Journal of Refractive Surgery

The articles prior to January 2013 are part of the back file collection and are not available with a current paid subscription. To access the article, you may purchase it or purchase the complete back file collection here

ORIGINAL ARTICLES 

Randomized Prospective Comparison of Visian Toric Implantable Collamer Lens and Conventional Photorefractive Keratectomy for Moderate to High Myopic Astigmatism

Steven Schallhorn, MD; David Tanzer, MD; Donald R Sanders, MD, PhD; Monica L Sanders, BS

Abstract

ABSTRACT

PURPOSE: To compare the Visian Toric Implantable Collamer Lens (TICL), a toric phakic intraocular lens (IOL), and photorefractive keratectomy (PRK) in 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 PRK with mitomycin C (22 bilateral cases) with 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. All patient treatment and follow-up occurred at the Naval Medical Center San Diego. Study follow-up was 1 day, 1 week, 1, 3, 6, and 12 months postoperative.

RESULTS: Mean best spectacle-corrected visual acuity (BSCVA), change in BSCVA, proportion of cases with improvement of 1 or more lines of BSCVA, proportion of cases with BSCVA and uncorrected visual acuity (UCVA) 20/12.5 or better, proportion of cases with BSCVA and UCVA 20/16 or better (6 months, 88% vs 54%, P=. 002), and predictability ?1.00 D (6 months, 100% vs 67%, P<.001) were all significantly better in the TICL group than the PRK group at all time periods studied postoperatively. Similarly, contrast sensitivity, tested at both the 5% photopic level and the 25% mesopic level, was significantly better at all postoperative time points in the TICL group. Mean spherical equivalent refraction was closer to emmetropia (0.28?0.41 vs 0.76?0.86, P=. 005), and predictability ?0.50 D and stability of manifest refraction (?0.50 D and ?1.00 D) were significantly better in the TICL group at all postoperative visits through 6 months. Mean astigmatism correction at 6 months was not significantly different between the two groups (0.52?0.33 vs 0.46?0.35, P=.450).

CONCLUSIONS: The TICL performed better than PRK in all measures of safety (BSCVA), efficacy (UCVA), predictability, and stability in this comparison, supporting the TICL as a viable alternative to existing refractive surgical treatments. [J Refract Surg. 2007;23:853-867.]

Abstract

ABSTRACT

PURPOSE: To compare the Visian Toric Implantable Collamer Lens (TICL), a toric phakic intraocular lens (IOL), and photorefractive keratectomy (PRK) in 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 PRK with mitomycin C (22 bilateral cases) with 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. All patient treatment and follow-up occurred at the Naval Medical Center San Diego. Study follow-up was 1 day, 1 week, 1, 3, 6, and 12 months postoperative.

RESULTS: Mean best spectacle-corrected visual acuity (BSCVA), change in BSCVA, proportion of cases with improvement of 1 or more lines of BSCVA, proportion of cases with BSCVA and uncorrected visual acuity (UCVA) 20/12.5 or better, proportion of cases with BSCVA and UCVA 20/16 or better (6 months, 88% vs 54%, P=. 002), and predictability ?1.00 D (6 months, 100% vs 67%, P<.001) were all significantly better in the TICL group than the PRK group at all time periods studied postoperatively. Similarly, contrast sensitivity, tested at both the 5% photopic level and the 25% mesopic level, was significantly better at all postoperative time points in the TICL group. Mean spherical equivalent refraction was closer to emmetropia (0.28?0.41 vs 0.76?0.86, P=. 005), and predictability ?0.50 D and stability of manifest refraction (?0.50 D and ?1.00 D) were significantly better in the TICL group at all postoperative visits through 6 months. Mean astigmatism correction at 6 months was not significantly different between the two groups (0.52?0.33 vs 0.46?0.35, P=.450).

CONCLUSIONS: The TICL performed better than PRK in all measures of safety (BSCVA), efficacy (UCVA), predictability, and stability in this comparison, supporting the TICL as a viable alternative to existing refractive surgical treatments. [J Refract Surg. 2007;23:853-867.]

Only a few specialized and highly sought after military fields have the luxury of choosing from a large enough applicant pool to exclude those with inadequate uncorrected vision. Despite rigorous visual qualifications, optical appliances for correcting refractive errors and/or presbyopia were worn by 27% of pilots and 52% of navigators.1 In addition, those who wore glasses or contact lenses reported significant difficulties while flying.2 Refractive surgery has the potential to enhance job performance by reducing or eliminating the need to wear these optical aides. Refractive surgery can also improve the quality of life in active-duty military and civilian persons alike by reducing dependence on glasses and contact lenses.

The two most widely accepted methods to correct myopia and astigmatism are photorefractive keratectomy (PRK) and LASIK. Phakic intraocular lenses (IOLs) represent an alternative to the current modalities of refractive correction, especially for higher levels of ametropia. The Visian ICL (STAAR Surgical, Monrovia, Calif), a spherical phakic IOL, was granted US Food and Drug Administration (FDA) approval in December 2005 for commercial use in the United States for spherical myopia of 3.00 to 20.00 diopters (D). The Visian Toric Implantable Collamer Lens (TICL) represents an expansion of the earlier Visian ICL study and is currently awaiting approval in the United States. No toric phakic IOL is currently approved for use in the United States.

This study was completed at the Naval Medical Center San Diego with the objective of comparing the clinical outcomes of PRK to the unapproved toric phakic IOL for the correction of moderate to high myopic astigmatism.

PATIENTS AND METHODS

This prospective, randomized study consisted of 43 eyes implanted with the TICL (23 patients) and 45 eyes receiving PRK with mitomycin C (23 patients). This study was conducted with institution review board approval and was done in conjunction with the larger Toric Implantable Collamer Lens US FDA Trial. All patient treatment and follow-up occurred at the Naval Medical Center San Diego. All individuals who participated in this study had prior informed consent and all data were collected on standardized case report forms in a consecutive series of cases. Study follow-up was 1 day, 1 week, 1, 3, 6, and 12 months postoperative.

To participate in this prospective study, individuals had to be phakic patients with moderate to high myopia (?6.00 to ?20.00 D sphere) measured at the spectacle plane and astigmatism in the range of 1.00 to 4.00 D cylinder with a best spectacle-corrected visual acuity (BSCVA) of 20/40 or better in the eye to be treated. Patients had to be between the ages of 21 and 45 years, have a stable refraction for the last 12 months as documented by previous clinical records, and have a manifest refraction spherical equivalent (MRSE) progression at a rate of 0.50 D or less during the year prior to the baseline examination. Exclusion criteria included, but were not limited to, patients with a history of previous intraocular surgery, diabetes, glaucoma, ocular hypertension, amblyopia, and/or any serious ophthalmic or non-ophthalmic conditions that may have precluded study completion.

The PRK and TICL study populations were well matched for age (PRK, 32.6?7 years; TICL, 30.8?6 years; P=.52), gender (PRK, 63% male; TICL, 56% male; P=. 2 2), the mean level of preoperative MRSE (PRK, -8.30?1.28 D; TICL, -8.04?1.28 D; P=.64), and the mean preoperative cylinder (PRK, 1.73 ?0.72; TICL, 1.73?0.62;P=.96).

TORIC IMPLANTABLE COLLAMER LENS

The Visian TICL (STAAR Surgical) was implanted in all 43 eyes in this series. The TICL is identical (identical haptic design) to the current V4 STAAR Myopic ICL for which the manufacturer has approval from the US FDA; however, the TICL has an anterior toric surface. Both lenses are made from a new generation of biocompatible IOL materials, termed "collamer".3,4 Both are designed to vault anteriorly to the crystalline lens and are intended to have minimal contact with the natural lens. They are composed of a proprietary, hydrophilic porcine collagen (<0.1%) hydroxyethyl methacrylate (HEMA) copolymer into which an ultraviolet-absorbing chromophore has been incorporated into the polymer chains. Their plate haptic design resembles lenses already in use with cataract surgery; it also incorporates distinct footplates. All lens power calculations were performed by STAAR Surgical Company using the astigmatic power calculations for IOLs developed by Sarver and Sanders.5

PHOTOREFRACTIVE KERATECTOMY

All 45 eyes underwent PRK using a conventional PRK technique (approval of custom ablation for high myopia had not occurred at the time of the treatments) partnered with the use of mitomycin C (MMC) as an adjunct to modulate the healing response after surgery. The VISX Star S3 (VISX Ine, Santa Clara, Calif) excimer laser was used with specifications of a 6.5-mm optical zone (major axis) with an 8.0 -mm treatment zone.

TORIC IMPLANTABLE COLLAMER LENS PROCEDURE

Toric ICLs were manufactured to minimize rotation and required the surgeon to rotate the ICL no more than 22.5? (3/4 of a clock hour) from the horizontal meridian. Each TICL was sent to the surgeon with a guide demonstrating the amount and direction of rotation from the horizontal axis required of the ICL to exactly align the ICL cylinder axis to the patients' required cylinder correction.

Within the 2 weeks prior to surgery, the patient received two iridotomies performed 90? apart using an Nd:YAG laser to prevent possible pupillary block glaucoma postoperatively. The day of surgery, patients were administered dilating and cycloplegic agents, after which an anesthetic of the surgeon's choice was applied to the operative eye. All TICL implantations were performed under topical anesthesia. To control for potential cyclotorsion upon lying supine, the surgeons marked the horizontal axis at a slit lamp while the patient was sitting upright. The surgeon also used a M?ndez ring (Rhein Medical, Tampa, FIa) to measure required rotation from horizontal during the operative procedure. Following placement of viscoelastic into the anterior chamber, the TICL was inserted through a horizontal temporal 3 -mm corneal incision, then injected through the incision into the anterior chamber and allowed to slowly unfold. With the Vukich ICL manipulator (ASICO LLC, Westmont, 111) in contact with the footplate, the proper motion was gentle posterior pressure combined with slight rotation of one clock hour or less. This maneuver was repeated over each corner of the implant until all four footplates were posterior to the iris plane. Adjustment of the implant, if necessary, was accomplished by a gentle movement touching the ICL at the junction of the haptic and optic. Correct positioning of the ICL in the center of the pupillary zone was verified before intraocular miotic was used to decrease pupil size. Any remaining viscoelastic was irrigated out of the anterior chamber with balanced salt solution (BSS).

Patients were administered one drop of Ocuflox (ofloxacin solution 0.3%; Allergan Ine, Irvine, Calif) and prescribed Pred Forte (Prednisolone acetate, Allergan Ine) four times daily for a total of 16 days, beginning with one drop four times daily for the first 4 postoperative days and steadily reducing the dose by one drop every 4 days thereafter. No postoperative medication was routinely used after this time frame.

PRK SURGICAL TECHNIQUE

A systemic medication (analgesic or sedative) was given per the physician's discretion prior to surgery followed by a topical ophthalmic anesthetic of the physician's choice. After the lid speculum was placed into position, the epithelium over an area larger than the total ablation area was removed using an Amoils Epithelial Scrubber (Innova, Toronto, Canada) with a hyperopic head. The operative eye was aligned so that the laser system was centered and the eye tracking system was engaged according to the manufacturer's guidelines. The VISX Star S3 was used with an elliptical ablation profile. The major axis of the optical zone was 6.5 mm and the minor axis varied from 5.2 to 6.3 mm, depending on the amount of myopia and astigmatism. The transition zone was 8.0 mm in all cases.

After ensuring proper laser centration, the laser treatment was performed followed by an application of a 6.0-mm pre-formed circular sponge that was soaked in 0.01% MMC onto the central cornea for 1 minute. Mitomycin C, a DNA inhibiting anti-cancer agent, has been used for many years as an adjunct to modulate the healing response in a variety of ocular surgeries. Using a pharmacologic method of this kind reduces the chance of postoperative scarring. The cornea was immediately irrigated with at least 15 cc of chilled BSS. At the completion of the procedure, a bandage soft contact lens was applied along with the appropriate topical medications to the cornea.

The bandage contact lens was left in place until reepithelialization was complete. One drop of topical antibiotic four times a day (until complete reepithelialization), one drop of Tetracaine hydrochloride 0.5% (Alcon Laboratories Ine, Ft Worth, Tex) every 2 hours as needed for the first 72 hours, and one drop of fluorometholone 0.1% four times a day for 2 weeks (reduced by one daily treatment every 2 weeks) were prescribed. Artificial tears were recommended, one drop four times a day for 2 weeks and then as needed. For pain, Ibuprofen 800 mg taken orally every 8 hours and Percocet (Endo Pharmaceuticals, Chadds Ford, Pa) 1 to 2 tablets every 4 to 6 hours as needed were prescribed.

OUTCOME MEASURES

Visual measurements were collected to include uncorrected and best spectacle-corrected vision and contrast sensitivity. Uncorrected visual acuity (UCVA) and BSCVA (distance) were evaluated with a 4-m logMAR back-illuminated eye chart (Lighthouse Second Edition, New York, NY). Room illumination was standardized and verified with a handheld meter for all acuity measurements. Best spectacle-corrected visual acuity was tested with the patient viewing through a phoropter. Acuity measurements were recorded as the Snellen equivalent where at least three letters needed to be correctly identified to score a line. The number of letters missed or correctly identified in the next line was additionally recorded.

Contrast sensitivity was measured under photopic and mesopic conditions. Photopic testing was conducted with a back-illuminated chart (5% ETDRS Chart, 9X14, Model 2186; Precision Vision, LaSaIIe, 111) with all other room lights off at a 4-m test distance. The luminance of the chart was between 80 and 140 cd/m2. Mesopic testing was conducted with a back-illuminated chart and neutral density filter (25% ETDRS Chart behind two neutral density filters, 9X14, Model 2186; Precision Vision). The neutral density filters ("mesopic filter") decreased the 125 cd/m2 in the smaller light box down to between 0.8 and 1.2 cd/m2. Once again, the room lights were off and the test distance was 4 m. The patient was first dark-adapted for a minimum of 5 minutes before mesopic contrast sensitivity was tested.

Manifest refraction was obtained by a fogged "push plus" technique using a standardized phoropter with a vertex distance of 12.5 mm. Additionally, a psychometric questionnaire was given at the preoperative, 3to 6-month, and 12-month time points. The questionnaire assessed subjective quality of vision (glare, halos, night vision, etc) and satisfaction after the surgery.

STATISTICAL METHODS

Both TICL and PRK outcomes were collected from the prospective, standardized case report forms and compiled on a Microsoft Excel Spreadsheet (Microsoft Corp, Redmond, Wash). The following statistical analyses were used to compare the PRK and TICL series. For dichotomous variables (BSCVA or UCVA, % 20/12.5, 20/16, 20/20, and 20/40 or better, predictability ?0.50 or ?1.00 D), Fisher's Exact Test was performed. For ordered categories and interval level data (vision distributions, line changes in BSCVA and spherical equivalent, predictability, stability refractive distributions, and subjective responses), Mann Whitney U tests were performed. A probability less than or equal to 5% (P<.05) was considered statistically significant. StatXact4 (CYTEL Software Corp, Cambridge, Mass) and Microsoft Excel were used for all tabulations of data and statistics.

RESULTS

POSTOPERATIVE FOLLOW-UP

Toric ICL and PRK patients were examined at 1 day, 1 week, 1, 3, 6, and 12 months postoperatively. For the PRK series, follow-up was 93% at 1 week, 100% at 1 month, 96% at 3 months, 85% at 6 months, and 96% at 12 months. For the TICL series, follow-up was 98% at 1 week and 1 month, 93% at 3 months, 77% at 6 months, and 88% at 12 months.

CLINICAL OUTCOMES

Tables 1-3 provide an overall comparison of the major safety and efficacy outcomes between the PRK and TICL groups. The column labeled "P value" for values that were continuous, significance was determined by a Mann Whitney U test and for dichotomous variables Fisher's Exact tests were used. For these dichotomous variables, the entire distribution of outcomes for that variable was also analyzed and significance was determined by a Mann Whitney U test. The results of this test are given in the last column labeled "P value (entire distribution)".

SAFETY OUTCOMES

Best Spectacle-corrected Visual Acuity. The mean change in BSCVA was significantly better with the TICL than with PRK at all time periods from 1 week through 12-month follow-up (Table 1; Fig 1). At all time periods, the TICL group demonstrated significantly more improvement in BSCVA than the PRK group (P<.001).

Loss of 2 or more lines of BSCVA was significantly higher in the PRK series in the early healing period (1 week; 19% vs 0%, P=.006) (Table 1). Improvement in BSCVA (2 or more lines) was statistically better in the TICL group at 1-month follow-up (0% vs 10%, P=.010), and the entire distribution of change in BSCVA was statistically better with the TICL at all visits through 12 months (P<.001).

Losses of 1 or more lines of BSCVA were significantly higher in the PRK series at 1-week (67% vs 2%, P<.001) and 1-month postoperative follow-up (44% vs 0%, P<.001). Improvement of 1 or more lines of BSCVA was better with the TICL series at all time periods studied (P<.001). Ninety-five percent of patients had an improvement of 1 or more lines of BSCVA in the TICL series at 12-month follow-up compared to 39% in the PRK series. Figure 2 presents the entire distribution of BSCVA gains and losses at 12 months postoperatively demonstrating the shift of the cases to the right (toward more improvement in BSCVA) in the TICL group relative to the PRK group.

The proportion of cases with BSCVA of 20/12.5 or better was significantly higher in the TICL group at all postoperative time periods (12 months; 71% vs 14%, P<.001) (Table 1). Additionally, the proportion of cases with BSCVA 20/16 or better was also significantly higher in the TICL group at all postoperative periods. When using the entire distribution of BSCVA values and not just the breakdown of 20/12.5, 20/16, or 20/20, the TICL had significantly better BSCVA at all postoperative visits between 1 week and 12 months (P<.001).

Adverse Events. At 2 years postoperatively, the presence of a grade 2 anterior subcapsular cataract was noted in one (2.3%) TICL patient. The patient had a preoperative refraction of ?6.50 ?2.25 @ 170?. One month postoperatively, BSCVA was 20/25 (same as preoperatively) with a refraction of -0.25 -0.50 @ 019? and a clear crystalline lens. The patient subsequently was lost to follow-up until 2 years later. Best corrected vision at that time was 20/50-1. An anterior subcapsular cataract was noted with no vault between the TICL and crystalline lens. The patient underwent successful removal of the TICL and cataract with implantation of a posterior chamber Pseudophakie IOL. One month after cataract removal, BSCVA was 20/20 with a refraction of +0.50 -2.00 @ 5?.

One additional visually insignificant anterior lens opacity was also noted at the 1-month postoperative examination. This event was not associated with any significant loss of BSCVA, as the patient's UCVA was 20/2O+2 with BSCVA of 20/16. The patient's vision and lens opacity did not change throughout the follow-up period. No other adverse events were observed in either group.

EFFECTIVENESS OUTCOMES

Uncorrected visual acuity improved dramatically in both groups (Table 1, Figs 3 and 4). The proportion of cases seeing 20/12.5 or better and 20/16 or better was significantly higher in the TICL group at all postoperative time periods (Fig 3). Using the entire distribution of UCVA values and not just 20/12.5, 20/16, or 20/20 cutoffs, the TICL was significantly better than PRK at all follow-up examinations (P<.001).

Figure 5 provides a comparison of the level of preoperative BSCVA to the 12-month UCVA outcomes for the TICL and PRK procedures. The TICL showed a much larger percentage of eyes in which the postoperative UCVA was better than the preoperative BSCVA (61% vs 18%). Looking at the entire distribution of the relationship between preoperative BSCVA to the 12 -month UCVA outcomes for the TICL and PRK procedures, the TICL was statistically better (P<.001).

Table

TABLE 1Comparison of TICL vs PRK Visual Outcomes

TABLE 1

Comparison of TICL vs PRK Visual Outcomes

Table

TABLE 1 CONTINUEDComparison of TICL vs PRK Visual Outcomes

TABLE 1 CONTINUED

Comparison of TICL vs PRK Visual Outcomes

Table

TABLE 2Comparison of TICL vs PRK Refractive Outcomes

TABLE 2

Comparison of TICL vs PRK Refractive Outcomes

Predictability (attempted vs achieved correction) favored the TICL numerically at all postoperative visits (?0.50 D and ?1.00 D) and was statistically better at all time points except 12 months with regard to ?0.50 D (76% vs 57%, P=.101) (Table 2). The scattergrams at 12 months postoperatively (Fig 6) demonstrate more variability in the PRK group and a tendency to overcorrect.

Postoperative defocus equivalent refraction at 12 months favored the TICL numerically up to ?3.00 D; however, ? 1.00 D was the only point at which the differences were statistically significant (97% vs 73%, P=.002) (Fig 7).

The mean MRSE was not significantly different between groups preoperatively; however, the MRSE was significantly closer to emmetropia at all follow-up visits through 6 months postoperatively in the TICL group.

The manifest refractive cylinder was significantly lower in the TICL group at the 1-week visit (0.80 vs 0.52 D, P=. 020) but not significantly different at any other time points (Table 2).

The predictability of manifest refraction for the TICL and PRK groups is presented in Figure 8 and Table 2. The TICL group had a significantly higher proportion of cases within ?0.50 D of predicted at every follow-up through 6 months postoperatively and significantly better within ± 1.00 D at all postoperative visits than the PRK group.

Table

TABLE 3Comparison of TICL vs PRK Stability Outcomes

TABLE 3

Comparison of TICL vs PRK Stability Outcomes

The stability of refraction (proportion of cases with ≤0.50 D change) was significantly better in the TICL group compared to PRK through 6 months (Table 3). From 6 months to 12 months, the proportion was 85% for the PRK and 94% for the TICL series (P=.245). The stability of refraction (proportion of cases with ^1.00 D change) was again significantly better in the TICL group compared to PRK through 6 months. There was no statistical advantage with the TICL between 6 months and 12 months due to the high stability (>90%) in both groups (92% PRK, 100% TICL).

The stability of cylinder (proportion of cases with ≤50.50 D change) was significantly better in the TICL group compared to the PRK group through 3 months (Table 1). No statistical difference was noted with regard to a ≤0.50 D or ≤1.00 D change between 3 months and 12 months.

Contrast sensitivity was tested at the 5% photopic level and 25% mesopic level. In the 5% photopic contrast subset (Table 4), although the mean BSCVA (logMAR) was not statistically different between the PRK and TICL groups preoperatively, it was significantly better in the TICL series at all postoperative visits (Fig 9). Loss of 2 or more lines of BSCVA was significantly higher in the PRK series at all postoperative visits except 6 months where the TICL had 0% loss of 2 or more lines compared to a 13% loss with PRK (P=.058). Improvement in BSCVA (2 or more lines) was statistically better in the TICL group at all time points from 1 to 12 months. Losses of 1 or more lines of BSCVA were significantly higher in the PRK series at all time points after 1 week. Improvement of 1 or more lines of BSVCA was significantly better in the TICL series at all time points from 1 month through 12 months. Seventy-six percent of patients had an improvement of 1 or more lines of BSCVA in the TICL series at 12 -month follow-up compared to 21% in the PRK series. The mean change in BSCVA was significantly better with the TICL than with the PRK at all postoperative time points from 1 week through 12 months (P≤.003).

In the 25% mesopic contrast subset (Table 5), although the mean BSCVA (logMAR) was not statistically different between the PRK and TICL groups preoperatively, it was significantly better in the TICL series at all postoperative visits (Fig 10). Improvement in BSCVA (2 or more lines) was statistically better in the TICL group at all time points from 1 to 12 months. Losses of 1 or more lines of BSCVA were significantly higher in the PRK series at all time points after 1 week. Improvement of 1 or more lines of BSVCA was significantly better in the TICL series at 1 month, 3 months, and 12 months (63% vs 9%, P=.002). The mean change in BSCVA was significantly better with the TICL group than with the PRK group at all postoperative time points from 1 month through 12 months (P≤ .001).

Figure 1. Mean change in lines of BSCVA at each postoperative time period in the PRK and TICL series.Figure 2. Distribution of BSCVA line gains and losses at 12 months postoperatively in the PRK and TICL series.Figure 3. Proportion of cases with UCVA of 20/16 or better at each postoperative time period in the PRK and TICL series. Asterisks reflect the statistical significance of the difference between the PRK and TICL series.

Figure 1. Mean change in lines of BSCVA at each postoperative time period in the PRK and TICL series.

Figure 2. Distribution of BSCVA line gains and losses at 12 months postoperatively in the PRK and TICL series.

Figure 3. Proportion of cases with UCVA of 20/16 or better at each postoperative time period in the PRK and TICL series. Asterisks reflect the statistical significance of the difference between the PRK and TICL series.

A standardized subjective questionnaire was administered to all patients preoperatively (PRK: n=33, TICL: n=30), at 3 to 6 months (PRK: n= 30, TICL: n= 22), and 12 months (PRK: n=18, TICL: n=15). Virtually all questions presented used a numbered scale of 1 through 10; 1 representing no difficulty in vision, no glare, or no halos, 10 being extreme difficulty, disabling glare, or disabling halos. One of the few exceptions to this 10-point scale was a question referring to use of artificial tears. This question was answered on a scale from 1 to 5, 1 being no use, and 5 being four times or more daily. A Wilcoxon sum rank test was used to compare the responses between the TICL and PRK groups. When comparing the TICL cases to PRK at the 3- to 6-month time period, the PRK group showed significantly more need for artificial tears (median response: PRK=2, TICL=1; P=. 002) and more vision fluctuation (PRK=2, TICL=I; P=.001). The PRK group also had more glare symptoms at night (PRK=3, TICL=2; P=. 033) and from oncoming car headlights at night (PRK=3, TICL=2; P=.014). All other questions presented to the study participants at 3 to 6 months were answered similarly with no statistical difference. The 12-month questionnaire showed similar subjective visual results between the two study groups with the exception of continuing problems with dry eyes (greater use of artificial tears) in the PRK cases (median response: PRK=2, TICL=I; P=. 008) and significantly greater glare symptoms when watching television or using a computer monitor (median response: PRK=I, TICL=I; P=.043).

Figure 4. Proportion of cases with UCVA of 20/20 or better at each postoperative time period in the PRK and TICL series. Asterisks reflect the statistical significance of the difference between the PRK and TICL series.Figure 5. The proportion of eyes with preoperative BSCVA compared to 12-month postoperative uncorrected visual acuity (UCVA) in the PRK and TICL series.Figure 6. S e atte rg ram s illustrate the manifest refraction attempted versus achieved outcomes at 12 months postoperative for the A) TICL series and B) PRK series.Figure 7. Comparison of 12-month postoperative defocus equivalent refraction outcomes in the PRK and TICL series.Figure 8. The predictability of manifest refraction for the TICL and PRK series at 12 months postoperatively.

Figure 4. Proportion of cases with UCVA of 20/20 or better at each postoperative time period in the PRK and TICL series. Asterisks reflect the statistical significance of the difference between the PRK and TICL series.

Figure 5. The proportion of eyes with preoperative BSCVA compared to 12-month postoperative uncorrected visual acuity (UCVA) in the PRK and TICL series.

Figure 6. S e atte rg ram s illustrate the manifest refraction attempted versus achieved outcomes at 12 months postoperative for the A) TICL series and B) PRK series.

Figure 7. Comparison of 12-month postoperative defocus equivalent refraction outcomes in the PRK and TICL series.

Figure 8. The predictability of manifest refraction for the TICL and PRK series at 12 months postoperatively.

Table

TABLE 45% Photopic Contrast Comparison Data (5% Contrast Acuity)

TABLE 4

5% Photopic Contrast Comparison Data (5% Contrast Acuity)

Figure 9. Mean change in lines of 5% photopic contrast BSCVA at each postoperative time period in the PRK and TICL series.Figure 10. Mean change in lines of 25% mesopic contrast BSCVA at each postoperative time period in the PRK and TICL series.

Figure 9. Mean change in lines of 5% photopic contrast BSCVA at each postoperative time period in the PRK and TICL series.

Figure 10. Mean change in lines of 25% mesopic contrast BSCVA at each postoperative time period in the PRK and TICL series.

DISCUSSION

This study was conducted to compare the TICL to PRK in a randomized, prospective, clinical trial for the treatment of moderate to high myopia with astigmatism. Although LASIK is a more commonly performed refractive surgery, a surface procedure maybe preferred in some patients, such as those with thinner corneas or epithelial basement membrane dystrophy.

The superior outcomes of the TICL were evident in a number of important clinical measures: UCVA, refractive predictability, refractive stability, change in BSCVA, change in contrast acuity, and glare symptoms. In addition, dry eye complaints were lower with the TICL procedure.

Table

TABLE 525% Mesopic Contrast Comparison Data (25% Contrast Acuity)

TABLE 5

25% Mesopic Contrast Comparison Data (25% Contrast Acuity)

The quality of vision was significantly better with the TICL. The mean change in BSCVA and best corrected contrast sensitivity (photopic 5% and mesopic 25% contrast acuity) favored the TICL at all postoperative intervals, as shown in Figures 2, 9, and 10. At least a one line difference was noted with these vision tests pre- and postoperatively in the TICL and PRK groups. This difference has clinical relevance. Patients who underwent PRK had more glare symptoms at 3, 6, and 12 months postoperatively.

The differences in BSCVA and contrast sensitivity favoring the TICL are present despite the fact that no significant differences were found between groups with regard to sphere and cylinder at 12 months postoperatively. This finding is most likely caused by postoperative increase in higher order aberrations resulting in degradation of the retinal images not correctable with spherocylindrical lenses seen after PRK and after LASIK.69 Sarver et al10 reported improved image quality caused by less postoperative higher order aberrations, especially coma and spherical aberration, after ICL implantation relative to LASIK.

It was not surprising that the visual recovery of PRK was slower than the TICL; however, the magnitude of the difference was dramatic. The percentage of eyes that attained 20/20 UCVA after PRK increased significantly from 1 week (9%) to 6 months (82%) postoperatively, indicating a gradual recovery. This was in contrast to the TICL where 86% of eyes achieved 20/20 UCVA at 1 week postoperatively. Aside from benefiting the patient, the speed of visual recovery with the TICL has other important clinical advantages, such as early assessment of refractive and acuity outcomes.

A refined nomogram adjustment could improve the refractive results of PRK. Higher levels of preoperative myopia tended to result in overcorrection. Using the PRK attempted versus 12 -month achieved results in this study to create a nomogram, reducing the sphere by 17% and adding ?0.50 D to the treatment would improve the emmetropia target. Computing the projected refractive outcome using this nomogram, the percentage of eyes that would be expected to be within 0.50 D of emmetropia (59%) is still significantly lower than that observed with the TICL (76%). This is due to the greater 12 -month refractive variance of PRK as evidenced by the difference in the standard deviation of the mean MRSE, ?0.75 D for PRK versus ?0.36 D for TICL. Thus, even if an ideal nomogram would have been used for PRK, the refractive predictability would still favor the TICL. During the time frame of this study, wavefront-guided ablation and other subsequent improvements, such as iris registration, had not been approved and were not used as part of the comparison group but would provide a suitable comparator group for future studies.

One of the concerns of a phakic IOL is the safety of the procedure. A primary safety indication is the rate of loss of BSCVA. Through 12 months of follow-up in our study, no loss of vision occurred with the TICL. In fact, an average gain of one line of vision was noted. In this study, one eye developed a visually significant cataract. It was not noted during the 1-month examination, and unfortunately the patient was lost to followup until 2 years after the procedure. At that time, no vault was noted between the posterior TICL and the anterior lens capsule. The patient underwent removal of the TICL and cataract with subsequent Pseudophakie IOL implantation. Although the patient did well after this procedure, a permanent loss of accommodation occured. Sizing of the TICL in this study was based on the white-to- white measurement. Better methods to determine the optimal size of the TICL such as the use of ultrasonic biomicroscopy to determine ciliary sulcus size1112 may have prevented the lens opacity.

The risks of the TICL are different than those of PRK. Disabling scarring can occur months or years after PRK and has been associated with ultraviolet exposure. Mitomycin C has been shown to be effective at reducing the chance of scarring after PRK and was used in this study.1315 No significant scarring was noted throughout follow-up. Despite the absence of scarring in the PRK group, the TICL group still had a more favorable change in BSCVA and contrast sensitivity.

A number of other clinical trials have compared outcomes between the Visian ICL and LASIK or PRK.3,1016,17 All showed superior results of the ICL for various refractive ranges. The outcomes of this comparison of PRK and the TICL support these findings and demonstrate that in this study, TICL correction results in a more effective procedure than PRK surgery. The dramatic improvement in outcome of the ICL over LASIK or PRK is not unexpected as it is more accurate to manufacture the exact correction required in a HEMA material than to ablate the correction onto corneal tissue, which is then subject to tissue healing.

REFERENCES

1. Miller RE II, Woessner WM, Dennis RJ, O'Neal MR, Green RP Jr. Survey of spectacle wear and refractive error prevalence in USAF pilots and navigators. Optom Vis Sci. 1990;67:833-839.

2. Partner AM, Scott RA, Shaw P, Coker WJ. Contact lenses and corrective flying spectacles in military aircrew ? implications for flight safety. Aviat Space Environ Med. 2005;76:661-665.

3. ICL Treatment of Myopia (ITM) Study Group. U.S. FDA clinical trial of the implantable collamer lens (IC L?) for moderate to high myopia; three year follow-up. Ophthalmology. 2004;111:1683-1692.

4. Sanders D, Schneider D, Martin R, Brown D, Dulaney D, Vukich J, Slade S, Schallhorn S. Toric Implantable Collamer Lens for moderate to high myopic astigmatism. Ophthalmology. 2007;114:54-61.

5. Sarver EJ, Sanders DR. Astigmatic power calculations for intraocular lenses in the phakic and aphakic eye. / Refract Surg. 2004;20:472-477.

6. Oshika T, KIy ce SD, Applegate RA, Howland HC, El Danasoury MA. Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmol. 1999;127:1-7.

7. Hong X, Thibos LN. Longitudinal evaluation of optical aberrations following laser in situ keratomileusis surgery. ?Refract Surg. 2000;16:S647-S650.

8. Moreno -Barrius o E, Lio ves JM, Marcos S, Navarro R, Ll?rente L, Barbero S. Ocular aberrations before and after myopic corneal refractive surgery: LASIK-induced changes measured with laser ray tracing. Invest Ophthalmol Vis Sci. 2001;42:1396-1403.

9. Oshika T, Miyata K, Tokunaga T, Samejima T, Amano S, Tanaka S, Hirohara Y, Mihashi T, Maeda N, Fujikado T. Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser situ keratomileusis. Ophthalmology. 2002;109:1154-1158.

10. Sarver EJ, Sanders DR, Vukich JA. Image quality in myopic eyes corrected with laser in situ keratomileusis and phakic intraocular lens. J Refract Surg. 2003;19:397-404.

11. Pop M, Payette Y, Mansour M. Predicting sulcus size using ocular measurements. J Cataract Refract Surg. 2001;27:1033-1038.

12. Choi KH, Chung SE, Chung TY, Chung ES. Ultrasound biomicroscopy for determining visian implantable contact lens length in phakic IOL implantation. J Refract Surg. 2007;23:362-367.

13. Lee DH, Chung HS, Jeon YC, Boo SD, Yoon YD, Kim JG. Photorefractive keratectomy with intraoperative mitomycin-C application. J Cataract Refract Surg. 2005;31:2293-2299.

14. Gambato C, Ghirlando A, Moretto E, Busato F, Midena E. Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes. Ophthalmology. 2005;112:208-218.

15. Vigo L, Scandola E, Carones F. Scraping and mitomycin C to treat haze and regression after photorefractive keratectomy for myopia. J Refract Surg. 2003;19:449-454.

16. Sanders DR, Vukich, JA. Comparison of Implantable Contact Lens (ICL?) and laser assisted in situ keratomileusis for moderate to high myopia. Cornea. 2003;22:324-331.

17. Sanders DR, Vukich JA. Comparison of Implantable Contact Lens (ICL?) and laser assisted in situ keratomileusis (LASIK) for low myopia. Cornea. In press.

TABLE 1

Comparison of TICL vs PRK Visual Outcomes

TABLE 1 CONTINUED

Comparison of TICL vs PRK Visual Outcomes

TABLE 2

Comparison of TICL vs PRK Refractive Outcomes

TABLE 3

Comparison of TICL vs PRK Stability Outcomes

TABLE 4

5% Photopic Contrast Comparison Data (5% Contrast Acuity)

TABLE 5

25% Mesopic Contrast Comparison Data (25% Contrast Acuity)

10.3928/1081-597X-20071101-01

Sign up to receive

Journal E-contents