Radial keratotomy learning curve using the American technique.

PURPOSE: To delineate the learning curve for a beginning refractive surgeon using the centrifugal (American) technique. SETTING: Naval Medical Center, San Diego, California, USA. METHODS: The first 100 radial keratotomy (RK) cases (51 patients) of one surgeon, divided into five sequential groups of 20, were retrospectively reviewed. All patients had RK using the American technique. Emmetropia was the goal in all patients. Groups were compared with respect to preoperative refractive status, age, sex, and outcome. Outcomes analysis included visual acuity, refractive error, complications, and enhancement rates. Data were reviewed preoperatively and 1 and 3 months postoperatively. RESULTS: All five groups were age and sex matched. There was no difference in preoperative refractive error among the five groups. Sequential improvement in early postoperative refractive error from a mean of -1.73 diopters (D) +/- 1.00 (SD) (first 20) to 0.45 +/- 0.55 D (last 20) (P < .001) and decreased enhancement rates from 50% (first 20) to 0% (last 20) (P = .002) were statistically significant. Visual acuity at 1 month was 20/40 or better in 47% of patients in Group 1 (first 20), whereas all patients in Group 5 (last 20) had an acuity better than 20/40 (P < .001). There was no significant difference in complication rates among the five groups. CONCLUSION: The results of RK using the American technique can improve significantly with surgeon experience. Enhancement rates decreased with experience, and there was no difference in complication rates during the learning period of one surgeon.

Topographic detection of photorefractive keratectomy.

PURPOSE: This study aimed to evaluate the sensitivity and specificity of subjective review of corneal topography to detect patients who have undergone photorefractive keratectomy (PRK). METHODS: Topographic maps from 3 different devices were obtained from 19 patients with postoperative PRK and 9 control subjects with emmetropia and 10 control subjects with myopia. Each image was printed in an absolute and relative scale (total of 228 maps) and graded for overall shape and pattern. Fifteen masked reviewers independently rated each map as either postoperative PRK or not. RESULTS: The overall sensitivity (ability to detect PRK) and specificity rates (ability to exclude control subjects) by reviewers were 65% and 93%, respectively. Sensitivity was influenced independently by the scale (relative, 68%; absolute, 62%; P < 0.01), experience of reviewer (experienced, 77%; inexperienced, 53%; P < 0.001), and device (Alcon, 67 +/- 29.9; Eyesys, 75 +/- 29.4%; and Tomey, 54 +/- 31.7%; P < 0.001). Low levels of preoperative myopia were consistently more difficult to detect than higher levels (low myopia -1.50 to -2.99 diopters [D] sensitivity: 53 +/- 34.5%; medium level -3.00 to -4.49 D: 67 +/- 28.9%; and high level -4.50 to -6.00 D: 77 +/- 21.1%; P < 0.0001). Differences in specificity between experienced and inexperienced reviewers were obtained when maps had a homogeneous topographic pattern (97 +/- 5.6% and 85 +/- 13.7%, respectively; P < 0.05). Several control topography patterns (e.g., homogeneous, focal, and keyhole) were disproportionately more difficult to correctly identify on the Eyesys device. CONCLUSIONS: Topographic experience is a significant factor influencing the correct identification of PRK. Techniques also can be used to enhance detection, such as the use of different devices and scales. However, if subjective review of topography is used as the only method of detection, many patients with PRK will not be identified properly. In addition, the most prevalent preoperative myopic category in the general population (myopia < -3.00 D) also is the most difficult to detect after treatment. This reduces the usefulness of topography as a screening tool. Other techniques are needed to improve the detection of patients with postoperative PRK.

Refractive changes during 72-hour exposure to high altitude after refractive surgery.

PURPOSE: The authors prospectively analyzed refractive and pachymetric parameters during exposure to high altitude after radial keratotomy (RK) and photorefractive keratectomy (PRK). METHODS: The authors measured manifest and cycloplegic refraction, keratometry, computed video keratography, and central and peripheral pachymetry in six subjects who have undergone RK (11 eyes), six who have undergone PRK (12 eyes), and nine with myopia (17 eyes) at sea level and on three consecutive days at 14,100 feet. All measurements were repeated 1 week after subjects returned to sea level. RESULTS: Subjects who have undergone RK demonstrated a significant and progressive increase in spherical equivalence (+0.30 +/- 0.50 diopters on day 1 and +1.52 +/- 1.01 diopters on day 3; P < 0.001) and a decrease in keratometry values during exposure to altitude when compared with control subjects with myopia. Healthy subjects and those who have had PRK demonstrated no significant change in refractive error. Pachymetry measurements demonstrated significant peripheral corneal thickening in all three groups (RK, P < 0.004; PRK, P < 0.007; control subjects, P = 0.0006) by day 3 at high altitude. Refraction, keratometry, and pachymetry returned to baseline (P = 1.000) after return to sea level. CONCLUSIONS: Seventy-two-hour exposure to high altitude in subjects who have had RK induces a significant, progressive, and reversible hyperopic shift in refraction with corresponding video keratographic and keratometric changes. The authors hypothesize that the high-altitude hypoxic environment causes increased corneal hydration in the area of the RK incisions, which may lead to central corneal flattening and a hyperopic shift in refractive error. Subjects who have had PRK and those with myopia are not susceptible to this refractive shift. The authors' RK data suggest that the time since surgery and the amount of surgery are related to the degree of hyperopic shift during altitude exposure.

Initial treatment of microbial keratitis.

PURPOSE: The common occurrence of failed medical treatment in microbial keratitis led us to investigate this phenomenon. METHODS: We retrospectively reviewed all ulcers that presented to our department for 24 consecutive months. We classified each ulcer as either a therapeutic success or failure based on a precise definition of the response to initial antibiotic selection. We then analyzed multiple factors including: antibiotic selection, ophthalmic disease, ulcer characteristics, and management, to determine their significance in the success or failure in treating microbial keratitis. Complications were also examined. RESULTS: Important factors in failure were non-fortified antibiotics (P < 0.001), ocular surface disease (P = 0.0178) and outpatient management (P < 0.001). Large ulcers (P = 0.051) were of borderline significance. Sensitivity results reflect high sensitivity among successfully treated patients when appropriate antibiotics are chosen. CONCLUSIONS: This report provides insight into current practice patterns and potential means to improve success in managing microbial keratitis.

Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel.

PURPOSE: To evaluate the safety, efficacy, and quality of vision after photorefractive keratectomy (PRK) in active-duty military personnel. METHODS: Photorefractive keratectomy (6.0-mm ablation zone) was performed on 30 navy/marine personnel(-2.00 to -5.50 diopters [D]; mean, -3.35 D). Glare disability was assessed with a patient questionnaire and measurements of intraocular light scatter and near contrast acuity with glare. RESULTS: At 1 year, all 30 patients had 20/20 or better uncorrected visual acuity with no loss of best-corrected vision. By cycloplegic refraction, 53% (16/30) of patients were within +/- 0.50 D of emmetropia and 87% (26/30) were within +/- 1.00 D. The refraction (mean +/- standard deviation) was +0.45 +/- 0.56 D (range, -1.00 to 1.63 D). Four patients (13%) had an overcorrection of more than 1 D. Glare testing in the early (1 month) postoperative period demonstrated increased intraocular light scatter (P<0.01) and reduced contrast acuity (with and without glare, (P<0.01). These glare measurements statistically returned to preoperative levels by 3 months (undilated) and 12 months (dilated) postoperatively. Two patients reported moderate to severe visual symptoms (glare, halo, night vision) worsened by PRK. One patient had a decrease in the quality of night vision severe enough to decline treatment in the fellow eye. Intraocular light scatter was increased significantly (>2S D) in this patient after the procedure. CONCLUSIONS: Photorefractive keratectomy reduced myopia and improved the uncorrected vision acuity of all patients in this study. Refinement of the ablation algorithm is needed to decrease the incidence of hyperopia. Glare disability appears to be a transient event after PRK. However, a prolonged reduction in the quality of vision at night was observed in one patient and requires further study.

Myasthenia gravis by another name: an elusive imposter.

A patient with procainamide-induced "pseudo" myasthenia gravis is presented. This clinical entity is discussed in terms of its clinical features, diagnosis, and treatment. Attention is directed to the importance of role of the ophthalmologist in making the diagnosis.