Wing Kwong Chan

A Multicenter Trial of Photorefracti*ve Keratectomy for Residual Myopia after Previous Ocular Surgery

Purpose: The Summit Therapeutic Refractive Clinical Trial is a nine-center prospective, nonrandomized, self-controlled trial to assess the efficacy, stability, and safety of using a standardized technique of excimer laser photorefractive keratectomy (PRK) to correct residual myopia in eyes with previous refractive surgery or cataract surgery. Patients and Methods: Eligible eyes with a mean residual myopia of -3.7 ± 1.8 diopters (D) (range, -0.63 to -11.00 D) underwent PRK with a 193-nm excimer laser for myopic corrections between -1.50 and -7.50 D. Standardized settings were used for the ablation zone, ablation rate, repetition rate, and fluence. One hundred seven of the first 114 treated eyes were examined 1 year after PRK, with 98% of eyes having had refractive keratotomy and 2% having had cataract surgery. Results: One year postoperatively, the mean manifest spherical equivalent refraction was -0.6 ± 1.4 D (range, -6.50 to 2.50 D); 63% of eyes were within ±1.00 D of the attempted correction; and uncorrected visual acuity was 20/40 or better in 74% of eyes. Twenty-nine percent of eyes lost two or more Snellen lines of best-corrected visual acuity, and central corneal haze was moderate or severe in 8% of eyes. Conclusion: Excimer laser PRK is effective in reducing residual myopia after previous refractive and cataract surgery. However, it is less accurate than PRK in eyes that did not undergo surgery and is more likely to cause a loss of best-corrected visual acuity 1 year after treatment.

Evaluation of Higher Order Ocular Aberrations in Patients With Keratoconus

PURPOSE To describe higher order ocular aberrations in eyes with keratoconus. METHODS Prospective, observational, case-control study comparing higher order ocular aberrations in patients with keratoconus with control subjects with myopia. RESULTS One hundred sixteen patients with keratoconus were recruited. Data were analyzed in 35 keratoconus eyes, 38 keratoconus suspect eyes, and 166 right eyes with myopia. Mean total higher order root-mean-square (RMS) values (3rd to 5th order) were 1.73 +/- 0.71 microm in eyes with keratoconus, 0.94 +/- 0.66 microm in eyes with keratoconus suspect, and 0.49 +/- 0.16 microm in control eyes. Keratoconus eyes had greater total higher order RMS, 3rd to 5th order RMS, and RMS for all Zernike terms than those in the control group (P < .001). CONCLUSIONS Keratoconus and keratoconus suspect eyes had significantly larger higher order aberrations in total higher order RMS and 3rd order RMS than control eyes.

The prediction of surgically induced refractive change from corneal topography

PURPOSE To develop a method to predict the refractive power of the cornea from corneal topography. METHODS We reviewed preoperative and postoperative cycloplegic refraction, keratometry, and corneal topography in 40 eyes of 40 patients who had undergone photorefractive keratectomy, radial keratotomy, myopic keratomileusis in situ, or hyperopic lamellar keratoplasty. For each axial dioptric power map, we calculated the aspheric ellipsoid that best fit that map. Central corneal points were weighted more heavily than peripheral points, based on the Stiles-Crawford effect. The equation of the best-fit ellipsoid yielded the spherical and astigmatic power and axis for each cornea preoperatively and postoperatively. RESULTS The preoperative corneal spherical and astigmatic powers measured by the best-fit method were consistent with the spherical and astigmatic powers measured by keratometry and simulated keratometry. The change in corneal spherical power predicted by the best-fit method was significantly (P < .05) more accurate at predicting the change in spherical equivalent refraction than change either in spherical equivalent keratometry or in spherical equivalent simulated keratometry. The prediction of the astigmatic change was less precise than that of the spherical, but the best-fit method was the most accurate. CONCLUSIONS The best-fit method is more accurate than simulated keratometry and standard keratometry are in evaluating corneal refractive power after refractive surgery. An improved method of calculating corneal refractive power may facilitate subjective refraction after refractive surgery, improve the accuracy of intraocular lens power calculation for eyes that have had previous refractive surgery, and improve ablation profiles for excimer laser refractive surgery.

HIGHER ORDER OCULAR ABERRATIONS IN EYES WITH MYOPIA IN A CHINESE POPULATION

PURPOSE To describe the characteristics of higher order ocular aberrations of adult Chinese eyes with myopia. METHODS Higher order aberrations in consecutive right eyes of 166 Chinese patients with myopia who enrolled for preoperative assessment for LASIK were retrospectively reviewed. Wavefront aberrations were measured with the Bausch & Lomb Zywave over a 6-mm dilated pupil. The correlations between higher order aberrations and myopia, astigmatism, and age, respectively, were analyzed. RESULTS Mean patient age was 32.1 +/- 6.2 years, the mean refractive error was sphere -5.23 +/- 1.79 diopters (D) and cylinder -1.29 +/- 0.98 D. The mean of the total higher order root-mean-square (RMS) (third to fifth order) was 0.49 +/- 0.16 microm. Third-order RMS was largest (mean 0.37 +/- 0.16 microm), followed by fourth-order RMS (mean 0.29 +/- 0.11 microm). For individual higher order Zernike coefficients, spherical aberration (C4(0)) predominated with a mean of 0.23 +/- 0.14 microm. No correlation was found between total higher order RMS and myopia or between total higher order RMS and age. Small but statistically significant relationships were found in the following groups: age and vertical primary coma (C3(-1))(r=-0.206, P=.008); age and spherical aberration (C4(0)) (r=0.196, P=.012); and myopia and horizontal trefoil (C3(3)) (r=-0.158, P=.042). CONCLUSIONS Higher order aberrations varied among individuals with myopia. Third-order RMS was the predominant higher order aberration. Spherical aberration and vertical primary coma increased slightly with age. Our study helps establish ocular aberration standards for Chinese refractive surgery candidates.

Efficacy of an aspheric treatment algorithm in decreasing induced spherical aberration after laser in situ keratomileusis.

PURPOSE: To determine the effectiveness of an aspheric laser in situ keratomileusis (LASIK) algorithm for myopia with and without astigmatism in minimizing postoperative induction of spherical aberration. SETTING: Four sites in Asia. METHODS: Patients with −1.00 to −10.00 diopters (D) of spherical myopia with −4.00 D or less of astigmatism were recruited. Patients randomly had bilateral Zyoptix aspheric algorithm (aspheric group) or bilateral conventional Zyoptix Tissue Saving algorithm (control group). A Technolas 217z100 excimer system was used for LASIK ablation. Visual effectiveness, safety, higher‐order aberrations, and corneal asphericity (Q value) were evaluated postoperatively. RESULTS: The aspheric group comprised 86 eyes and the control group, 84 eyes. At 3 months, the high‐contrast uncorrected distance visual acuity was 20/20 or better in 78% of eyes in the aspheric group and 83% of eyes in the control group. The control treatment induced 0.22 μm of spherical aberration, which was significantly higher than the 0.04 μm induced with the aspheric treatment (6.0 mm pupil) (P<.0001). The aspheric treatment induced significantly less vertical coma and trefoil (P = .02). Eyes in the aspheric group had significantly lower Q values (P<.0001). There was no statistically significant difference in the manifest refraction spherical equivalent between the 2 groups (P >.05). Although high‐ and low‐contrast corrected distance visual acuity (CDVA) was similar between the groups, the aspheric group gained more lines of low‐contrast CDVA. CONCLUSION: The aspheric algorithm was more effective than the conventional algorithm in reducing induced spherical aberration and maintaining corneal asphericity after myopic LASIK.

Harvesting a Lamellar Graft From a Corneoscleral Button: A New Technique

PURPOSE To describe a new technique for harvesting a lamellar graft from a corneoscleral button in the absence of an artificial anterior chamber. METHODS Two layers of sterile fine-weave fabric were wrapped tightly around a glass orbital implant. The corneoscleral button was sutured firmly at its scleral rim onto the fabric. The lamellar graft then was dissected in the regular fashion. RESULTS The lamellar graft was successfully obtained. During the dissection, the donor cornea and its supporting fabric-covered glass ball were easily handled, and there was minimal risk of perforation of the posterior lamella of the donor cornea. CONCLUSION This simple technique allows a lamellar graft to be easily obtained from a corneoscleral button without specialized and expensive equipment.

Diffuse lamellar keratitis after laser in situ keratomileusis associated with surgical marker pens

PURPOSE: To describe a series of cases of diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK) associated with intraoperative use of a surgical marker pen. SETTING: Singapore National Eye Centre, Singapore, Singapore. METHODS: A review of all 115 patients (125 eyes) who had myopic LASIK from July 23 to July 26, 2007, was performed to determine whether eyes in which the Codman surgical marker pen (Johnson & Johnson Medical) was used intraoperatively developed postoperative DLK. RESULTS: Nine of 12 eyes that had LASIK or flap relifting with a Codman surgical marker pen developed grade 1 to grade 3 DLK on the first postoperative day. The 113 other eyes that had LASIK in the same week with another brand of surgical marker pen (Securline, Precision Dynamics Corp.) did not develop DLK. All eyes with DLK were treated with intensive topical steroid therapy. The DLK resolved in 2 eyes after the steroid treatment; 7 eyes required flap relifting with interface irrigation. One month postoperatively, 6 eyes with DLK had an uncorrected visual acuity of 6/7.5 or better. Two eyes developed central corneal scarring with consecutive hyperopia with a best corrected visual acuity of 6/12 after 1 month. CONCLUSIONS: There was a strong association between the occurrence of DLK after LASIK with the use of the Codman surgical marker pen. One or more constituents of the ink in the Codman pen may have been responsible for this series of cases.

Performance of the Hansatome microsuction ring for laser in situ keratomileusis in eyes with narrow palpebral apertures

Purpose: To evaluate the performance of a new microsuction ring during laser in situ keratomileusis (LASIK) in eyes with narrow palpebral apertures. Setting: Singapore National Eye Centre, Singapore, Republic of Singapore. Methods: Laser in situ keratomileusis was performed sequentially in both eyes of 33 Chinese patients. A randomization table was used to determine the control and test eyes. A standard suction ring (20.3 mm diameter) was used in control eyes, and a microsuction ring (19.0 mm diameter) was used in test eyes. Corneal flaps were created using the Hansatome® microkeratome (Baush & Lomb). The following ring performance parameters were evaluated: flap diameter deviation (actual minus nominal flap diameter), ease of suction ring application, adequacy of suction, and overall microkeratome performance. Parameters 2 to 4 were rated by the surgeons using a subjective 1 to 100 scale. Results: The mean flap diameter deviation was 0.45 mm in the control eyes and 0.22 mm in the study eyes; the mean difference was 0.23 mm (95% confidence interval, 0.39‐0.07) (P<.001). For ease of application, the mean score of the microsuction ring was 100 and of the standard suction ring, 89.9. For adequacy of suction, the mean score of the microsuction ring was 99.7 and of the standard suction ring score, 98.2 (P = .13). The mean overall microkeratome performance score using the microsuction ring was 99.4 and using the standard suction ring, 94.6 (P = .011). Conclusion: The Hansatome microsuction ring was easy to apply during LASIK in eyes with narrow palpebral apertures, and there appeared to be no compromise of ring performance and safety.

Autologous Keratophakia for the Correction of Consecutive Hyperopia After Automated Lamellar Keratoplasty for Myopia

PURPOSE Consecutive hyperopia occurs if too much corneal tissue is resected during automated lamellar keratoplasty for myopia. We report what are, to our knowledge, the first two cases of consecutive hyperopia after automated lamellar keratoplasty that were treated by keratophakia with autologous corneal tissue. METHODS The patient in case 1 had a spherical equivalent refraction of +3.38 diopters (D) and the patient in case 2 a refraction of +3.63 D in each eye after automated lamellar keratoplasty for myopia. Corneal tissue from the contralateral eye of each patient was obtained with an automated microkeratome and transferred to the overcorrected eye in an autologous keratophakia procedure. RESULTS The patient in case 1 had an unaided visual acuity of 20/20, with a spherical equivalent refraction of +0.63 D 4 months after the autologous keratophakia. The patient in case 2 had an unaided visual acuity of 20/60, with a spherical equivalent refraction of -2.25 D 2.5 months postoperatively. CONCLUSION These two cases illustrate the use of simultaneous contralateral myopic automated lamellar keratoplasty with autologous keratophakia to treat eyes overcorrected following previous automated lamellar keratoplasty for myopia.