Use of various keratometry data (ring and zone) in trifocal IOL calculation

Purpose. To compare the results of trifocal IOL calculation using various corneal tomographic data (ring and zone). Methods. This retrospective study involved 46 patients (46 eyes), underwent cataract surgery with trifocal IOL implantation (AcrySof IQ PanOptix). The calculation was performed using Tomey OA-2000 according to 2 formulas (Barrett II Universal, Olsen). Keratometry values included Km (the average of two main meridians of a cornea) provided by Pentacam HR Power Distribution Apex map, which describes total corneal refractive power (TCRP) with diameter of 3.0, 4.0 and 5.0 mm on a ring and zone. Mean (MAE) and median (MedAE) predicted postoperative refraction errors were assessed after surgery. Results. Mean Km value on 3 mm zone and ring was: 42.75±1,46 D and 42,91±1,43 D, respectively (p<0,0001). Mean Km on 4 mm zone and ring was: 42.6±1.5 D and 43.3 ± 1.5 D, respectively (p <0.005). Mean Km value on 5 mm zone and ring was: 43,09±1,5 D and 43,55±1,48 D, respectively (p<0,0001). Calculations using the Barrett II Universal formula revealed significant difference between MAE and MedAE of the predicted postoperative refraction on 5mm zone and ring (p=0.045). When using the Olsen formula in the calculations, significant difference was revealed using the Km data with a diameter of 3 mm and 5 mm (p=0.001 и p=0.009, respectively). The calculation on 3 mm ring was more accurate than for 3 mm zone. With a 5 mm diameter, the calculation is more accurate according to the zone data. Conclusion. Mean Km value on Power Distribution Apex map according to ring is significantly greater then according to zone. 1) The calculation of the trifocal IOL based on the TCRP zone data is reliably more accurate than the ring data according to both formulas (Barrett II Universal and Olsen) with a diameter of 5 mm. 2) According to the Olsen formula with a diameter of 3 mm, the calculation of the optical power of trifocal IOL based on TCRP ring data is more accurate. Key words: IOL calculation, Trifocal IOL, corneal topography

Comparison of surgically induced astigmatism between anterior and total cornea in 2.2 mm steep meridian incision cataract surgery

Background This study aimed to compare surgically induced astigmatism (SIA) on the anterior and total cornea during cataract surgery through a 2.2 mm steep meridian incision. Methods The study included 69 left eyes of 69 patients who had undergone cataract surgery. The 69 eyes were classified into three subgroups according to the preoperative steep meridian. Following phacoemulsification, an intraocular lens was inserted into the bag. The keratometric measurements were taken 12 months postoperatively, on the anterior cornea (automated keratometer and anterior keratometry [K] from a rotating Scheimpflug camera) and total cornea (equivalent K reading [EKR] 3.0 mm, EKR 4.5 mm, total corneal refractive power (TCRP) 2.0 mm ring, TCRP 3.0 mm zone, TCRP 4.0 mm zone). The SIA was analyzed for each parameter. Results On the double-angle polar plot, the summated vector mean values of SIA determined by the automated keratometer and Scheimpflug anterior K were 0.28 diopter (axis: 177°) and 0.37 diopter (axis: 175°) in with-the-rule (WTR) astigmatism; 0.03 diopter (axis: 156°) and 0.18 diopter (axis: 177°) in oblique astigmatism; 0.15 diopter (axis: 96°) and 0.17 diopter (axis: 73°) in against-the-rule (ATR) astigmatism. The mean SIAs on the total cornea ranged from 0.31 to 0.42 diopter in WTR astigmatism; from 0.16 to 0.27 diopter in oblique astigmatism; from 0.04 to 0.11 diopter in ATR astigmatism. Mean magnitude SIA ranged from 0.41 to 0.46 diopter on anterior corneal surface and 0.50 to 0.62 diopter on total cornea. J0 and J45 of the posterior cornea showed no significant changes after cataract surgery, and the changes in J0 and J45 did not show any statistical differences between the anterior and total cornea (all p > 0.05). Conclusions There were no differences in the summed vector mean values of SIA between the anterior cornea and the total cornea.

Axial length and its associations in the Ural Very Old Study

To assess the distribution of axial length as surrogate for myopia and its determinants in an old population, we performed the Ural Very Old Study as a population-based cohort study. Out of 1882 eligible individuals aged 85 + years, the Ural Very Old Study performed in an urban and rural region in Bashkortostan/Russia included 1526 (81.1%) individuals undergoing ophthalmological and medical examinations with sonographic axial length measurement. Biometric data were available for 717 (47.0%) individuals with a mean age of 88.0 ± 2.6 years (range 85–98 years; 25%). Mean axial length was 23.1 ± 1.1 mm (range 19.37–28.89 mm). Prevalences of moderate myopia (axial length 24.5–< 26.5 mm) and high myopia (axial length ≥ 26.5 mm) were 47/717 (6.6%; 95% CI 4.7, 8.4) and 10/717 (1.4%; 95% CI 0.5, 2.3), respectively. In multivariable analysis, longer axial length was associated (coefficient of determination r2 0.25) with taller body height (standardized regression coefficient beta:0.16;non-standardized regression coefficient B: 0.02; 95% confidence interval (CI) 0.01, 0.03; P < 0.001), higher level of education (beta: 0.12; B: 0.07; 95% CI 0.02, 0.11; P = 0.002), and lower corneal refractive power (beta: − 0.35; B: − 0.23; 95% CI − 0.28, − 0.18; P < 0.001). Higher prevalence of moderate myopia, however not of high myopia, was associated with higher educational level (OR 1.39; 95% CI 1.09, 1.68; P = 0.007) and lower corneal refractive power (OR 0.77; 95% CI 0.63, 0.94; P = 0.01). In this old study population, prevalence of moderate axial myopia (6.6% versus 9.7%) was lower than, and prevalence of high axial myopia (1.4% versus 1.4%) was similar as, in a corresponding study on a younger population from the same Russian region. Both myopia prevalence rates were higher than in rural Central India (1.5% and 0.4%, respectively). As in other, younger, populations, axial length and moderate myopia prevalence increased with higher educational level, while high myopia prevalence was independent of the educational level.

Anthropometric measures and their relationship to corneal refractive power in the United States population

Purpose: To determine the relationship between anthropometric measures and corneal refractive power (CRP). Methods: Participants from the 1999-2008 United States National Health and Nutrition Examination Survey (NHANES) visual exam with demographic, ocular, and anthropometric data (20,165 subjects) were included. Cases with steep cornea were defined by corneal power ≥ 48.0 diopters (n = 171) while controls had dioptric power < 48.0 D (n = 19,994). Multivariable analyses were performed for pooled and sex-stratified populations. Separate models assessed body mass index, height, and weight in relation to steep cornea. Results: A relationship between BMI and steep cornea in the pooled population was not detected (P for trend = 0.78). There was a strong inverse relationship between height and steep cornea in the pooled population (P for trend <0.0001) and women (P for trend <0.0001). For every 1-inch increase in height, there was a 16% reduced odds of steep cornea in the pooled population (OR, 0.84; 95% CI: 0.78-0.91). There was also a significant inverse relationship between weight and steep cornea in the pooled population (P for trend = 0.01) and in men (P for trend = 0.02). For each 10-pound increase in weight there was a 7% reduced odds of steep cornea (OR, 0.927; 95% CI: 0.882-0.975) in the pooled analysis. Conclusions: Greater height and greater weight were associated with a lower risk of steep cornea. These findings can contribute to an improved understanding of the pathogenesis of corneal ectasias.

Evaluation of axial length/total corneal refractive power ratio as a potential marker for ocular diagnosis of Marfan’s syndrome in children

AIM: To investigate whether the axial length (AL)/total corneal refractive power (TCRP) ratio is a sensitive and simple factor that can be used for the early diagnosis of Marfan’s syndrome (MFS) in children. METHODS: The relationship between the AL/TCRP ratio and the diagnosis of MFS for 192 eyes in 97 children were evaluate. The biological characteristics, including age, sex, AL, and TCRP, were collected from medical records. Receiver operating characteristic (ROC) curve analysis was performed to investigate whether the AL/TCRP ratio effectively distinguishes MFS from other subjects. The Youden index was used to re-divide the whole population into two groups according to an AL/TCRP ratio of 0.59. RESULTS: Of 96 subjects (mean age 7.46±3.28y) evaluated, 56 (110 eyes) had a definite diagnosis of MFS in childhood based on the revised Ghent criteria, 41 (82 eyes) with diagnosis of congenital ectopia lentis (EL) were included as a control group. AL was negatively correlated with TCRP, with a linear regression coefficient of -0.36 (R2=0.08). A significant correlation was found between age and the AL/TCRP ratio (P=0.023). ROC curve analysis showed that the AL/TCRP ratio distinguished MFS from the other patients at a threshold of 0.59. MFS patients were present in 24/58 (41.38%) patients with an AL/TCRP ratio of ≤0.59 and in 34/39 (87.18%) patients with an AL/TCRP ratio of >0.59. CONCLUSION: An AL/TCRP ratio of >0.59 is significantly associated with the risk of MFS. The AL/TCRP ratio should be measured as a promising marker for the prognosis of children MFS. Changes in the AL/TCRP ratio should be monitored over time.

Predicting corneal refractive power changes after orthokeratology

This study aimed to characterise corneal refractive power (CRP) changes along the principal corneal meridians during orthokeratology (OK). Nineteen myopes (mean age 28 ± 7 years) were fitted with OK lenses in both eyes. Corneal topography was captured before and after 14 nights of OK lens wear. CRP was calculated for the central 8 mm cornea along the horizontal and vertical meridians. The central-paracentral (CPC) power ratio was calculated as the ratio between maximum central and paracentral CRP change from individual data. There was a significant reduction in CRP at all locations in the central 4 mm of the cornea (all p < 0.001) except at 2 mm on the superior cornea (p = 0.071). A significant increase in CRP was evident in the paracentral zone at 2.5, 3 and 3.5 mm on the nasal and superior cornea and at 3.5 and 4 mm on the temporal cornea (all p < 0.05). No significant change in CRP was measured in the inferior cornea except decreased CRP at 2.5 mm (p < 0.001). CPC power ratio in the nasal and temporal paracentral regions was 2.49 and 2.23, respectively, and 2.09 for both the inferior and superior paracentral corneal regions. Our results demonstrates that OK induced significant changes in CRP along the horizontal and vertical corneal meridians. If peripheral defocus changes are inferred from corneal topography, this study suggests that the amount of myopia experienced on the peripheral retina was greater than twice the amount of central corneal power reduction achieved after OK. However, this relationship may be dependent on lens design and vary with pupil size. CPC power ratios may provide an alternative method to estimate peripheral defocus experienced after OK.

The Spatial Distribution of Relative Corneal Refractive Power Shift and Axial Growth in Myopic Children: Orthokeratology Versus Multifocal Contact Lens

PurposeTo determine if the spatial distribution of the relative corneal refractive power shift (RCRPS) explains the retardation of axial length (AL) elongation after treatment by either orthokeratology (OK) or multifocal soft contact lenses (MFCLs).MethodsChildren (8–14 years) were enrolled in the OK (n = 35) or MFCL (n = 36) groups. RCRPS maps were derived by computing the difference between baseline and 12-month corneal topography maps and then subtracting the apex values. Values at the same radius were averaged to obtain the RCRPS profile, from which four parameters were extracted: (1) Half_x and (2) Half_y, i.e., the x- and y-coordinates where each profile first reached the half peak; (3) Sum4 and (4) Sum7, i.e., the summation of powers within a corneal area of 4- and 7-mm diameters. Correlations between AL elongation and these parameters were analyzed by multiple linear regression.ResultsAL elongation in the OK group was significantly smaller than that in the MFCL group (p = 0.040). Half_x and Half_y were also smaller in the OK group than the MFCL group (p &lt; 0.001 each). Half_x was correlated with AL elongation in the OK group (p = 0.005), but not in the MFCL group (p = 0.600). In an analysis that combined eyes of both groups, Half_x was correlated with AL elongation (β = 0.161, p &lt; 0.001).ConclusionsThe OK-induced AL elongation and associated RCRPS Half_x were smaller than for the MFCL. Contact lenses that induce RCRPS closer to the corneal center may exert better myopia control.

Effect of Gender, Age, and Ocular and Growth-Related Factors on Corneal Epithelial and Stromal Thickness in Children

Data on corneal epithelial and stromal thickness in school-aged children in relation to gender, age, and ocular and growth parameters are limited. In this retrospective study, we analyzed corneal epithelial and stromal thickness measured with the RTVue system (Optovue, Inc., Fremont, CA, USA) in 122 male and 201 female Korean children (mean age 9.59 ± 2.18 years) with myopia. We used simple and multiple regression analysis to establish the relationships between gender, age, refractive status, axial length, anterior chamber depth (ACD), corneal refractive power, white-to-white corneal diameter (WTW), height, and body weight. Age, body weight, height, and central corneal thickness were positively associated with corneal epithelial thickness, whereas WTW was negatively associated. The multiple regression analysis showed corneal epithelial thickness was affected by sex, body weight, WTW, and central corneal thickness (CCT), while stromal thickness was influenced by age, sex, and WTW. Both corneal epithelial and stromal thickness were significantly greater in male than in female children and were affected by growth. Neither corneal epithelial nor stromal thickness were associated with the severity of myopia, corneal refractive power, or axial length.