PCLI OD Newsletter (Fall 2004)

Pacific Cataract and Laser Institute

OD News - A Quarterly Newsletter for Northwest Optometric Physicians

Surface laser vision correction is a treatment option for some patients. Brian Johnson’s article sheds light on the procedure, indications for treatment and post-op recovery. I hope this will help you in pre-op evaluation and counseling of your refractive surgery patients. As always, enjoy! Lori Youngman, OD PCLI—Vancouver, WA

Introduction LASIK is our preferred treatment for most laser vision correction (LVC) candidates. It offers quick visual recovery and minimal post-op discomfort. However, LASIK is not always a viable option—or the best option. Time and experience is teaching us that patients not suited for LASIK may be good candidates for what we call surface LVC. Surface LVC includes several procedures that remove corneal epithelium before laser ablation. Each avoids the use of a conventional LASIK flap and creates a more superficial correction. PRK—epithelium removed with a blade or Amoils brush and discarded LASEK—epithelium loosened with dilute alcohol solution and pushed aside Epi-LASIK—thin epithelial flap created with an epikeratome (mechanical epithelial separator) Indications Thin Corneas We most commonly consider surface LVC when corneas are too thin for LASIK. These patients typically have high refractive errors requiring deeper laser ablations which would lead to an unacceptably thin stromal bed. We take a cautious approach to any LASIK patient having central corneal thickness of less than 500 microns—regardless of refractive error. There is a growing consensus among experienced refractive surgeons that abnormally thin corneas are at increased risk for unfavorable and unpredictable outcomes with LASIK. Surface LVC has less impact on the cornea’s mechanical stability—so is a safer option for these patients. Irregular Corneas Another indication for surface LVC is when patients have subtle corneal irregularities or mild irregular astigmatism on corneal topography. They may be described as keratoconus suspects due to the appearance of corneal topography, but they lack abnormal corneal biomicroscopy findings and pathological corneal thinning found in true keratoconus. A traditional LASIK flap weakens the biomechanical stability of the cornea and would put these patients at increased risk of developing corneal ectasia. Surface LVC may be a good alternative. Large Pupils Patients with very large scotopic pupils may be better candidates for surface LVC. The laser treatment zone should be larger in these patients to minimize risk of annoying glare and night vision problems. However, larger treatment zones require removal of more central corneal tissue—which could lead to unacceptably thin corneal stroma. Surface LVC will often allow for an acceptable residual stromal thickness. In addition, the size of LASIK flap can vary and potentially be smaller than the scotopic pupil—particularly with flatter corneal curvatures. For those with extremely large pupils (>8 mm), the flap edge could contribute to night vision problems. Surface LVC would avoid this potential complication. Hyperopic Patients Surface LVC may offer an advantage for some hyperopic patients. This is related to 2 things: The LASIK flap, which is often smaller in hyperopic patients The ablation pattern required for hyperopia Hyperopic patients usually have flat keratometric measurements that lead to smaller flap sizes. And, to create a steeper central cornea, laser ablation is primarily in the peripheral area of treatment zone. This creates an annular gutter which may not interface as nicely with the flap. So the LASIK flap edge can be a little more prone to epithelial ingrowth, microstria, and irregular topography. Surface LVC may avoid some of these potential complications but the advantages of LASIK need to be considered as well in each individual case.		EBMD Patients Surface LVC is an excellent option for patients with epithelial basement membrane dystrophy (EBMD). As you know, symptoms can vary from nothing to recurrent episodes of intense pain and photophobia. Clinical signs of EBMD include corneal basement membrane whorling defects or fingerprints, irregular map patterns, and epithelial dots or microcysts. Epithelial cells do not adhere to the underlying basement membrane as well as they do in a normal cornea, so LASIK can result in recurrent corneal erosions and poor epithelial healing. Surface LVC can avoid these problems as it allows for a more normally adherent epithelial layer to regenerate and replace the dystrophic epithelial basement membrane. In some severe cases of EBMD with painful, frequent recurrent corneal erosions, surface laser ablation (phototherapeutic keratectomy or PTK) has been successful as a therapeutic procedure. High Risk Patients Patients who spend a lot of time in remote areas far from surgical eye care, or those with occupations and hobbies which increase their risk of getting hit in the eye may be better served with surface LVC. Corneal trauma after LASIK can compromise the corneal flap and have a higher likelihood of needing surgical repair vs. corneal trauma after surface LVC. Glaucoma Patients Finally, surface LVC should be considered for patients with glaucoma. This is particularly true for more advanced cases with significant optic nerve damage and visual field loss. The vacuum required to hold the microkeratome’s suction ring in place while the LASIK flap is created causes a 10 to 15 second spike in IOP. This can be 60 mm Hg or higher. The short increase in pressure could further compromise patients’ optic nerve and visual field. Surface LVC avoids use of a suction ring (except in the case of epi-LASIK, which requires low suction). Remember that LASIK and surface LVC thin the cornea and artificially lower IOP readings. This must be taken into account for ongoing glaucoma management. Conclusion While surface LVC is less appealing than LASIK, it may be the best option for some patients—if they are willing to put up with: Discomfort for 2-5 days as the epithelium heals under a bandage contact lens 2-4 weeks of visual recovery Tapering doses of mild topical steroids for approximately 3 months If you have patients who might be best served with surface LVC, please feel free to call one of our doctors to discuss the details.


Corneal Thickness Calculator for LVC Now you can determine if your patients have enough corneal thickness for LASIK—or if they are better suited for surface LVC. The corneal thickness calculator we created as a tool for our technicians and doctors is available to you. Click here to view or download it to your computer. The file may take one minute to download. You’ll be able to quickly see if patients have enough corneal thickness to safely proceed with surgery. The size of the treatment zone should be as large or larger than the scotopic pupil.		Patient data needed from you: Scotopic pupil size Sphere Cylinder Target refraction Central pachymetry If you do not have a pachymeter, the calculations will be based on the average corneal thickness. For accurate measurements, you can always send patients in question to us for a quick pachymetry/topography visit. This 30 minute service is free of charge if patients proceed with surgery.

PCLI’s Web Services Visit the “For Doctors” section of our website for free services that can benefit your practice. Order our materials online CE events calendar Provide LASIK Financing See the carriers and networks we are providers for—and give suggestions Buy or sell used equipment Buy or sell a practice Hire an associate Seek employment See the top of this page for shortcuts to these services.		New Item LASIK DVD

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