Volume 80, Issue 11 , Pages 662-667, November 2009
Surgical refractive correction
Article Outline
Laser refractive correction outcomes are better than many realize, and technological advances are improving procedures. However, the U.S. Food and Drug Administration is warning that some patients are not being adequately advised about the limitations of laser correction. Proper counseling and evaluation of laser correction candidates by optometrists is critical.
But today, advancing technology and better patient selection are producing improved results, according to Paul Karpecki, O.D., chair of the American Optometric Association (AOA) Contact Lens and Cornea Section's Refractive Surgery Project Team. Fewer laser patients are requiring follow-up enhancement procedures. Up to 95% of laser correction patients now achieve 20/20 uncorrected visual acuity, Dr. Karpecki says. An analysis of the global peer-reviewed literature found that more than 95% of patients were satisfied with the outcome of their laser-assisted in situ keratomileusis (LASIK) surgery.2
Technical advancements
Technical advancements include faster lasers, larger spot areas, bladeless flap incisions, intraoperative pachymetry, and wavefront-guided procedures. New techniques have significantly improved the reliability of the procedure compared with that of 1991. In an effort to overcome the need for severing of corneal nerves, a number of alternatives to LASIK have been developed, including laser epithelial keratomileusis (LASEK), Epi-LASIK, sub-Bowman's keratomileusis (thin-flap LASIK), wavefront-guided photorefractive keratectomy (PRK), and conductive keratoplasty (CK) (see Box 1).
LASIK. Laser-assisted in situ keratomileusis (LASIK) has been the most popular procedure for treatment of refractive errors since its introduction in the mid-1990s. Despite the popularity and success of LASIK, complications have arisen from the use of the mechanical microkeratome. These complications include incomplete flaps, variation in flap thickness, buttonholes, corneal ectasia, and undercorrections and regressions.1, 2, 3, 4 Such complications have led to further advances in surface ablation techniques or the use of femtosecond technology.
LASEK. Introduced in 1999, laser epithelial keratomileusis (LASEK) creates an epithelial flap. The epithelial flap is pushed aside to permit corneal reshaping. After ablation is complete, the epithelium is replaced, and a bandage contact lens is inserted. LASEK avoids all flap-related complications associated with LASIK, and it has less postoperative pain and a faster recovery than photorefractive keratectomy (PRK).
Epi-LASIK. The epi-LASIK technique was developed after LASEK. Epi-LASIK creates an epithelial flap with an epikeratome. Unlike the microkeratome, the epikeratome does not cut down into the corneal stroma, thus avoiding such complications as epithelial ingrowth, striae, interface infections, and diffuse lamellar keratitis. Epi-LASIK–treated eyes show a faster rehabilitation of corneal sensitivity and tear function compared with LASIK-treated eyes.5 A recent study in the Journal of Refractive Surgery concluded that neither technique seems to offer a major advantage over the other in clinical and confocal microscopic results.6
Epi-LASEK. Invented in 2001, LASEK and epi-LASIK are combined to create epi-LASEK. This procedure unites the use of diluted alcohol along with an epikeratome to improve flap separation. The addition of alcohol contributes to better flap and hinge creation without increased pain or haze.7
Thin flap LASIK. Thin flap LASIK creates a 60- to 100-μm flap versus a traditional flap of 130 to 160 μm. The obvious advantage with thin flap LASIK is that a thicker posterior stromal bed is maintained.8 The literature also shows that in comparison with traditional LASIK, thin flap LASIK achieves excellent refractive outcomes, a lower rate of enhancements, and a good visual performance with better contrast sensitivity.8
Femtosecond LASIK (IntraLase™). Introduced in 2002, the femtosecond (FS) laser creates a corneal resection plane by delivering laser pulses at a predetermined depth in the cornea and producing thousands of microscopic expanding bubbles of carbon dioxide gas and water, which separate the corneal lamellae. The major advantage of the FS laser is its predictability, reproducibility, and accuracy in creating the flap, which has important implications for reducing intra- and postoperative complications.9
Conductive keratoplasty (CK) (NearVision CK). Not actually a laser procedure, CK involves the use of radio-frequency (RF) energy for corneal shaping to correct mild hyperopia. A hand-held instrument with a tiny probe is used to apply low-level RF to targeted spots in a circular pattern around the outer cornea. The tissue to which the RF energy is applied forms a band that tightens and steepens the corneal curvature. Unlike LASIK or PRK, no tissue is removed and the procedure takes only a few minutes.
(Adapted from Modern Corneal Refractive Therapies by Mandy Mataya, O.D., as it appeared in the March 25, 2009, edition of the AOA Contact Lens and Cornea Section newsletter.)
The development of new, faster ophthalmic lasers is far and away the most important factor driving the improvement in laser correction, Dr. Karpecki said. There are 6 major LASIK platforms today:
VISX lasers account for about 60% of the laser refractive procedures performed in the United States today, according to the St. Louis–based market research firm, MarketScope.
The new lasers achieve the same ablation as older models by striking the targeted area more times with a lower-intensity beam. All offer faster (200-Hz) ablation rate lasers providing faster corrections (requiring only 4 seconds per diopter for a 6.5-mm optical zone). That means faster procedures for the patient. It also means the patient enjoys clear vision more quickly (generally within a few days), as well as targeted correction (within a few weeks), and with less pain and other side effects. Trauma to the eye is greatly reduced, and less moisture is lost, helping to possibly reduce dry eye symptoms (one of the most common problems associated with laser correction). Most of the newer laser platforms now utilize small flying spot scanning, as opposed to the broad beam ablation used in previous models, helping to reduce the glare and halos that have been common complaints among LASIK patients. In addition, femtosecond lasers are now being used in many cases to cut the corneal flaps necessary for LASIK. Results are comparable to those achieved with microkeratomes.
Advances are also being made in postsurgical care, Dr. Karpecki notes. The postprocedure administration of the immunosuppressive drug cyclosporine, normally used to promote faster wound healing, is proving effective in not only reducing dry eye but in helping to achieve desired correction, Dr. Karpecki notes.
Patient selection
The U.S. Food and Drug Administration (FDA) recently stepped up efforts regarding the marketing and promotion of laser refractive correction (see related article in this issue). An FDA letter to eye care practitioners emphasizes that patients should be provided accurate information regarding the procedure. The warning emphasizes the role that optometrists, as primary eye care practitioners, must play in assessing patients who may be appropriate for laser correction, adequately counseling them on the risks and benefits of the procedure, and helping them determine whether laser correction can meet their needs and expectations, Dr. Karpecki observed. The AOA Clinical and Practice Advancement Group's Clinical Practice Recommendations on Optometric Co-Management of Refractive Surgery provides an outline for patient education (see Table 1), preoperative considerations (see Table 2), and preoperative evaluation (see Table 3) of candidates for laser refractive correction. Complete copies of the recommendations can be accessed on the AOA Web site at www.aoa.org/x5495.xml.
Table 1. AOA Clinical Practice Recommendations on Optometric Co-Management of Refractive Surgery regarding patient education
| Factors to consider in patient education |
| Realistic expectations ▪Elective procedure and costs ▪Risks vs. benefits ▪Enhancement potential |
| Alternative corrections ▪Spectacles ▪Contact lenses ▪Other surgical procedures (e.g., Phakic intraocular lenses [IOLs] or refractive lens exchange procedures with accommodation [Crystalens] or multifocal IOLs). |
| Normal symptoms and side effects ▪Discomfort ▪Dry eye (3 to 9 months, depending on pre-existing condition) ▪Fluctuating vision (from 4 to 6 weeks to 3 months, depending on dry eye and other factors) ▪Halos and glare at night (4 to 6 weeks) ▪Foreign body sensation (lasting 24 to 48 hours) |
| Risk for complications ▪Intraoperative problems ▪Abnormal healing ▪Corneal haze ▪Loss of best-corrected visual acuity (BCVA) ▪Higher-order aberrations ▪Infection ▪Other surgical complications like corneal ectasia |
| Presbyopia ▪Increased dependence on reading glasses in later years when both eyes are surgically corrected for distance ▪Optional slight undercorrection of nondominant eye for reading in patients of presbyopic and prepresbyopic age |
| Intraoperative role of patient ▪Maintain fixation on target |
| Postoperative eye care ▪Lubrication, instillation of drops ▪Oral medication, including precautions for use of oral narcotic analgesics and avoidance of alcoholic beverages ▪Do not rub eyes and wear protective shield at night for first week ▪Follow-up visits ▪Reporting of symptoms |
Table 2. AOA Clinical Practice Recommendations on Optometric Co-Management of Refractive Surgery regarding preoperative considerations.
| Unstable refractive error ▪Age <21 years (some female patients will reach a stable refractive error before age 21, typically not before age 18) ▪Cataract development ▪Corneal warpage secondary to long-term contact lens wear |
| Systemic disease ▪Uncontrolled diabetes, type 1 (insulin-dependent) or uncontrolled type 2. ▪Rheumatoid arthritis or other autoimmune diseases (e.g., lupus) that are not well controlled. |
| Ocular disease ▪Keratoconus ▪Pellucid marginal degeneration of the cornea ▪Cataracts ▪Glaucoma manifesting visual field defects ▪Fuchs' corneal dystrophy ▪Other corneal dystrophy that results in recurrent erosion (e.g., granular or lattice dystrophy) may be better served with PRK ▪Nonresponsive keratoconjunctivitis sicca (KCS) or severe dry eye as indicated by patient symptoms and signs ▪Corneal staining with a vital dye (e.g., Lissamine green, rose bengal, etc.) greater than grade 3 and not responding to dry eye therapy or Schirmer tear tests <5 mm ▪Untreated lid disease, e.g., blepharitis or meibomitis ▪High-positioned scleral buckles after retinal detachment surgery ▪Neurotrophic keratitis ▪Herpes simplex virus (HSV) keratitis ≤12 months before surgery |
| Unrealistic expectations ▪Expectation of better than 20/20 vision ▪Expectation of never needing to use reading glasses |
| Corneal thickness ▪Predicted postoperative corneal thickness <410 μm (i.e., < about 300 μm under the flap) |
| Large pupils ▪Patients with larger pupils especially in dim illumination may be at greater risk of observing higher-order aberrations should they be present or remain after laser surgery. Patient education and documentation is important. |
| Preoperative keratometry readings ▪A cornea that is too flat or too steep (predictive K readings for myopic eyes <36 D) may result in poor postoperative optics, and for hyperopic eyes (>49 D), may result in greater dry eye symptoms. |
| High refractive error ▪Caution should be taken in hyperopia exceeding +4.00 D or myopia over –9.00 D in patients not otherwise excluded by pachymetry or pupil size. Lens procedures (e.g., clear lens exchange or phakic intraocular lens [IOL] should be considered or discussed for certain patients in this refractive error range). |
Table 3. AOA Clinical Practice Recommendations on Optometric Co-Management of Refractive Surgery regarding preoperative evaluation
| Pachymetry (corneal thickness measurement) ▪Postoperative corneal thickness ≥410 μm ▪Ablation depth is based on optical zone (OZ) diameter, blend zone (BZ), and refractive error ∼ 15 μm per diopter |
| Pupil diameter ▪The patient with larger pupils may be more likely than one with smaller pupils to notice any existing higher-order aberration, which may manifest as night vision problem ▪Measure pupils under both photopic (or mesopic) and scotopic conditions and document for dim illumination |
| Topography ▪Evaluation of surface contour of cornea to determine the potential of early keratoconus |
| Keratometry ▪Preoperative corneal curvature (K readings) and dioptric value of refractive error predict postoperative K readings |
| Manifest/cycloplegic refraction ▪Measurement of refractive error (myopia, hyperopia, astigmatism) needed to ensure against overcorrection |
| Phorometry ▪A cover test should be performed to rule out strabismus, since patients with intermittent strabismus may not tolerate monovision corrections |
| Tear film assessment ▪Significant dry eye may delay healing and decrease visual acuity during early healing ▪Reduced tear quantity: Schirmer's tear test <5 mm ▪Corneal staining: Rose Bengal dye, Lissamine green dye, or fluoresceine dye ▪Conjunctival staining alone: Rose Bengal dye, Lissamine green dye ▪Treat pre- and postoperatively with artificial tears or punctal occlusion, cyclosporine, or corticosteroid drops such as loteprednol |
| Slit lamp examination (anterior segment evaluation) ▪Patients with blepharitis and meibomitis are more likely to experience dry eye and have more postoperative symptoms ▪The presence of staphylococcal bacteria in these conditions poses a risk for infection during refractive surgery ▪Patients with blepharitis should be treated with lid scrubs, antibiotics etc ▪Intrastromal scars may result in an irregular ablation rate ▪Larger pingueculae may increase difficulty of proper suction of microkeratome |
| Dilated fundus examination ▪A thorough peripheral fundus examination is required to rule out retinal thinning, holes, or partial detachments that could lead to potential problems during refractive surgery |
Screening out candidates with objectively identifiable contraindications for laser correction is obviously important to favorable outcomes, Dr. Karpecki notes. The AOA recommendations note that contraindications for laser correction include unstable refractive error (such as found in virtually all patients under 18 years of age), systemic disease (including diabetes and autoimmune conditions such as rheumatoid arthritis), and ocular disease (such as keratoconus, cataracts, or glaucoma with ocular field defects). In addition, patients with very thin corneas, large pupils, corneas that are too flat or too steep, high refractive errors (hyperopia over 4.00 diopters [D] or myopia over −9.00 D), atypical topography, or dry eye may not be good candidates for the procedure. The AOA Clinical and Practice Advancement Group recommends a 9-step preoperative evaluation including pachymetry, measurement of the pupil diameter, and corneal topography.
However, the AOA Practice Recommendations also cite unrealistic expectations—such as better than 20/20 visual acuity or complete freedom from reading glasses—as contraindications for laser refractive correction. The AOA Clinical and Practice Advancement Group recommends for those considering laser refractive surgery a 7-step program of patient education covering:
It is essential that patients truly understand exactly what benefits laser correction might provide them as well as the risks and potential side effects they might face, Dr. Karpecki said. Patients who enter into the procedure with unrealistic expectations, such as 20/15 distance acuity and the elimination of reading glasses for life, are probably going to be disappointed, he notes.
It may be even more important to determine whether the patient's temperament is appropriate. A “psychological” evaluation is probably at least as important as objective indications and contraindications in determining who will be an appropriate laser patient, Dr. Karpecki contends. “Before referring a patient to an ophthalmologist for laser correction, the patient's optometrist should assess the patient's personality traits to determine if the patient is likely to be satisfied with laser correction,” he said. Demanding patients who like to have products and services custom-tailored to their needs down to the final detail, or perfectionists who like to “tinker” with products, may not be well suited for laser vision correction. “Patient interest in freedom from corrective lenses is not enough,” Dr. Karpecki said. “If the patient is hypercritical—the type of patient who notices every quarter diopter of change in a prescription or who is highly exacting with the phoropter; wanting to get every setting exactly right—this is not the type of patient who is well suited for laser correction. Such patients will probably be happier with spectacles or contact lenses. Patients should also be advised of the cost of laser correction and should understand that the procedure is not covered by insurance.”
The future of laser correction
Even with the improvements in laser correction procedures over recent years, procedure volume has yet to increase markedly, Dr. Karpecki acknowledges. That is primarily because of economic factors, he believes. However, some industry observers believe that as the economy picks up, demand for laser vision correction will increase. As it does, optometrists must be ready to provide patients with the most accurate, up-to-date information on both the pros and the cons of laser correction, Dr. Karpecki said. Laser correction researchers and laser manufacturers increasingly feel patients do not understand the benefits the correction can provide. Government regulators are increasingly concerned that patients are not being properly apprised regarding outcomes. As the nation's primary eye care providers, optometrists are in an excellent position to ensure patients have the information they need regarding laser correction, Dr. Karpecki said. Both patients and the growing field of non–lens refractive correction will benefit when they do.
References
- Laser in situ keratomileusis in myopic patients with congenital nystagmus. J Cataract Refract Surg. 2006;32(3):464–467
- LASIK world literature review: Quality of life and patient satisfaction. Ophthalmology. 2009;116(4):691–701
References
- Complication of laser in situ keratomileus for the correction of myopia. Ophthalmology. 1999;106:13–30
- For the Flap Thickness Study Group. Flap thickness accuracy: comparison of 6 Microkeratome models. J Cataract Refract Surg. 2004;30:964–977
- Retreatment after laser in situ keratomileusis. Ophthalmology. 1999;106:21–28
- . Regression after LASIK for the treatment of myopia: the role of the corneal epithelium. Semin Ophthalmol. 1998;13:70–82
- Comparison of corneal sensitivity and tear function following epi-LASIK for laser in situ keratomileusis for myopia. Am J Ophthalmol. 2006;142:669–671
- . A prospective bilateral comparison of epi-LASIK and LASEK for myopia. J Refract Surg. 2008;24:928–934
- . Epi-LASIK versus epi-LASEK. J Refract Surg. 2008;24:S57–S63
- Thin flap in situ keratomileusis: analysis of contrast sensitivity, visual and refractive outcomes. J Cataract Refract Surg. 2005;31:1357–1365
- . Accuracy and precision of LASIK flap thickness using the IntraLase femtosecond laser in 1000 consecutive cases. J Refract Surg. 2008;24:802–806
This is the final article in a special “Practice Strategies” series on “Doctor-driven dispensing: Providing patients a complete range of vision correction options.” The series began in the August edition of Optometry with articles outlining the latest developments in eyeglasses and contact lenses. The series continued in the September edition with a look at the emerging fields of intraocular lens correction and corneal reshaping. Opinions expressed are not necessarily those of the American Optometric Association.
PII: S1529-1839(09)00490-4
doi:10.1016/j.optm.2009.09.009
Volume 80, Issue 11 , Pages 662-667, November 2009
