Corneal thickness in trachomatous dry eye

PURPOSE: To investigate the effect of severe desiccation on corneal thickness in scarring trachoma by comparing the thickness of normal and trachomatous dry eye corneas. METHODS: Ultrasonic pachymetry was used to measure the corneal thickness at nine points in the central and peripheral cornea (superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal, superotemporal) in 45 eyes of 27 patients with trachomatous dry eye and 54 eyes of 31 normal subjects. RESULTS: The average thickness of the nine sites in the central and midperipheral cornea was significantly less in trachomatous dry eyes than normal eyes. The superior cornea was the thickest area in both groups, measuring 574.03+/-31.62 microm in trachomatous dry eyes and 611.33+/-34.99 microm in normal eyes (p<0.001). The centre of the cornea was the thinnest, measuring 510.43+/-32.12 microm in trachomatous dry eyes and 546.27+/-36.20 microm in normal eyes (p<0.001). CONCLUSIONS: The thickness of the central and midperipheral cornea was significantly reduced in patients with trachomatous dry eye. The chronic state of severe desiccation, tear film instability and increased immune activation in trachomatous dry eye may contribute to this thinning.     

Reliability coefficients of three corneal pachymeters.

We compared the accuracy and reproducibility of a hand-held portable ultrasound pachymeter, the Pach-Pen (Bio-Rad, Ophthalmic Division, Santa Ana, California); another ultrasound pachymeter, the DGH 1000 (DGH Technology, Inc., Frazer, Pennsylvania); and the Pro-Cem 4 endothelial specular microscope (Alcon-Surgical, Inc., Irvine, California). Each eye of 18 healthy human subjects was examined to determine corneal thickness using the three different instruments. For each instrument, five repeated measurements were obtained at each of five corneal locations (one central, four peripheral), for a total of 25 measurements per eye. The accuracy of the two ultrasound pachymeters was tested by comparing measurements obtained on specially designed test blocks of known thickness. The Pach-Pen was the more accurate of the two ultrasound pachymeters, with measurements within the range of 0.003 to 0.065 mm from the true thickness. The three instruments were most consistent in mean thickness in the center of the cornea. All three instruments showed excellent intraobserver reproducibility, as measured by reliability coefficients over 90%. Overall, the Pach-Pen pachymeter had high reproducibility, and produced more accurate measurements than the DGH 1000 pachymeter.     

Central and peripheral pachymetry measurements according to age using the Pentacam rotating Scheimpflug camera

PURPOSE: To investigate the mean values and standard deviations as well as the reliability of consecutive examinations of central and peripheral corneal thickness measurements according to age using the Pentacam rotating Scheimpflug camera (Oculus, Inc.). SETTING: Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany. METHODS: Seventy-six healthy volunteers were enrolled in a clinical prospective study. Three consecutive Pentacam measurements of 1 eye per subject were taken. Evaluated were the central corneal thickness (CCT), corneal thickness at 4 peripheral points (3.0 mm superior, inferior, nasal, and temporal), and the thinnest point of the cornea. The volunteers were then assigned to 3 groups to assess the influence of increasing age on the study parameters. RESULTS: The mean age of the subjects was 46.6 years +/- 16.8 (SD). The mean CCT was 539.62 +/- 31.87 microm. Peripherally, the corneal thickness was between 11% and 19% higher than centrally, with the superior cornea being the thickest followed by the nasal, the inferior, and the temporal cornea. The thinnest point was located in the inferotemporal quadrant in 92% of eyes and in the superotemporal quadrant in 8%. There was no correlation between age and corneal thickness. Minor mean standard deviations of consecutive measurements were noted in the corneal center (4.33 microm), increasing significantly toward the periphery (mean 8.31 microm). Increasing age was not associated with decreasing reliability. CONCLUSIONS: Using the Pentacam, it was possible to acquire information about corneal thickness across the entire cornea. No correlation was found between increasing age and change in peripheral or CCT. Good reliability was noted for pachymetry measurements decreasing slightly toward the periphery, which was independent of age.     

Comparison of human central cornea and limbus in vivo using optical coherence tomography.

PURPOSE: The purpose of this study was to compare central corneal and limbal total and epithelial thickness using a commercially available optical coherence tomographer. METHODS: A Humphrey-Zeiss Optical Coherence Tomographer (OCT [Carl Zeiss, Meditec, Dublin, CA]) was used to obtain corneal images from 10 subjects. Central corneal and limbal total and epithelial thickness of both eyes were measured using the OCT. Each OCT image comprised 100 measurements, 10 nasal, 10 central, and 10 temporal measurements from each image were analysed. RESULTS: The central corneal and epithelial thickness of the right and the left eyes were 507.9 +/- 35.8 microm, 58.4 +/- 2.5 microm, 506.9 +/- 37.4 microm, and 58.5 +/- 2.5 microm, respectively. There were no differences between eyes (p > 0.05). The nasal and temporal limbal total and epithelial thickness of the right and left eyes were 703.8 +/- 32.1 microm, 704.9 +/- 31.0 microm, 76.8 +/- 3.5 microm, 77.9 +/- 2.9 microm, 704.4 +/- 31.8 microm, 706.3 +/- 32.5 microm, 77.5 +/- 2.8 microm, and 77.8 +/- 2.5 microm, respectively. There were no differences between the nasal and temporal total and epithelial thickness of both eyes (p > 0.05). However, there was a statistical difference between the central corneal and limbal total and epithelial thickness (both p < 0.05). CONCLUSIONS: Central cornea and limbus are measurably different using OCT. Central cornea is thinner than limbus for both total thickness and epithelial thickness. There is no difference between eyes of central corneal and limbal total and epithelial thickness. Optical Coherence Tomography is a useful instrument for in vivo human limbal morphometry.     

Central corneal thickness measurement with the Pentacam Scheimpflug system, optical low-coherence reflectometry pachymeter, and ultrasound pachymetry

PURPOSE: To assess the intraoperator repeatability and interoperator reproducibility of central corneal thickness measurements by the Pentacam Scheimpflug imaging system (Oculus) and the optical low-coherence reflectometer (OLCR) pachymeter (Haag-Streit) and to compare them with those of ultrasound (US) pachymetry. SETTING: Assaf Harofe Medical Center Ophthalmology Outpatient Clinic, Zerifin, Israel. METHODS: Repeatability was determined from 10 successive measurements in each of 4 healthy patients. Reproducibility for the Pentacam Scheimpflug system was determined from measurements by 2 operators in each of 24 patients; in these 24 patients, central corneal thickness measurements were compared between the Pentacam and US pachymetry. For the OLCR pachymeter, reproducibility was determined from measurements by 2 operators in each of 16 patients, in whom central corneal thickness was also measured with the Pentacam. RESULTS: Mean coefficient of repeatability was 0.84% for the Pentacam Scheimpflug system and 0.33% for the OLCR pachymeter. For the Pentacam, the coefficient of interoperator reproducibility was 1.10% and the 95% limits of agreement were -10.2 microm to +11.9 microm. Mean difference between Pentacam and US was 6.09 microm. For the OLCR pachymeter, the coefficient of interoperator reproducibility was 0.59% and the 95% limits of agreement were -5.4 microm to +7.0 microm. Mean difference between central corneal thickness values obtained with the OLCR pachymeter and Pentacam Scheimpflug system was 1.7 microm. CONCLUSIONS: Objective, noncontact measurement of central corneal thickness with the Pentacam Scheimpflug system and OLCR pachymeter was convenient and yielded excellent intraoperator repeatability and interoperator reproducibility. Central corneal thickness values obtained with the Pentacam were similar to those obtained with both the OLCR pachymeter and an US pachymeter. Further research is needed to corroborate whether central corneal thickness measurements by the Pentacam and OLCR devices can be used interchangeably and are more clinically useful than US pachymetry.     

Anatomic study of the corneal thickness of young emmetropic subjects

PURPOSE: To study the corneal thickness of young emmetropic subjects. METHODS: One thousand eyes of 1000 young healthy emmetropic subjects were analyzed with the Orbscan Topography System II (Orbscan, Inc, Salt Lake City, UT) from January 2001 to May 2003. The age of the subjects ranged from 20 to 30 years old (mean +/- SD = 27.12 +/- 2.86). The mean of 5 consecutive measurements of the corneal thickness in the center of the cornea and at temporal, superotemporal, inferotemporal, nasal, inferonasal, and superonasal cornea were recorded. RESULTS: The corneal thickness at the following areas ranged as follows: 518 to 589 microm center; 603 to 678 microm nasal; 620 to 689 microm superonasal; 600 to 669 microm inferonasal; 571 to 639 microm temporal; 601 to 669 microm superotemporal; and 572 to 647 microm inferotemporal. In each individual the difference between the central thickness and the maximum paracentral thickness ranged from 85 to 107 microm (mean +/- SD, 99.21 +/- 3.80). The difference between the central thickness and the minimum paracentral thickness ranged from 36 to 59 microm (48.97 +/- 4.23 microm). The difference between the minimum paracentral corneal thickness and the maximum paracentral corneal thickness ranged from 37 to 58 microm (50.24 +/- 4.30). The tonometry was statistically correlated with the corneal thickness (P < 0.05 at each corneal location analyzed). CONCLUSIONS: In emmetropic corneas the difference between the minimum paracentral thickness and the maximum paracentral thickness was similar to the difference between the central thickness and the minimum paracentral thickness.     

Central and peripheral corneal pachymetry--standard evaluation with the Pentacam system

BACKGROUND: Corneal thickness measurements are important in refractive surgery, for interpretation of IOP and in corneal diseases. The purpose of this study was to generate specific standard values for the Pentacam system and to investigate the influence of body size, body mass index, body weight, gender and refraction on central and peripheral corneal thickness for a more detailed characterization of the corneal anatomy. MATERIALS AND METHODS: The Pentacam system is based on a 180 degrees rotating computer-aided Scheimpflug camera, which generates reconstructions of the anterior segment from 12 to 50 single captures. The central corneal thickness was calculated from 25 single captures in both eyes of 182 normal Caucasian subjects (age: 18 - 83 years). The peripheral corneal thickness was measured within 3 mm distances at 0 degrees , 90 degrees , 180 degrees and 270 degrees . All subjects underwent an ophthalmological examination. Correlations between corneal thickness and body size, body mass index, body weight, gender and refraction were analyzed statistically by non-parametric tests. RESULTS: The mean central corneal thickness of all 364 eyes was 534 +/- 36 microm. Divided into sides it was the same, 534 +/- 36 microm, in the right and in the left eyes. The mean central corneal thickness for female subjects was 533 +/- 40 microm, for males it was 534 +/- 35 microm. Statistically there was no proof of any dependence of the central corneal thickness values on the sides, gender, age, height, body mass index (BMI) or refraction. However, there was a positive significant correlation between central corneal thickness and body weight. The peripheral corneal thickness values were lowest in the temporal and inferior areas and greatest in the superior and in the nasal areas. In the superior and in the nasal areas there was a statistically significant negative correlation between age and peripheral corneal thickness. CONCLUSIONS: The corneal thickness can be measured touchless with the Pentacam system. The central corneal thickness seems to be correlated with the body weight. Anatomical features lead to lower peripheral corneal thickness values in the temporal and inferior areas than in the nasal and superior areas. In the nasal and in the superior areas the corneal thickness seems to decrease with age. Further trials are necessary to confirm these findings and to evaluate the precision, reproducibilitiy and independence of investigators of the corneal pachymetry with the Pentacam system.     

Quantitative corneal anatomy in emmetropic subjects

PURPOSE: Currently there is little information available about the corneal thickness values of healthy emmetropic subjects. Therefore, the authors decided to analyze the corneal thickness in healthy emmetropic subjects. METHODS: The authors analyzed the difference in thickness values between the thinnest corneal site and the central and paracentral cornea in 124 eyes of 124 healthy emmetropic white subjects. RESULTS: The mean difference between the thinnest site of the cornea and the thickness values obtained in the areas analyzed was as follows: 12+/-6 microm center; 140+/-19 microm superonasal; 133+/-23 microm nasal; 117+/-26 microm inferonasal; 122+/-19 microm superotemporal ; 89+/-22 microm temporal; and 99+/-29 microm inferotemporal (p<0.001; one way analysis of variance test). CONCLUSIONS: In healthy emmetropic white subjects the thinnest site of the cornea is statistically lower than the central and paracentral cornea.     

Ultrasound and partial coherence interferometry with measurement of central corneal thickness

PURPOSE: To compare noncontact pachymeter measurements with ultrasound pachymeter measurements and assess their reproducibility. METHODS: Central corneal thickness was measured in 104 eyes of 56 patients with three laser interference pachymeters (OLCR [Haag Streit, K?nitz, Switzerland], OCP [4optics AG, Lübeck, Germany], and ACMaster [Carl Zeiss Meditec, Jena, Germany]) and an ultrasound pachymeter (Tomey AL2000 [Tomey Corp, Nagoya, Japan]). RESULTS: Compared to the ultrasound measurements, the mean difference for the laser interference pachymeter measurements were +8.8 microm (standard deviation [SD] 5.68) for the OLCR, -8.0 microm (SD 5.39) for the OCP, and -0.12 microm (SD 5.88) for the ACMaster. Reproducibility could only be estimated as not all of the devices allowed access to individual measurements. For all laser interference devices, reproducibility was estimated to be approximately 2 microm. Ultrasound measurements yielded a reproducibility of approximately 3.4 microm. CONCLUSIONS: Although ultrasound pachymeter measurements differed significantly from OLCR and OCP measurements, agreement was considered good because the mean differences were <10 microm, and the results can be regarded as clinically interchangeable.     

Repeatability of corneal thickness measurements made by a scanning slit topography system

Two sets of corneal thickness (CT) measurements at five corneal locations were made with Orbscan on 33 normal young adults. No significant intravisit and intervisit differences at any of the corneal locations were found (Repeated measures ANOVA, F < 0.49, p > 0.49). The 95% limits of agreement (95% LA) for between-measurement differences for the central cornea was about +/-19 microm (or 3%), indicating good repeatability; for the inferior, temporal and nasal corneal locations, the 95% LA were close to +/-30 microm (approximately 4-5%); and for the superior corneal location, they were about +/-35 microm (or 5.5%). The estimated number of repeated measurements that should be taken for accurate CT measurements (at any of the five corneal locations and excluding outliers of >3 S.D.) of 2% (standard error) is < or =2, and of 3% is 1. This study shows that only central CT measurements with the Orbscan are repeatable. The role of the Orbscan pachometry is therefore limited and is recommended for central CT measurements only.     

Intraoperative corneal thickness measurement using optical coherence pachymetry and corneo-gage plus ultrasound pachymetry

PURPOSE: To compare the central corneal thickness measured by online optical coherence pachymetry (OCP) and ultrasound pachymetry in normal cornea. METHODS: Forty-eight right eyes of 48 consecutive patients were enrolled in this prospective study. Central corneal thickness measurements were taken intraoperatively with the online OCP and ultrasound pachymeter before flap creation. The precision repeatability, intraclass correlation coefficient, and correlation of variation for each instrument was calculated. Intraclass correlation coefficient was based on Bland-Altman plot of differences between instruments. RESULTS: Mean central corneal thickness for ultrasound pachymetry and online OCP was 559.45+/-33.05 microm (range: 475.50 to 650.50 microm) and 521.19+/-28.97 microm (range: 447.50 to 606.00 microm), respectively. The precision (repeatability) was 7.86 microm and 9.47 microm, respectively. The intraclass correlation coefficient for the ultrasound pachymeter was 0.997 (95% CI, 0.993-0.998) and 0.993 (95% CI, 0.988-0.996) for the online OCP. The coefficient of variance was 0.50% and 0.66%, respectively. The mean difference between ultrasound pachymetry and online OCP was 38.26+/-9.96 microm. The limits of agreement were: upper=58.19 microm (95% CI, 53.30-63.07 microm) and lower=18.34 microm (95% CI, 13.45-23.22 microm). CONCLUSIONS: Online OCP can be used as a reliable alternative to ultrasound pachymetry as both instruments gave highly repeatable measurements of central corneal thickness. However, measurements using the OCP were consistently lower than those with the ultrasound pachymeter; therefore, the two techniques should not be used interchangeably. Further studies are needed to determine the implications of thinner central corneal thickness measured with online OCP as well as to resolve the systematic differences in measurements by these pachymetric technologies.     

Central corneal thickness in children with congenital glaucoma

PURPOSE: To evaluate central corneal thickness in children with congenital glaucoma. MATERIAL AND METHODS: Central corneal thickness was measured with the use of ultrasound pachymeter in 49 eyes of 30 children, with congenital glaucoma aged 0-12 years. RESULTS: Mean central corneal thickness was 462 microm. Very wide differences between minimum and maximum recorded values were observed (380-780 microm). Three groups of patients could be distinguished: with very thin cornea of 380-450 microm (73% children), with normal corneal thickness of about 550 microm (15%) and with very thick cornea of 680-780 microm (12% patients). CONCLUSIONS: 1. Mean central corneal thickness in children with congenital glaucoma is significantly thinner than in healthy children in the same age and in adult patients with glaucoma. A very wide differences between minimum and maximum recorded values, are observed in these patients. 2. The results of applanation tonometric measurements are underestimated in most cases or less frequently overestimated. 3. The measurements of central corneal thickness should be performed in every patient with congenital glaucoma to correct the IOP values.     

Central corneal thickness and measured IOP: a clinical study.

PURPOSE: We have attempted to document that the pachometer used in primary eye care practices will show the same corneal thickness relationship with measured intraocular pressure (mIOP) as the research studies. A second purpose of the study is to determine what role, if any, corneal thickness has on the increase in mIOP with age. METHODS: Sonogage Corneo-Gage Plus ultrasound central corneal thickness (CCT) measurements were taken on 101 white ocular hypertensive (OHT) patients with mIOP at or above 21 mmHg, as measured by Goldmann tonometry, and compared with age-matched controls with mIOP of 16 mmHg or less. To evaluate the impact of CCT on mIOP with age, a subset of patients was selected from the subjects and controls who had had a Goldmann tonometry reading recorded more than 10 years before the collection of the study data. RESULTS: The mean age of the (OHT) patients was 65.3 years +/- 12.3. The average CCT of the OHT patients was 595 pm +/- 36 microm, and for the control patients the average CCT was 554 microm +/- 34 microm. This difference was statistically significant (P < 0.0001). Evaluation of the age subset revealed that patients with thick corneas showed a 1.22 mmHg increase in mIOP per decade, whereas the patients with thin corneas showed a 0.69 mmHg decrease in mIOP per decade. This difference was statistically significant (P = 0.0001). This study demonstrates the same relationship between corneal thickness and mIOP in clinical practice as has been reported from research settings. This finding suggests that knowledge of corneal thickness is necessary to adjust the mIOP to better monitor and evaluate patients for glaucoma risk in the primary eye care practice. Of more significance is the finding that mIOP increases in the thick cornea patients over time. This suggests an age-related change in corneal resistance to applanation that impacts on mIOP measurements. More study is needed pertaining to the role of CCT on mIOP.     

A comparison of two pachymetric systems: slit-scanning and ultrasonic.

PURPOSE: This article compares measurements of corneal thickness obtained with the Orbscan Topography System with those obtained with the ultrasonic pachymeter, when used to measure central-comeal thickness in normal subjects. METHODS: Slit-scan topography (Orbscan II system, version 3.0, Bausch & Lomb, Rochester, NY) and ultrasonic pachymetry (Ophthasonic A-Scan/ Pachometer III, Accutome, Malvern, PA) were used to measure central-corneal thickness in 92 right corneas of 92 healthy adult subjects. A correlation analysis was used to evaluate the relationship between both instruments. Measurements were also compared by plotting the difference between the methods against the average. The hypothesis of zero bias was examined by a paired t-test. The 95% limits of agreement also were calculated. RESULTS: The mean corneal thickness was 559.9 microm +/-3.73 SEM with the Orbscan system and 551.2 microm +/- 4.57 SEM with the ultrasonic pachymeter, values that were significantly different (paired t-test, P = 0.000). The coefficient of determination was 0.860 (y = -65.78 + 1.135 x; P = 0.000). The mean difference between the measurements from both devices was found to be significantly different from zero (mean: 8.74 microm; paired t-test; P = 0.000), with Orbscan being slightly higher than the Ophthasonic A-Scan. CONCLUSIONS: The Orbscan system measurements of central corneal thickness were greater than ultrasonic pachymeter measurements, a difference that was statistically significantly.     

Corneal thickness is reduced in dry eye.

PURPOSE: To evaluate and compare corneal thickness in normal and dry eyes. METHODS: The Orbscan corneal topography system was used to measure the corneal thickness at nine locations in the central and peripheral (superior, superonasal, nasal, inferonasal, inferior, inferotemporal, temporal, superotemporal) cornea in 38 eyes of 21 patients with aqueous tear deficiency dry eye and 34 eyes of 21 normal subjects. RESULTS: The average thickness of nine sites in the central and midperipheral cornea was significantly decreased in dry eyes compared with that of normal eyes. The superior cornea was found to be the thickest area in both groups, measuring 0.629 +/- 0.030 mm in normal eyes and 0.589 +/- 0.031 mm in dry eyes. The center of the cornea was noted to be the thinnest in both groups, measuring 0.571 +/- 0.028 mm and 0.534 +/- 0.034 mm in normal and dry eyes, respectively. In color-coded pachymetry maps, the oval pattern was observed in 67.6% of normal corneas and 39.5% of dry eyes, while the decentered oval pattern was noted in 2.9% and 31.6% of normal and dry eyes, respectively (p < 0.025 for oval pattern and p < 0.005 for decentered oval map). The mean astigmatism was 0.99 +/- 0.43 diopter (D) in normal corneas and 1.42 +/- 0.92 D in dry eyes (p = 0.015). In the anterior elevation maps, the island pattern was the most commonly observed pattern in both groups, 88.3% in normal corneas and 60.5% in dry eyes (p < 0.01). No significant difference in the patterns of posterior corneal elevation maps and axial power maps of the anterior corneal surface was noted between groups. CONCLUSION: The corneal thickness of the central and midperipheral cornea was significantly decreased in the dry eyes. It is possible that the chronic state of desiccation and immune activation in dry eye may contribute to the observed corneal thinning. Perhaps the frank corneal ulceration that occurs in some dry eyes is a more severe manifestation of this phenomenon.     

Central corneal thickness in high myopia

PURPOSE: To examine if central corneal thickness (CCT) is different in emmetropia and high myopia. METHODS: 57 emmetropic subjects (0 to + 1.5 D) and 48 high myopes (all more than - 6 D in spherical equivalent refraction) were studied. CCT was measured by a Haag-Streit Optical Low-Coherence Reflectometry (OLCR) pachymeter, a recently developed high precision pachymeter with a standard deviation (SD) for repeated measurements of 1 microm. RESULTS: Mean CCT for the emmetropic group was 538.6 microm (SD = 32.1), and for the myopic group 527.7 microm (SD = 35.0). Neither the mean CCT nor the variance from the two groups showed a statistically significant different (p > 0.05). CONCLUSION: CCT is not systematically altered in myopia. The process by which the myopia progresses does not to a measurable degree influence the central cornea.     

Comparison of optical low-coherence reflectometry and ultrasound pachymetry in measuring corneal graft thickness

PURPOSE: To compare optical low-coherence reflectometry (OLCR) and ultrasound pachymetry in measuring corneal graft thickness in patients after keratoplasty. METHODS: We retrospectively measured the central graft thickness in 41 eyes of 41 patients with the OLCR pachymeter (Haag Streit, Koeniz, Switzerland) and the SP-2000 contact ultrasound pachymeter (Tomey, Nagoya, Japan). Five separate measurements were performed on each eye with both methods. Mean, SD, repeatability, and coefficient of variation of measurements were calculated, and the correlation between the 2 methods was studied with Spearman regression. RESULTS: Mean central graft thickness was 546 +/- 51 (SD) microm with the contact ultrasound pachymeter and 546 +/- 47 microm with the OLCR pachymeter. The correlation between both methods was strong (rs = 0.96). No significant differences in mean SD of measurements were observed between OLCR pachymetry (mean SD = 4.66 microm) and contact ultrasound pachymetry (mean SD = 4.88 microm). The repeatability of both methods was comparable (P = 0.06) and high (the average coefficient of variation of the central corneal graft thickness was 0.9% with both pachymeters). The postoperative time did not affect the correlation between both pachymeters (P > 0.05). CONCLUSIONS: Central corneal graft thickness values obtained with the OLCR pachymeter were similar to those obtained with a contact ultrasound pachymeter. In some cases of lamellar keratoplasty, the corneal refractive index could change at the interface level that could affect OLCR measurements.     

Corneal epithelial thinning profile induced by long-term wear of hydrogel lenses

PURPOSE: To characterize the epithelial thickness profile and study the effects of long-term wear of hydrogel lenses on this profile. METHODS: A cross-sectional study was designed. Epithelial thickness was evaluated in 15 subjects who had worn one of two types of low oxygen transmissibility (Dk) hydrogel contact lenses for an average of 10 years (range, 7-16) and compared with a group of 18 control subjects who had never worn contact lenses. Epithelial thickness was measured at the center and at four mid-peripheral and four peripheral locations in the vertical and horizontal meridians of the cornea using a modified optical pachymeter. RESULTS: Lens wearers had significantly thinner epithelium than controls [analysis of variance (ANOVA), p < 0.001] in the central (41 +/- 7 microm versus 48 +/- 5 microm), mid-peripheral (41 +/- 7 microm versus 48 +/- 7 microm), and peripheral (42 +/- 9 microm versus 48 +/- 6 microm) cornea. The extent of this difference ranged from 8.7% to 18.4% of the total epithelial thickness, was not associated with the duration of wear (ANOVA, p = 0.87, power = 0.05), and was significantly greater for the lower Dk contact lens type (ANOVA, p < 0.001). Topographical position did not have a significant effect on epithelial thickness (ANOVA, p > 0.13, power > 0.22). CONCLUSION: This study establishes that the epithelial thinning associated with hydrogel lens wear is topographically uniform. It also confirms that this effect is inversely related to lens oxygen transmissibility but does not appear to increase with longer duration of wear.     

Corneal thickness values before and after oxybuprocaine 0.4% eye drops

PURPOSE: To determine changes in corneal thickness after topical anesthesia. METHODS: Corneal thickness was measured before and 3 minutes after administration of two drops of oxybuprocaine 0.4% to 26 patients (26 eyes). We analyzed the corneal thickness of a control group, which was made up of 26 patients (26 eyes) before and 3 minutes after administration of two drops of saline solution. Corneal thickness was measured with the Orbscan Topography System II (Bausch Lomb Surg., Barcelona). RESULTS: Variations higher than +/- 10 microm were found following the instillation of 2 oxybuprocaine eye drops in eight eyes (30.76%) at the inferonasal cornea, in six eyes (23.08%) at the superotemporal, temporal and inferotemporal cornea, in five eyes (19.23%) at the nasal cornea, in three eyes (11.53%) at the central cornea, and in two eyes (7.69%) at the superonasal cornea. Nevertheless, no significant differences in the mean corneal thickness at each corneal location between the first and the second corneal thickness measurements were found in anesthetized eyes. CONCLUSIONS: Some individuals can present important increases and decreases in corneal thickness values after anesthetic eye drops. This effect of anesthetic eye drops must be considered by refractive surgeons when carrying out preoperative laser in situ keratomileusis corneal thickness measurements.     

Cornea in Marfan disease: Orbscan and in vivo confocal microscopy analysis

PURPOSE: To investigate corneal thickness, curvature, and morphology with the Orbscan Topography System I (Bausch & Lomb, Inc., Salt Lake City, UT) in patients with Marfan syndrome (MFS) and to study MFS with in vivo confocal microscopy. METHODS: This prospective, clinical, comparative case series included 60 eyes of 31 patients with MFS and 32 eyes of 17 control subjects. First, biomicroscopic examination was conducted to search for ectopia lentis. Then, mean keratometry and ocular refractive power were calculated by the autokeratorefractometer. In each group, the Orbscan System I mean (and mean simulated) keratometry and pachymetric measurements (at the central location and at eight midperipheral locations) were obtained and compared, and correlations were established. In vivo confocal microscopy was performed to evaluate tissue morphology and Z-scan analysis of 14 thin MFS corneas compared with 14 control corneas. RESULTS: A significant decrease (ANOVA, P < 0.0001) of mean simulated keratometry measurement appeared in the MFS group (sim K, 40.8 +/- 1.4 D) compared with the control group (42.9 +/- 1.1 D). Pachymetry in the MFS group was significantly decreased (P < 0.0001) compared with that in the control group, in the center (respectively, 502 +/- 41.9 microm and 552 +/- 23.6 microm) and the eight midperipheral locations. Ectopia lentis was highly linked with mean keratometry and pachymetry (P < 0.0001). Confocal microscopy performed on MFS-affected thin corneas confirmed the corneal thinning and showed an opaque stromal matrix, and Z-scan profiles were abnormal with increased stromal back scattering of light. CONCLUSIONS: MFS is known to be associated with a flattened cornea. This study demonstrated an association with corneal thinning and described confocal microscopy findings in this syndrome.