Keratomileusis For Myopia Research Articles

Comparison of corneal ablation depth predictability between small incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis for myopia

Background Recently, small incision lenticule extraction (SMILE) procedure is used to correct myopia.The clinical safety and efficiency of SMILE have been approved, but its predictability to corneal ablation depth is brought into focus. Objective This study was to compare the predictability of ablation depth in central cornea between SMILE and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) for myopia. Methods A non-randomized controlled clinical study was performed.Two hundred and seventy eyes of 135 myopic patients who were going to receive corneal refractive surgery were included in Beijing Tongren Hospital from October 2015 to May 2016.SMILE and FS-LASIK were performed on 138 eyes of 69 patients and 132 eyes of 66 patients matched in demography respectively under the informed consent.Central corneal thickness was measured by RTVue FD-OCT before and 1 week after surgery.The refractive power, actual ablation depth (difference of central corneal thickness before and after surgery) and central corneal cutting error (difference between theoretically expected ablation depth and real ablation depth) were intergrouply compared, and the correlation of real ablation depth with theoretically expected ablation depth was assessed. Results No significant difference was found in spherical power, astigmatic power and spherical equivalent after surgery between SMILE group and FS-LASIK group (t=-1.826, -1.405, -1.420, all at P>0.05). The actual ablation depth was (76.96±15.27)μm in the SMILE group, which was significant lower than (96.76±16.52)μm of theoretically expected ablation depth (t=-23.016, P<0.01); however, there was no significant difference in the FS-LASIK group between actual and expected ablation depth([77.92±18.69] μm versus [77.42±15.60] μm) (t=-0.604, P=0.547). The central corneal cutting error was (20.55±8.51)μm in the SMILE group and (7.17±5.97)μm in the FS-LASIK group, showing a significant difference between them (t=14.950, P<0.01). The positive linear correlations were seen between actual and expected ablation depth in both SMILE group and FS-LASIK group (r=0.799, 0.867, both at P<0.01). The actual ablation depth was increased over expected ablation depth, with the regression equations of Y=3.892+ 0.749X in the SMILE group and Y=3.443+ 0.957X in the FS-LASIK group. Conclusions The actual corneal ablation depth is less than expected corneal ablation depth in SMILE procedure, while in FS-LASIK procedure, the actual corneal ablation depth appears to be consistent with the expected one, inferring a good predictability in corneal ablation depth in FS-LASIK surgery. Key words: Myopia/surgery; Corneal stroma/surgery; Lasers, excimer/therapeutic use; Central corneal thickness; Ablated depth; Predictability; Comparative study

Wavefront-guided Versus Standard Laser in situ Keratomileusis in Myopia Using a 213 nm Wavelength Solid-state Laser: Comparison of Higher-order Aberrations

Wavefront-guided Versus Standard Laser in situ Keratomileusis in Myopia Using a 213 nm Wavelength Solid-state Laser: Comparison of Higher-order Aberrations

Clinical efficacy of sub-Bowman keratomileusis for myopia

Objective To explore the clinical efficacy of sub-Bowman keratomileusis (SBK) for myopia.Methods The uncorrected visual acuity (UCVA),best corrected visual acuity (BCVA),refractive condition,recovery time of corneal sensation and occurrence of dry eye were retrospectively analyzed in 228 eyes of 115 cases undergoing SBK at 3 months after surgery.Results The UCVA were 0.8 ～ 1.5(mean 1.12-±0.19) at 3 months after surgery.The UCVA were ≥1.0 in 222 eyes (97.37％) and ≥1.2in 113 eyes (49.56％).The BCVA were better than UCVA in all cases at 3 months after surgery.The spherical equivalent (SE) refraction were (-0.65 ～ + 0.97) D (mean 0.15 ± 0.41 D) in all cases and 92.54％ cases had SE at ≤0.5D.The recovery time of corneal sensation was about 3 months after surgery.The dry eye condition was very slight which did not need long-time artificial tear treatment.Conclusion SBK can correct myopia with high predictability,efficacy and safety. Key words: Keratomileusis, sub-Bowman; Myopia; Efficacy, clinical

An analysis of the relationship between Q-value with parameters of corneal allterior surface before laser in situ keratomileusis for myopia

Objective To measure the corneal Q value and other anterior surface refractive parameters in myopic population and analyze the relationship. Methods The Q valve and other related anterior comeal refractive parameters included comneal curvature, simulated keratometry, irregular index in 3 and 6 mm area and Diff value were measured with Orbscan Ⅱ anterior segment systemin on 300 myopic patients ( 600 eyes). The relationship betweend the Q value and other refractive parameters were analyzed. Results In the 600 eyes,the Q value ranged from -0.51 to 0.37 and averged -0. 17 ±0. 11 ,corneal curvature,was (43.59 ± 1.54) D, simulated keratometry was (43.89 ± 1.46) D, cornael irregular index in 3 and 5 mm area were ( 1. 324 ± 0.41 ) D and ( 1.72 ± 0.63 ) D and anterior corneal surface Diff was (0.07 ± 0.05 ) mm. Statistic analysis showed negative relationship between Q value with other refractive parameters. Conclusion In myopic eyes,the Q value has negative relationship with other corneal anterior surface refractive parameters. Key words: Corneal anterior surface; Q-value;

Changes in the visual field following laser in situ keratomileusis for myopia

To assess the changes of the visual field (VF) caused by transient intraocular pressure (IOP) peaks during laser in situ keratomileusis (LASIK) surgery for myopia using automated perimetry. This prospective study involved 94 eyes of 94 patients who underwent a conventional LASIK procedure. A complete eye examination was carried out in which the IOP measurement, and Humphrey 24-2 SITA standard VF were tested prior to LASIK and 6 and 12 months after LASIK. Patients were divided into two subgroups according to their refractive error. VF global indices, Glaucoma Hemifield Test and the number of depressed points deviating at p < 5%, p < 2%, p < 1% and p < 0.5% on the Pattern Deviation probability maps were compared using the analysis of variance. In the low myopia group, there were no significant differences in the analysed variables, except a slight decrease in mean deviation (MD) when comparing results prior to and 6 months following LASIK (p = 0.036; anova) that returned to baseline values at 12 months after surgery. In the moderate and high myopia group, there were no statistically significant differences in any of the variables analysed. No significant correlation was found between the transitory reduction in MD and any of the variables studied. In patients with low myopia, the VF undergoes a transitory increase in diffuse defects 6 months after surgery, with spontaneous recovery at 12 months after LASIK procedure. Possible explanations for these findings are discussed.

Comparison of ocular higher-order aberrations and visual performance between photorefractive keratectomy and laser in situ keratomileusis for myopia

The purpose was to compare the ocular higher-order aberrations and the visual performance between photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK). Ocular aberrations and visual performance were measured after PRK in 26 eyes, after LASIK in 39 eyes, and in 29 normal myopic control eyes. Ocular aberrations were measured with a Hartmann-Shack aberrometer. Visual performance was evaluated with grating contrast sensitivity, high and low contrast visual acuity, and letter contrast sensitivity under full correction with spectacles. The results were that the root mean square (RMS) values of ocular higher-order aberrations after PRK or LASIK were significantly greater than that of normal controls for both 4-mm and 6-mm zones (PRK; 0.22 ± 0.09 and 0.85 ± 0.24µm, LASIK; 0.20 ± 0.06 and 0.82 ± 0.24µm, normal; 0.10 ± 0.03 and 0.33 ± 0.11µm. P < 0.05 between PRK and normal, LASIK and normal, One Way ANOVA on Ranks). There were no significant differences between PRK and LASIK. The ocular higher-order aberrations increased in proportion with the attempted refractive correction by PRK and LASIK. The ocular higherorder aberrations correlated better with grating contrast sensitivity, low contrast visual acuity, and letter contrast sensitivity than with high contrast visual acuity. There was no difference among normal, PRK and LASIK in all the visual function tests, except between normal and PRK, or between normal and LASIK with letter contrast sensitivity. In conclusion, there was no difference in both ocular higher-order aberrations and visual performance between PRK and LASIK. The result suggests that surgeons can choose refractive procedures according to the corneal conditions or daily activities of patients.

Vitreoretinal alterations following laser in situ keratomileusis: clinical and experimental studies.

The presence of vitreoretinal changes following laser in situ keratomileusis in myopia is evaluated. Clinically, 50 patients (100 eyes) with marked anisometropic myopia, 50 low-myopic eyes (<4.00 D) and 50 high-myopic eyes (>7.00 D) were prospectively evaluated pre- and postoperatively for the presence of newly recognized entoptic phenomena (vitreous floaters, light flashes, or both), and for vitreoretinal changes using indirect depressed fundus examination, a +90 D preset lens, Goldman three-mirror contact lens, and kinetic ultrasound (KU) before and after bilateral LASIK. Patients with previous partial or total posterior vitreous cortex detachment (PVD) were excluded. Experimentally, groups of adult pigs underwent KU, retinal fluorescein angiography (FA), and electroretinography (ERG) before and after applying the microkeratome suction ring for 30 s. Clinically, 8% (4 eyes) had positive perception of postoperative vitreous floaters in the low myopia group, and 32% (16 eyes) in the high myopia group. Postoperative light flashes were noted only in the high myopia group, in 12% of cases. Partial or total posterior vitreous cortex detachment was detected by biomicroscopy in 2% (1 eye) of the low and in 10% (5 eyes) of the high myopia group and by KU in 4% (2 eyes) of the low and in 24% (12 eyes) of the high myopia group. Experimentally, 2 pig eyes out of 12 developed partial PVD by KU, immediately after microkeratome suction ring application. All pig eyes showed significantly diminished ERG amplitudes during and immediately after suction ring application. No FA changes or delays in retinal circulation time were noted during or immediately after removal of the suction ring. Vitreoretinal alterations after LASIK were demonstrated clinically mainly by KU in high myopes. Experimentally, PVD were also demonstrated. Diminished ERG recordings with normal retinal circulation following suction ring application may suggest some transient choroidal circulation abnormalities.

Automated keratoconus detection using the EyeSys videokeratoscope

Purpose To evaluate the effectiveness of indices derived from the EyeSys System 2000 in detecting keratoconic corneas. Setting Department of Ophthalmology, Hôpital Saint Antoine, Paris VI University, Paris, France. Methods Topographies of 208 corneas were evaluated. The corneas were from 8 groups of patients classified by the following diagnoses: normal, regular astigmatism, cataract, radial keratotomy, photorefractive keratectomy, myopic keratomileusis, penetrating keratoplasty (PKP), and keratoconus. Nine statistical indices derived from EyeSys data, 2 Holladay Diagnosis Summary indices (coefficient of uniformity and coefficient of asphericity [Asph]), and our refractive power symmetry index were studied. A training set of 104 corneas was used to determine the most efficient threshold value of each index based on sensitivity and specificity curves. Decision trees combining 2 indices were generated. Sensitivity and specificity were calculated in a validation set composed of the remaining 104 corneas. Results Based on the results of the training set, the optimum indices were SDSD (standard deviation of the standard deviations of the radii of curvature of each ring) and Asph. In the validation set, the decision tree using these indices featured 88.5% sensitivity and 94.9% specificity; the 4 false-positive cases were in corneas in the PKP group of patients. Conclusions Clinically apparent keratoconus can be detected among normal corneas and irregular corneal shape patterns using the EyeSys System 2000 data and a decision tree combining 2 indices.

FLAP COMPLICATIONS ASSOCIATED WITH LAMELLAR REFRACTIVE SURGERY

Abstract PURPOSE: Corneal lamellar refractive surgery for myopia reduces the risk of corneal haze but adds to the risk of flap complications. We retrospectively determined the incidence of flap complications in the initial series of eyes undergoing lamellar refractive surgery by one surgeon. We assessed the incidence of flap complications overall, the trend in these complications during the surgeon's learning curve, and the impact of the complications on best spectacle-corrected visual acuity. METHODS: Charts of the first 1,019 eyes that underwent myopic keratomileusis in situ or laser in situ keratomileusis were reviewed for flap complications and visual outcome. RESULTS: Of the 1,019 eyes, 490 eyes underwent myopic keratomileusis in situ, and 529 eyes underwent laser in situ keratomileusis. Eighty-eight (8.6%) of 1,019 eyes had flap-related complications. Six eyes had two complications. Intraoperative complications included irregular keratectomy in nine eyes (0.9%), incomplete keratectomy in three eyes (0.3%), and a free cap in 10 eyes (1.0%). The incidence of intraoperative complications was six (6.0%) in the first 100 consecutive eyes, 14 (2.3%) in the next 600 consecutive eyes ( P = .04, chi-square test), and one (0.3%) in the last 300 eyes ( P = .03, chi-square test). Postoperative complications included displaced flaps that required repositioning in 20 eyes (2.0%), folds in the flap that required repositioning in 11 eyes (1.1%), diffuse lamellar keratitis in 18 eyes (1.8%), infectious keratitis in one eye (0.1%), and epithelial ingrowth that required removal in 22 eyes (2.2%). The incidence of flap displacement and folds in 200 eyes in which we irrigated under the flap and allowed it to settle without further manipulation averaged 8.5%, whereas the incidence in other groups of 100 consecutive eyes averaged 0.8% ( P P = .0003, chi-square test). No eye lost 2 or more lines of best spectacle-corrected visual acuity because of flap complications. CONCLUSION: Flap complications after lamellar refractive surgery are relatively common but rarely lead to a permanent decrease in visual acuity. Physician experience with the microkeratome and with the handling of the corneal flap decreases the incidence of flap complications.

Fitting contact lenses after myopic keratomileusis

Purpose: To evaluate the long-term efficacy and results of contact lens fittingfollowing myopic keratomileusis (MKM). Setting: Department of Ophthalmology, Manhattan Eye, Ear, and Throat Hospital, and Swinger Vision Center, New York, New York, USA. Methods: Postoperative fitting of contact lenses was studied as part of a prospectiveevaluation of myopic keratomileusis. In this series, 27 eyes of 20 patients had residual postoperative refractive errors that were corrected with contact lenses. Patients were fit at a mean of 9.4 months after surgery by the trial-lens method. Preoperative keratometry readings and refractions, as well as postoperative keratometry readings, refractions, and contact lens specifications, were recorded and used for fitting. Results: Twenty-six eyes (96%) were fit successfully: 24 (89%) with rigid gas-permeablelenses and 2 (7%) with daily-wear soft lenses. The mean diameter of the rigid lenses was 10.00 mm (range 9.4 to 11.0 mm) and the mean base curve, 8.52 mm (range 7.9 to 9.2 mm). The 2 soft lenses had base curves of 8.6 and 8.9 mm. The mean lens power was −5.24 diopters (D) (range −0.37 to −14.75 D), which was, on average, 4.06 D more myopic than the postoperative spectacle refraction. Postoperative keratometry provided a good starting point for the trial lens. Lenses were tolerated for up to 16 years. One eye, fit with a soft lens, developed significant myopia during the fifth year. Conclusion: After lamellar refractive surgery, the topography of the cornea is significantly altered. Although the postoperative keratometry readings are steeper than the actual curvature, they are reasonably reliable for determining the base curve of the initial trial lens, validating the use of conventional methods of fitting rigid contact lenses in patients who have had MKM.

Flap complications associated with lamellar refractive surgery

PURPOSE: Corneal lamellar refractive surgery for myopia reduces the risk of corneal haze but adds to the risk of flap complications. We retrospectively determined the incidence of flap complications in the initial series of eyes undergoing lamellar refractive surgery by one surgeon. We assessed the incidence of flap complications overall, the trend in these complications during the surgeon’s learning curve, and the impact of the complications on best spectacle-corrected visual acuity.METHODS: Charts of the first 1,019 eyes that underwent myopic keratomileusis in situ or laser in situ keratomileusis were reviewed for flap complications and visual outcome.RESULTS: Of the 1,019 eyes, 490 eyes underwent myopic keratomileusis in situ, and 529 eyes underwent laser in situ keratomileusis. Eighty-eight (8.6%) of 1,019 eyes had flap-related complications. Six eyes had two complications. Intraoperative complications included irregular keratectomy in nine eyes (0.9%), incomplete keratectomy in three eyes (0.3%), and a free cap in 10 eyes (1.0%). The incidence of intraoperative complications was six (6.0%) in the first 100 consecutive eyes, 14 (2.3%) in the next 600 consecutive eyes (P= .04, chi-square test), and one (0.3%) in the last 300 eyes (P = .03, chi-square test). Postoperative complications included displaced flaps that required repositioning in 20 eyes (2.0%), folds in the flap that required repositioning in 11 eyes (1.1%), diffuse lamellar keratitis in 18 eyes (1.8%), infectious keratitis in one eye (0.1%), and epithelial ingrowth that required removal in 22 eyes (2.2%). The incidence of flap displacement and folds in 200 eyes in which we irrigated under the flap and allowed it to settle without further manipulation averaged 8.5%, whereas the incidence in other groups of 100 consecutive eyes averaged 0.8% (P < .00001, chi-square test). The incidence of diffuse lamellar keratitis was 0.2% in eyes that had undergone myopic keratomileusis in situ and 3.2% in eyes treated by laser in situ keratomileusis (P = .0003, chi-square test). No eye lost 2 or more lines of best spectacle-corrected visual acuity because of flap complications.CONCLUSION: Flap complications after lamellar refractive surgery are relatively common but rarely lead to a permanent decrease in visual acuity. Physician experience with the microkeratome and with the handling of the corneal flap decreases the incidence of flap complications.

Diffuse lamellar keratitis: A new syndrome in lamellar refractive surgery

Objective This study aimed to describe a syndrome that the authors call diffuse lamellar keratitis that follows laser in situ keratomileusis (LASIK) and related lamellar corneal surgery. Design Noncomparative case series and record review. Participants Thirteen eyes of 12 patients in whom infiltrates developed in the interface after lamellar refractive surgery were studied. Intervention Topical antibiotics or corticosteroids or both were administered. Main outcome measures Corneal infiltrate appearance, focality, location, and clinical course were measured. Results Patients presented between 2 and 6 days after surgery with pain, photophobia, redness, or tearing. Ten cases directly followed either myopic keratomileusis or LASIK. Three cases followed enhancement surgery without the use of a microkeratome. All 13 cases had infiltrates that were diffuse, multifocal, and confined to the flap interface with no posterior or anterior extension. The overlying epithelium was intact in each case. Cultures were negative in the two cases cultured. Ten eyes were treated with antibacterial agents; two eyes had fluorometholone four times daily added to the routine postoperative antibacterial regimen, and one eye had the antibacterial agent discontinued and was treated with topical fluorometholone alone. All infiltrates resolved without sequelae. Conclusions A distinct syndrome of unknown cause of noninfectious diffuse infiltrates in the lamellar interface is described. It can be distinguished from infectious infiltrates by clinical presentation and close follow-up. Patients with the syndrome should be spared the more invasive treatment of infectious keratitis.

Treatment of topographic central islands following refractive surgery

Purpose: To evaluate the safety and efficacy of using central reablation to treat topographic central islands following photorefractive keratectomy (PRK), myopic keratomileusis in situ, and laser in situ keratomileusis (LASIK).Setting: Department of Ophthalmology, Stanford University School of Medicine, Stanford, and Jules Stein Eye Institute, Los Angeles, California, USA.Methods: Central reablation was performed on eight eyes with clinically significant topographic central islands after refractive surgery. Two eyes developed central islands after PRK, five eyes after LASIK, and one eye after myopic keratomileusis in situ. A clinically significant topographic central island was defined as an area of steepening of at least 3.0 diopters by at least 1.5 mm in diameter documented by computerized videokeratography. Reablation was tailored to each eye based on the diameter and power of the topographic central island using the Munnerlyn formula.Results: All eyes experienced a reduction or elimination of the topographic central islands following central reablation. Six eyes experienced an improvement in uncorrected visual acuity, and all eyes returned to within one line of their preoperative level of best spectacle-corrected visual acuity 1 month after the procedure.Conclusion: Topographic central islands following PRK, myopic keratomileusis in situ, and LASIK can be effectively treated using the excimer laser. Poor predictability of the refractive effect of central reablation may be the limitation of this treatment modality.

The prediction of surgically induced refractive change from corneal topography

To develop a method to predict the refractive power of the cornea from corneal topography. 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. 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. 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.

Keratomileusis in situ for high myopia

Purpose: To examine the safety and efficacy of myopic keratomileusis in situ (automated lamellar keratoplasty) using an automated microkeratome.Setting: Jules Stein Eye Institute and the Department of Ophthalmology, UCLA School of Medicine, Los Angeles, California.Methods: A retrospective study was done on 135 consecutive eyes of 91 patients who had keratomileusis in situ for myopia by one surgeon between October 4, 1993, and February 23, 1995. Mean preoperative myopia was 8.30 ± 2.50 diopters (D) (range 4.50 to 20.50). Follow-up ranged from 1 (108 eyes) to 6 months (52 eyes). No eye had enhancement surgery before 3 months; eyes were dropped from the study at the time of enhancement.Results: Three months after myopic keratomileusis in situ, the mean difference between attempted and achieved correction was an undercorrection of 0.90 ± 1.50 D; 32 of 83 eyes were within 1.00 D of attempted correction. Forty eyes were undercorrected by more than 1.00 D, and 11 were overcorrected by more than 1.00 D. Uncorrected visual acuity improved to 20/40 or better in 42 of 83 eyes at 3 months. Best spectacle-corrected visual acuity (BSCVA) declined by two or more lines in 8 of 83 eyes at 3 months and 1 of 52 eyes at 6 months. In eyes with 6 months of follow-up, a mean myopic shift of 0.40 D occurred between 3 and 6 months. Two eyes had clinically significant ingrowth into the interface. The variability in outcome (standard deviation in achieved less attempted correction) at 3 months was 1.70 D in the first 45 cases, 1.20 D in the second 45 cases, and 1.10 D in the last 45 cases.Conclusion: Myopic keratomileusis in situ is relatively effective and safe for the correction of high myopia; however, a mild loss of BSCVA is not uncommon in the early postoperative period. Surgeon experience may be important for refractive accuracy.

Astigmatic Keratotomy Combined With Myopic Keratomileusis In Situ for Compound Myopic Astigmatism

Myopic keratomileusis in situ by an automated microkeratome corrects myopia but not astigmatism, which is traditionally corrected by astigmatic keratotomy months after keratomileusis. We developed a technique for simultaneously correcting astigmatism and severe myopia, and examined its effectiveness in a retrospective case-control study. Thirty-four eyes (23 patients) underwent myopic keratomileusis in situ combined with one or two arcuate keratotomy incisions performed after the refractive cut, in the bed of the primary keratectomy flap. The myopic keratomileusis control group consisted of 34 matched eyes (30 patients) undergoing keratomileusis without astigmatic keratotomy. The astigmatic control group consisted of 117 unmatched eyes (85 patients) undergoing astigmatic keratotomy combined with radial keratotomy. Mean refractive astigmatism in the study group decreased from 2.4 diopters (range, 1.0 to 4.0 diopters) preoperatively to 1.7 diopters (range, 1.0 to 4.0 diopters) at three months postoperatively, and increased by 0.4 diopter in the myopic keratomileusis control group at three months postoperatively (P < .005). Eighteen of 27 eyes in the study group showed decreased refractive astigmatism compared with ten of 34 eyes in the myopic keratomileusis control group (P < .0001). Combining astigmatic keratotomy with myopic keratomileusis produced 0.2 +/- 0.9 diopter less astigmatic correction than that expected from the astigmatic control group. One of 27 eyes lost two or more lines of best spectacle-corrected visual acuity at the three-month postoperative visit. No eye lost two or more lines of best spectacle-corrected visual acuity at postoperative month 6. Eyes with substantial preoperative refractive astigmatism that undergo myopic keratomileusis in situ may benefit from simultaneous astigmatic keratotomy to reduce residual post-operative refractive astigmatism.

Measurement of irregular astigmatism using semimeridian data from videokeratographs.

Irregular astigmatism is one of the most troublesome side effects of corneal surgery. We attempted to quantify irregular astigmatism in a simple way, using semimeridian data from videokeratographs of corneas with different amounts of irregular astigmatism. We studied the corneal topography of 30 normal corneas to be used as controls, 30 corneas from patients after radial keratotomy, 30 corneas from patients after nonfreeze myopic keratomileusis, and 30 corneas with clinically apparent keratoconus. We developed two diagnostic formulas, a refractive power symmetry index and an angle symmetry index, using the absolute-scale, color-coded map, and semimeridian data from the EyeSys Corneal Analysis System, and used them to compare the four groups of corneas. In the corneas with irregular astigmatism, values for the refractive power symmetry index and angle symmetry index were significantly higher than in the normal corneas. The refractive power symmetry index confidence interval set at 95% was 0.58 diopters (D) (range 0.00 D to 0.58 D) in the control group. Using these limits, most values in the radial keratotomy, keratomileusis, and keratoconus groups were abnormal. Spectacle-corrected visual acuity correlated negatively with the refractive power symmetry index (rs = -0.58, p < .001). The refractive power symmetry index sensitivity and specificity were respectively 97% and 66%. Spectacle-corrected visual acuity did not correlate with the angle symmetry index. Semimeridian data from videokeratographs can be used to quantify irregular astigmatism.

Photorefractive keratectomy following radial keratotomy.

Excimer laser photorefractive keratectomy (PRK) has been used to correct residual myopia in eyes that have had refractive keratotomy. Nine eyes of eight patients were studied at a mean of 13 months after PRK. Previous procedures included radial keratotomy (9 eyes) and myopic keratomileusis (1 eye). PRK was performed using a Summit Technology excimer laser with a 5.0-mm diameter ablation zone. Uncorrected visual acuity improved in 7 of 9 eyes. The refractive outcome was within 1.00 diopter (D) of attempted correction for 3 of 9 eyes. Spectacle-corrected visual acuity decreased 2 or more Snellen lines in 2 of 9 eyes. Subepithelial corneal stromal haze was seen 1 month postoperatively in 6 of 8 eyes and was present in 4 of 6 eyes at 1 year. Stromal haze was associated with regression of the refractive effect of the PRK. PRK in eyes with previous radial keratotomy appears to be less predictable and may be associated with greater corneal haze and regression of refractive correction than in previously unoperated eyes. Activation of stromal fibroblasts in the previous corneal incisions may cause these findings.

Excimer Laser in Situ Keratomileusis

Excimer laser in situ keratomileusis (LASIK) is the most recent evolution of the family of lamellar refractive surgery, which includes keratophakia, freeze myopic keratomileusis, epikeratoplasty, keratomileusis in situ, and Buratto-style excimer laser keratomileusis. LASIK is the marriage of the microkeratome, with its ability to resect a piano lamellar disc of corneal tissue, and the precision of the argon-fluoride excimer laser, operating at 193 nm to remove submicron layers of corneal stroma to achieve a highly predictable refractive result. Myopia, astigmatism, hyperopia, presbyopia, and complex ablations for abnormal topography have been attempted. Although LASIK as a technique is relatively young, the early results are very encouraging. Investigators worldwide are vigorously investigating its efficacy, predictability, stability, and safety.

Myopic keratomileusis in situ combined with VISX 20/20 photorefractive keratectomy

We present the results of myopic keratomileusis in situ combined with photorefractive keratectomy (PRK) in five eyes with high myopia and low astigmatism. Follow-up ranged from 10 to 12 months. A hinge was used to perform subtotal lamellar keratectomy and the spherical component of myopia was corrected by three-zone PRK. The mean preoperative spheroequivalent was −21.00 diopters (D) and the postoperative spheroequivalent was −1.50 D. In four eyes the best corrected visual acuity was unchanged or improved; in one eye it decreased because of epithelial ingrowth in the lamellar interface. Persistent oblique longitudinal folds were noted in the corneal disc in one eye, and induced cylinder was found postoperatively in one eye.