To analyze the accuracy of 18 intraocular lens (IOL) power calculation formulas in eyes with axial length (AL) ≤ 22 mm.We analyzed 241 eyes of 241 patients. Eighteen formulas were evaluated: Barret...

Purpose. To determine the significance of any association between intersessional changes in ocular residual astigmatism (RA) and astigmatism at corneal front (FSA) and back (BSA) surfaces following uneventful routine phacoemulsification.Methods. Astigmatism was evaluated by autorefractometry and subjective refraction and at both the corneal surfaces with Orbscan II (TM) (Bausch & Lomb) over central 3 mm and 5 mm optical zones at 1, 2, and 3 months after routine phacoemulsification in 103 patients implanted with monofocal nontoric intraocular lenses (IOLs, one eye/patient). Data were subjected to vector analysis to determine the actual change (Delta) in astigmatism (power and axis) for the refractive and Orbscan II findings.Results. The number of cases that attended where Delta RA was >= 0.50 DC between 1 and 2 months was 52 by autorefractometry and 36 by subjective refraction and between 2 and 3 months was 24 by autorefractometry and 19 by subjective refraction. Vector analysis revealed significant correlations between Delta FSA and Delta RA for data obtained by autorefractometry but not by subjective refraction. At all times, Delta BSA was greater than Delta FSA (p<0.01). Key findings for Delta BSA values over the central 3 mm zone were between (A) the sine of the axis of Delta RA (y) and sine of the axis of Delta BSA (x) for the data obtained by autorefractometry (between 1 and 2 months,y = 0.749 - 0.303x,r = 0.299,n = 52,p=0.031) and subjective refraction (between 2 and 3 months,y = 0.6614 - 0.4755x,r = 0.474,n = 19,p=0.040) and (B) Delta RA (y) and Delta BSA (x) powers between 2 and 3 months postoperatively for the data obtained by autorefractometry (Delta RA = 0.118 Delta BSA + 0.681r = 0.467,n = 24,p=0.021) and subjective refraction (Delta RA = 0.072 Delta BSA + 0.545r = 0.510,n = 19,p=0.026).Conclusion. Changes in the ocular residual refractive astigmatic error after implanting a monofocal nontoric IOL are associated with changes in astigmatism at the back surface of the cornea within the central optical zone.

Purpose: To noninvasively estimate the refractive index (RI) of the central cornea along the antero–posterior direction before and after routine phacoemulsification. Methods: Using 2 setups for a standard optical pachymeter, the ratio of observed optical section widths (OSWs) is a function of the RI. Thus, the corneal RI could be estimated using a calibration equating OSW ratios with known RI values. The OSW was measured by 2 observers for 1) normal subjects for estimating interoperator errors and effects of sex and age on the RI and 2) before and after patients underwent routine phacoemulsification. Results: First, the average interoperator difference (ΔRI) was +0.0005 (SD = ±0.0044, 95% confidence limit, −0.0002 to +0.0012). The root mean square difference between measurements obtained by the observers was 0.0032. There was a significant correlation between the ΔRI and the mean of each pair of measured values (r = −0.172, n = 153, P = 0.003). The mean RI (±SD) was 1.435 (±0.005, n = 82) for females and 1.429 (±0.005, n = 71) for males. There was no significant between-sex difference or association between the RI and age (mean age, ±SD, and range, 44.31, 20.38, and 19–88 years, respectively). Second, the difference (y) between the preoperative (x) and postoperative RI was, y = 0.844x − 1.203 (r = 0.694, n = 31, P ≤ 0.001) according to observer 1 and according to observer 2, y = 0.755x − 1.108 (r = 0.681, n = 31, P ≤ 0.001). Conclusions: The RI of the human cornea along the antero–posterior axis can be estimated using a modified application of traditional optical pachymetry. The average values for the corneal RI were higher compared with those reported in previous reports. The change in the RI after phacoemulsification could be predicted from the preoperative value.

Purpose: To explore the significance of changes in anterior chamber depth (ΔACD) and astigmatism between 4 and 8 weeks following uneventful phacoemulsification. Patients and Methods: Anterior chamber depth (ACD, mm), autorefractometry and subjective refraction were monitored in pseudophakic eyes implanted with non-toric IOLs (group 1, SA60AT, n=36; group 2, SN60WF, n=34; group 3, ICBOO, n=16) and phakic control group (n=30, group 4a, for ACD and autorefractometry) over four weeks. Changes in subjective refractions were compared with repeatability in normal phakic eyes (n=30, group 4b). Results: Reporting key results (p< 0.01), mean (±sd 95% CI) ΔACD values (ACD at start minus ACD at four weeks) were +0.02 (± 0.37, − 0.16 to 0.08), +0.22 (± 0.51,0.05 to 0.39), − 0.33 (± 0.51, − 0.58 to − 0.08), − 0.02 (± 0.07, − 0.04 to 0.01) in groups 1– 4a respectively. Differences were significant (1-way ANOVA, F=7.02). Pooling data from the pseudophakic eyes (n=86) induced astigmatism (IA) by autorefractometry was significantly greater in comparison with group 4a [− 0.78D (± 0.67, − 0.92 to − 0.64) and − 0.19D (± 0.16, − 0.25 to - 0.13)]. IA power correlated with the initial power of refractive astigmatism at 4 weeks (A), [IA = 0.36A− 0.30 (r²=0.207) and IA = 0.39A− 0.29 (r²=0.232) by autorefractometry and subjective refraction, respectively]. In groups 1– 3, vector analysis revealed i) the change in refraction in over 55% of eyes was beyond the 95% confidence interval limits observed in groups 4a and 4b, ii) some significant associations between changes in vectors describing astigmatism with ΔACD and IOL labelled power. Conclusion: Changes in ACD and refraction still occur four weeks after unremarkable phacoemulsification and the inter-relationship depends on IOL design/type. Other factors, such as tilt or dislocation of the IOL along the X-Y axes parallel to Listing’s plane, accompanying changes in ACD are expected to affect the postop astigmatism.