Factors influencing corneal flap thickness in laser in situ keratomileusis with a femtosecond laser

Purpose

To evaluate factors responsible for the variability between intended and achieved corneal-flap thickness during femtosecond laser-assisted laser in situ keratomileusis (LASIK).

Methods

A prospective, nonrandomized, case study was performed on 35 eyes of 18 consecutive patients who underwent LASIK surgery using the 60 kHz femtosecond laser microkeratome. Eyes were assigned to three different thickness groups, with 110-, 120-, or 130-µm cut depths. Anterior segment optical coherence tomography was used to assess the morphology of 35 LASIK flaps at postoperative one week postoperatively. The flap thickness was assessed at seven measuring points across each flap. Patient age, preoperative spherical equivalent, manual keratometry, preoperative central pachymetry, and regional variability of the cornea were evaluated to determine where they influenced the achieved corneal flap thickness.

Results

Cuttings of all flaps were easily performed without any intraoperative complications. Flap-thickness measurements had a mean of 115.21 ± 4.98 µm (intended thickness, 110 µm), 121.90 ± 5.79 µm (intended, 120 µm), and 134.38 ± 5.04 µm (intended, 130 µm), respectively. There was no significant difference between the 110-µm and 120-µm groups when compared with the 130-µm group (one-way analysis of variance test, p > 0.05). Patients'' age, preoperative spherical equivalent, manual keratometry, and preoperative central pachymetry did not affect the achieved flap thickness (Pearson correlations test, p > 0.05). The reproducibility of flap thickness in the central 1.5-mm radius area was more accurate than that in the peripheral 3.0 to 4.0-mm radius area (paired samples t-test, p < 0.05).

Conclusions

Femtosecond laser-assisted LASIK is likely to reproduce a reliable thickness of the corneal flap, which is independent of corneal shape factors or refractive status. Future studies should focus on variations in corneal biomechanical factors, which may also play an important role in determining flap thickness.     

尼日利亚儿童眼部生物测量和中央角膜厚度分析

目的:评估尼日利亚儿童眼部生物特征测量和中央角膜厚度(CCT),建立参考数据库。方法:对2017-11/2018-01在我院招募的儿童进行横断面观察。采用LogMAR图表和Lea图表对不同年龄组患者的社会人口学资料、视力(VA)进行评估。对8岁及以下儿童进行麻醉检查(EUA),行瞳孔扩张前后节段检查,使用卡尺测量角膜直径(CD)。采用手持式眼压计测量眼内压(IOP),用超声角膜厚度仪测量中央角膜厚度和眼轴长度(AL)。临床检查后进行睫状肌麻痹性屈光检查。采用SPSS version 17对数据进行输入和分析,通过描述性统计得出结果,完成频率和变量交叉表(P<0.05)。结果:研究共纳入66例132眼患者,年龄3~16(平均9.13±3.70)岁,男女比例为1∶1.7。年龄集中于6~10岁(42.4%),大多数患者为小学生(54.5%)。父母的职业主要是商人/非技术工人(51.6%)和专业人员/公务员(30.3%)。平均右眼、左眼VA(LogMAR)为0.45±0.46和0.45±0.44。右、左眼角膜水平直径(HCD)平均值分别为10.5±1.6、10.37±1.45 mm。右、左眼角膜垂直直径(VCD)分别为9.7±1.2 mm和9.7±1.3 mm。右、左眼平均CCT分别为556.71±2.61μm和556.47±45.53μm。近视[23例(34.8%)],近视散光[18例(27.3%)],单纯性散光[16例(24.2%)]是最常见的屈光不正类型。CCT和HCD(P=0.739)、VA(P=0.058)和屈光不正(P=0.199)之间无显著相关性。但CCT与年龄组有轻度显著相关(P=0.055)。结论:尼日利亚儿童的CCT、IOP和CD的平均值首次为人所知。CCT与VA、CD与屈光不正之间无显著相关性,需要进一步的研究来确定结果。     

Factors affecting the central corneal thickness of Hong Kong-Chinese.

PURPOSE: The aims of this study were to investigate the effect of age, intraocular pressure, refractive error (spherical equivalent) and corneal curvatures on the central corneal thickness of Hong Kong-Chinese. We also compared the central corneal thickness of Hong Kong-Chinese with those previously reported for other national/ethnic groups. METHODS: The central corneal thicknesses of 151 subjects of age 10-60 yrs were measured using an ultrasound pachometer. Intraocular pressure, refractive error and the corneal curvatures of these subjects were also recorded. RESULTS: The mean +/- SD central corneal thickness of the right eye and left eye were 575 +/- 32 microm and 574 +/- 31 microm respectively. No significant difference in central corneal thickness was found between the right and left eyes or between male and female subjects. Central corneal thickness decreased with increasing age but the effect appeared to be due to differences in female subjects only. The maximum decrease in central corneal thickness occurred in subjects in the age group of 10-25 yrs, and in this age group, central corneal thickness and age was significantly correlated in both male and female subjects. Intraocular pressure and central corneal thickness was significantly correlated. There was no correlation between central corneal thickness and refractive error or between central corneal thickness and corneal curvatures. CONCLUSIONS: Central corneal thickness decreased with increasing age but this appeared to be due to female subjects only. Central corneal thickness was significantly correlated with intraocular pressure, but not with refractive error or corneal curvatures. Our subjects also had significantly thicker corneas than those reported for Caucasian subjects.     

Central corneal thickness in a healthy Spanish population

ObjectiveTo study the central corneal thickness of a Spanish population group and determine the influence of age, gender, axial length and refractive error on central corneal thickness (CCT) values.MethodsAn observational, cross-sectional, double masked study was conducted on 357 eyes of consecutive Caucasian patients without ophthalmic disease. They were distributed according to age, and high refractive defects were excluded. Ultrasonic pachymetry and a complete eye examination were performed on all patients. The relationship between the central corneal thickness values and variables of age, refractive error, axial length and gender was assessed.ResultsThe mean central corneal thickness was 548.21 μm with a standard deviation (SD) of 30.7 μm (range 464 to 633 μm). The normal central corneal thickness value of the population studied was 486.81 to 609.61 μm (95% confidence interval). No statistical association was found between central corneal thickness values and variables of age, refractive error, axial length and gender.ConclusionsCentral corneal thickness varies according to race. We have analysed, for the first time, normal central corneal thickness values of a healthy Spanish population.     

Genetic factors influencing the reduction of central corneal thickness in disorders affecting the eye

Background: The aim was to summarize and discuss the current knowledge about genetic factors influencing the reduction of central corneal thickness (CCT) in disorders affecting the eye, such as primary open-angle glaucoma (POAG), brittle cornea syndrome (BCS), keratoconus (KTCN), Ehlers–Danlos syndrome (EDS; types I, II, and VI), osteogenesis imperfecta (OI), and myopia.

Materials and methods: A review of the published literature by use of key databases such as PubMed was undertaken in accordance with PRISMA guidelines and experience based on own research findings was applied.

Results: The differences in CCT measurements among those affected with diverse disorders and healthy individuals were evaluated. Then we considered the influence of genetic factors on CCT reduction. Disorders were compared based on phenotypes and sequence variants found in patients.

Conclusions: Specific sequence variants in COL8A2, PRDM5 and ZNF469, COL5A1 and ZNF469, and COL5A1 and COL5A2 could probably contribute to a CCT reduction in POAG, BCS, KTCN, and EDS, respectively. Similar sequence variants and phenotypes were identified and assessed in more than one disease.     

Profile of central corneal thickness in diabetics with and without dry eye in a Saudi population

PurposeThe aim of this study was to determine the impact of diabetes in patients with and without dry eyes (DE) on central corneal thickness (CCT) measurements.MethodsEighty-six subjects (51 diabetics and 35 controls) participated in the study. Ultrasound pachymetry was used to measure the CCT, whereas tear break-up time (TBUT) and Schirmer tests were conducted for tear assessments. The participants were divided into group 1 (diabetics without DE), group 2 (diabetics with DE), and group 3 (nondiabetics controls). The measurements were compared using analysis of variance.ResultsThe mean (95% confidence interval [CI]) of CCT was 610 (599 to 620), 601 (582 to 618), and 583 (576 to 589) μm, respectively, in diabetics without DE, with DE, and the control groups. There was significant difference in mean CCT between diabetics without DE and controls (P < 0.0001), but no significant difference in diabetics with DE versus controls (P > 0.05). The mean (95% CI) values for TBUT and Schirmer tests were 14 (13 to 15), 6 (4 to 6), 14 (14 to 15) seconds, and 21 (19 to 23), 7 (6 to 8), and 20 (19 to 21) mm, respectively, for diabetics without DE, with DE, and the nondiabetic groups.ConclusionsDE affects the CCT in diabetic subjects, having a predilection for lower values in those exhibiting DE. In addition, the results also support the view that diabetics tend to present with higher CCT values when compared with nondiabetic patients.     

Effect of corneal drying on central corneal thickness

PURPOSE: To determine the amount of corneal thinning induced by corneal drying, and to discuss its possible consequences on applanation pressure. PATIENTS AND METHODS: Two sets of central corneal thickness measurement from 100 eyes of 100 patients were taken by ultrasonic pachymeter at time settings of 0, 15, 30, 45, and 60 seconds. During the first set (group 1), patients were asked to blink voluntarily between the measurements. During the second set (group 2), the same patients were prevented from blinking during the measurements. RESULTS: Mean central corneal thickness at 0 second in groups 1 and 2 were 547.0 +/- 37.4 microm, and 546.7 +/- 37.6 microm, respectively. Corneal thickness did not change significantly in group 1, but did significantly decrease in group 2. Rate of thinning increased linearly during the first 30 seconds, and then leveled around 0.3 microm/s up to 60 seconds. Mean corneal thickness decreased 3.0% during the 60 second drying. The decrease in thickness was significant when each time point in group 2 was compared with the preceding one (P < 0.01). Neither age nor 0 second corneal thickness in group 2 showed a significant correlation with the amount of corneal thinning at 60 seconds. CONCLUSION: Corneal thickness may significantly decrease during 1 minute of drying. Decreased thickness may result in underestimation of applanated pressure as well as central corneal thickness.     

Decreased central corneal thickness in ankylosing spondylitis

Central corneal thickness and dry eye tests were evaluated in a study population consisting of 68 ankylosing spondylitis patients diagnosed according to the modified New York criteria, and 61 age-matched controls without ankylosing spondylitis. A full ophthalmological evaluation was performed on each subject. All subjects were screened for age, gender, HLA-B27, tear break-up time test, Schirmer test, and duration of disease. Central corneal thickness was measured under topical anesthesia with an ultrasonic pachymeter. The mean central corneal thickness was 537.3 ± 30.6 μm, range 462–600 μm, in ankylosing spondylitis patients, whereas it was 551.7 ± 25.2 μm, range 510–620 μm, in controls (p = 0.005). The Schirmer test result was 7.3 ± 5.9 mm for the ankylosing spondylitis patients and 11.7 ± 5.8 mm for the control group (p = 0.002). Tear break-up time was 7.3 ± 3.2 s for the ankylosing spondylitis patients and 14.0 ± 4.5 s for the control group (p < 0.001). The possibility of a thinner cornea should be taken into consideration in ankylosing spondylitis. In addition, attention must be given to lower dry eye tests in surgical interventions such as photorefractive keratectomy and laser in situ keratomileusis in ankylosing spondylitis patients.     

近视眼中央角膜厚度和最薄角膜厚度的关系

目的 研究近视患者中央角膜厚度和最薄角膜厚度的大小、位置关系,以及近视程度对角膜厚度的影响.方法 回顾性病例对照研究.以接受近视性屈光手术的150例(300眼)为研究对象,根据等效球镜分为低、中、高近视3组,提取他们的术前Pentacam检查资料.左右眼参数的相关性和差异分别采用Pearson相关分析和配对t检验,多组比较采用方差分析,同一侧眼不同参数差异采用独立样本t检验.结果 左眼平均中央角膜厚度和最薄角膜厚度分别为(555.83±31.83)μm和(552.88±31.48)μm,右眼平均中央角膜厚度和最薄角膜厚度分别为(554.10±31.47) μm和(549.26±31.25)μm.左眼角膜最薄点72.00％(108/150)位于颞下方;右眼角膜最薄点70.67％(106/150)位于颞下方.不同程度近视组间的角膜厚度差异无统计学意义.结论 最薄角膜厚度与中央角膜厚度并不一致,双眼角膜最薄点均主要位于颞下方,其次在鼻下方.角膜厚度与近视程度无关.     

Long-term change in central corneal thickness from a glaucoma perspective

Aim:

To investigate the longitudinal change in central corneal thickness (CCT) over 3 years in patients with glaucoma.

Materials and Methods:

The Chennai Glaucoma Follow-up Study, an offshoot of the Chennai Glaucoma Study, was designed to evaluate the progression of glaucoma. A cohort of participants in the Chennai Glaucoma Study that were suffering from glaucoma or were at a higher risk for glaucoma underwent comprehensive ophthalmic evaluation at the base hospital at 6-month intervals during the years 2004 to 2007. The CCT (average of 10 readings) was measured between 11 am and 1 pm on any given day using an ultrasonic pachymeter. Patients with a history of ocular surgery, corneal disease and usage of topical carbonic anhydrase inhibitor were excluded. No patient was a contact lens wearer.

Results:

One hundred and ninety-six patients (84 male, 112 female) met the inclusion criteria. We analyzed data from the right eye. The mean age of the patients was 59.97 ± 9.06 years. Fifty-nine (30.1%) of the patients were diabetic. The mean change in CCT (CCT at first patient visit – CCT at last patient visit) was 3.46 ± 7.63 μm. The mean change in CCT was 0.75 μm per year (R² = 0.00). Age, gender, intraocular pressure at the first patient visit and diabetic status had no significant influence on the magnitude of change in CCT.

Conclusion:

A carefully obtained CCT reading by a trained examiner need not be repeated for at least 3 years as long as the ocular and systemic factors known to affect the measurement of CCT are constant.     

The central corneal thickness in keratoconjunctivitis sicca.

The central corneal thickness of 17 patients with keratoconjunctivitis sicca was compared with the thickness recorded in a control group of 105 subjects with healthy eyes. A moderate, but highly statistically significant central corneal thinning was found in the keratoconjunctivitis sicca group. The possible etiology and clinical importance of this finding is briefly discussed.     

配戴软性角膜接触镜对角膜中央厚度影响的临床研究

目的:探讨配戴软性角膜接触镜对中央角膜厚度的影响。方法:应用超声角膜测厚仪检测中央角膜厚度,在我院近视患者中随机抽取配戴软性角膜接触镜者及不戴镜者各100例200眼,做统计分析。再在近视患者中按戴镜时间<1a,1～3a,3～5a,5～7a,≥7a分组,每组随机抽取60例120眼,做统计分析。结果:配戴软性角膜接触镜者与不戴镜者的角膜厚度比较,差异有统计学意义(P<0.05)。戴镜时间<1a,1～3a,3～5a,5～7a者的角膜厚度比较,差异有统计学意义(P<0.05)。结论:配戴软性角膜接触镜者平均中央角膜厚度薄于不戴角膜接触镜者,并且配戴软性角膜接触镜的时间越长中央角膜厚度越薄。