Late natural history of corneal topography after excimer laser photorefractive keratectomy

PURPOSE: To investigate the 3 month to 1 year natural history of corneal topography after excimer laser photorefractive keratectomy (PRK). DESIGN: A prospective, multicenter, nonrandomized comparative study. PARTICIPANTS: A total of 75 eyes of 68 patients with myopia were studied. INTERVENTION: Excimer laser photorefractive keratectomy and computer-assisted videokeratography were performed. MAIN OUTCOME MEASURES: Preoperative and 3, 6, and 12 month postoperative topography patterns were compared and changes assessed by averaging defined sectors of the ablation zone in individual maps to produce composite "average" topography maps. RESULTS: Corneal topography was relatively smooth 3 months after PRK. By 12 months, the corneal contour in general had become even more uniform. No "central island" effect was observed. When looking at right and left eyes independently, there was a tendency toward maximum flattening nasally. CONCLUSIONS: Corneal topography in general continues to smooth from 3 to 12 months after PRK, possibly as a result of epithelial and stromal healing and remodeling. Right and left eyes on average show mirror-image, spatially oriented topography patterns.     

Changes in Spherical Aberration after Various Corneal Surface Ablation Techniques

Purpose

The corneal change induced by refractive procedures influence both the postoperative refractive status and the ocular spherical aberration (SA). We evaluated changes in corneal SA after three types of surface ablation: phototherapeutic keratectomy (PTK), myopic photorefractive keratectomy (PRK), and myopic wavefront-guided laser epithelial keratomileusis (LASEK).

Methods

Twenty-six eyes (25 patients) were subjected to PTK 26 eyes (14 patients) to PRK, and 34 eyes (17 patients) to wavefront-guided LASEK. Corneal SA was measured with the iTrace in all patients both preoperatively and 6 months postoperatively.

Results

Six months after surgery, mean corneal SA was -0.173 ± 0.171 µm in the PTK group, 0.672 ± 0.200 µm in the PRK group, and 0.143 ± 0.136 µm in the wavefront-guided LASEK group. The mean difference between the preoperative and postoperative corneal SA (ΔSA) was -0.475 µm in the PTK group, 0.402 µm in the PRK group, and -0.143 µm in the wavefront-guided LASEK group.

Conclusions

Surgically induced changes in corneal SA vary with procedure. The prediction of the pattern of SA change induced by various surface ablation procedures may be helpful for developing future surgical procedures.     

Reliability of intraocular pressure measurements after myopic excimer photorefractive keratectomy

Objective

To determine the reliability of intraocular pressure (IOP) measurements by Goldmann applanation tonometry and pneumotonometry in eyes treated with excimer myopic photorefractive keratectomy (PRK).

Design

A prospective case series.

Participants

Forty consecutive eyes treated with PRK were evaluated.

Intervention and main outcome measures

Central and peripheral corneal Goldmann tonometry and pneumotonometry measurements were done before surgery, at 1 week, and at 1 and 3 months after surgery.

Results

The IOP by Goldmann tonometry from the central cornea was significantly lower than the peripheral IOP; however, there was no difference between IOP measured from central and peripheral corneas by pneumotonometry, which, in turn, correlated with peripheral Goldmann measurements. There was a trend, but not a statistically significant correlation, between the spherical equivalent of the treatment and the amount of decrease in central Goldmann IOP.

Conclusions

Pneumotonometry measures the IOP reliably after PRK from all parts of the cornea, whereas central Goldmann tonometry underestimates the IOP by 2.40 ± 1.23 mmHg.     

Meta-analysis of Pentacam vs. ultrasound pachymetry in central corneal thickness measurement in normal, post–LASIK or PRK, and keratoconic or keratoconus-suspect eyes

Background

The aim of this meta-analysis is to evaluate the central corneal thickness (CCT) measurement differences between Pentacam (Oculus Inc., Germany) and Ultrasound Pachymetry (USP) in normal (unoperated eyes , myopic and astigmatic eyes without corneal disease or topographic irregularity), after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK), and keratoconic or keratoconus suspected eyes. We assess whether Pentacam and USP have similar CCT differences in normal, thinner corneas after LASIK or PRK procedures, and kerotoconic or keratoconus suspected eyes.

Methods

Data sources, including PubMed, Medline, EMBASE, and Cochrane Central Registry of Controlled Trials on the Cochrane Library, were searched to find the relevant studies. Primary outcome measures were CCT measurement between Pentacam and USP. Three groups of eyes were analyzed: normal; LASIK or PRK eyes; and keratoconus suspected or keratoconic eyes.

Results

Nineteen studies describing 1,908 eyes were enrolled in the normal group. Pentacam results were 1.47 μm ,95 % confidence interval (CI) -2.32 to 5.27, higher than USP without statistically significant difference (P?=?0.45). Nine studies with total 539 eyes were included in the corneas after LASIK or PRK. The mean difference in the CCT measurement with Pentacam and ultrasound pachymetry was 1.03 μm, with the 95 % CI ?3.36 to 5.42, there was no statistically difference (P?=?0.64). Four studies with a total of 185 eyes were included in the keratoconic eyes or keratoconus-suspect group, however,the mean difference was ?6.33 μm (95 % CI ?9.17 to-3.49), which was statistically different between Pentacam and ultrasound pachymetry in the CCT measurement (P?<?0.0001).

Conclusions

Pentacam offers similar CCT results to ultrasound pachymetry in normal eyes, thinner corneas after LASIK or PRK procedures. However, in keratoconic or keratoconus-suspect eyes, Pentacam slightly underestimates the central corneal thickness than does ultrasound pachymetry, which may result from the difficulty in fixation of keratoconic eyes, misalignment of Pentacam and the variation of ultrasonic velocity due to the histological deformation.     

Anterior corneal surface after Nidek EC-5000 multipass and multizone photorefractive keratectomy for myopia

PURPOSE: To evaluate the correlation between the presence of irregularities in corneal ablation and the number of ablation zones with multipass and multizone photorefractive keratectomy (PRK). METHODS: The differential maps obtained from corneal topography performed before and 1 month after PRK in 62 eyes that had undergone PRK with the Nidek EC-5000 excimer laser were assessed for irregularities. PRK treatment ranged from -1.00 to -16.00 D (mean -5.25 +/- 2.72 D), and the number of zones ranged from one to five. RESULTS: Of 62 differential maps, 27 had an irregular pattern according to the Hersh classification, with a non-significant correlation with the number of treatment zones (chi2 = 5.09, P >.1). CONCLUSION: Our results suggest that corneal topography irregularities arising from multizone PRK were not related to the amount of treatment or to the number of ablation zones.     

Early Postoperative Pain and Visual Outcomes Following Epipolis-Laser In Situ Keratomileusis and Photorefractive Keratectomy

Purpose

To compare early postoperative pain and visual outcomes after epipolis-laser in situ keratomileusis (epi-LASIK) and photorefractive keratectomy (PRK) in the treatment of myopia.

Methods

A retrospective chart review was designed and included 49 eyes in 30 patients who underwent epi-LASIK and 54 eyes in 29 patients who underwent PRK. During the early postoperative period (days 1 to 5), pain, uncorrected visual acuity (UCVA), and time to epithelial healing were recorded. Visual outcomes were followed for up to six months.

Results

Mean preoperative spherical equivalent refraction for the epi-LASIK group was -3.99±1.39 diopters (D) and that of the PRK group was -3.54±1.27 D. The pain scores on the fourth postoperative day were significantly higher in the epi-LASIK group than in the PRK group (p=0.017). Duration of pain in the epi-LASIK group was longer than in the PRK group (p=0.010). Mean healing time was significantly longer in the epi-LASIK group than in the PRK group (p<0.000). In addition, UCVA in the epi-LASIK group at postoperative days 1 and 3 were significantly lower than those in the PRK group (p=0.021 and p<0.000, respectively). Uncorrected visual acuity at one week and one month after epi-LASIK were lower than those after PRK (p=0.023 and p=0.004, respectively).

Conclusions

In the epi-LASIK patients, pain relief, corneal healing, and visual recovery seemed to be slower during the early postoperative period compared to those of the PRK patients. With longer duration of follow-up, however, there were no significant differences in visual outcome between the two groups.     

准分子激光角膜切削术前后的角膜地形图分析

了解准分子激光角膜切削术（ｐｈｏｔｏｒｅｆｒａｃｔｉｖｅｋｅｒａｔｅｃｔｏｍｙ，ＰＲＫ）前、后角膜表面形态变化并对切削区偏中心进行分析。方法应用计算机辅助的角膜地形图仪对８０例（１２２只眼）ＰＲＫ前、后角膜地形图进行检测和分析。结果术前角膜地形图的形态呈对称或非对称性蝴蝶结形者占７５．４％；术后圆形或近似圆形者占６３．９％。切削区偏离瞳孔中心的距离与术前屈光度无关。切削区偏中心距离越大，术后角膜散光增加及术后最佳矫正视力下降越明显。结论ＰＲＫ前、后角膜地形图检查和分析能清楚地显示角膜表面形态变化及定量评估切削区偏中心问题。     

PTK在再次准分子激光角膜切削术中的应用

目的 探讨用PTK技术矫治因PRK术后出现的严重不规则角膜散光并欠矫的方法,观察其疗效。方法 参考角膜地形图,先使用阻滞剂粘弹剂保护角膜凹面再行PTK术,得到光滑的角膜表面后,再次准分子激光角膜切削术。结果 3例5眼均获得良好的疗效,术后裸眼视力1.0,角膜透明。随访2年疗效巩固,手术前后的角膜地形图可以证明。结论 采用PTK技术治疗因PRK术出现的不规则散光是有效的。     

Change in Corneal Permeability to Timolol After Laser In Situ Keratomileusis and Photorefractive Keratectomy in Rabbit

Purpose To evaluate the change in corneal permeability to timolol 1 month after laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) in rabbits.Methods LASIK or PRK was performed on one eye of each of 20 rabbits. One month later, 20µl of 0.5% timolol was instilled into the 10 LASIK eyes, 10 PRK eyes, and the 20 control contralateral eyes. One hour later, 150µl of aqueous humor was collected from all eyes, and the concentration of timolol in the aqueous humor was measured by high-performance liquid chromatography. The effect of LASIK and PRK on the corneal permeability to timolol was analyzed.Results The average timolol concentrations in the aqueous humor of the ten eyes 1 month after LASIK and in the ten contralateral eyes were 1.16 ± 0.58µg/ml and 1.07 ± 0.39µg/ml (average ± SD, P = 0.678), respectively. The average timolol concentrations in the aqueous humor of the ten eyes 1 month after PRK and in the ten contralateral eyes were 1.24 ± 0.43µg/ml and 1.12 ± 0.30µg/ml (P = 0.483), respectively. The average ratio of timolol concentration in the aqueous humor of the LASIK or PRK eyes 1 month after surgery to that of the contralateral normal eyes was 1.18 ± 0.58 or 1.19 ± 0.67 (P = 0.972), respectively.Conclusions LASIK and PRK do not affect corneal permeability to timolol 1 month after surgery. Jpn J Ophthalmol 2005;49:12–14 © Japanese Ophthalmological Society 2005     

Central corneal thickness measurements in unoperated eyes and eyes after PRK for myopia using Pentacam, Orbscan II, and ultrasonic pachymetry

PURPOSE: To compare central corneal thickness measurements obtained in unoperated eyes and eyes after myopic photorefractive keratectomy (PRK) using a rotating Scheimpflug camera (Pentacam), a scanning slit corneal topography system (Orbscan II), and ultrasonic pachymetry. METHODS: Corneal thickness was measured using Pentacam, Orbscan II, and ultrasonic pachymetry in 25 unoperated eyes (unoperated group), 24 eyes 1 to 3 months after myopic PRK (early postoperative PRK group), and 21 eyes 4 months or more after myopic PRK (late postoperative PRK group). RESULTS: In the unoperated group, corneal thickness measurements were similar for all three methods (P=.125). In the early postoperative PRK group, Orbscan measurements were thinner than Pentacam and ultrasonic measurements by a mean of 69.4 microm and 63.4 microm (P<.001 and P=.002, respectively). In the late postoperative PRK group, Orbscan measurements were thinner than Pentacam measurements by a mean of 36.0 microm (P=.017). Pentacam and ultrasonic pachymetry measurements were similar for all three groups with a mean difference of approximately 10 microm. CONCLUSIONS: Following myopic PRK, Pentacam was comparable to ultrasonic pachymetry in measuring corneal thickness, whereas Orbscan measurements were thinner.     

Comparación de 5.468 retratamientos tras láser in situ queratomileusis levantando el lentículo o mediante queratectomía fotorrefractiva sobre el lentículo

Purpose

To assess visual outcomes of retreatment after laser in situ keratomileusis (LASIK) by lifting the flap or performing photorefractive keratectomy (PRK) on the flap, as well as to establish whether there was an increased risk of epithelial ingrowth (EIG) when LASIK and lifting of the flap are separated by a long time interval and to determine the incidence of corneal haze after PRK.

Predictability of spherical photorefractive keratectomy for myopia

Objective

This study aimed to examine the effects of purely spherical excimer laser photorefractive keratectomy (PRK) for myopia.

Design

Consecutive case series.

Participants

A total of 3218 eyes with a mean preoperative mean spherical equivalent (MSE) of −3.75 diopters (D) ± 1.73 D standard deviation (SD) (range, −1.00 D to −11.88 D) underwent PRK with a Nidek EC-5000 excimer laser. Eyes were divided into groups based on the degree of preoperative myopia in 1 D steps

Intervention

All eyes underwent PRK with a Nidek EC-5000 excimer laser.

Main outcome measure

Visual and refractive outcome of PRK treatment was measured.

Results

After a mean follow-up period of 52.6 weeks (range, 26–150 weeks), the final MSE was −0.07 D (±0.68 D) (range, −5.50 D to +4.50 D). Of the 3218 eyes, 2919 (90.7%) were within 1.00 D of emmetropia, and 3038 (94.4%) of eyes had an uncorrected visual acuity of 20/40 or better, with 1886 (58.6%) achieving 20/20 or better visual acuity. Eyes in the lower preoperative myopia groups had a greater chance of attaining 20/40 unaided visual acuity than those in the higher groups (e.g., 98.3% of the −2D group and 53.6% of the −9D group achieved 20/40 unaided visual acuity). Overall, mean postoperative haze was 0.29 ± 0.39 SD (scale, 0–3), and 29 eyes (0.9%) lost 0.3 or more logarithm of the minimum angle of resolution (LogMAR) unit of best-corrected visual acuity.

Conclusions

Excimer laser PRK is an effective treatment for myopia of up to −9.00 D. The outcome parameters are less predictable for eyes with greater than −9.00 D of myopia.     

Effect of the combination of basic fibroblast growth factor and cysteine on corneal epithelial healing after photorefractive keratectomy in patients affected by myopia

Background:

This study sought to evaluate the effect of basic fibroblast growth factor eye drops and cysteine oral supplements on corneal healing in patients treated with photorefractive keratectomy (PRK).

Materials and Methods:

One hundred and twenty patients treated bilaterally with PRK for myopia were enrolled at one of two eye centers (Clinica Santa Lucia, Bologna, Italy and Department of Ophthalmology, University of Magna Graecia, Catanzaro, Italy) and were treated at the former center. Sixty patients included in the study group (Group 1) were treated postoperatively with topical basic fibroblast growth factor plus oral L-cysteine supplements, whereas 60 subjects included in the control group (Group 2) received basic fibroblast growth factor eye drops. We recorded the rate of corneal re-epithelialization and patients were followed-up every 30 days for 6 months. Statistical analyses were performed on the collected data.

Results:

The eyes in Group 1 demonstrated complete re-epithelialization at Day 5, whereas the eyes in Group 2 achieved this status on Day 6. No side-effects were reported.

Conclusions:

Patients treated with basic fibroblast growth factor eye drops and L-cysteine oral supplements benefit from more rapid corneal re-epithelialization. In human eyes, this combination treatment appeared to be safe and effective in accelerating corneal surfacing after surgery.

Financial Disclosure:

No author has any financial or proprietary interest in any material or method used in this study.

Trial Registration:

Current Controlled Trials ISRCTN73824458.     

Photorefractive Keratectomy in Keratoconus

PurposeTo assess the efficacy and safety of topography-guided photorefractive keratectomy (PRK) for keratoconus and to estimate the subsequent risk of progression.MethodsThis is a retrospective follow-up study. Between 1998 and 2013, 28 eyes of 23 patients (age 17–60) with grade 1–3 keratoconus received topography-guided PRK. Corrected-distance visual acuity (CDVA), keratometry, pachymetry, and corneal topography were assessed before, after 3 months, and at a late follow-up of a median of 7 years after the procedure. Postoperative complications including subsequent keratoplasty were noted.ResultsOf the 28 eyes, 5 (18%percnt;) had undergone corneal transplantation at a median of 7 years (range 3–10) after PRK. Four eyes were not available for follow-up. In the remaining 19 eyes, CDVA was improved in 16 eyes (84.3%percnt;), reduced in 2 eyes (10.5%percnt;), and unchanged in 1 eye (5.2%percnt;). Thus, average CDVA had improved from 0.49 logMAR before PRK to 0.27 logMAR at 3 months, and to 0.24 at the long-term follow-up. The mean spherical equivalent was reduced from − 6.2 to −3.7 dpt after 3 months and to −2.1 dpt at the late follow-up. Similarly, the mean cylinder was reduced from −4.2 to −3.0 dpt after 3 months and at the late follow-up.ConclusionTopography-guided PRK in keratoconus may be effective for reducing myopia and astigmatism and may offer a temporary or permanent alternative to keratoplasty in contact lens-intolerant keratoconus. In the present study, we found a low risk of keratoconus progression after PRK.Key Words: Photorefractive keratectomy, Keratoconus, Refractive surgical procedures     

A comparison between Goldmann applanation tonometry and dynamic contour tonometry after photorefractive keratectomy

Background

The intraocular pressure (IOP) could be measured by both Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT). Although these two methods have been discussed widely after laser-assisted sub-epithelial keratectomy (LASIK), there is little data in the cases undergoing photorefractive keratectomy (PRK). We aimed to compare the changes of IOP measurements obtained by GAT and DCT after PRK for myopia/myopic astigmatism.

Methods

This prospective study enrolled 77 candidates (154 eyes) for PRK to correct myopia or myopic astigmatism and 30 matched patients (30 eyes) with myopia or myopic astigmatism who served as controls. Changes of the IOP measurements (ΔIOP) obtained by GAT and DCT before and at 6 months after PRK in the operated eyes, and at baseline and 6 months later in the controls, were documented. Changes of the central corneal thickness (ΔCCT) were determined in the same fashion.

Results

The mean IOP readings obtained by DCT were comparable before and at 6 months after procedure (18.34 ± 3.03 mmHg and 17.87 ± 2.61 mmHg respectively, p?=?0.41); whereas the mean IOP reading obtained by GAT decreased significantly 6 months postoperatively (17.92 ± 3.63 mmHg and 16.25 ± 2.66 mmHg, p?<?0.001). A significant correlation was present between the ΔIOP obtained by GAT and ΔCCT (r?=?0.61, p?<?0.001). Similar correlation was not significant between the DCT-obtained ΔIOP and the ΔCCT (r?=?0.07, p?=?0.44). The mean ΔIOP obtained by GAT was significantly higher in the operated eyes than in the controls (?1.54?±?1.45 vs 0.07?±?0.44 mmHg, p?=?0.02). The mean DCT-obtained ΔIOP was just marginally insignificant between the operated and nonoperated eyes (?0.63?±?0.59 vs 0.02?±?0.38 mmHg respectively; p?=?0.09).

Conclusions

The authors recommend DCT after PRK in the cases with myopia or myopic astigmatism     

Differences in nasal and temporal responses of the cornea after photorefractive keratectomy

PURPOSE: To examine the differences in the biomechanical response of the peripheral regions of the cornea after photorefractive keratectomy (PRK). SETTING: Department of Ophthalmology, Catholic University of Rome, Rome, Italy. METHODS: Preoperative and 1-, 3-, 6-, and 12-month postoperative corneal topographies of 70 eyes that had PRK with the Technolas 217C excimer laser (Bausch & Lomb) were obtained. The eyes were divided into 4 groups according to the preoperative spherical equivalent refraction. Preoperative and follow-up topographic data were imported into custom software that computed the average composite corneal map and difference maps in each group to scientifically evaluate the corneal response to the surgery. The software was also used to analyze regional corneal changes after the laser ablation. Corneal peripheries up to 9.0 mm were evaluated. RESULTS: The preoperative corneas had a flatter nasal periphery than temporal periphery. The corneal surfaces in the right eyes and left eyes showed a mirror symmetry. Significant differences in the regional response of the cornea were observed (P<.05), with a greater increase in the curvature of the nasal periphery than in the temporal periphery. CONCLUSIONS: To refine modeling of the cornea, the different regional anatomic features and biomechanical responses must be considered. Modifying existing ablation algorithms to compensate for the differences between nasal and temporal corneal flattening of the preoperative corneal surface and between the nasal and temporal responses may improve the postoperative corneal shape and quality of peripheral optics.     

Photorefractive keratectomy in the correction of astigmatism using Schwind Amaris 750s laser

AIM:To evaluate the results of three photorefractive keratectomy (PRK) procedures in the treatment of astigmatism.METHODS:In thisretrospective comparative case series, 89 eyes of 50 patients who underwent PRK treatment for astigmatism were enrolled. The patients were divided into 3 groups based on the PRK procedure:Group 1:PRK without mitomycin-C (MMC) application, Group 2:PRK with MMC application, and Group 3:Trans-Photorefractive Keratectomy(T-PRK). The efficacy, safety, predictability, and complications of treatment were assessed at 1, 3 and 6 months after the treatment.RESULTS: At postoperative 6 months, the percentage of postoperative uncorrected visual acuity (UCVA) of 20/20 or better was 55.6% (20 eyes) in group 1, 75% (15 eyes) in group 2, and 75.8% (25 eyes) in group 3 (P=0.144).The percentage of postoperative best corrected visual acuity (BCVA) of unchanged or gained ≥1 lines was 80.6% (29 eyes) in group 1, 70% (14 eyes) in group 2, and 90.9% (30 eyes) in group 3 (P=0.151). The percentage of postoperative BCVA of lost ≥2 lines was 11.1% (4 eyes) in group 1, 20% (4 eyes) in group 2, and 6.1% (2 eyes) in group 3. The mean manifest refractivespherical equivalent (MRSE) and mean cylindrical refraction were not significantly different among the each groups (P>0.05). At postoperative 6 months, the percentage of MRSE of within ±0.50 D was 100% (36 eyes) in Group 1, 100% (20 eyes) in Group 2, and 93.9% (31 eyes) in Group 3. At the each follow-up period, there was no significant difference in number of eyes with haze and mean haze score(P>0.05).CONCLUSION:The study showed that PRK without MMC, PRK with MMC and T-PRK appears to have similar effectiveness, safety and predictability in the treatment of astigmatism. The incidence of haze was also similar between the three groups.     

Evaluation of prior photorefractive keratectomy in donor tissue.

PURPOSE: To describe a case in which an eye donor had prior bilateral photorefractive keratectomies and to elucidate possible methods of evaluation and screening of donor tissue. METHODS: Case report. A 62-year-old eye donor was reported to have received radial keratotomy before his death. Further investigation by the eye bank showed a history of photorefractive keratectomy (PRK), not radial keratotomy. The corneas were therefore not used for transplantation, and the eyes were evaluated by slit-lamp examination, photography, corneal topography, and histology. RESULTS: Slit-lamp and photographic examination did not indicate the presence of PRK ablations. Corneal topography mapping with the TMS-1 was relatively ambiguous for identifying PRK flattening, while multiple data formatting of the cornea with the Orbscan resulted in the strongest suggestion of prior PRK. Histologic analysis showed central corneal thinning and loss of Bowman's membrane consistent with PRK. CONCLUSIONS: In the absence of a positive donor history for PRK, current methods of screening donor tissue for prior PRK often are insufficient to exclude these corneas from use in transplantation. More refined placido imagery corneal topography or newer technologies such as the Orbscan may allow more sensitive and specific methods of donor tissue screening.     

The Recovery of Optical Quality after Laser Vision Correction

Purpose

To evaluate the optical quality after laser in situ keratomileusis (LASIK) or serial photorefractive keratectomy (PRK) using a double-pass system and to follow the recovery of optical quality after laser vision correction.

Methods

This study measured the visual acuity, manifest refraction and optical quality before and one day, one week, one month, and three months after laser vision correction. Optical quality parameters including the modulation transfer function, Strehl ratio and intraocular scattering were evaluated with a double-pass system.

Results

This study included 51 eyes that underwent LASIK and 57 that underwent PRK. The optical quality three months post-surgery did not differ significantly between these laser vision correction techniques. Furthermore, the preoperative and postoperative optical quality did not differ significantly in either group. Optical quality recovered within one week after LASIK but took between one and three months to recover after PRK. The optical quality of patients in the PRK group seemed to recover slightly more slowly than their uncorrected distance visual acuity.

Conclusions

Optical quality recovers to the preoperative level after laser vision correction, so laser vision correction is efficacious for correcting myopia. The double-pass system is a useful tool for clinical assessment of optical quality.     

准分子激光角膜切削术前后角膜地形图对比分析

应用角膜地形图仪对比分析了９０例（１７６眼）ＰＲＫ手术前后角膜表面的形态特征及其变化。结果表明,术前角膜地形图以蝴蝶结形为多（７３．３％）;术后７９．０％为圆形或钥匙孔形,半圆形和蝶形为１８．８％中央岛形占２．２％。ＰＲＫ对散光的一次最大矫正量为－１．７５Ｄ,切削中心偏位是最佳矫正视力下降,复视和屈光度回退的重要原因。提示：ＰＲＫ术后角膜地形图的检查可准确显示角膜形态的细微变化,有利于手术设计的不断完善和效果的提高。