LASIK vs LASEK vs PRK: advantages and indications

The advent of the excimer laser as an instrument for use in reshaping the corneal stroma was a great step forward in refractive surgery. Laser energy can be delivered on the stromal surface in the photorefractive keratectomy (PRK) procedure or deeper on the corneal stroma by the means of a lamellar surgery in which a flap is created with the microkeratome in the laser in situ keratomileusis (LASIK) procedure. LASIK is currently the dominant procedure in refractive surgery. The main advantage of LASIK over PRK is related to maintaining the central corneal epithelium. This increases comfort during the early post-operative period, allows for rapid visual recovery, and reduces the wound healing response. Reduced wound healing correlates with less regression for high corrections and a lower rate of complications such as significant stromal opacity (haze). PRK, however, remains as an excellent option for mild to moderate corrections, particularly for cases associated with thin corneas, recurrent erosions, or a predisposition for trauma (Martial arts, military, etc.). Recently, a modification of PRK, laser subepithelial keratomileusis (LASEK), was introduced. In the LASEK procedure, an epithelial flap is created and replaced after the ablation. The benefits, if any, of the creation of an epithelial flap compared to traditional PRK are not fully appreciated. Advocates of LASEK suggest that there is less discomfort in the early postoperative period, faster visual recovery, and less haze compared to standard PRK for correction of similar levels of refractive error. Additional long-term clinical studies, along with laboratory research, will be crucial to validate these potential advantages of LASEK procedure.     

Laser subepithelial keratomileusis: electron microscopy and visual outcomes of flap photorefractive keratectomy

Laser epithelial keratomileusis (LASEK) is a surgical technique that may be performed in patients with low myopia who are considering conventional photorefractive keratectomy (PRK), in patients with thin corneas, and in patients with professions or lifestyles that predispose them to trauma. Ethanol (18%) is applied for 25 seconds and a hinged epithelial flap is created. After laser ablation, the flap is repositioned over the ablated stroma. Our data showed that epithelial defects occurred in 63% eyes on Day 1. Postoperative pain was absent in 47%. Uncorrected visual acuity of 20/40 or better was achieved in all patients at 1 week. Data from several studies suggest that LASEK may reduce postoperative pain and corneal haze associated with PRK. LASEK offers the potential advantage of avoiding flap-related complications associated with laser in situ keratomileusis and decreasing postoperative pain and corneal scarring associated with PRK. Long-term studies are needed to confirm these potential advantages and to determine the safety, efficacy, and predictability of this surgical technique.     

Evolution, techniques, clinical outcomes, and pathophysiology of LASEK: review of the literature

Laser subepithelial keratomileusis (LASEK) is a relatively new laser surgical procedure that combines certain elements of both laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) to improve the risk/benefit ratio. Diluted alcohol is used to loosen the epithelial adhesion to the corneal stroma. The loosened epithelium is moved aside from the treatment zone as a hinged sheet. Laser ablation of the subepithelial stroma is performed before the epithelial sheet is returned to its original position. We reviewed the literature regarding modifications of the technique, indications, outcomes, and complications, as well as wound healing after LASEK surgery. This literature review of 1,421 LASEK-treated eyes provided many findings: 1) The long-term stable results in the absence of serious complications, such as infections, recurrent erosions, scars, or late-onset corneal haze formation in patients re-examined up to 5 years after LASEK; 2) Epithelial closure with recovery of functional vision was completed at days 4 to 7 in most cases; 3) A tendency toward overcorrection with PRK nomograms; 4) We hypothesize that this tendency may be due to the decreased wound healing response, which may lead to myopic regression in PRK; and 5) Postoperative discomfort and prolonged visual recovery until the epithelium closes remain the biggest disadvantages of LASEK compared to LASIK. LASEK surgery is especially valuable in patients with thin corneas who would not qualify for LASIK surgery. However, a potential superiority of LASEK to LASIK in wavefront guided ablations still remains speculative.     

In vivo evaluation of corneal structure changes after refractive procedures

PURPOSE: The aim of the study was to evaluate and compare in vivo the corneal structure changes after refractive procedures (PRK, LASIK, LASEK). MATERIAL AND METHOD: The analysed group of patients consisted of 226 corneas in 126 patients, who underwent correction of myopia and myopic astigmatism, using the procedures: PRK (120 eyes), LASIK (56 eyes) and LASEK (50 eyes). The photoablation of the corneas was performed with the Excimer Laser MEL 60 and MEL 70 G-Scan Aesculap Meditec. Postoperative observations were made using a confocal microscopes Confoscan P4 (Tomey) and ConoScan 2 (Fortune Technologies). The evaluations were performed in the early (up to 3 months) and late postoperative period (after PRK and LASIK-up to 2 years; after LASEK-up to 6 months). RESULTS: The confocal microscopy revealed some changes within the corneal epithelium and anterior part of stroma after PRK, LASIK and LASEK. After PRK, there was increased desquamation of superficial epithelial cells in early postoperative period. These cells were elongated after LASIK and LASEK procedures. After PRK and LASEK, the Bowman's membrane was absent in the central part of the cornea, during the whole observation period. After all these procedures, the anterior part of the corneal stroma in the ablation zone, showed increased background illumination of collagen fibres and an irregular pattern of elongated keratocytic nuclei, in the early postoperative period. No scar tissue--"haze" was found in cases after LASEK, what may occur after PRK procedure. The findings kept changing in the course of the follow up time. CONCLUSIONS: Confocal microscopy enables in vivo monitoring of changes, which occur in the corneal structure after refractive procedures; this facilitates the evaluation of corneal healing. LASEK is the least invasive refractive procedure, which allows prompt stabilization of the corneal structure.     

替代PRK和LASIK的激光角膜上皮磨削術(LASEK)

Objective To introduce and compare the one year' s result of LASEK (Laser Epithelial Keratomileusis) as an alternative to concurrent PRK and LASIK procedures for myopia. Methods This retrospective clinical study comprised operative and postoperative notes of consecutive 16 myopic patients (27 eyes, M:F=9:18) who had receied LASEK procedures with at least one year or more follow-up (12～18 months). And we comparved the LASEK with other surgeries such as PRK and LASEK in view-point of surgical advantages, visual improvement, and post-operative. complications such as corneal haziness, etc. Results We divided two groups of myopic patients according to the degrees of myopia (group 1 (N=14 eyes)-2.5D.～-6.00D.) and group 2 (N=13 eyes); -6.25D. ～-10.25D.). Through the LASEK procedure, surgical tension was surely less than that of LASIK which has always a possible complications concerned directly with a microkeratome. One week after LASEK, post-operative. Refractive powers and uncorrected visual improvement showed up to near normal ranges in all 27 eye cases. But In post-operative, corneal haziness, only trace-degree (0.5) was noted in one eye case of high myopic group. As other complications, we observed a failed case of epithelial flap making with a case of T-lens related central epithelial defect and a case of tight lens syndrome. Conclusion LASEK is to be the most safe and effective excimer laser refractive surgery as an alternative procedure of PRK and LASIK. LASEK has also an advantageous choice in high myopic cases having thin cornea, or narrow interpalpebral fissure or deep sunken eyeball etc.     

LASEK与LASIK治疗高度近视

目的:对比观察准分子激光上皮瓣下角膜磨削术(LASEK)与准分子激光原位角膜磨削术(LASIK)治疗高度近视的临床疗效。评估2种手术的安全性和有效性。方法:对行LASEK治疗的39例75只眼和同期行LASIK治疗的41例79只眼高度近视分别进行6个月以上的临床观察。结果:LASEK组术后1周至1个月达最佳矫正视力,术后3个月部分出现视力回退,术后6个月裸眼视力达术前矫正视力占95.83%,主要并发症有术后高眼压及Haze形成;LASIK组术后6个月裸眼视力达术前矫正视力占94.35%,主要并发症为屈光回退,角膜上皮内生或角膜瓣皱折等。结论:LASIK与LASEK均能安全、有效地矫正高度近视。     

激光角膜上皮瓣下磨镶术和激光原位角膜磨镶术治疗中高度近视的对比研究

目的比较激光角膜瓣下磨镶术(LASEK)和激光原位角膜磨镶术(LASIK)治疗中高度近视的临床效果. 方法中高度近视患者198例(394只眼).其中LASEK手术治疗93例(184只眼), LASIK手术治疗105例(210只眼). 结果术后1天,LASIK 组28 %裸眼视力达到1.0,LASEK组无1例裸眼视力达到1.0.术后1周、1、3、6月裸眼视力大于或等于1.0者,两组比较差异无显著性 (P=0.36,P=0.58,P=0.44,P=0.64).角膜地形图分析平均角膜中央屈光力与周边屈光力的差异,LASEK组(0.69)明显小于LASIK组(2.62).结论 LASEK手术矫正中高度近视均有良好的治疗效果,是一种安全、有效、预测性好的屈光手术.     

准分子激光角膜上皮瓣下磨镶术的临床观察

目的 观察准分子激光角膜上皮瓣下磨镶术（LASEK）治疗近视眼的临床效果。方法：选择术后随访达到6个月的146例（280眼），观察术后3天、10天，1、2、3、6个月的症状、视力、屈光状态、角膜并发症情况。结果 观察Nidek EC-5000准分子激光治疗结果表明，LASEK术后症状轻微，手术稳定性、预测性及安全性优于准分子激光屈光性角膜切削术（PRK）及准分子激光原位角膜磨镶术（LASIK）。结论 LASEK手术有可能成为今后主要的屈光治疗方法。     

LASEK results

Laser subepithelial keratomileusis (LASEK) has become a viable alternative to photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in selected patients. LASEK may decrease the complications associated with PRK, including postoperative pain and slow visual rehabilitation. In this article, the authors present the visual outcomes and complication rates of LASEK based on the retrospective case review of 101 consecutive patients (163 eyes) treated with LASEK surgery over the past 6 years. Seventy-eight percent of these eyes showed complete epithelial healing by day 3, and there were no incidents of recurrent erosions. As with LASIK, the achieved correction for LASEK was greater than the treatment dose (requiring undercorrection nomogram adjustments). Mean logMAR UCVA was 0.03 (20/20) at 1 year. LASEK seems to be a safe and effective option for patients who request refractive surgery.     

Laser epithelial keratomileusis for myopia

PURPOSE: To describe a new technique for excimer laser corneal surgery: laser epithelial keratomileusis (LASEK). METHODS: We report 76 eyes with spherical equivalent refractive myopia ranging from -8.00 to -22.00 D (mean -11.00 +/- 3.00 D). Using ethanol applied over an 8.5-mm-diameter area for 20 seconds, the epithelium was detached and photorefractive keratectomy (PRK) was performed. The epithelium was reapplied to the ocular surface and covered with a therapeutic soft contact lens. Treatments were carried out with the Nidek EC-5000 excimer laser. RESULTS: At a mean of 803 days after LASEK, mean spherical equivalent refraction was -1.80 +/- 2.40 D (range -9.27 to +2.00 D). Stability was reached in approximately 60 days. Fifty-nine percent of the epithelial flaps were easy to detach intact during surgery and 62.7% of patients reported no postoperative pain. Eighty-four percent of eyes had the therapeutic bandage lens removed by the fourth postoperative day. Twelve percent of eyes had incomplete epithelial flap removal. Epithelium can fall off the cornea during the healing phase. No significant subepithelial haze was seen in 95% of eyes. CONCLUSION: With LASEK, it may be possible to treat a larger diameter ablation zone in thinner corneas without the problems of a LASIK stromal flap and with less postoperative pain than PRK, with minimal subepithelial haze.     

Unilateral corneal ectasia after laser in situ keratomileusis in a patient with uncomplicated photorefractive keratectomy in the fellow eye

We report a patient treated for low myopia with laser in situ keratomileusis (LASIK) in one eye and photorefractive keratectomy (PRK) in the fellow eye. Corneal ectasia developed in the LASIK-treated eye. Preoperative corneal pachymetry, topography, and attempted correction were similar in both eyes. In patients whose corneas may be predisposed to instability, PRK may be a safer alternative procedure than LASIK.     

Long-term results of thin corneas after refractive laser surgery

PURPOSE: To report the long-term refractive results of photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) in patients with thin corneas. DESIGN: A long-term, retrospective, non-randomized follow-up study. METHODS: Sixty-three patients (124 eyes) (28 males and 35 females), who had a preoperative central corneal thickness (CCT) of less than 500 microns and completed at least one year of follow-up examinations after surgery. Thirty-five patients (68 eyes) underwent PRK and 28 patients (56 eyes) underwent LASIK. RESULTS: Mean preoperative corneal pachymetry was 484.95 +/- 6.65 microm (range, 470 to 498 microm) and 482.38 +/- 10.73 microm (range, 453 to 499 microm) for LASIK and PRK, respectively. No intraoperative complications were found in both groups. None of the included eyes developed postrefractive corneal ectasia. The mean predictability for the PRK group was 0.08 diopters (D) with a standard deviation of 0.40 D (range, -1.38 to 1.00 D), and the mean predictability for the LASIK group was 0.14 D with a standard deviation of 0.55 D (range, -1.25 to 1.33 D). CONCLUSIONS: Refractive laser surgery with LASIK or PRK in patients with thin corneas (less than 500 microm) seems to be a safe and predictable technique for myopic refractive corrections.     

准分子激光原位与上皮瓣下角膜磨镶术对角膜中央知觉恢复的影响

目的 比较准分子激光原位角膜磨镶术(laser in situ keratomileusis, LASIK)与激光上皮瓣下角膜磨镶术(laser-assisted subepithelial keratomileusis,LASEK)治疗近视对角膜中央知觉的影响.方法 观察2008年1月至2009年1月行LASIK与LASEK的患者共566例(1 132眼),其中LASIK者1 032眼,LASEK者100眼,分别于术前1周,术后1周,1、3、6、12个月检测角膜中央知觉.结果 两种手术后角膜知觉均下降,LASIK组术后1周检查均无知觉,6～12个月角膜中央知觉恢复到术前水平;LASEK组术后1周20眼角膜知觉为50～100 mm,3个月均恢复到术前水平.结论 LASEK术后角膜知觉恢复较LASIK术后快.     

The safety and efficacy of photorefractive keratectomy after laser in situ keratomileusis

PURPOSE: To determine the safety and efficacy of performing photorefractive keratectomy (PRK) in corneas previously treated with laser in situ keratomileusis (LASIK) surgery. METHODS: Fifteen eyes of 14 patients who had initially received LASIK for the treatment of myopia and compound myopic astigmatism were evaluated. Variables included existence of and/or type of flap complication associated with the original LASIK procedure, refractions before and after (3 and 6 months) PRK, uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), and the development of complications after PRK such as haze, scarring, double vision, or ghosting. RESULTS: All 15 eyes were available for analysis at 6 months. Eleven eyes had experienced flap complications during the initial LASIK procedure and 4 eyes had experienced complications in the LASIK postoperative period. Characteristics prior to performing PRK included 11 myopic and 4 hyperopic eyes. By 6 months after PRK treatment, 87% of eyes had UCVA > or = 20/40, 53% had > or = 20/25, and 40% had > or = 20/20. All eyes had BSCVA of > or = 20/30, with 73% being > or = 20/20. No eye had lost 2 lines of BSCVA and only 1 eye lost 1 line of BSCVA. Sixty percent of eyes were within 1.0 diopters (D) of emmetropia, and 40% were within 0.5 D of emmetropia. A trend towards undercorrection and surgical induction of astigmatism as confirmed by vector analysis was noted. No eye developed significant haze or scarring. CONCLUSIONS: Photorefractive keratectomy may be a safe procedure to perform in corneas previously treated with LASIK surgery. Results show good reduction of refractive error and improvement of UCVA and BSCVA. A significant undercorrection of astigmatism was attributed to surgically induced astigmatism. Further studies are necessary to determine the long-term safety and stability of outcomes.     

Excimer laser subepithelial ablation (ELSA) or laser epithelial keratomileusis (LASEK) - a new kerato-refractive procedure for myopia. Surgical technique and first clinical results on 24 eyes and 3 months follow-up

BACKGROUND: Laser epithelial keratomileusis (LASEK) is a new keratorefractive surgical procedure to treat myopia and possibly other refractive errors, which combines the advantages while eliminating the disadvantages of both PRK (pain, corneal haze) and LASIK (flap complications, interface complications). Our results with LASEK are very promising and because this technique is currently not very popular in Germany we here with introduce the surgical technique and our first clinical results. PATIENTS AND METHODS: We treated 24 eyes (18 patients) by LASEK. The preoperative myopia was between - 1.50 and - 6.00 D with an astigmatism less than 1.00 D. Surgery starts with an incision in the epithelium by using a special microtrephine. After the application of 20 % ethanol for 20 seconds a hinged epithelial flap is created and the laser ablation performed with a Keracor 117 excimer laser. Finally, the epithelial flap is repositioned and secured using a bandage contact lens and artificial tears for 3 days. RESULTS: In all eyes the creation of the epithelial flap and its repositioning presented no problems. None of the eyes showed any postoperative epithelial instability. However, one eye lost the contact lens and the epithelial flap during the first postoperative day. Postoperatively, none of the patients complained of significant pain; however, the contact lens caused some foreign body sensation. After 3 months all eyes were within +/- 1.0 D and 20/24 eyes (84 %) within +/- 0.50 D of emmetropia (spherical equivalent). None of the eyes showed significant haze. CONCLUSIONS: Although, the number of treated eyes is small and the postoperative follow-up is short LASEK seems to be an effective and safe procedure for the treatment of myopia.     

Corneal power, thickness, and stiffness: results of a prospective randomized controlled trial of PRK and LASIK for myopia

PURPOSE: To compare the short-, medium-, and long-term changes in corneal optical power and corneal aberrations, central corneal thickness, and corneal "stiffness" assessed by pneumotonometry readings in patients having laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) for myopia. SETTING: Department of Ophthalmology, Arhus University Hospital, Arhus, Denmark. METHODS: One eye of each of 45 patients with myopia ranging from -6.00 to -8.00 diopters (D) (spherical equivalent spectacle refraction [SER]) was randomized to LASIK (n=25; mean SER -7.12 D +/- 0.57 [SD]) or PRK (n=20; mean SER -6.91 +/- 0.57 D). Data were collected prospectively before and 1, 3, 6, 12, and 36 months after surgery. Measurements included corneal topography (TMS-1, Tomey), corneal thickness (ultrasound pachymetry), and apparent intraocular pressure (IOP) (pneumotonometry). Retreatments were not performed during the first year, and retreated eyes were excluded from the 3-year follow-up. Changes in corneal power and aberrations, thickness, and apparent IOP were calculated in a pair-wise manner for 3 time periods: short term (preoperative to 1 month after surgery), medium term (1 to 12 months after surgery), and long term (1 to 3 years after surgery). RESULTS: In the short term, corneal power decreased equally in LASIK and PRK eyes. Spherical aberrations and coma-like aberrations increased equally, while corneal thickness decreased significantly less in LASIK eyes than in PRK eyes. The apparent IOP decreased more in LASIK eyes than in PRK eyes. In the medium term, corneal power increased significantly in both groups. Spherical aberrations decreased significantly in PRK eyes but not in LASIK eyes. From 1 to 12 months, corneal thickness increased more in PRK eyes than in LASIK eyes. During this period, the apparent IOP increased significantly in LASIK eyes. In the long term, corneal power and corneal aberrations did not change significantly in either group. Corneal thickness increased slightly but significantly in both groups. The apparent IOP increased significantly more in PRK eyes. CONCLUSIONS: Differences between LASIK and PRK related to time-dependent events affecting corneal shape and structural integrity were present. Peripheral changes in flap hydration in LASIK eyes and epithelial and/or stromal thickening in PRK eyes appeared to be the most important factors in optical power changes in the first year after treatment. The changes in apparent IOP suggest that some interlamellar healing occurred during the first year after LASIK. After LASIK and PRK, corneal bending stiffness seemed permanently decreased, although some restiffening may occur in PRK eyes in the long term.     

Lower intraoperative flap complication rate with the Hansatome microkeratome compared to the Automated Corneal Shaper

PURPOSE: The purpose of this study was to retrospectively compare the incidence of intraoperative flap complications, such as partial flaps, donut-shaped flaps, central corneal cuts, and complete caps with the Hansatome and Automated Corneal Shaper (ACS) microkeratomes. METHODS: All laser in situ keratomileusis (LASIK) procedures performed by a single surgeon with the Hansatome or Automated Corneal Shaper in which intraocular pressure was verified with a pneumotonometer were reviewed. RESULTS: A total of 90 eyes had LASIK with the ACS microkeratome. Six of the ACS eyes (6.7%) had intraoperative flap complications (4 partial flaps, 1 donut-shaped flap, 0 central corneal cuts, 1 complete cap). Partial flaps and donut-shaped flaps were replaced without laser application and the procedure repeated 2 to 3 months later. Two of these eyes lost 2 lines and one lost 1 line of spectacle-corrected visual acuity at 6 months after repeat LASIK. The eye with the donut-shaped flap was treated with transepithelial photorefractive keratectomy (PRK) and had no change in spectacle-corrected visual acuity at 6 months after PRK. The eye with the complete cap had no change in spectacle-corrected visual acuity after laser ablation. Five hundred ninety-eight (598) eyes had LASIK with the Hansatome microkeratome. Two of the Hansatome eyes (0.3%) had a flap complication (1 partial flap and 1 donut-shaped flap). The first eye retained spectacle-corrected visual acuity at 6 months after repeat LASIK. The second eye had transepithelial PRK to eliminate the donut shaped flap with no loss of spectacle-corrected visual acuity at 6 months after surgery. The difference in flap complications between the two procedures was statistically significant (P < .01). There were no flap displacements following surgery in either group. CONCLUSION: Intraoperative flap complications are less likely to occur with the Hansatome microkeratome than with the ACS microkeratome.     

Laser in situ keratomileusis for residual myopia after radial keratotomy and photorefractive keratectomy.

PURPOSE: To evaluate the visual outcome, stability, and complications of laser in situ keratomileusis (LASIK) for residual myopia after radial keratotomy (RK) and photorefractive keratectomy (PRK). SETTING: Dr. Agarwal's Eye Hospital, Chennai, India. METHODS: Twenty eyes that had LASIK treatment for residual myopia after RK (10 eyes) or PRK (10 eyes) were retrospectively analyzed. Laser in situ keratomileusis was performed after a mean period of 24.3 months +/- 0.75 (SD) in the RK group and 22.0 +/- 1.07 months in the PRK group. RESULTS: At the last follow-up, the mean spherical equivalent was reduced from -6.05 +/- 1.98 diopters (D) to -1.26 +/- 0.32 D (P <.05) in the RK group and from -3.38 +/- 1.30 D to -0.55 +/- 0.40 D (P <.005) in the PRK group. The mean uncorrected visual acuity improved from 20/300 (range 20/600 to 20/200) to 20/40 (range 20/60 to 20/20) (P <.05) and from 20/200 (range 20/800 to 20/80) to 20/25 (range 20/40 to 20/20) (P <.05), respectively. Two eyes in the RK group and 3 in the PRK group gained 1 line of best corrected visual acuity, and 2 eyes in the RK group lost 1 line. No sight-threatening complications such as a free flap, corneal ectasia, or a retinal complication occurred. There was no statistically significant difference in corneal haze before and after LASIK. Two eyes in the RK group required repositioning of the flap because of irregular apposition to the stromal bed. CONCLUSION: Laser in situ keratomileusis was safe, effective, and stable in the treatment of residual myopia after RK and PRK.     

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.     

准分子激光角膜切削术与准分子激光原位角膜磨镶术角膜创口愈合的对比实验研究

比较准分子激光角膜切削术(photorefractive keratectomy,PRK)与准分子激光原位角膜磨镶术(1aser in situ keratomileusis,LASIK)后激光对角膜组织的切削效应及角膜的愈合情况,从组织学角度探讨角膜雾状混浊(Haze)及屈光度数回退的成因。方法24只新西兰白兔按预矫屈光度数随机分为-4.00 D组和-8.00 D组,每只兔右眼行PRK,左眼行LASIK。术后10d,1、3及6个月观察Haze情况并验光,每组随机处死3只兔取角膜行光镜、电镜及免疫组化检查,检测胶原Ⅲ、胶原Ⅳ、纤维连结蛋白(fibronectine,FN)及转化生长因子-β(transforming growth factor-β1,TGF-β2)的含量。结果行PRK术的右眼术后出现不同程度的Haze及屈光度数回退,其程度与预矫正屈光度数成正比。行LASIK术的左眼术后除少数角膜瓣周围半环形混浊外,手术区域角膜透明,屈光度数回退较右眼轻。-4.00 D组右眼与左眼术后屈光度数均稳定,-8.00 D组右眼较左眼屈光度数回退明显。右眼术后角膜愈合反应重,恢复慢。6个月时角膜基质仍处于修复阶段。左眼术后除形成角膜上皮栓及对应处基质轻度增生外,手术区域角膜瓣与基质床间界面清晰,无明显增生,角膜基质愈合反应轻、恢复快。术后所有兔眼角膜均有TGF-β1表达及活化,持续时间与角膜愈合时间一致。Haze及屈光度数回退组织学改变为：角膜上皮细胞增生,基底膜不成熟,前基质角膜细胞活化、增殖,新生胶原Ⅲ合成、排列紊乱,细胞外基质FN在角膜上皮下沉积。结论LASIK矫正近视尤其是高度近视优于PRK;角膜伤口愈合特别是基质愈合的反应程度,是。Haze及屈光度数回退的关键;TGF-β1是角膜愈合过程中重要调节因子,可通过介导角膜上皮一基质相互作用,调节胶原Ⅲ及FN的含量,参与瘢痕形成。