Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism.

PURPOSE: To demonstrate analytical methods for evaluating the results of keratorefractive surgical procedures and emphasize the importance of intraocular astigmatism. SETTING: University of Texas Medical School, Houston, Texas, USA. METHODS: A standard data set, provided by an editor of this journal, comprising the preoperative and postoperative keratometric and refractive measurements of 100 eyes that had keratorefractive surgery was evaluated by 2 methods, vector and spheroequivalent (SEQ) analysis. The individual and aggregate surgically induced refractive changes (SIRCs) and prediction errors were determined from the refractive and keratometric measurements using both methods and then compared. The refraction vertex distance, keratometric index of refraction, and corneal asphericity were used to make the results calculated from refractive data directly comparable to those derived from keratometric data. Doubled-angle and equivalency plots as well as frequency and cumulative histograms were used to display the data. Standard descriptive statistics were used to determine the mean and standard deviation of the aggregate induced astigmatism after converting the polar values (cylinder and axis) to Cartesian (x and y) values. RESULTS: The preoperative SEQ refractive errors were undercorrected by at least 0.25 diopter (D) in most cases (78%). Six percent were corrected within +/- 0.24 D, and 16% were overcorrected by at least 0.25 D SEQ. The mean SEQ was -6.68 D +/- 2.49 (SD) before and -0.61 +/- 0.82 D after surgery, reflecting a SIRC SEQ of -6.07 +/- 2.40 D. The defocus equivalent (DEQ) was 7.41 +/- 2.53 D before and 0.96 +/- 0.74 D after surgery; for a nominal 3.0 mm pupil, this corresponded to an estimated improvement in uncorrected visual acuity (UCVA) from worse than 20/200 to better than 20/25, respectively. The predictability of the treatment decreased as the attempted refractive correction increased. The average magnitude of the refractive astigmatism was 1.46 +/- 0.61 D before and 0.40 +/- 0.38 D after surgery. The centroid of the refractive astigmatism was +0.96 x 87.9 +/- 0.85 D, rho = 0.43 before and +0.11 x 83.1 +/- 0.37, rho = 0.49 after surgery. The decrease in the square root of the centroid standard deviation shape factor (rho1/2) indicated an 8% increase in the amount of oblique astigmatism in the population. The prevalence of preoperative keratometric irregular astigmatism in excess of 0.5 D in this group of patients was 13%. The correlation between keratometric and refractive astigmatism was extremely poor before (r2 = 0.26) and especially after surgery (r2 = 0.02), demonstrating the presence of intraocular astigmatism and the limitations of manual keratometry. The centroid of intraocular astigmatism at the corneal plane was +0.48 x 178 +/- 0.49 D, rho = 0.59, and was compensatory. CONCLUSIONS: The 2 analytical methods are complimentary and permit thorough and quantitative evaluation of SIRCs and allow valid statistical comparisons within and between data sets. The DEQ allows comparison of refractive and visual results. The decrease in refractive predictability with higher corrections is well demonstrated by the SEQ and doubled-angle plots of the SIRC. Doubled-angle plots were particularly useful in interpreting errors of cylinder treatment amount and errors in alignment. The correlation between refractive and keratometric astigmatism was poor for preoperative, postoperative, and SIRC data, indicating the presence of astigmatic elements beyond the corneal surface (ie, intraocular astigmatism). Sources of error in refractive outcome statistics include the use of multiple lens systems in the phoropter, errors in vertex calculations, difficulty in accurately defining the axis of astigmatism, and failure to consider measurement errors when working with keratometric data. The analysis of this particular data set demonstrates the significant clinical benefits of refractive surgery: an 8-fold increase in UCVA, an 11-fold decrease in SEQ refractive error, as well as a 9-fold and nearly a 2 1/2-fold decrease in the magnitude and distribution of astigmatism, respectively.

Laser in situ keratomileusis for high myopia with the VISX star laser.

PURPOSE: To evaluate the results of laser in situ keratomileusis (LASIK) for spherical and spherocylindrical myopia (range, 9-22 diopters [D]) with the VISX Star laser, (VISX Inc., Santa Clara, CA). DESIGN: Non-comparative, single-surgeon interventional case series. PARTICIPANTS: Two hundred ninety eyes of 175 patients. METHODS: Consecutive patients who underwent LASIK in the study range with the VISX Star laser were evaluated for early (approximately 1 month) and late (after 9 months) outcomes. Both single procedure outcomes and results after reoperation for refractive enhancement were included. MAIN OUTCOME MEASURES: Outcome measures included uncorrected visual acuity, manifest refraction, refractive predictability, refractive stability, best spectacle-corrected visual acuity (BSCVA), results of reoperations, and complications. RESULTS: At the early postoperative examination, approximately 1 month after surgery, 285 of 290 eyes (98.3%) were examined. Uncorrected visual acuity of 20/40 or better occurred in 209 of 285 (73.3%) eyes, and 198 of 285 (69.5%) eyes had a manifest spheroequivalent between +/-1.00 D. Subsequently, 60 eyes (20.7%) underwent reoperation for refractive enhancement. Late results, beyond 8 months from the initial surgery and including reoperations, were available in 195 of 290 eyes (67.2%). Uncorrected visual acuity results of 20/40 or better were found in 166 of 195 eyes (85.1%) and of 20/25 or better in 99 of 195 eyes (50.8%). Manifest spheroequivalent results were +/-2.00 D in 187 of 195 eyes (95.9%) and +/-1.00 D in 148 of 195 eyes (75.9%). In a paired-cohort analysis of 131 single-procedure eyes seen at both intervals, refractive stability (change in manifest refractive spheroequivalent of less than 1.00 D) was present in 101 of 131 eyes (77.1%) between the two observation intervals. Overall, approximately 3.6% eyes lost 2 lines or more of BSCVA, and other complications (flap wrinkling and epithelial ingrowth) were reported in 2% of eyes. Improvement in BSCVA of 1 line or more occurred in 5.6% eyes. CONCLUSIONS: Laser in situ keratomileusis for high myopia with the VISX Star laser provided satisfactory refractive and visual results that compare well with other reports in the literature. Subjective results and other measures of visual function need further evaluation.

Outcomes of spherocylinder treatments in the comprehensive refractive surgery LASIK study.

The CRS LASIK Study is a surgeon-sponsored collaborative project to evaluate LASIK outcomes with the Summit and VISX lasers. The current report includes 3-month outcomes in the first group of patients who underwent spherocylindrical corrections of 1 to 10 diopters of myopia and 1 to 4 diopters of astigmatism with the Summit Apex Plus and VISX Star lasers. Cohort selection criteria were applied to select 911 eyes that underwent surgery between April 1, 1996 and October 1, 1997 in the range of study. Eyes with preoperative best spectacle-corrected visual acuity of worse than 20/40 (0.5) were excluded. Outcomes were stratified according to myopic treatment range. One day uncorrected visual acuity was 20/40 or better in 83% of eyes with both lasers. At 3 months, 20/40 uncorrected acuity was found in 93% of Summit and 90% of VISX eyes in the -1.00 to -4.00 D group, in 88% of Summit and 84% of VISX eyes in the -4.01 to -7.00 D group, and in 67% of Summit and 70% of VISX eyes in the -7.01 to -10 D group. Three-month manifest refractive outcomes in the -1.00 to -4. 00 D group were within +/- 1 D of target in 91% of the Summit eyes, and 89% of the VISX Eyes. In the -4.01 to -7.00 D range, 72% of the Summit eyes and 74% of the VISX eyes fell within +/- 1 D, and in the -7.01 to -10 D range, the rates were 53% for Summit and 56% for VISX. No eyes lost two lines or more acuity with either laser. Three-month visual and refractive outcomes in LASIK are comparable with the Summit Apex Plus and VISX Star lasers. Loss of BSCVA of two lines or more was not seen. CRS LASIK Study protocols are ongoing to provide longer follow-up and to study other refractive indications.

Laser in situ keratomileusis for myopia and astigmatism: 6 month results.

PURPOSE: To evaluate the visual and refractive results of laser in situ keratomileusis (LASIK) for mild to moderate myopia with or without astigmatism. SETTING: Barnet-Dulaney Eye Center, Phoenix, Arizona, USA. METHODS: Data were prospectively collected on 124 consecutive eyes having LASIK over 12 weeks. Eyes with a preoperative spherical equivalent (SE) from -1.35 to -10.00 diopters (D) (mean -4.81 D +/- 2.21 [SD]) and cylinder from 0 to 5.00 D (mean 1.12 +/- 1.12 D) were entered in the study. Thirty-one eyes had spherical corrections. Ninety-three eyes had spherocylinder corrections; preoperative astigmatism in these eyes ranged from 0.50 to 5.00 D (mean 1.47 +/- 1.09 D). Surgery included creation of a corneal flap using an automated microkeratome with a 160 microns plate followed by photoablation on the exposed stromal bed. Photoablation was performed using five zones varying from 5.0 to 6.6 mm in eyes with 6.25 D of myopia or less and with five passes at a 5.0 mm zone in eyes with 6.50 D of myopia or more. Astigmatism was corrected using a single-pass ablation through a 6.0 mm slit of varying diameter. RESULTS: Six month follow-up was obtained in 89 eyes (72%). All eyes were completely re-epithelialized by the first postoperative day. Uncorrected visual acuity was 20/40 or better in 81% of eyes at 1 day and in 91% at 6 months. At 6 months, the mean SE was -0.35 +/- 0.77 D; 83% were within +/- 1.00 D of plano. Postoperative astigmatism in the 93 eyes having cylinder correction ranged from 0 to 1.22 D (mean 0.38 +/- 0.42 D). No eye lost more than two lines of best spectacle-corrected visual acuity. Three eyes (2%) required surgical intervention for cap problems. Visually significant corneal haze was not observed. CONCLUSION: In eyes with myopia with or without astigmatism, LASIK provided rapid visual recovery with satisfactory visual and refractive outcomes. The effect of LASIK on visual function (night glare, contrast sensitivity) awaits further study.

Removal of corneal epithelium with phototherapeutic technique during multizone, multipass photorefractive keratectomy.

BACKGROUND: The therapeutic mode of the VISX 20/20 excimer laser was used to remove the corneal epithelium prior to performing photorefractive keratectomy (PRK) with a multizone, multipass technique. METHODS: A retrospective analysis was performed of 120 eyes of 90 patients that were treated for preoperative spherical refractive errors from -1.00 to -7.00 diopters (D) (mean -3.90 D, SD 1.54) by one surgeon (DGJ) over 7 months. RESULTS: Six-month follow-up was obtained in 76 eyes (63%). Sixty-nine eyes (91%) achieved a spherical equivalent refraction within +/-1.00 D of emmetropia. Regression of effect averaged -0.35 D (SD 0.53 D) from 1 to 6 months after surgery. Mean postoperative uncorrected visual acuity at 6 months was 20/25 (range 20/15 to 20/200). Seventy-three eyes (96%) achieved uncorrected visual acuity of 20/40 or better, 67 (88%) achieved uncorrected visual acuity of 20/25 or better, and 76 (71%) achieved 20/20 or better. Three eyes (4%) lost one line of spectacle-corrected visual acuity; no eye lost more than one line. There were no significant surgical complications. CONCLUSION: Removal of corneal epithelium with the Summit Excimed UV 200 LA excimer laser using multizone, multipass photoablation yields visual and refractive results that compare favorably with published PRK series with excellent short-term stability.

Sutureless homoplastic lamellar keratoplasty.

BACKGROUND: Previously, penetrating keratoplasty has been used to treat corneal cap complications related to keratomileusis. We sought to develop a technique to avoid the unnecessary use of penetrating procedures for lamellar problems, that would be technically easier than standard lamellar keratoplasty--sutureless homoplastic lamellar keratoplasty. METHODS: Five eyes with complications from automated lamellar keratoplasty underwent sutureless homoplastic lamellar keratoplasty utilizing an automated microkeratome and topical anesthesia. RESULTS: Three of the five eyes had improved vision; two eyes with final visual acuities of 20/20 and 20/30. The two remaining eyes had poor host stromal beds and required penetrating keratoplasty. The mean follow-up time was 13 months (range 3 to 36 months). All lamellar grafts were clear and well-seated at the last postoperative examination. CONCLUSION: Sutureless homoplastic lamellar keratoplasty is an alternative to penetrating keratoplasty in some eyes that have cap-related problems.

Automated lamellar keratoplasty for the correction of hyperopia.

Hyperopic automated lamellar keratoplasty (H-ALK) is a refractive procedure that corrects low to moderate hyperopia of up to +5.00 diopters (D). In this retrospective series, we examined the efficacy, predictability, and safety of H-ALK in 85 eyes in 49 patients. Follow-up was from 4 to 34 weeks (mean 18 weeks). Eyes were divided into three subsets: those in which we attempted an emmetropic result (n = 45), those in which we attempted to reduce, but not eliminate, hyperopia greater than 5.00 D (n = 23), and those in which we attempted a monovision result of -1.50 D (n = 17). In the eyes in which we attempted emmetropia, 76% achieved uncorrected visual acuity of 20/40 or better and 78.6% were within a range of -1.00 to +0.87 D. In those in which we attempted monovision, 47% achieved a spherical equivalent result between -2.50 and -1.00 D because of a tendency toward undercorrection. In those in which we attempted to reduce hyperopia, there was a mean correction of 4.33 D (standard deviation 1.36 D), with a range of 2.12 to 6.75 D. The most significant complication was a reduction in best corrected visual acuity of one to three lines in 11 of 85 eyes; this was transient in six eyes. These preliminary results compare favorably with those of other procedures to correct hyperopia.

Treatment of localized trichiasis with radiosurgery.

Several treatments exist for trichiasis, a condition in which misdirected lashes come in contact with the globe. The treatments can be considered in two groups, those that destroy the lash follicle and those that redirect the lashes. No technique is without potential complications, and none is 100% effective. The Ellman Surgitron FFPF offers a new treatment for trichiasis directed at destroying the lash follicle. This instrument utilizes energy at 3.8 MHz in the radiofrequency band of the electromagnetic spectrum, hence the term radiosurgery. This report presents a prospective, non-masked study of 30 eyelids in 26 patients with localized trichiasis treated with the Ellman Surgitron FFPF. Single treatment success rate in patient cure was 67%. Complications included lash recurrence in 8 patients, eyelid notching in 2, granuloma formation in 1, and persistent erythema and tenderness for 1 month in 1 patient. This series demonstrates that the instrument can be effectively used to treat localized trichiasis. A review of the literature reveals that this technique offers potential advantages over some others in use. Further study must determine its efficacy in the treatment of diffuse trichiasis and distichiasis.

A new instrument for fascia placement.

An orthopedic instrument is presented as an alternative to the Wright needle for placement of fascia lata in the tarsofrontalis. This tool is easier to handle and allows more accurate fascia placement than the Wright needle.

Peribulbar anesthesia for the repair of orbital floor fractures.

Four patients underwent successful repair of an isolated orbital floor fracture under local anesthesia. The surgical approach was by antero-inferior orbitotomy, with placement of a Nylamid plate (S Jackson Inc, Washington, DC). The anesthetic technique used was a peribulbar and infratrochlear nerve block with local supplementation. Digital control of the globe was maintained during the peribulbar injection to prevent ocular perforation. We conclude that local anesthetic for this procedure in carefully selected cases is safe and efficacious, avoiding the morbidity of a general anesthetic.