Wavefront particulars

Optometric Management: How can higher order aberrations affect the quality of vision even among those patients whose acuity measures 20/20?

Sondra Black, O.D.: Please understand that 20/20 is a quantitative measurement, not a qualitative one. Standard laser tech- nology corrects for lower-order aberrations only. Wavefront technology also addresses higher order aberrations such as spherical aberration, coma and trefoil. Each of the higher order aberrations can cause different quality of vision issues postoperatively. An increase in spherical aberration can cause night vision difficulties such as halos and decreased visual comfort in dim lighting conditions. An increase in the amount of trefoil and coma can cause reduced quality, i.e., "smearing of vision" and lack of "crispness." These can also contribute to glare and streaking of lights at night.

OM: What is the relationship between contrast sensitivity and quality of vision?

Dr. Black: Standard LASIK has a tendency to reduce contrast sensitivity in most patients. Typically patients are happy as they are no longer dependent on their glasses or contact lenses and don't notice the reduced quality of their vision. However, if they were measured on a contrast sensitivity unit, it would likely manifest itself. There can be a reduc- tion in the ability to see fine detail, to discriminate objects clearly in low-light conditions, or decreased brightness or sharpness of images.

While with the majority of patients this goes unnoticed, some patients are very unhappy postoperatively. We can reduce these problems by using wavefront-guided treatments.

Know the difference

OM: What are the differences between conventional LASIK and wavefront-guided LASIK in terms of necessary equipment, the surgery, patient satisfaction and enhancement rates?

Dr. Black: Conventional LASIK involves a standard eye exam as well as measurements of corneal curvature, pachymetry and pupil size to determine candidacy. The measured refraction is then entered into the laser. The laser has a standard ablation pattern for that prescription, which is ablated on the cornea. Patients are happy with the results 90% of the time. About 10% of the patients postoperatively experience night vision problems or quality of vision issues.

With wavefront-guided LASIK, as well as the above tests, an aberrometer is used to take a wavefront map of the eye. The refractive surgeon then uses these refractive points to create a treatment map so the surgeon can treat each area individually. This means treating not only the refraction, but the aberrations or distortions in the patient's visual system. This treatment plan is transferred by memory stick into the laser for treatment.

VISX (Advanced Medical Optics) utilizes something called "Iris registration" to ensure that the treatment is lasered exactly as mapped. It lines up the iris landmarks and adjusts for cyclorotation and pupil shift under the laser to increase the accuracy of the ablation. The risk of night glare with custom ablation is less than 1%. Our enhancement rate is also significantly lower versus standard treatment.

OM: How does conventional LASIK affect quality of vision?

Dr. Black: In approximately 10% of patients, quality of vision is reduced, usually manifesting itself in night glare or mild loss of BCVA. In a standard treatment, the shape that's lasered on the cornea is based on a shape from the patient's glasses or contact lenses. This shape is flatter than the natural corneal shape. Postoperatively, patients then have an increase in their spherical aberration as the central cornea is much flatter than the periphery. The peripheral "knee" that's formed causes peripheral light to scatter, causing difficulties in low-light situations.

OM: How does wavefront-guided LASIK address contrast sensitivity?

Dr. Black: With custom or wavefront-guided technology, contrast sensitivity comes back to its pre-operative levels at around six months postoperatively as opposed to a permanent reduction that's seen in most cases using standard ablation.

OM: Is there any clinical research addressing these issues?

Dr. Black: We've done some in-house studies to measure contrast sensitivity, which have proved the above point. In a personal vein, I had standard LASIK surgery eight years ago. I was happy as I was plano and no longer severely myopic, but I did experience mild night vision issues. Two months ago, I underwent a custom enhancement. I have been measuring my aberrations during the healing process and have seen my higher order aberrations decrease by 72%. My night vision is now sharp and crisp and my BCVA has increased by two lines.

Patient selection

OM: Does the candidate selection criteria for wavefront-guided LASIK differ from conventional LASIK?

Dr. Black: Our center has elected to treat 100% wavefront, as we don't believe that patients can adequately understand the postoperative differences they will notice in their vision. In many cases patients make their decision based on cost and are then unhappy with the outcome.

The biggest difference we see is the counseling of patients with large pupils. Studies have shown that patient satisfaction is not related to pre-operative pupil size as long as custom technology is used for treatment. The hardest thing, though, is that as technology has evolved, patient expectations have increased. Patients are no longer happy with a 20/40 outcome. If they are not 20/20 or better, they're disappointed and return seeking an enhancement.

We also get a population of well-educated, visually "picky" patients seeking refractive surgery. They believe that surgery is a commodity. They don't always understand that this is still surgery and we have no control over individual healing patterns.

OM: What group(s) of patients would benefit most from wavefront-guide LASIK (as opposed to conventional)?

Dr. Black: We believe that everyone benefits from this technology but if I have to break it down, I would say that patients with visually demanding jobs or personalities (dentists, doctors, pilots, long-distance truck drivers, engineers), and GP wearers who are used to crisp vision pre-operatively, would benefit most. I would add patients with large pupils and patients with reduced or excellent BCVA pre-operatively (they'll notice any degradation in their vision).

OM: Are there any groups of patients who would experience no additional benefits from wavefront-guided LASIK?

Dr. Black: If wavefront technology is available for that patient, then the answer is no. In some patients, such as those with a prominent corneal scar or a longstanding lenticular opacity, we can't obtain a wavefront map, so for them the only option is conventional LASIK.

Bringing it to the patient

OM: How do you educate patients about the differences between wavefront-guided and conventional LASIK?

Dr. Black: I tell patients that with conventional LASIK we are lasering their lens prescription onto the eye in a standard treatment profile. It may give them 20/20 vision but it can result in loss of quality of night vision due to the peripheral "knee." Wavefront-guided LASIK treats all the irregularities and aberrations in your visual system, thereby giving patients the potential for better quality day and night vision and the least risk of having a problem. One of our surgeons, Dr. Machat, uses the analogy that standard LASIK is like buying a suit off the rack; it may look okay but will not necessarily fit you properly, while wavefront-guided LASIK is like buying a tailor-made suit that will fit you perfectly.

OM: Is there anything else you would like to say to our readers who refer patients for refractive procedures?

Dr. Black: The best way for referring practitioners to benefit their patients is to provide them with accurate information and keep up-to-date with technology so patients will perceive him or her as an "expert." If you don't get involved in their laser care, patients these days will find someone who will. Form a relationship with a refractive surgery clinic so that you're current on what the center has to offer. These are your patients and it's in your interest to make sure they achieve the best possible results.

If you refer a patient to a TLC clinic, we promise to refer back to you for post-op care. We require patients to undergo annual eye exams with their own optometrists to maintain eye health.

Just because a patient is undergoing refractive surgery does not mean that's the end of his or her eyecare needs. Some may require reading glasses, etc. We're trying to reduce their dependency on glasses, not necessarily eliminate them in all cases. Your laser patients will be your happiest patients and will refer their friends and colleagues to you. I was in private practice for 20 years before joining TLC and when I became actively involved in the referral process, I saw my practice begin to grow more than ever before as my laser patients were my best referral source.

Optometric Management, Issue: June 2006