Shiva Mehravaran

Central corneal thickness measurement with Pentacam, Orbscan II, and ultrasound devices before and after laser refractive surgery for myopia

PURPOSE: To determine the agreement in central corneal thickness (CCT) measurements between the gold standard method of ultrasound (US) pachymetry (UP‐1000, Nidek) and 2 noncontact systems based on Scheimpflug imaging (Pentacam, Oculus) and scanning‐slit topography (Orbscan II, Bausch & Lomb) in myopic eyes before and after laser refractive surgery. SETTING: Noor Vision Correction Center, Tehran, Iran. METHODS: In this prospective study, 30 consecutive patients having refractive surgery for myopia were enrolled. All 60 eyes were examined with the 3 devices preoperatively and 6 weeks after surgery; the US measurements were performed last. The Pentacam and Orbscan II CCT readings were compared with the US readings. Both the original and corrected Orbscan II readings were used in the analyses. RESULTS: The mean CCT readings with US, Pentacam, and Orbscan II were, respectively, 555 μm, 548 μm, and 580 μm before surgery and 478 μm, 468 μm, and 474 μm after surgery. Preoperatively, the 95% limits of agreement (LoA) with US were −31 μm and +19 μm for the Pentacam device and −5 μm and +57 μm for the Orbscan II device. Postoperatively, the LoA were −40 μm and +19 μm and −51 μm and +50 μm, respectively. Corrected Orbscan II measurements gave 95% LoA of −48 μm and +6 μm before surgery and −85 μm and +5 μm after surgery. CONCLUSIONS: Refractive surgery had a modest effect on the agreement between Pentacam readings and US measurements. With Orbscan II, the 95% LoA width nearly doubled after surgery. Although the Pentacam seems to show better agreement than Orbscan II, especially after refractive surgery, it is not advisable to use the 3 devices interchangeably in every clinical situation.

Corneal changes after laser refractive surgery for myopia: Comparison of Orbscan II and Pentacam findings

PURPOSE: To determine the agreement between scanning slit topography (Orbscan II, Bausch & Lomb) and Scheimpflug imaging (Pentacam, Oculus) in corneal elevation, corneal curvature, and anterior chamber depth (ACD) measurements before and after laser refractive surgery for myopia and to compare the postoperative changes seen with these devices. SETTING: Noor Vision Correction Center, Tehran, Iran. METHODS: In a prospective observational case‐series study, 23 consecutive myopic patients having laser refractive surgery were examined with the Orbscan II and Pentacam preoperatively and 6 weeks postoperatively. Readings of ACD, anterior (A‐) and posterior (P‐) best‐fit sphere (BFS) size, central elevation (CE), maximum elevation (ME), axial power in the 3.0 mm zone (AX3) and 5.0 mm zone (AX5), and tangential power in these zones (TG3 and TG5, respectively) were collected and used in the analyses. RESULTS: Statistically significant interdevice differences were found preoperatively for all parameters except P‐TG3 (P = .014) and in operated eyes for ACD, anterior parameters of A‐AX3 and A‐AX5, and all posterior corneal parameters. In posterior corneal measurements, Orbscan II demonstrated significant postoperative changes in all parameters except P‐AX5 (P = .004) and P‐TG5 (P = .034), although none of the differences was statistically significant with the Pentacam. The devices measured similar postoperative changes in anterior curvature parameters and in P‐AX5 and P‐TG5; all other changes were significantly different. CONCLUSIONS: Compared to the Pentacam, the Orbscan II yielded larger posterior elevation values before and after surgery and significant postoperative changes in P‐CE and P‐ME. Further studies can determine which device gives more accurate images of the cornea and redefine screening criteria.

The Prevalence of Refractive Errors and its Determinants in the Elderly Population of Mashhad, Iran

Purpose: To determine the prevalence rates of refractive errors in elderly people in Mashhad, Iran. Methods: In a cross-sectional study with a cluster sampling method, the sample population was selected proportionate to the total population of Mashhad. The selected citizens were then invited for eye examinations at the clinic. After an interview, refractive data were collected using objective and subjective refractions. Refractive error data were converted into spherical equivalent (SE), and myopia was defined as an SE worse than -0.50 diopters (D) and hyperopia worse than +0.50 D. Results: Of the 1540 selected samples, 93.5% participated in the study. Data were analyzed for 1367 adults without previous cataract surgery who had right eye refraction data; 35.4% were women, and 64.6% were men. The mean age was 63.7 ± 7.1 years. The prevalence of myopia was 27.2% (95% confidence interval (CI) 24.8–29.5); 29.6% in men and 22.5% in women (P < 0.001). The rate of myopia showed an increase with age (P < 0.001). The prevalence of hyperopia was 51.6% (95% CI, 48.9% to 54.3%); 57.6% in women and 48.3% in men (P < 0.001). The rate of hyperopia showed a significant decrease with age. The prevalence of astigmatism in the studied sample was 37.5% (95% CI, 34.9% to 40.0%). Conclusions: Refractive errors are a major issue among the elderly and their prevalence rates vary greatly depending on age and gender. The present study was able to examine this public health issue among the elderly in Mashhad.

Distribution of angle kappa measurements with Orbscan II in a population-based survey.

PURPOSE To determine the mean angle kappa and its determinants in the population of Tehran, Iran. METHODS In a cross-sectional survey with random cluster sampling, a total of 442 participants aged >14 years were selected from 4 municipality districts of Tehran for Orbscan acquisitions. Exclusion criteria were history of eye surgery for refractive errors, cataract or glaucoma, and use of topical medication or any type of contact lens at the time of the study. Mean angle kappa in different age and gender groups and its association with other factors was assessed. Considering the high correlation between the right and left eyes, only results of the right eyes are presented. RESULTS After applying exclusion criteria, 800 eyes (399 right eyes and 401 left eyes) were examined. Mean participant age was 40.6±16.8 years (range: 14 to 81 years), and 38.8% of eyes were from men. Mean angle kappa was 5.46±1.33° in total; 5.41±1.32° in men and 5.49±1.34° in women (P=.558). It decreased significantly with age; 0.015°/year (P<.001). In individuals with myopia, emmetropia, and hypermetropia, the mean value was 5.13±1.50°, 5.72±1.10°, and 5.52±1.19°, respectively (P=.025); the post-hoc test indicated this was due to the difference between emmetropes and myopes. CONCLUSIONS According to our results, angle kappa reduces with age, and the inter-gender difference is not significant. Largest angle kappas were seen among individuals with emmetropia. Angle kappas were larger in the hypermetropic population compared to the myopic population.

Corneal thickness in a population-based, cross-sectional study: the Tehran Eye Study.

Purpose: To determine the distribution of corneal thickness at 6 different points in an Iranian population and find any possible relationship between the thickness values and some independent variables. Methods: As part of the “Tehran Eye Study,” 410 people (800 eyes) aged 14 years and older, residing in the first 4 municipality areas of Tehran, were selected through a stratified random cluster sampling method. The participants were examined with Orbscan II to measure the corneal thickness at the central, thinnest, and 4 peripheral points of the cornea. In addition, the relationships between central corneal thickness (CCT) values and variables of age, sex, refractive error, pupil diameter, corneal diameter, anterior chamber depth (ACD), and body mass index were assessed. The design effect was also considered, and all estimates were standardized for age and sex. The reported results pertain to the right eyes only. Results: The mean thickness (±SD) at the central and thinnest points was 555.6 ± 39.9 and 550.7 ± 40.6 μm, respectively. The minimum corneal thickness was below 500 μm in 9.6% of the participants. The superior area showed the largest thickness, and the thinnest point was most commonly in the inferotemporal quadrant. The mean “distance” and “thickness difference” between the central and thinnest points were 0.52 ± 0.31 mm and 4.85 ± 6.2 μm, respectively, and they showed a significant direct relationship (r = 0.708 and P < 0.001). Neither sex had a significant relationship with thickness values at different areas. Participants younger than 20 years, compared with those older than 20, had significantly thicker corneas (P = 0.001 for the central and thinnest points, P < 0.001 for peripheral areas). In the multiple regression model, age and ACD showed significant inverse correlations with CCT. Conclusions: The mean CCT in the present study was 555.6 μm, which is relatively higher in comparison with that in other ethnic groups. In the multiple regression model, age and ACD were correlated with the CCT, but refractive errors showed no correlation.

White-to-white corneal diameter in the Tehran Eye Study.

Purpose: To determine the mean corneal diameter and its determinants in the population of Tehran. Methods: From the Tehran Eye Study participants who were sampled through a stratified cluster approach, those in the first 4 municipality districts of Tehran were selected, and after applying the inclusion and exclusion criteria, 399 right eyes and 401 left eyes of 410 people aged 14 years and older were examined with the Orbscan II. The corneal diameter was defined as the horizontal limbus-to-limbus distance. Linear regression was used to detect separate and multiple correlations. The design effect of cluster sampling was also considered and adjusted for. Results: The studied participants were male in 38.80%, and their mean age was 40.68 ± 16.80 years. The mean corneal diameter was 11.68 mm (95% confidence interval: 11.63-11.73). The 95% range (mean ± 2 SDs) was 10.76-12.60 mm. The mean corneal diameter was 11.76 and 11.63 mm in males and females, respectively. The corneal diameter in the studied population had no significant correlation with age (P = 0.186) but showed an increase of 0.18 mm for each millimeter increase in the anterior chamber depth (P = 0.028). Conclusion: Although the mean corneal diameter in the present population was not different from that reported in other studies, the data suggest that slightly different cutoff values for the definition of macrocornea (>12.60 mm) and microcornea (<10.76 mm) can be used with this population.

Effect of corneal thickness on the agreement between ultrasound and Orbscan II pachymetry

PURPOSE: To study the agreement between ultrasound (US) and Orbscan II (Bausch & Lomb) measurements with different ranges of central thickness in normal corneas. SETTING: Noor Ophthalmology Research Center, Tehran, Iran. METHODS: The central corneal thickness was measured first by the Orbscan II and then with a US pachymeter in 177 right eyes. Data were compared in 3 thickness groups: less than 500 μm, 500 to 600 μm, and more than 600 μm. In all cases, uncorrected Orbscan II data were used. For each range, a correction factor was calculated through regression analysis, which was then used in a new set of analyses. To study the agreement between the 2 methods, the 95% limits of agreement (LoA) and intraclass correlations coefficients (ICC) were determined. RESULTS: The mean interdevice difference was 2.7 ± 16.9 (SD) in the less than 500 μm group (P = .365), 21.3 ± 3.1 in the 500 to 600 μm group (P = .0001), and 27.2 ± 20.9 in the more than 600 μm group (P = .0001). No clinically acceptable LoA were found in any group. The application of regression equations to the Orbscan II readings improved the agreement in the less than 500 μm group better than the other 2 groups. The ICC was 0.76, 0.61, and 0.43 in the less than 500 μm, 500 to 600 μm, and more than 600 μm groups, respectively. CONCLUSIONS: The Orbscan corneal thickness readings had relatively lower validity than US measurements. The 2 devices should not be used interchangeably, especially when the validity of the measurement is vital. In patient screening for corneal surgery, it is advisable to recheck corneal thickness with a US pachymeter.

Five Year Cataract Surgical Rate in Iran

Purpose. To determine the number of cataract surgeries per million population per year or the cataract surgical rate (CSR) in Iran for every year from 2000 to 2005 as part of the objectives of the Vision 2020 initiative by the World Health Organization (WHO) to eliminate cataract blindness. Methods. This study is part of the Iranian Cataract Surgery Survey, which was conducted as a retrospective cross-sectional study. All major cataract surgery centers and 10% of randomly selected minor centers throughout the nation were approached. Excluding the 2-week Iranian New Year holiday, 1 week per season between 2000 and 2005 (a total of 24 weeks) was selected for each center, and data concerning all cataract surgeries performed during these weeks were recorded by reviewing records of patients operated for cataracts. Results. A total of 13,409 surgical records from 2000 to 2005 were evaluated, and CSR was calculated for each year based on the population data obtained from the Statistical Center of Iran. CSR showed an increasing trend in Iran, rising from 526 (95% confidence interval: 352 to 700) in year 2000 to 1331 (95% confidence interval: 1084 to 1577) in 2005. Conclusions. CSR has significantly increased in Iran in recent years but is still below the target suggested by WHO. Considering the age structure of the young population of Iran, the present CSR may suffice. However, it is necessary to implement plans to increase CSR and obviate obstacles to eliminating cataract blindness.

National Eye Institute Visual Function Questionnaire: usefulness in glaucoma.

ABSTRACT The National Eye Institute Visual Function Questionnaire 25 (NEI-VFQ-25) is the most commonly used patient-reported outcome measure to assess vision-related quality of life in patients with glaucoma. Glaucoma negatively affects the composite and several NEI-VFQ subscale scores; this effect is correlated with the severity of glaucomatous visual field loss. Contrast sensitivity, glare, and dark adaptation are potential items that could be added to the NEI-VFQ to make it more responsive to changes in vision-related quality of life in patients with glaucoma.

The distribution of corneal thickness in a 40- to 64-year-old population of Shahroud, Iran.

Purpose: To determine the distribution of central and peripheral corneal thickness values and its determinants in an Iranian population. Methods: This population-based study was conducted between 2009 and 2010 in Shahroud, with a response rate of 82.2%. Here in, we present the data on central and peripheral corneal thickness in 3890 participants of the study, which included all 40- to 64-year-old participants except those with a history of ocular surgery. Measurements were done with the Pentacam, and correlations with age, gender, height, body mass index, and refraction were tested. Results: The mean age (± standard deviation) of the participants was 50.7 years (±6.2 years). Mean corneal thickness in the thinnest point, the center, and 3 mm away from it in the inferior, superior, nasal, and temporal directions were 525.5 ± 35.9 μm, 528.5 ± 35.8 μm, 608.2 ± 39.8 μm, 635.5 ± 41.9 μm, 611.7 ± 43.2 μm, and 601.0 ± 40.4 μm, respectively. The thinnest point was in the inferotemporal quadrant in 87.5% of cases. The center of the cornea was thinner than 500 μm in 36.6% of myopic cases and 21.8% of hyperopic cases. The thickness and location difference between the center and thinnest point were statistically significant (P < 0.001). Central corneal thickness was directly correlated with refraction (P = 0.028) and inversely with age (P = 0.027). Conclusions: In this population-based study, the thinnest point was usually located inferotemporally and the thickest point superiorly. The peripheral cornea was significantly thicker than the central cornea but thinned faster with age. The thickness difference between the thinnest and central points was significantly greater in men. People with hyperopia had thicker corneas compared with those with myopia.