Corneal refractive power and eccentricity in the 40- to 64-year-old population of Shahroud, Iran

Corneal Eccentricity in a Rural Japanese Population: The Locomotive Syndrome and Health Outcome in Aizu Cohort Study (LOHAS)

PURPOSE

To determine normal corneal eccentricity in a rural Japanese population and to examine factors associated with eccentricity value.

METHODS

This used data from the Locomotive Syndrome and Health Outcome in Aizu Cohort Study (LOHAS) project between 2009 and 2012. Residents of Minamiaizu and Tadami in Fukushima, Japan, who were aged 40 years or over, were invited for a comprehensive eye examination. For 1371 patients with no history of internal eye surgery, corneal eccentricity was measured using a Pentacam.

RESULTS

Of 1371 people recruited to the study, 1215 (1215 eyes) met the inclusion criteria. The overall mean eccentricity was 0.46 (SD = 0.18; range, -0.85 to 0.88). Corneal eccentricity was significantly associated with age, spherical equivalent, pupil diameter, anterior chamber angle, anterior chamber volume, and central corneal thickness, but not with gender or body mass index.

CONCLUSIONS

In this study, the normal cornea in this Japanese population was prolate. Corneal eccentricity was likely to decrease with increasing age. Also, spherical equivalent and other anterior segment parameters had an influence on corneal eccentricity. Corneal eccentricity measurements might be helpful in the diagnosis of corneal diseases and in calculations for intraocular lens implantation and corneal refractive surgery.

Distribution of Eccentricity in Children Aged 6-12 Years

PURPOSE

To determine the distribution of eccentricity and its association with some biometric and demographic parameters.

METHODS

In this cross-sectional study, the target population was primary school children aged 6 to 12 years from Shahroud, northeast Iran. Scheimpflug imaging was done using the Pentacam. Multiple linear regression analysis was applied to study the association between Eccentricity (ECC) and independent variables like age, sex, living place as well as biometric parameters.

RESULTS

Of the 6624 selected students, 5620 participated in the study of whom 4968 were eligible for analysis in this study. About half (52.4%) of the students were boys. The mean ECC was 0.600 (95% CI: 0.597-0.602) in total, 0.597 (95% CI: 0.594-0.600) in boys and 0.603 (95% CI: 0.599-0.607) in girls. The mean ECC was 0.611 in 6-year-old and 0.588 in 12-year-old children. The mean ECC was 0.590 in rural and 0.601 in urban children. The mean ECC was 0.600, 0.604, and 0.604 in emmetropic, myopic, and hyperopic children, respectively. Multiple linear regression analysis showed that ECC decreased with age (Coefficient: -0.004; 95%CI: -0.006 to -0.003), was higher in urban areas (Coefficient: 0.008; 95%CI: 0.002 to 0.014), had a direct association with axial length, and had an indirect association with lens thickness, central corneal thickness, and anterior chamber depth.

CONCLUSION

The cornea had a prolate shape in children and eccentricity value decreased with age. The results of this study add to the existing knowledge and can be used in differentiating normal from abnormal corneal shapes in children.

Anterior chamber dimensions, angles and pupil diameter in patients with Down syndrome: A comparative population-based study

Purpose

To study the anterior chamber (AC) dimensions, angles and pupil diameter (PD) in patients with Down syndrome compared to normal controls.

Methods

Prospective study is comparing the AC parameters in patients with Down syndrome aged 10-30 years and age-matched controls. Extracted indices included average anterior chamber depth on the 2-mm ring (ACD-2 mm), 4-mm ring (ACD-4 mm), at the corneal apex from the endothelium (endo-ACD), at the corneal apex from the epithelium (epi-ACD), anterior chamber volume (ACV), mean anterior chamber angle (ACA), and PD measured by Pentacam.

Results

Data from 202 patients with Down syndrome (age 17.2 ± 4.8 years) were compared with 190 normal controls (age 17.2 ± 4.5 years). In Down and normal groups, mean ± SD were 2.51 ± 0.31 and 2.83 ± 0.34 mm for ACD-2 mm, 1.65 ± 0.30 and 1.93 ± 0.31 mm for ACD-4 mm, and 3.03 ± 0.29 and 3.24 ± 0.26 mm for endo-ACD, 3.54 ± 0.29 and 3.80 ± 0.26 mm for epi-ACD, mean 169.31 ± 30.38 and 200.17 ± 33.20 mm³ for ACV, 40.69 ± 4.50 and 39.97 ± 4.12° for ACA, and 2.79 ± 0.62 and 3.59 ± 0.80 mm for PD, respectively (all P < 0.001). None of the studied indices significantly correlated with age, except for ACA (P = 0.011). All parameters, except for PD, were significantly higher in males compared to females (all P < 0.001). Temporal ACA was significantly wider in male subjects (44.61 ± 6.52 vs. 42.24 ± 6.52°; P < 0.001).

Conclusion

The AC in patients with Down syndrome is smaller than normal individuals. AC in females with Down syndrome is smaller than males, and the narrower ACA is attributable to the difference in the temporal angle and not the ACA in other meridians.

The normal distribution of corneal eccentricity and its determinants in two rural areas of north and south of Iran

Purpose

The aim of this study was to determine the distribution of corneal eccentricity (E-value) in a normal population and to examine related factors.

Methods

In this cross-sectional study, two villages were selected in Iran using multistage cluster sampling. Selected persons were invited to have a comprehensive eye examination. Examinations in each village were performed at a specific location under standard conditions. After testing for vision and refraction and conducting the slit-lamp exam, E-value was measured with Pentacam.

Results

Of the 3851 selected individuals, 3314 participated in the study. After applying the exclusion criteria, data from 2610 subjects was used in the analysis for this report. Mean E-value was 0.53 [95% confidence interval (CI): 0.52 to 0.54]. E-value was not significantly different between males and females. Mean E-value reduced with age from 0.60 in subjects aged 6–20 years to 0.47 in subjects older than 70 years. The hyperopic group of participants had significantly lower E-value than myopic and emmetropic ones (P < 0.001). The relationship of E-value with age, gender, and other anterior segment variables and spherical equivalent was examined in a multiple linear regression model. In multiple linear regression model, age (coef = −0.003), spherical equivalent refraction (coef = −0.005), pupil diameter (coef = 0.018), anterior chamber volume (coef = −0.001), and anterior chamber angle (coef = 0.003) significantly correlated with E-value.

Conclusions

The results of this study showed that the cornea in normal populations is prolate, and the degree of prolateness varies by age, such that older age is associated with a less prolate cornea. This study showed that factors such as age and refractive errors and anterior chamber indices influence the E-value.

Two-year results of femtosecond assisted LASIK versus PRK for different severity of astigmatism

Purpose

To compare two-year results of femtosecond laser assisted LASIK (femto-LASIK) and photorefractive keratectomy (PRK) in terms of astigmatism correction in patients with less than 2.0 diopters (D) of spherical error and more than 2.0 D of cylinder error.

Methods

In this retrospective study, data were extracted from 100 patient charts. The two study groups were matched by age, gender, and baseline uncorrected distance visual acuity (UDVA) and refractive astigmatism (RA). Preoperative astigmatism was categorized as mild: 2.00 to <3.00 D, moderate: 3.00 to <4.00 D, and severe: ≥4.00 D.

Results

Mean RA in the femto-LASIK and PRK groups was respectively -3.15 ± 0.94 D (-7.00 to -2.00 D) and -3.29 ± 0.95 D (-6.25 to -2.00 D) at baseline (P = 0.284), and -0.61 ± 0.40 D and -0.62 ± 0.60 D one year after surgery (P = 0.674), but significantly lower in the femto-LASIK group (-0.61 ± 0.39 vs. -0.83 ± 0.56 D, P = 0.021) at 2 years when the rate of residual astigmatism more than 1.0 D was 6.3% in the femto-LASIK and 19.6% in the PRK group (P = 0.046). Mean UDVA in the femto-LASIK group (0.02 ± 0.05 logMAR) was better than the PRK group (0.06 ± 0.10 logMAR) (P = 0.025). Mean corrected distance visual acuity (CDVA) was not significantly different between groups (0.01 ± 0.03 vs. 0.01 ± 0.04 logMAR, P = 0.714). Both groups had 1-4 Snellen lines CDVA improvement. The three subgroups of baseline astigmatism did not differ significantly in terms of residual astigmatism (all P > 0.05). However, in subgroups with ≥4.00 D cylinder, there was less astigmatic regression at 1 year in the femto-LASIK group (0.28 ± 0.43 D) than the PRK group (0.54 ± 0.68 D) (P = 0.007).

Conclusions

Our results pointed to better two-year results with femto-LASIK in the treatment of different degrees of astigmatism. UDVA improvement was superior with femto-LASIK, but the two methods did not significantly differ in terms of CDVA improvement.

Biometry and visual function of a healthy cohort in Leipzig, Germany

Background

Cross-sectional survey of ocular biometry and visual function in healthy eyes across the life span of a German population aged 20 to 69 years (n = 218). Subject number in percent per age category reflected the percentage within the respective age band of the population of Leipzig, Germany.

Methods

Measurements obtained: subjective and objective refraction, best-corrected visual acuity, accommodation, contrast sensitivity, topography and pachymetry with Scheimpflug camera, axial length with non-contact partial coherence interferometry, and spectral-domain optical coherence tomography of the retina. Pearson correlation coefficients with corresponding p-values were given to present interrelationships between stature, biometric and refractive parameters or their associations with age. Two-sample T-tests were used to calculate gender differences. The area under the logarithmic contrast sensitivity function (AULCSF) was calculated for the analysis of contrast sensitivity as a single figure across a range of spatial frequencies.

Results

The results of axial length (AL), anterior chamber depth (ACD) and anterior chamber volume (ACV) differed as a function of the age of the participants (rho (p value): AL −0.19 (0.006), ACD −0.56 (< 0.001), ACV-0.52 (< 0.001)). Longer eyes had deeper ACD (AL:ACD 0.62 (< 0.001), greater ACV (AL:ACV 0.65 (< 0.001) and steeper corneal radii (AL:R1ant; R2ant; R1post; R2post 0.40; 0.35; 0.36; 0.36 (all with (< 0.001)). Spherical equivalent was associated with age (towards hyperopia: 0.34 (< 0.001)), AL (−0.66 (< 0.001)), ACD (−0.52 (< 0.001)) and ACV (−0.46 (< 0.001)). Accommodation was found lower for older subjects (negative association with age, r = −0.82 (< 0.001)) and contrast sensitivity presented with smaller values for older ages (AULCSF −0.38, (< 0.001)), no change of retinal thickness with age. 58 % of the study cohort presented with a change of refractive correction above ±0.50 D in one or both eyes (64 % of these were habitual spectacle wearers), need for improvement was present in the young age-group and for older subjects with increasing age.

Conclusion

Biometrical data of healthy German eyes, stratified by age, gender and refractive status, enabled cross-comparison of all parameters, providing an important reference database for future patient-based research and specific in-depth investigations of biometric data in epidemiological research.

Trial registration

ClinicalTrials.gov # NCT01173614 July 28, 2010

Effect of anterior chamber depth on the choice of intraocular lens calculation formula in patients with normal axial length

Purpose:

To compare the accuracy of  Sanders-Retzlaff-Kraff II (SRK II) and 3^rd and 4^th generation intraocular lens (IOL) formulas and to compare the effect of different anterior chamber depths among the IOL formulas in cataract patients with normal axial length (AL; 22.0-24.5 millimeters, mm).

Materials and Methods:

A retrospective chart review was performed of patients with normal AL who underwent cataract surgery. The SRK II and 3^rd generation IOL formulas (Hoffer Q, SRK T, Holladay 1) were compared to the 4^th generation Haigis formula. For analysis, preoperative anterior chamber depth (ACD) was divided into three subgroups: ≤3, 3-3.5, and ≥ 3.5 mm. The mean error (ME) and mean absolute error (MAE) of each formula was compared for each subgroup against the total. The difference between the ME and MAE of the formulas were compared for each ACD subgroup. P < 0.05 was considered statistically significant.

Results:

The study sample was comprised of 309 eyes. The MAE were 0.56 D, 0.52 D, 0.51 D, 0.50 D, and 0.50 D with Haigis, Hoffer Q, SRK T, Holladay 1, and SRK II formulas, respectively. The Haigis formula was a significantly weaker predictor than the SRK T (P < 0.001) and Holladay 1 (P = 0.035) formulas. The ME with Haigis formula was -0.23 D which changed to -0.06 D with ACD ≥ 3.5 mm (P = 0.002). The ME was -0.24 D with SRK II and changed to -0.09D with ACD ≤ 3 mm (P = 0.004). There was no statistically significant difference between Hoffer Q, SRK T, and Holladay formulas 1 in ACD subgroups (P > 0.05, all comparisons).

Conclusion:

The SRK II formula can predict refraction in patients with normal AL and ACD less than 3 mm with less error and is preferred over other formulas. The Haigis formula is the preferred choice in patients with a normal AL and ACD longer than 3.5 mm. The prediction accuracy of Hoffer Q, SRK T, and Holladay 1 is comparable in normal AL.

Agreement study of keratometric values measured by Biograph/LENSTAR, auto-kerato-refractometer and Pentacam: decision for IOL calculation

BACKGROUND

The aim was to determine the agreement in keratometric readings measured with the Biograph/LENSTAR, the Pentacam and an auto-kerato-refractometer in a 40- to 64-year-old population.

METHODS

This report is part of the first phase of the population-based Shahroud Cohort Eye Study. In virgin eyes, agreement among keratometry readings of three devices was examined in 7,260 eyes using the Bland-Altman method. The inter-device 95 per cent limits of agreement (95% LoA) and 95% confidence interval for upper and lower limits of agreement were calculated. Comparisons were made for keratometric readings of the flat and steep meridians as maximum keratometry (max-K), minimum keratometry (min-K) and their average (mean-K).

RESULTS

Based on Biograph/LENSTAR measurements, averages of max-K, min-K and mean-K were 44.70 ± 1.64, 43.87 ± 1.54 and 44.28 ± 1.58 D, respectively. The quantile-quantile plot revealed that all three variables had normal distributions in this population. Agreement between the Biograph/LENSTAR and the auto-kerato-refractometer (max-K difference: -0.03 D, 95% LoA: -0.81 to 0.75; min-K difference: -0.08 D, 95% LoA: -0.85 to 0.68) was better than the agreement between the Biograph/LENSTAR and the Pentacam (max-K difference: 0.50 D, 95% LoA: -3.24 to 4.25; min-K difference: 0.59 D, 95% LoA: -3.00 to 4.17). The agreement between the Pentacam and the auto-kerato-refractometer (max-K difference: 0.54 D, 95% LoA: -3.16 to 4.24; min-K difference: 0.66 D, 95% LoA: -0.77 to 0.53) was worse than the other two pairs.

CONCLUSION

These three devices are not interchangeable in terms of keratometry for calculation of the intraocular lens power. Agreement between the Biograph/LENSTAR and the auto-kerato-refractometer can be increased with regression models but this is not true in case of Biograph/LENSTAR and Pentacam.

The prevalence of astigmatism and its determinants in a rural population of Iran: the "Nooravaran Salamat" mobile eye clinic experience

Purpose:

The prevalence of astigmatism, and the astigmatic axis, and their determinants were evaluated in a rural population of Iran.

Materials and Methods:

In a cross-sectional study conducted from May to August 2011, 13 villages in the vicinity of the city of Khaf in northeast Iran were investigated in this study. All the examinations including visual acuity, refraction, slit-lamp biomicroscopy and fundoscopy were performed in a Mobile Eye Clinic. Written informed consent was obtained from all participants. Only phakic eye that could be reliably refracted without a previous history of ocular surgery were included.

Results:

Out of 2635 participants who were screened, 2124 were analysed for this study of whom 52% were female. The prevalence of astigmatism was 32.2% (95% confidence intervals (CI): 30.2-34.2). Astigmatism significantly increased from 14.3% in the under 15-year-old age group to 67.2% in the age group of over 65-years old (P < 0.001). The prevalence of With-The-Rule (WTR), Against-The-Rule (ATR), and oblique astigmatism was 11.7%, 18.1%, and 2.4 %, respectively. ATR significantly increased with age (P < 0.001). The mean corneal astigmatism was 0.73 D which linearly increased with age (P < 0.001).

Conclusion:

Attention must be paid to astigmatism in rural areas due to the high prevalence. Further studies are suggested to discover the role of the environmental and genetic factors. It seems that environmental and occupational factors in the villages cause a significant increase in the prevalence of astigmatism with age. A high percentage of participants had ATR astigmatism, which was more common at older ages.

Evaluation of anterior segment parameters and possible influencing factors in normal subjects using a dual Scheimpflug analyzer

PURPOSE

To investigate normal anterior segment parameters and analyze the possible influencing factors using a dual Scheimpflug system.

SETTING

Department of Ophthalmology, Affiliated Sixth People's Hospital Shanghai Jiao Tong University, Shanghai, China.

DESIGN

A prospective observational case series.

METHODS

A total of 153 normal subjects (153 eyes) were studied. The anterior segment parameters, including the central corneal thickness (CCT), anterior chamber depth (ACD), pupil diameter (PD), keratoconus prediction index (KPI), simulated keratometry (SimK) values, anterior instantaneous curvature (AIC), posterior axial curvature (PAC), corneal eccentricity, total corneal power (TCP), axial curvature (AC), total corneal wavefront (TCW), high order aberration (HOA), and spherical aberration (SA), were determined using a dual Scheimpflug analyzer.

RESULTS

The CCT and ACD were both negatively correlated with age (r = -0.203, p = 0.012; r = -0.589, p<0.001). There was no significant difference in the refractive indices of AIC and SimK. Compared with the negative correlation of HOA and SA (r = -0.358, p<0.001), a positive correlation was found between TCW and HOA (r = 0.561, p<0.001). Unlike the decreased tendency of AC, the TCP increased gradually from the center to the periphery in the central 8 mm diameter. TCP showed a significant correlation with AC in the analyzed area.

CONCLUSIONS

AIC and SimK provide different information in clinic, but the refractive indices of them showed no difference in this healthy study population, and age should be considered when using CCT and ACD values.