Article Date: 11/1/2009

Correctly Choose and Prepare LASIK Candidates

Correctly Choose and Prepare LASIK Candidates

Your ability to determine candidacy and properly prepare candidates not only impacts surgical outcomes but also the success of your practice.


Because we're the refraction experts by virtue of our optometric education and we tend to have long-standing relationships with our patients, we are in the best position to not only determine whether a patient is a good candidate for LASIK but also how to properly prepare him prior to the procedure.

Here, I review the criteria for patient selection and proper preoperative preparation, so you can continue to ensure patient satisfaction and an influx of referrals as a result.

Patient selection

To determine whether a patient is a good LASIK candidate, you must assess the following:

Medical/ocular history. Pregnancy, uncontrolled rheumatologic diseases, various ocular conditions and the use of certain medications should immediately raise a red flag when evaluating a patient's LASIK candidacy.

You shouldn't refer pregnant patients for LASIK because pregnancy can negate an accurate refraction, both pre- and postoperatively. The best course of action here: Educate the patient about this contraindication; though explain she may be a viable candidate after the birth of her child. Most refractive surgeons wait at least three months postpartum and after the discontinuation of breast feeding before performing surgery.

Dissuade patients from LASIK whose medical history reveals uncontrolled rheumatologic disease, such as lupus erythematosus, as these conditions compromise the strength of their immune system and therefore threaten the postoperative healing process. Further, council patients who have had herpes simplex or herpes zoster against LASIK because both are recurrent corneal diseases that can affect healing and scar potential.

Although glaucoma isn't an absolute contraindication for LASIK, it's important to educate these patients that it is challenging to obtain the most accurate intraocular pressure (IOP) measurement post-LASIK and that glaucoma drops can cause keratitis. It's most helpful for you to take IOP measurements a couple of weeks post surgery to see whether thinning the cornea has changed the patient's IOP measurements.

The presence of a visually significant cataract is an automatic contraindication for LASIK candidacy. As a result, switch the discussion from LASIK candidacy to the various intraocular lens options. However, keep in mind that refractive surgeons do use LASIK to fine tune a cataract operation. This has been most helpful with multifocal and toric IOLs. It's usually best to wait three months after the cataract wound has healed before the surgeon fine tunes the IOL.

Should the patient's medical history reveal the current use of any drug that causes ocular dryness, he may not be a LASIK candidate. You can reduce or change some of these systemic or topical medications but only after consulting with the physician who prescribed them.

Other medications of which to be aware: Research has shown that the use of the acne medication Isotretinoin (Accutane, Hoffman-La Roche, Inc.) increases the risk of post-LASIK and post-photo refractive keratectomy (PRK) corneal scarring and complications from ocular dryness. As a result, if the patient passes all other candidacy requirements, have him cease using the medication six months prior to the refractive surgery. A treatment regiment of cyclosporine ophthalmic emulsion 0.05% (Restasis, Allergan, Inc.) both pre- and postoperatively can often be helpful in alleviating dryness in these situations.

The arrhythmia-controlling drug amiodarone (Cordarone, Wyeth pharmaceuticals) can cause vortex keratopathy. Therefore, PRK is a better option in these rare patients.

Tear function. This may be one of the most debated and misunderstood topics when it comes to assessing LASIK candidacy. This is because not every patient who presents complaining of ocular dryness has tear production issues, or aqueous tear deficiency, and it is serious tear production issues, not meibomian gland disease (MGD), that precludes candidacy. LASIK temporarily decreases the lacrimal gland's ability to produce tears. So, when an aqueous tear-deficient patient undergoes the procedure, he or she has even more difficulty producing tears, typically for a period of approximately six to eight weeks … but it can be longer.

To determine the source of dryness, inspect the patient's meibomian gland orifices first. If, indeed, they reveal disease, have the patient begin a regimen of lid massage with a tissue or clean cloth, b.i.d. for 20 seconds for a couple weeks. Mild steroids drops are also helpful during this two week trial. If the MGD appears under control (e.g., the tear film appears stable), you can refer the patient for LASIK.

Equally important is your evaluation of the patient's dermatologic status. Subtle rosacea changes are very common in individuals with blue or green eyes who have had contact lens failures. Sometimes, oral "cyclines" are required.

To see whether the patient has aqueous tear deficiency, evaluate the patient's tear production with a Schirmer strip or similar devices. Make sure to ask about a history of dry mouth (xerostomia), as the two conditions tend to go hand in hand.

Mental stability. Because our radios and TVs are rife with commercials that present LASIK as a "perfect" procedure, most patients who present with an interest in the surgery aren't aware of its possible complications, such as haloes, glare or reduced vision. While some patients have the mental ability to accept these possible less-than-ideal outcomes, others do not. As a result, it's essential you educate all prospective LASIK patients on these, among other possible complications, and ask them: "Could you live with these possible outcomes?" This question really makes patients assess their ability to deal with a possible less-than-ideal event.

For instance, I've found that patients who have a medical history of psychiatric issues, such as clinical depression or bipolar disorder, often make poor candidates. Therefore, when these patients answer "yes," to the aforementioned question, I try to dissuade them from pursuing the procedure. If, however, they remain motivated to undergo the surgery, and further testing reveals they're otherwise good candidates, I refer them to the refractive surgeon, explain the patient�s medical background, and let the surgeon take over.

And, of course, I'd be remiss if I didn't mention that presbyopic patients aren't always the easiest LASIK candidates, as they can have unrealistic expectations — fueled by the aforementioned radio and TV advertisements — that LASIK is the eye's fountain of youth, and they'll never have to wear spectacles again. (See "The Monovision Option," below.)

The Monovision Option
Two types of presbyopes tend to make excellent candidates for this procedure: Those who've been wearing monovision contact lenses comfortably, as LASIK monovision mirrors contact lens monovision, and those who have presbyopic hyperopia, as they tend to be less binocularly astute. In other words, the neuroadaptation monovision requires is often not an issue for these patients.
Explain to your presbyopic patient who presents with an interest in LASIK why you believe monovision may be the best option, and that you can actually give him the ability to "test drive" it with a pair of trial contact lenses — something I've found both impresses and puts these patients at ease regarding the LASIK candidacy process. Check the simulation in a couple of days to determine whether the patient is able to accept this strategy.
As is the case with all LASIK candidates, it's crucial you manage patient expectations by providing patient education regarding the possible outcomes of the monovision procedure. Specifically, let these patients know that in the early postoperative period, the eye the refractive surgeon treats for near acuity may provide better distance vision initially. Also, educate these patients prior to monovision that a possibility for future enhancements does exist, and that on rare occasion, spectacle or contact lens wear is required while they're adjusting to their new vision. Finally, tell these patients that they may not be comfortable driving long distances at night and may require a pair of glasses that reverse the monovision for this task.

Occupation. Fire fighters, police officers, military personnel and construction workers tend to make the most ideal candidates for LASIK because their jobs make wearing spectacles a challenge. Also, police officers and pilots must have uncorrected visual acuities that often times only refractive surgery can achieve for them. Truck drivers, among others who do a great deal of driving at night, may make better custom LASIK candidates to avoid the incidence of postoperative glare and haloes that can occur post-standard LASIK.

Pupil size. Assessing the patient's pupil size in dim light is important in determining LASIK candidacy, as patients who have large pupils — greater than 7mm — are at an increased relative risk of postoperative glare and haloes. This is because the treatment zone or "sweet spot" for a LASIK procedure is between 6mm and 8mm. Therefore, if the laser is even slightly off center of the cornea, the pupil can dilate around the treatment zone. Fortunately, tracking devices which are incorporated into most current laser systems have helped reduce this problem.

Corneal thickness/curvature. Determining corneal thickness and anterior surface curvature is essential for deciding LASIK candidacy. A cornea that is thinned too much can result in ectasia and/or irregular astigmatism. This, in turn, results in a very poor visual outcome that will likely only be correctable via an RGP contact lens or a corneal transplant — not a very acceptable outcome. If the refractive surgeon flattens or steepens a cornea too much, vision can be less than perfect, and contrast sensitivity can be greatly reduced. This translates to reduced night vision.

My rule of thumb: If the patient's corneal thickness measures less than 500 microns, I usually suggest PRK. (The refractive surgeon's corneal thickness "cut off" may be different.) Keep in mind that the refractive surgeon eliminates approximately 15 microns of corneal stroma per diopter of laser treatment. LASIK flaps are usually 100mm thick. To avoid ectasia, most large studies suggest a resultant corneal bed thickness of at least 250 microns, though 300 to 350 microns is obviously safer.

To assess corneal curvature, you must employ both a keratometer (K) and topographer. The topographer has the advantage of diagnosing asymmetric astigmatism as well as subtle keratoconus. The post-LASIK K reading should be between 39.00D and 50.00D. To obtain an accurate resultant K value, take .7 times the spherical equivalent of the patient�s refractive error, and add or subtract this amount from the K reading. Add for hyperopic patients, and subtract for myopic patients. You want to rule out forme fruste keratoconus, which puts the patient at risk for developing post- LASIK ectasia. Some surgeons consider PRK for these mild cases of asymmetric astigmatism if corneal thickness isn't an issue.

Proper preoperative preparation

Once you've assessed the aforementioned issues and deemed the patient a suitable LASIK candidate, you must properly prepare him for the procedure, so you can increase the odds of a successful outcome even further. Your to-do list

Perform bi-ocular refraction. Although you should perform a wet refraction for medico-legal reasons, you should also perform a bi-ocular refraction, as I've found doing so provides an extremely accurate refraction, and therefore, an excellent chance of optimal vision post-LASIK. To do this refraction, fog the fellow eye with a plus lens in the phoropter while making sure both eyes are open. This is extremely helpful in controlling accommodation while not affecting the pupillary diameter.

A caveat: If the patient is a contact lens wearer, discontinue lens wear prior to the refraction, so the cornea goes back to its natural shape, and you can obtain the most precise refraction. A general rule of thumb is as follows: If the patient has been wearing a spherical daily wear contact lens, discontinue wear one week prior to refraction. If the patient has been wearing an extended wear lens or toric lens, cease wear two weeks prior to refraction. Finally, if the patient has been wearing an RGP lens, discontinue wear six to eight weeks prior to refraction. (As a brief note, sometimes, you can fit an RGP wearer with interim soft contact lenses to make this two-month rehab period more acceptable.)

Determine the corneal refractive power. Because LASIK surgery alters both the anterior and posterior surfaces of the cornea, it's crucial you record the patient's exact amount of laser treatment. This is so you can determine the convergence factor, should the patient require cataract surgery in the future. Several IOL adjustment formulas exist. In my practice, I employ Dr. Masket's formula, which is: IOL adjustment = LSE X (-.326) + .101 in which LSE is the spherical equivalent of applied laser treatment. This formula works great, though it does require you to know how much laser the refractive surgeon applied.

Perform a careful fundus evaluation and IOP measurements.

Reiterate pertinent patient education. Before the refractive surgeon referral, briefly reiterate the patient education you provided regarding the procedure itself and the possible outcomes, and invite the patient to ask any last-minute questions or pose any concerns. This step ensures both you and the patient are on the same page in terms of expectations. Also, it shows the patient you genuinely care about him, which goes a long way in maintaining patient satisfaction.

Reviewing the criteria for patient selection and proper preoperative preparation is critical in enabling you to continue to best comanage these patients. Remember: Many patients interested in LASIK have preconceived notions about the procedure that can be inflated. As a result, they need someone who can help them navigate through the process, so the procedure meets their expectations. Since we're the refraction experts and have established relationships with our patients, there's no one better suited to do this. The rewards: patient loyalty to your practice and referrals to friends and family members for your care in the exciting arena of refractive surgery. OM

Dr. Den Beste practices at Den Beste & Associates LASIK Pro Vision Consultants in Orlando, Fla. He has assisted in more than 35,000 LASIK procedures and has helped several companies obtain FDA approval for both laser applications and keratome approval. E-mail him at

Optometric Management, Issue: November 2009