Post-photorefractive Keratectomy Research Articles

Collagen Corneal Cross-Linking followed by Intac Implantation in a Case of Post-PRK Ectasia

ABSTRACT Collagen corneal cross-linking (CXL) has proved to be effective in halting the progression of keratoconus and post-LASIK ectasia. Post-photorefractive keratectomy (PRK) ectasia, a rare PRK complication, has been reported in only a few cases, although PRK is the oldest form of laser refractive surgery. CXL for post- PRK ectasia has not been reported yet. Here is a case of a 22-year-old male who developed post- PRK ectasia more than 1 year after the procedure and was treated using CXL. A few months after CXL, an Intac (Addition Technology) was implanted due to contact lens intolerance. How to cite this article Barbara R, Zadok D, Pikkel J, Marcovich A, Garzozi H, Nasser O, Abdelaziz L, Barbara A. Collagen Corneal Cross-Linking followed by Intac Implantation in a Case of Post-PRK Ectasia. Int J Keratoco Ectatic Corneal Dis 2012;1(1):68-72.

Microkeratome-Assisted Superficial Anterior Lamellar Keratoplasty for Anterior Stromal Corneal Opacities After Penetrating Keratoplasty

To describe the surgical technique and report the outcomes of patients treated with microkeratome-assisted superficial anterior lamellar keratoplasty for anterior stromal corneal opacities developing after penetrating keratoplasty (PK). All patients with post-penetrating keratoplasty anterior stromal opacities treated with microkeratome-assisted superficial anterior lamellar keratoplasty between July 2005 and June 2007 were reviewed. A 130-μm superficial keratectomy was performed, followed by the placement of an appropriately sized donor graft, which was secured with overlay sutures. Refraction, corneal topography, and uncorrected and best-corrected visual acuities (UCVA, BCVA, respectively) were noted at each examination. Nine eyes of 8 consecutive patients were identified. Causes of anterior stromal opacities included dystrophy recurrence (n = 3), post-photorefractive keratectomy haze (n = 2), and scarring after stromal melt (n = 4). BCVA improved in all 9 eyes at final follow-up, and 7 of 9 eyes achieved ≥20/40 within the first month. Average follow-up period was 28 ± 3.9 months. Refractive astigmatism also improved by an average of 0.7 diopters. Superficial anterior lamellar keratoplasty is a viable and effective alternative to repeat PK in treating anterior stromal scars. It avoids open-globe surgery and exposure to endothelial rejection associated with repeat PK, and visual rehabilitation is considerably quicker.

Effects of cooling cornea by Low-Temperature Saline Washing on postoperative pain in Photorefractive Keratectomy

Several studies have reported that cooling cornea has effects on alleviating pain post Photorefractive Keratectomy (PRK). However, our random prospective self-control study using 52 eyes of 26 myopic patients revealed that there was no significant statistical difference (P > 0.74) in the postoperative pains at both day-1 and day-3 between the experimental eye group (26 myopic eyes, treated with chilled lactated Ringer's saline of 4°C) and the control eye group (26 self control eyes, treated with lactated Ringer's saline of ˜20°C). The result suggests that applying low-temperature balanced saline solution onto corneal surfaces is not an effective analgesia for PRK surgery.

A fibrin-related line of research and theoretical possibilities for the use of fibrin glue as a temporary basal membrane in non-perforated corneal ulcers and in photorefractive keratectomy (PRK)-operated corneas

To report a specific line of research developed at the University of São Paulo/Brazil on fibrin glue used for sealing corneal perforations and the perspectives of use on non-perforated corneal ulcers and photorefractive keratectomy-operated corneas. To describe fibrin glue manufacture, development of a device to test the glued perforated corneal area resistance, subsequent experimental investigations of the use of the fibrin glue in corneal perforations, reporting its efficacy, mechanical resistance experiments and histological study. Finally, the medical literature basis is searched to propose studies on the use of fibrin as a temporary basal membrane on non-perforated corneal surfaces like non-infectious corneal ulcers and on post-photorefractive keratectomy corneal surfaces. The development of fibrin glue, the device for resistance experiments, the efficacy, resistance and histological studies on fibrin glue used for sealing corneal perforations are reported as well as the scientific literature basis for the proposed studies on the use of fibrin as a temporary basal membrane on non-perforated corneas like non-perforated corneal ulcers and photorefractive keratectomy corneal surfaces. A specific line of research was reported on fibrin glue to seal corneal perforations at the University of São Paulo/Brazil and the theoretical perspectives for the use of fibrin in non-perforated corneal ulcers and on photorefractive keratectomy-operated corneas in an attempt to reduce corneal haze.

Automated Keratoconus Detection Using Height Data of Anterior and Posterior Corneal Surfaces

To develop a keratoconus detection algorithm using the corneal topographic data of the anterior and posterior corneal surfaces. Topographic measurements of the cornea were made with a slit-scanning corneal topographer. We examined 120 subjects (165 eyes); keratoconus patients and keratoconus suspect patients comprised the keratoconus group, and post-photorefractive keratectomy patients, with-the-rule astigmatism patients, and controls without disease comprised the nonkeratoconus group. Two variables of the anterior corneal surface, two variables of the posterior corneal surface, and one corneal thickness variable were obtained by applying the Fourier harmonic decomposition formula. By performing a logistic regression analysis with a training set to differentiate the keratoconus group from the nonkeratoconus group, the Fourier-incorporated keratoconus detection Index (FKI) was created. The validity of the FKI was determined by using independent validation sets. The FKI distinguished the keratoconus group from the nonkeratoconus group with 96.9% sensitivity and 95.4% specificity in the validation set. A newly developed automated keratoconus classifier can be used to screen keratoconic patients. The index is based on information obtained by Fourier analysis from not only the anterior corneal surface but also from the posterior corneal surface and corneal thickness.

Automated lamellar therapeutic keratoplasty for post-PRK corneal scarring and thinning

To present the use of automated lamellar therapeutic keratoplasty (ALTK) for the treatment of post-photorefractive keratectomy (PRK) corneal scarring and thinning with significant residual myopia. Interventional case report. A patient with high myopia of -12 diopters previously underwent PRK that resulted in corneal scarring, myopic regression, moderate loss of best-corrected visual acuity, a residual refractive error of -6.50/-1.00 x 175 degrees, and a remaining corneal thickness of 300 mum. ALTK was first performed to remove the scar and to augment corneal thickness, and a subsequent laser-assisted in-situ keratomileusis (LASIK) procedure was performed to correct the residual myopia. ALTK effectively removed the corneal scar and augmented the corneal thickness to 639 mum. LASIK effectively treated the residual myopia, resulting in an unaided visual acuity of 20/25 and a stable refractive error of plano/-0.50 x 40 degrees. The ALTK interface remained clear throughout the follow-up period of 26 months. ALTK may be a reasonable alternative to conventional penetrating keratoplasty in the treatment of post-PRK corneal scarring and thinning, with a moderate loss of best-corrected visual acuity, and LASIK can be subsequently performed to correct the residual refractive error and achieve an excellent refractive and visual outcome.

Custom-contoured ablation pattern method for the treatment of decentered laser ablations

Purpose: To evaluate the custom-contoured ablation pattern (C-CAP) method as a tool for providing customized laser ablations for decentered ablations based on corneal topography data. Setting: Department of Ophthalmology, Stanford University, Stanford, California, USA. Methods: In a prospective noncomparative interventional case series, 8 eyes from 7 post-laser in situ keratomileusis (LASIK) patients and 1 post-photorefractive keratectomy (PRK) patient with symptomatic laser decentration were treated with the C-CAP method. The Zeiss Humphrey topography system was used to identify and analyze decentered ablations. The computer software allowed the surgeon to preoperatively model the effect of various ablation schemes on the preoperative topography until a scheme that alleviated the decentration was identified. The planned ablation parameters, which included size, depth, and location of the ablation, were programmed into the Visx S4 excimer laser before treatment. Results: The mean follow-up after C-CAP ablation was 4.2 months (range 1.8 to 6.3 months). At the last postoperative examination, no eye lost a line of best spectacle-corrected visual acuity (BSCVA). The uncorrected visual acuity (UCVA) improved by 3 lines in 1 eye (12.5%), by 2 lines in 1 eye (12.5%), and by 1 line in 3 eyes (37.5%); it remained unchanged in 2 eyes (25.0%) and decreased by 1 line in 1 eye (12.5%). The BSCVA improved by 3 lines in 1 eye (12.5%), by 2 lines in 2 eyes (25.0%), and by 1 line in 3 eyes (37.5%); it remained unchanged in 2 eyes (25.0%). In all eyes, including those without improvement in UCVA or BSCVA, a significant improvement in centration and subjective complaints was achieved. The pre-C-CAP and post-C-CAP root-mean-square (RMS) wavefront data were available in 5 of 8 eyes. The total and higher-order RMS aberrations decreased by 41.7% ( P = .0027) and 45.5% ( P = .039), respectively, after C-CAP treatment. Conclusions: Early U.S. results show the topography-driven C-CAP method is an effective tool to address untreatable postsurgical decentration. This method is presented as a technique to enhance the overall quality of vision, reduce patient-perceived visual aberrations, regularize the corneal surface, and maximize BSCVA.

Safety and efficacy of ketorolac tromethamine 0.4% ophthalmic solution in post-photorefractive keratectomy patients

Purpose: To evaluate the safety and analgesic efficacy of ketorolac tromethamine 0.4% ophthalmic solution in postoperative photorefractive keratectomy (PRK) patients. Setting: Fifteen clinical sites in the eastern and southern United States. Methods: This pooled analysis of 2 multicenter, randomized, double-masked, vehicle-controlled, parallel-group studies comprised 313 patients having unilateral PRK. After surgery, patients were treated with 1 drop of ketorolac tromethamine 0.4% ophthalmic solution (Acular® LS) (n = 156) or vehicle (n = 157) 4 times daily for up to 4 days. Pain intensity, pain relief, use of escape medication, and severity of ocular symptoms were assessed. Adverse events, epithelial healing, and visual acuity were recorded. Results: There was significantly less pain intensity experienced by patients in the ketorolac group ( P<.001). During the first 12 hours post PRK, 50% fewer patients in the ketorolac group than in the vehicle group had severe to intolerable pain (41.6% [64/154] and 84.5% [131/155], respectively). The median time to no pain was 30 hours in the ketorolac group and 54 hours in the vehicle group ( P<.001, survival analysis). Ketorolac patients reported significantly greater pain relief than vehicle patients throughout the study ( P<.001). Ketorolac patients used significantly less escape medication than vehicle patients for 48 hours post PRK ( P≤.008). Treatment-related adverse events occurred in 2.6% (4/156) of ketorolac patients and 6.4% (10/157) of vehicle patients. Conclusion: Ketorolac 0.4% ophthalmic solution is safe and effective in reducing ocular pain when used 4 times daily for up to 4 days post PRK.

Laser in situ keratomileusis flap tear during lifting for enhancement in the presence of post-photorefractive keratectomy corneal haze

A patient who had photorefractive keratectomy for low myopia 6 years earlier had an enhancement by hyperopic laser in situ keratomileusis (LASIK). Moderate reticular corneal haze developed after LASIK. An attempted flap lift 4 months after LASIK resulted in a flap tear at the edge of the zone of corneal haze. Because haze can indicate an area of exuberant wound healing that can result in flap adhesion to the bed, recutting a LASIK flap may be safer than lifting it in the presence of haze.

Stiles-Crawford effect of the first kind (SCE-I) in post-photorefractive keratectomy and anisometropic subjects.

The Stiles-Crawford effect of the first kind (SCE-I) was measured on both post-photorefractive keratectomy (PRK) and anisometropic subjects at six different locations of retina. The eye that underwent the PRK procedure showed results that were typical of myopic eyes, although the vision in that eye has been maintained at 6/5 (or 20/15) since the operation. The anisometropic subject had one eye that was emmetropic and the other eye was myopic with a refractive error of -3.00 DS. The emmetropic eye showed the normal well-centered SCE-I functions across the retina, whereas the myopic eye of the same subject showed the nasal tilting of receptors in the nasal retina, which has been the typical finding among myopic subjects.

Simulation of airbag impact on eyes after photorefractive keratectomy by finite element analysis method.

A simulation model of the human eye which we have developed was applied to simulated airbag ocular injury, to determine the physical and mechanical conditions of the impacting airbag that would cause globe rupture in a post-photorefractive keratectomy (PRK) eye. Simulations were performed with a computer using the finite element analysis program PAM-CRASH()(Nihon ESI, Tokyo, Japan). The airbag was set to impact on the surface of post-PRK eyes-D3, D6, D10, and D15-and an intact eye at various impact velocities. Strain on the cornea and sclera exceeding 18.0% and 6.8%, respectively, was assumed to indicate the possibility of rupture of each tissue. In contrast to the intact eye, in post-PRK eyes, at the lowest velocity of 20 m/s, some of the element reached the strain threshold in D15. At the medium velocity of 30 m/s, limited corneal rupture was observed in all situations. At the high velocity, 40 m/s, scleral laceration was found in eyes with all diopters, and apparent corneal rupture was observed in D10 and D15, indicating that globe rupture was very likely to occur. These results suggest that severe ocular trauma can be caused in post-PRK eyes by airbags at high impact velocities. Preoperative discussion with candidates for laser refractive surgery regarding the potential for severe ocular injury if the normal integrity of the eye is compromised by surgery may be appropriate. Research on modification of airbag design and deployment to minimize the risk of ocular injury is important.

Treatment of intraocular pressure elevation after photorefractive keratectomy

Purpose: To study the effect of timolol maleate, dorzolamide, or a combination of both in post photorefractive keratectomy (PRK) eyes with an elevated intraocular pressure (IOP) after topical steroid administration. Setting: Refractive Surgery Outpatient Department, 1st Department of Ophthalmology, Semmelweis University, Budapest, Hungary. Methods: Forty-five patients with elevated IOP were randomly enrolled in 3 groups: Group 1 received timolol maleate 0.5% twice a day; Group 2 received timolol maleate 0.5% twice a day and dorzolamide 2% 3 times a day; and Group 3 received only topical dorzolamide 2% 3 times a day. Intraocular pressure was measured 3 days and 1, 3, and 6 weeks after the antiglaucoma medication was started. Results: The mean preoperative IOP was 15.25 mm Hg ± 1.28 (SD). Following administration of topical fluorometholone, the IOP increased a mean of 27.39 ± 2.88 mm Hg. Six weeks after the antiglaucoma therapy was started, the mean IOP reduction was 6.6 mm Hg in Group 1, 8.86 mm Hg in Group 2, and 4.64 mm Hg in Group 3. Conclusions: A combination therapy of timolol 0.5% and dorzolamide 2% was most effective in treating secondary IOP elevation after PRK. Dorzolamide alone did not adequately control secondary post-PRK IOP elevation.

Author’s reply

We concur with Dr. Perilli et al’s suggestion that a number of nonsteroidal anti-inflammatory drugs (NSAIDs) may have an affect on microbial attachment and that the field warrants further study. We certainly welcome the extension of the concept of the benefit of NSAIDs with contact lenses to the more specialized application of postphotorefractive keratectomy bandage lenses, which of course is particularly important because of the compromised cornea in such cases. Naturally, the use of diclofenac in a contact lens disinfecting solution would be problematic in light of its therapeutic actions, which we want to minimize in our application. But it is a nice side benefit when used postoperatively.

Topographically-guided laser in situ keratomileusis to treat corneal irregularities

Objective To evaluate the predictability and safety of topographically guided laser in situ keratomileusis (LASIK) to treat corneal irregularities. Design Prospective, noncomparative interventional case series. Participants Twenty-seven patients (29 eyes) with postsurgical corneal irregularities, divided into four subgroups (postkeratoplasty, 6 eyes; posttrauma, 6 eyes; postphotorefractive keratectomy (PRK)/LASIK with decentered or small ablations, 11 eyes; post-PRK/LASIK with central islands, 6 eyes). Intervention: LASIK was performed using the Automatic Corneal Shaper and the Keracor 117 C spot-scanning excimer laser (Bausch & Lomb Surgical Technolas, Munich, Germany). Individual ablation patterns were calculated on the basis of axial radii of curvature data obtained with the Corneal Analysis System (EyeSys Premier, Irvine, CA). Main outcome measures Change of corneal topography pattern, patient satisfaction, manifest spectacle refraction, and visual acuity at 12 months after surgery. Results Corneal topography showed improved corneal regularity in 66% of eyes in the postkeratoplasty group, whereas 34% remained irregular. In the posttrauma group, 83% improved and 17% remained irregular. In the decentered/small optical zone group, 91% improved and 9% remained irregular. In the central islands group, 50% improved and 50% remained irregular. Refractive cylinder decreased from 5.83 ± 1.25 diopters (D) to 2.96 ± 1.23 D in the postkeratoplasty group ( P = 0.01), from 2.21 ± 1.35 D to 0.50 ± 0.84 D in the posttrauma group ( P = 0.001), from 0.73 ± 0.71 D to 0.36 ± 1.05 D in the decentered/small optical zone group (NS), and from 1.42 ± 1.13 D to 0.50 ± 0.84 D in the central island group ( P = 0.01). Uncorrected visual acuity improved from 20/200 ± 0.07 to 20/50 ± 0.17 in the postkeratoplasty group ( P = 0.01), from 20/83 ± 0.12 to 20/50 ± 0.28 in the posttrauma group ( P = 0.01), from 20/60 ± 0.16 to 20/50 ± 0.29 in the decentered/small optical zone group (NS), and from 20/71 ± 0.12 to 20/60 ± 0.24 in the central island group (NS). Conclusions The topographically-guided LASIK method used in this study resulted in a significant reduction of refractive cylinder, a significant increase of uncorrected visual acuity, and improved corneal regularity in a large percentage of patients with severe corneal irregularities such as decentered/small optical zones after LASIK or irregular astigmatism after keratoplasty or trauma. With small irregularities such as central islands, results were sufficiently poor to advise against the use of our technique in these patients.

Photorefractive keratectomy after intrastromal corneal ring segment explantation

PURPOSE: To describe a case of photorefractive keratectomy after removal of intrastromal corneal ring segments from the cornea. METHODS: During United States Food and Drug Administration Phase III Trials for intrastromal corneal ring segments (ICRS), the implanted segments were removed from the cornea of the right eye of a patient because of dissatisfaction with glare, halos, and fluctuating vision. Ten months after ICRS explantation, the patient underwent a photorefractive keratectomy procedure to the same eye. RESULTS: One month after removal of the ICRS, the patient’s manifest refraction was within ±0.50 diopters of his original manifest refraction. Photorefractive keratectomy was planned to the same eye 6 months later. At the first attempt, the epithelium could not be removed with the laser and scrape technique, and residual epithelium was noted at the vertical meridian (12 o’clock) corneal incision site, which had been used for ICRS surgery and explant; therefore, the procedure was aborted. At the second attempt, with a mechanical epithelial brush (AMOILS Epithelial Scrubber; Innova, Inc, Toronto, Canada), the epithelium was removed with ease. After this, photorefractive keratectomy was done without difficulty or complication. At his most recent 8-month postphotorefractive keratectomy examination, the patient had an uncorrected visual acuity of RE: 20/16, with a manifest refraction of −0.75 to 0.75 × 170 degrees, a faint haze at the site of the stromal channel, and a small scar at the incision site on slit-lamp examination. CONCLUSIONS: Intrastromal corneal ring segments can be readily removed from the cornea, if required. In this case, the refraction returned to its preoperative state soon after the explant procedure and remained stable over time. Photorefractive keratectomy was performed as a secondary refractive surgical procedure after the removal of ICRS without difficulty or complication. However, removal of the epithelium is probably best accomplished with the use of an epithelial brush, considering the changes in the epithelial adherence in a postsurgical cornea. Further studies are required to establish the safety and efficacy of secondary refractive surgical procedures after ICRS explantation.

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 μm (standard deviation, n = 12). Repeated measures on the subject demonstrated a mean standard deviation of 9.08 μm 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 subject’s 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.

Tono-Pen versus Goldmann tonometry after excimer laser photorefractive keratectomy

Purpose: To compare intraocular pressure (IOP) measurements by the Tono-Pen 2tonometer and Goldmann applanation tonometer (GAT) in post-photorefractive keratectomy (PRK) patients. Setting: Refractive Surgery Center, Assaf Harofeh Medical Center, Zerifin, Israel. Methods: In 18 patients, IOP was measured by GAT and then by Tono-Pen 2tonometer 2 to 18 months following PRK (mean 6.6 months ± 5.1 [SD]). Photorefractive keratectomy had been performed in 1 eye of each patient; the fellow eyes served as controls. Corneal curvature and thickness were evaluated. Ten of the 18 patients were treated with topical steroids. Results: In the post-PRK eyes, mean GAT IOP was 1.8 ± 3.1 mm Hg lower than meanTono-Pen IOP ( P = .012); there was no significant IOP difference in the control (fellow) eyes. In steroid-treated post-PRK eyes, mean GAT IOP (12.2 mm Hg) was 2.2 ± 1.3 mm Hg lower than mean Tono-Pen IOP (14.4 mm Hg) ( P = .0007). Mean Tono-Pen IOP in steroid-treated post-PRK eyes was 4.3 ± 3 mm Hg higher than in the fellow eyes ( P = .0014); mean GAT IOP was only 2.3 ± 3.5 mm Hg higher ( P = .04). In post-PRK eyes without topical steroid treatment, mean GAT IOP was 2.0 ± 1.18 mm Hg lower than in the fellow eyes ( P = .001); there was no significant difference in Tono-Pen OP. There was a negative correlation between the difference in IOP values (Tono-Pen minus GAT) and corneal curvature in post-PRK eyes ( r = 0.76, P = .0108, n = 15). Conclusions: The Tono-Pen tonometer appeared to be less affected than the GAT by the relative flattening, thinning, and anterior stromal decreased rigidity of the central cornea that occur following PRK. Post-PRK steroid-induced IOP elevation may be masked by the artifactual decrease in GAT IOP.

Comparison of corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis

PURPOSE: To compare changes in the corneal wavefront aberrations after photorefractive keratectomy and laser in situ keratomileusis. METHODS: In a prospective randomized study, 22 patients with bilateral myopia received photorefractive keratectomy on one eye and laser in situ keratomileusis on the other eye. The procedure assigned to each eye and the sequence of surgery for each patient were randomized. Corneal topography measurements were performed preoperatively, 2 and 6 weeks, 3, 6, and 12 months after surgery. The data were used to calculate the wavefront aberrations of the cornea for both small (3-mm) and large (7-mm) pupils. RESULTS: Both photorefractive keratectomy and laser in situ keratomileusis significantly increased the total wavefront aberrations for 3- and 7-mm pupils, and values did not return to the preoperative level throughout the 12-month follow-up period. For a 3-mm pupil, there was no statistically significant difference between photorefractive keratectomy and laser in situ keratomileusis at any postoperative point. For a 7-mm pupil, the post–laser in situ keratomileusis eyes exhibited significantly larger total aberrations than the post–photorefractive keratectomy eyes, where a significant intergroup difference was observed for spherical-like aberration, but not for coma-like aberration. This discrepancy seemed to be attributable to the smaller transition zone of the laser ablation in the laser in situ keratomileusis procedure. Before surgery, simulated pupillary dilation from 3 to 7 mm caused a five- to six-fold increase in the total aberrations. After surgery, the same dilation resulted in a 25- to 32-fold increase in the photorefractive keratectomy group and a 28- to 46-fold increase in the laser in situ keratomileusis group. For a 3-mm pupil, the proportion of coma-like aberration increased after both photorefractive keratectomy and laser in situ keratomileusis. For a 7-mm pupil, coma-like aberration was dominant before surgery, but spherical-like aberration became dominant postoperatively. CONCLUSIONS: Both photorefractive keratectomy and laser in situ keratomileusis increase the wavefront aberrations of the cornea and change the relative contribution of coma- and spherical-like aberrations. For a large pupil, laser in situ keratomileusis induces more spherical aberrations than photorefractive keratectomy. This finding could be attributable to the smaller transition zone of the laser ablation in the laser in situ keratomileusis procedure.

Efficacy and safety of the proTek (Vifilcon A) therapeutic soft contact lens after photorefractive keratectomy

To test the ProTek (Vifilcon A) therapeutic soft contact lens in the alleviation of post-photorefractive keratectomy pain, its effect on epithelial healing, and its safety. Forty-seven consecutive eligible patients undergoing unilateral excimer laser photorefractive keratectomy for myopia were randomly assigned to receive standard postoperative care with or without the use of a ProTek soft contact lens. Patients prospectively graded a self-administered 5-point scale for pain and a 4-point scale for abnormal sensations at 4, 8, 12, 16, and 20 hours after surgery. They also recorded the type and dose of all medications taken during that time period. All patients were examined on the first and third days after surgery. The lenses were worn continuously for 3 days. The soft contact lens group (n = 24) disclosed a statistically significant (P < .05) reduction in pain intensity and abnormal sensations that was greatest at 8, 12, 16, and 20 hours postoperatively. Compared with control patients (n = 23), the soft contact lens group showed significant decreased dependence on most pain medications after the 12th hour (P < .05) and faster epithelial healing (P = .03). However, one case of bacterial keratitis, two cases of subepithelial infiltrates, and seven cases of contact lens intolerance were present in the soft contact lens group. The ProTek therapeutic soft contact lenses were effective in decreasing pain and other related abnormal sensations after excimer photorefractive keratectomy. They decreased dependence on pain medications and hastened epithelial healing but were not well tolerated in some patients.

Lack of Diurnal Variation in Vision, Refraction, or Keratometry After Excimer Laser Photorefractive Keratectomy

To examine whether diurnal variation in visual acuity, spherical equivalent, keratometry, or intraocular pressure occurs in patients who have undergone photorefractive keratectomy. Twenty-nine post-photorefractive keratectomy patients underwent morning and evening measurements of visual acuity, spherical equivalent, keratometry, and intraocular pressure at intervals between 5 and 13 months after photorefractive keratectomy. There was no statistically significant post-photorefractive keratectomy diurnal variation in visual acuity, spherical equivalent, or keratometry in the group studied. Diurnal variation in post-photorefractive keratectomy intraocular pressure was not significantly different between patients' treated and untreated eyes. Photorefractive keratectomy does not appear to result in diurnal variation in visual acuity, spherical equivalent, or keratometry post-operatively, nor does it seem to effect normal diurnal variation in intraocular pressure.