Comparison of glistenings in intraocular lenses with three different materials: 12-year follow-up.

PURPOSE: To compare the degree of lens glistenings associated with three intraocular lenses (IOLs) of different materials and examine the relationship between the dioptric power of the optics and lens glistenings in a long-term study. SETTING: St. Erik Eye Hospital, Stockholm, Sweden. METHODS: Forty-six eyes of 46 patients underwent standard phacoemulsification and implantation with a heparin-surface-modified (HSM) polymethylmethacrylate (PMMA) IOL, a silicone IOL or a hydrophobic acrylic IOL. Evaluations of the patients and the glistenings were conducted 11.3-13.4 years postoperatively. The glistenings were examined using Scheimpflug imaging and subsequently analysed using an image analysis program. RESULTS: The median follow-up time was 12.2 years (range, 11.3-13.4). The hydrophobic acrylic IOL had significantly more lens glistenings than the silicone (p = 0.003) and the PMMA (p = 0.000) IOLs. The silicone IOL had significantly more lens glistenings than the PMMA lens (p = 0.048). The IOL power did not affect the degree of lens glistenings in the hydrophobic acrylic IOL group (p = 0.64). The other groups had too little lens glistenings to evaluate the relationship. CONCLUSION: In this long-term follow-up study, the hydrophobic acrylic IOL had a significantly higher degree of lens glistenings compared to the silicone and PMMA IOLs. The PMMA IOL had almost no lens glistenings. The IOL dioptric power was not significantly correlated with the degree of lens glistenings associated with the hydrophobic acrylic IOL.

Phakic refractive lens: two-year results.

PURPOSE: To evaluate the surgical outcome and adverse events associated with correction of myopia and hyperopia with a phakic refractive lens (PRL), and to determine the random errors of the analytical methods used in the trial. METHODS: In this prospective clinical study, 14 myopic and 6 hyperopic PRLs were implanted in 20 eyes of 20 patients from April to November 2002. Follow-up included evaluation of the PRL rotation with retroillumination photography, the distance between the PRL and crystalline lens with Scheimpflug images, laser flare meter, endothelial cell count, uncorrected (UCVA) and best spectacle-corrected visual acuity (BSCVA), refraction, intraocular pressure, and induced cataract. The random errors of the measurements with laser flare meter were 17%, with Scheimpflug images 10%, and with endothelial cell count 2.8%. RESULTS: Postoperatively, 25% of eyes gained 2 or more lines and no eye lost 2 or more lines of BSCVA. Mean UCVA was 0.89 +/- 0.34. Laser flare values returned to baseline at 3 months and had no changes at 1 or 2 years (P > .05). The PRL rotated less during the second year than the first year. The distance between the PRL and crystalline lens was less at 1 year than at baseline (P < .05) but had no change during the second year. No statistically significant endothelial cell loss was noted between 1 week and 1 or 2 years postoperatively (P > .05). Two (10%) eyes developed pupillary block, one (5%) hyperopic eye showed unexpected postoperative myopia, and in another hyperopic eye (5%) the horizontal iris transillumination defects were noticed at 1 year combined with slight pupil ovalization at 2 years. No induced cataract, glaucoma, or inflammation was observed. CONCLUSIONS: Safety and efficacy indexes were high at 2-year follow-up. The distance between the PRL and crystalline lens decreased by 59% during the first year but seemed to stabilize thereafter. The PRL rotated in only a few eyes after the first year.

Clinical application of the lens haptic plane concept with transformed axial lengths.

PURPOSE: To clinically evaluate the lens haptic plane (LHP) concept in combination with thick-lens ray tracing for intraocular lens (IOL) power calculation. SETTING: St. Erik's Eye Hospital, Stockholm, Sweden. METHODS: Prospective study of normal cataract cases implanted with Pharmacia CeeOn 809C IOL. Axial length was measured by A-scan. The measured value was first transformed by addition of a constant value to correct for systematic error. Using the transformed axial length and corneal radius measured by keratometry, the LHP position was determined. Knowing the IOL design and the power implanted, expected refractive outcome was calculated and compared to manifest refraction at 6 weeks in terms of mean absolute error (MAE). Thick-lens ray tracing in the paraxial limit was used for the optical calculation. RESULTS: The mean transformed axial length was 23.87 mm. An LHP position algorithm in linear terms of transformed axial length and corneal radius gave an MAE of 0.38 D. There was no trend with axial length. On the present data, the Holladay 1, Hoffer Q, and SRK/T formulas produced MAEs of 0.39 D, 0.39 D, and 0.41 D, respectively, with optimized formula constants. The differences were not statistically significant (P > .05). CONCLUSIONS: The LHP concept in combination with thick-lens ray tracing achieved MAE comparable to that with currently used formulas. The lack of trend with axial length is important for patients with short and long eyes.

Comparison of 2 A-scans.

PURPOSE: To compare 2 A-scan instruments with regard to differences in measured results for the same patient sample. SETTING: St. Erik's Eye Hospital, Stockholm, Sweden. METHODS: In a study to evaluate the lens-haptic plane concept of intraocular lens (IOL) power calculation, 148 patients eligible for cataract surgery were measured with 2 different A-scan instruments (BVI Axis and Sonomed 1500). The axial length (AL), anterior chamber depth (ACD), and lens thickness (LT) results were analyzed for systematic differences and random errors. RESULTS: The Sonomed 1500 measured systematically longer than the BVI Axis for AL (0.41 mm) and ACD (0.28 mm), although the correlation was good (r = 0.99 and r = 0.87, respectively). The LT correlated poorly (r = 0.18) and showed no systematic trend. The relative random errors (standard deviations) in ACD (7.2%) and LT (18.6%) were larger than that of the AL (0.8%). The systematic difference in the AL corresponds to a 1.0 diopter difference in the A-constant. CONCLUSIONS: The large random errors in the ACD and LT reduce their value as predictors of postoperative IOL position in formulas that use them. Systematic differences in AL can be large enough to require separate formula constants for different pieces of equipment. If this is the situation in 1 setting, there is a risk of mistakes. This confusion could be avoided if there were an agreed standard and a universal calibration procedure for instruments intended for AL measurement.

Reduction of trend errors in power calculation by linear transformation of measured axial lengths.

PURPOSE: To find a method to improve the refractive outcome in short eyes and long eyes without sacrificing the outcome in normal eyes. SETTING: St. Erik's Eye Hospital, Stockholm, Sweden. METHODS: In a prospective study, 148 patients eligible for cataract surgery were measured with 2 different A-scans (BVI Axis, B.V. International; Sonomed 1500, Sonomed Inc.). Refraction was determined 6 weeks postoperatively. The postoperative refraction was compared with the refraction predicted by the Holladay 1, Hoffer Q, and SRK/T formulas; formula constants were optimized to give a zero mean error. The mean absolute error (MAE) was used as an outcome measure. RESULTS: The BVI Axis measured consistently shorter than Sonomed 1500. The mean axial lengths (ALs) were 23.033 mm and 23.435 mm, respectively. With the BVI Axis, an MAE of 0.44 diopter (D), 0.44 D, and 0.47 D was obtained, with the Holladay 1, Hoffer Q, and SRK/T formulas, respectively, with a trend toward undercorrecting short eyes and overcorrecting long eyes. The MAE with the Sonomed 1500 was 0.38 D, 0.39 D, and 0.40 D, respectively. By adding 0.402 mm to each measured value in the BVI Axis data set, the mean AL was transformed to 23.435 mm. With the transformed data, the MAE improved to 0.42 D, 0.43 D, and 0.44 D, respectively, with a reduced trend toward undercorrection and overcorrection. The 0.04 D difference between the instruments, although not statistically significant, may depend on measurement precision. Extending the concept of transformation, a minimum MAE of 0.41 D was obtained with the Holladay 1 at a mean AL of 24.0 mm, 0.43 D with Hoffer Q at 23.9 mm, and 0.40 D with SRK/T at 24.4 mm. The trend toward undercorrection and overcorrection was eliminated at the optimum for each formula. CONCLUSIONS: There were systematic differences in measured AL depending on equipment. Thus, the calculated powers differed and caused error in the degree of compliance between the labeled formula constant of an intraocular lens and the equipment used. Although personalization of formula constants reduces the mean error, in general a trend toward undercorrection of short eyes and overcorrection of long eyes will persist. Transforming the AL scale can eliminate the trend error and improve the overall refractive outcome. Transformation to a population mean AL of about 24.0 mm was close to optimum for the 3 formulas.

Healon5: comparison of 2 removal techniques.

PURPOSE: To evaluate the effect on intraocular pressure (IOP) of the rock 'n roll and behind-the-lens techniques of removing Healon(R)5 (sodium hyaluronate 2.3%). SETTING: St. Erik's Eye Hospital, Stockholm, Sweden. METHODS: In a prospective randomized study of 159 patients, 2 techniques to remove Healon5--rock 'n roll and behind-the-lens--were compared during cataract surgery. Cataract surgery included identical phacoemulsification performed by 1 surgeon and implantation of a silicone intraocular lens (IOL) in the capsular bag. The removal time of Healon5 was recorded. The IOP was measured preoperatively and 5 and 24 hours postoperatively. RESULTS: The mean IOP before surgery was 15.7 mm Hg +/- 2.8 (SD) in the rock 'n roll group and 15.9 +/- 2.7 mm Hg in the behind-the-lens group. Five hours postoperatively, the mean IOP was 25.6 +/- 10.4 mm Hg and 22.4 +/- 7.6 mm Hg, respectively; the difference between the groups was statistically significant. By 24 hours postoperatively, the mean IOP was at preoperative levels in both groups. The mean removal time of Healon5 was 50 seconds in the rock 'n roll group and 39 seconds in the behind-the-lens group; the difference between the groups was statistically significant. CONCLUSIONS: Results indicate that the behind-the-lens technique for removing Healon5 is quicker and safer than the rock 'n roll technique.

Anterior chamber depth measurement: a-scan versus optical methods.

PURPOSE: To evaluate methods of measuring anterior chamber depth (ACD) before and after cataract surgery. SETTING: St. Erik's Eye Hospital, Stockholm, Sweden. METHODS: A-scan (BVI Axis) and Scheimpflug imaging (Nidek EAS-1000) were used to measure ACD preoperatively and 6 and 18 weeks after phacoemulsification with implantation of a poly(methyl methacrylate) (PMMA) intraocular lens (IOL) in 23 patients. Because of a large systematic difference between the 2 methods, measurement with Orbscan (Orbtek) and optical pachymetry (Haag-Streit) were included when measurements were repeated 36 weeks postoperatively. A t test for paired observations was used for statistical analysis. RESULTS: Preoperatively, the mean A-scan measurements were significantly shorter than the Scheimpflug values: 3.05 mm +/- 0.36 (SD) and 3.37 +/- 0.35 mm, respectively (P < .001). At 6 weeks, the difference was more pronounced: 3.73 +/- 0.26 mm and 4.65 +/- 0.33 mm, respectively (P < .001). At 36 weeks, the A-scan and Scheimpflug values remained unchanged. The results of the Scheimpflug measurements were confirmed with optical pachymetry and Orbscan analysis. CONCLUSIONS: There was good agreement between results obtained with 3 methods based on optical principles. Considering the basic and simple measurement principle of these instruments, they appear to provide the correct result. The A-scan equipment used in this study is unsuitable for determination of ACD in eyes with PMMA IOLs.