Sandor Kaupp

Orbscan pachymetry: Implications of a repeated measures and diurnal variation analysis ∗

INTRODUCTION Corneal thickness changes reflect alterations in hydration and metabolism. Ultrasound pachymetry determinations may be adversely influenced by fluctuations in tissue hydration, whereas optical systems are apparently unaffected by these fluxes. A recently marketed, optical-based, topographic mapping system (Orbscan; Orbtek, Inc.) uses anterior and posterior corneal surface data to calculate corneal thickness. OBJECTIVE This new instrumentation presents as a potentially useful pachymetry tool for evaluation of corneas under hydration flux or challenge (e.g., postphotorefractive keratectomy [PRK] healing studies) and was therefore evaluated for accuracy and variability. MEASUREMENTS Three calibrated standards were measured in repeated fashion. Additionally, 1 test subject was measured 30 times in 1 day (5 measurements each at 8:00, 9:30, and 11:00 AM and at 1:00, 2:30, and 4:00 PM). Corresponding measurements were made at 8:00 and 11:00 AM and at 4:00 PM on 3 separate days to assess repeatability. Grouped data from 18 volunteer subjects were compared to the data of the test subject as well. RESULTS Pachymetry accuracy on a calibrated standard was determined to be +/-2 microm (standard deviation, n = 12). Repeated measures on the subject demonstrated a mean standard deviation of 9.08 microm for 750 thickness data points across the central 7 mm of the cornea; peripheral measurement points exhibited progressively greater variability than at the apex (analysis of variance; P<0.0001). A plot of thickness by corneal location and time of day exhibited a diurnal pattern, with the peripheral cornea exhibiting progressively greater thickness changes than the central cornea (two-way analysis of variance; P<0.00001). The data significantly correlated across days when all times of day were considered (r = 0.999). However, thickness values obtained at 8:00 AM were significantly different across days (t test; P<0.0002). The subjects data correlated very well (r = 0.9996) with the grouped volunteer data. CONCLUSIONS These data show this system to be useful in corneal research and in clinical settings. The data confirm early morning pachymetry to be highly variable. Additionally, the data not only indicate a diurnal variation of corneal hydration over time, but also imply the presence of a diurnal-based hydration gradient across the peripheral cornea, both of which can have significance for PRK, since excimer tissue ablation effectiveness is influenced by tissue hydration.

Pupil size and quality of vision after LASIK.

PURPOSE To evaluate factors related to the quality of vision after LASIK. DESIGN Survey study. PARTICIPANTS One hundred consecutive patients. INTERVENTION LASIK with a 6.0-mm elliptical ablation pattern without transition zone to treat mild to moderate myopia or astigmatism (preoperative manifest spherical equivalent [MSE], -4.79 +/- 1.33 diopters [D]; range, -2.88 to -9.25 D). The second eye was treated 1 month after the first. MAIN OUTCOME MEASURES Completed questionnaires assessing night vision problems (glare, haze, and halo symptoms) before surgery and at 1, 3, and 6 months after surgery in 97, 75, 81, and 66 subjects, respectively. Mesopic pupil size and preoperative and postoperative variables were analyzed with questionnaire data using an analysis of variance (ANOVA) and multivariate regression analysis. RESULTS Patients with large mesopic pupils had significantly more reports of glare, haze, and halo than did those with smaller pupils in the treated eye at 1 month after surgery (P=0.02, P=0.03, and P=0.02, respectively ANOVA) and of glare at 3 months (P=0.05). Significant predictors of symptoms at 6 months, identified through multivariate regression analysis, included preoperative MSE (for glare and haze), preoperative contrast acuity (glare), postoperative uncorrected visual acuity (UCVA; haze), and residual cylinder (haze). Together, these factors accounted for only 19% of the overall variability in glare and 37% of the variability in haze responses. No relationship between pupils and symptoms was noted at 6 months after surgery in either the ANOVA or regression analysis group. CONCLUSIONS Patients with large pupils had more quality of vision symptoms in the early postoperative period, but no correlation was observed 6 months after surgery. Factors related to long-term symptoms include the level of treatment (preoperative myopia), preoperative contrast acuity, postoperative UCVA, and residual cylinder. Most of the variability in visual quality could not be explained by preoperative or clinical outcome measures, including pupil size.

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.

Comparison of tropicamide and cyclopentolate for cycloplegic refractions in myopic adult refractive surgery patients

Purpose: To compare tropicamide 1%, a shorter‐acting cycloplegic agent, with cyclopentolate 1% for cycloplegic refractions in adult refractive surgery patients. Setting: Navy Refractive Surgery Center, Ophthalmology, Naval Medical Center, San Diego, California. Methods: The study was prospective, single center, with randomized sequencing of cycloplegic agent; each patient received both agents. Thirty consecutive myopic adult refractive surgery patients (mean age 35.4 years) participated. A complete preoperative examination, including cycloplegic refraction, was obtained twice, 1 week apart. The patient and the examiner were masked to the medication. Main outcome measures included cycloplegic and manifest refractions, best corrected distance acuity, near‐point accommodation, pupil diameters, and subjective appraisal of experience with cycloplegic agents. Results: Twenty‐eight of 30 patients completed both examinations. Both eyes were measured, but comparisons were limited to right and left eyes, independently. No statistically significant difference was found between the tropicamide and cyclopentolate cycloplegic refractions (mean difference in MSE ± SD, OD = 0.054 ± 0.214 diopters (D), t = 1.33, P = .10; OS = 0.054 ± 0.253 D, t = 1.12, P = .14). Five eyes of 3 patients had a difference of 0.50 D or greater between the 2 agents; less myopia with cyclopentolate. Near‐point testing revealed less residual accommodation with cyclopentolate (difference in MSE, OD = −0.27 ± 0.51 D, t = 2.68, P = .006; OS = −0.32 ± 0.49 D, t = 3.46, P = .001). Subjectively, 24 of 28 (86%) patients preferred tropicamide, 1 (4%) preferred cyclopentolate, and 3 (10%) had no preference. Conclusions: There was no statistically significant difference in mean cycloplegic refractions. Cyclopentolate was more effective than tropicamide in reducing accommodative amplitude in adult myopes (near‐point testing). Patients strongly preferred tropicamide.

Laser in situ keratomileusis in United States Naval aviators.

Purpose To evaluate the safety and efficacy of femtosecond‐assisted wavefront‐guided laser in situ keratomileusis (LASIK) as well as higher‐order aberrometric changes in a population of active‐duty United States Naval aviators. Setting Navy Refractive Surgery Centers, San Diego, California, and Portsmouth, Virginia, USA. Design Prospective noncomparative 2‐site study. Methods In this study of femtosecond‐assisted wavefront‐guided LASIK, 3 groups were differentiated according to the refractive status: myopia, mixed astigmatism, and hyperopia. Uncorrected (UDVA) and corrected (CDVA) distance visual acuities, refraction, mesopic low‐contrast CDVA, higher‐order aberrations (HOAs), and patient satisfaction were evaluated during a 3‐month follow‐up. Results The study enrolled, treated, and included for analysis 548 eyes with myopia, 60 eyes with mixed astigmatism, and 25 eyes with hyperopia. The UDVA was 20/20 or better in 98.3% of eyes with myopia and mixed astigmatism at all postoperative visits and in 95.7% of hyperopic eyes 3 months postoperatively. The gain in CDVA was 1 or more lines in 39.2%, 41.1%, and 30.4% of myopic, mixed astigmatic and hyperopic eyes, respectively. Loss of 2 lines of CDVA after surgery occurred in 2 myopic eyes (0.4%). At 3 months, a mean change of +0.03 &mgr;m ± 0.10 (SD) and +0.05 ± 0.08 &mgr;m was observed in higher‐order root mean square and primary spherical aberration, respectively. Of the patients, 95.9% said they believed that LASIK had helped their effectiveness as Naval aviators and 99.6% would recommend the same treatment to others. Conclusion Femtosecond‐assisted wavefront‐guided LASIK was an efficacious and safe option for refractive correction in Naval aviators, enabling a quick return to flight status. Financial Disclosure Drs. Tanzer and Schallhorn are consultants to Abbott Medical Optics, Inc. No author has a financial or proprietary interest in any material or method mentioned.

Randomized dose-response analysis of mitomycin-C to prevent haze after photorefractive keratectomy for high myopia

Purpose To evaluate the safety and efficacy of mitomycin‐C (MMC) 0.01% (0.1 mg/mL) in preventing haze formation after wavefront‐guided photorefractive keratectomy (PRK) for higher myopia at 3 exposures. Setting United States Navy Refractive Surgery Center, San Diego, California, USA. Design Double‐masked randomized prospective trial. Methods Sixty‐, 30‐, and 15‐second exposures of MMC 0.01% were compared in wavefront‐guided PRK for higher myopia. One eye received MMC (surgical sponge) and the other a placebo. All eyes received a 4‐month tapering postoperative topical steroid regimen. Endothelial cell densities, haze scores, high‐ and low‐contrast acuities, and manifest refraction were measured preoperatively and 1, 3, 6, and 12 months postoperatively. Outcomes were analyzed as repeated measures over time. Results The mean preoperative manifest refraction spherical equivalent was −5.98 diopters (D) (range −4.4 to −8.0 D). No eye developed more than trace haze. There was a significant difference in haze scores between MMC‐treated eyes and untreated eyes at 1 and 3 months (P=.034) but no difference at 6 and 12 months. Endothelial cell densities decreased in the treated eyes and untreated eyes at all 3 exposures at 1 month but returned to baseline by 6 months. There was no difference in acuities or refractions with or without MMC. Conclusions Mitomycin‐C may not be needed to prevent haze after modern PRK with a 4‐month steroid taper. There was no clinically significant difference in haze formation between MMC eyes and control eyes at the concentration and exposures used. Financial Disclosure Dr. Schallhorn is a consultant to Abbott Medical Optics, Inc. No author has a financial or proprietary interest in any material or method mentioned.

Topical cyclosporine A for postoperative photorefractive keratectomy and laser in situ keratomileusis

Purpose To compare the stability and predictability of the refractive outcomes in eyes treated with photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) with and without postoperative use of topical cyclosporine A emulsion. Setting Naval Medical Center San Diego Refractive Surgery Center, San Diego, California, USA. Design Randomized clinical trial. Methods Patients had PRK or LASIK and were randomized, pairwise, to a standard postoperative treatment regimen with or without the addition of topical cyclosporine A 0.05% emulsion twice daily for 3 months postoperatively. Visual acuity, mesopic contrast acuity, refractions, and ocular symptoms were assessed through the 3‐month examination. Tear‐film samples (cytokines and chemokines) were analyzed preoperatively and 1 week and 1 and 3 months postoperatively. Results The PRK group comprised 70 patients and the LASIK group, 54 patients. The addition of topical cyclosporine A twice a day after PRK or LASIK did not confer special benefits in terms of achievement of target refraction, final uncorrected distance visual acuity (UDVA), or rate of visual recovery (all P>.05, multivariate analysis of variance [MANOVA]). There was no significant difference in tear‐film composition based on measurement of matrix metalloproteinase‐9, interleukin (IL)‐6, or IL‐8 recovery (all P>.05, MANOVA). Conclusion The addition of topical cyclosporine A twice daily for 3 months after PRK or LASIK did not provide a significant benefit in the rate of visual recovery, final UDVA, or patient symptoms, nor did it significantly change measured inflammatory mediators (cytokines) present in the tear film. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Night Driving Simulation in a Randomized Prospective Comparison of Visian Toric Implantable Collamer Lens and Conventional PRK for Moderate to High Myopic Astigmatism

PURPOSE To compare changes in simulated night driving performance after Visian Toric Implantable Collamer Lens (TICL; STAAR Surgical) implantation and photorefractive keratectomy (PRK) for the correction of moderate to high myopic astigmatism. METHODS This prospective, randomized study consisted of 43 eyes implanted with the TICL (20 bilateral cases) and 45 eyes receiving conventional PRK (VISX Star S3 excimer laser) with mitomycin C (22 bilateral cases) for moderate to high myopia (-6.00 to -20.00 diopters[D] sphere) measured at the spectacle plane and 1.00 to 4.00 D of astigmatism. As a substudy, 27 eyes of 14 TICL patients and 41 eyes of 21 PRK patients underwent a simulated night driving test. The detection and identification distances of road signs and hazards with the Night Driving Simulator (Vision Sciences Research Corp) were measured with and without a glare source before and 6 months after each procedure. RESULTS No significant difference was noted in the pre- to postoperative Night Driving Simulator in detection distances with and without the glare source between the TICL and PRK groups. The differences in identification distances without glare were significantly better for business and traffic road signs and pedestrian hazards in the TICL group relative to the PRK group whereas with glare, only the pedestrian hazards were significantly better. A clinically relevant change of Night Driving Simulator performance (>0.5 seconds change in ability to identify tasks postoperatively) was significantly better in the TICL group (with and without glare) for all identification tasks. CONCLUSIONS The TICL performed better than conventional PRK in the pre- to postoperative Night Driving Simulator testing with and without a glare source present.

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.