symptoms start suddenly, or did they develop gradually? Do symptoms occur in clearly delineated episodes or is this a continuous problem?

5.      Duration. How long have the symptoms been present?

6.      Aggravating factors. Do the symptoms get worse under specific conditions -- in wind, smoke, low humidity (e.g., airplane cabins), or when reading, watching TV, wearing contact lenses or using artificial tears?

7.      Alleviating factors. Does anything make the symptoms better -- hot compresses, eye closure, humidity, artificial tears?

Divide by examination

Signs of meibomitis can be subtle. Here are the key elements to consider when examining these patients.

�         Palpebral fissure width. Tear film evaporation is proportional to the distance between the upper and lower lids.
With the patient looking directly at your eye, measure the distance between the upper and lower lids. As the palpebral fissure width increases, there is increasing evaporative stress on the tear film. With palpebral fissure widths of 10 mm or more, it's common to see dry eye symptoms.

�         Meibomian gland orifice. As meibomian gland function declines, the meibomian gland orifice goes from patent to stenosed to closed (see illustration, right).

�         Lid margin. The earliest change seen with meibomitis is the appearance of telangiectatic blood vessels crossing the lid margin. (A normal lid margin is free of visible blood vessels.)

�         Tear volume and quality. I prefer to examine the tear film by using a wetted fluorescein strip. (The problem with using a drop from a bottle is that it replaces the tear film; you end up examining the drop instead of the tear film.)

o       Take a fluorescein strip, wet it with a drop of sterile saline or irrigating solution, shake off the excess, pull the lower lid down, and paint the strip along the inferior tarsal conjunctiva. With decreased tear volume, the fluorescein will remain dark under the cobalt blue light of the slit lamp, instead of fluorescing.

o       As tear volume decreases further, the tear film will assume a more viscous appearance. As the upper lid rises following a blink, the tear film, rather than snapping up quickly with it, will rise more slowly. (Ultimately, patients with decreased volume develop debris in the tear film as well.)

o       In patients with meibomian gland dysfunction, the tear film assumes a watery appearance because of loss of the lipid layer. It will be apparent in these cases that the tear film isn't lying tight to the globe.

�         Ocular surface staining. Staining can help determine whether the problem is dry eye or posterior blepharitis:

o       In the presence of dry eye alone, the conjunctiva always stains more than the cornea. (This is true whether the dye used is fluorescein, lissamine green or rose bengal.)

o       With posterior blepharitis alone, if there is any staining, the cornea always stains at least as much as the conjunctiva.
In both early dry eye and mild blepharitis, there is usually no ocular surface staining at all.

�         Corneal sensation. In patients with long-standing eye irritation following LASIK -- especially those with a history of contact lens wear -- it makes sense to test corneal sensation. This can be done easily with a cotton wisp. With experience, the range of normal responses is easily appreciated.

Now you're ready to conquer

Once you've zeroed in on the precise cause of a patient's post-LASIK eye irritation, you can treat with the same level of precision you've used in your surgery. The end result will be a happy patient who is truly satisfied with his LASIK experience, from start to finish.

Dr. Gilbard is founder and CEO of Advanced Vision Research, and the inventor of TheraTears. He is also medical director of the Cornea & Vision Correction Center, clinical associate scientist at the Schepens Eye Research Institute and clinical assistant professor at Harvard Medical School.