Capsule complication during cataract surgery: Case-control study of preoperative and intraoperative risk factors: Swedish Capsule Rupture Study Group report 2.

PURPOSE: To identify preoperative and intraoperative factors associated with a capsule complication; that is, a capsule tear or a zonular dehiscence during cataract surgery. SETTING: Ten ophthalmic surgery departments in Sweden. METHODS: A retrospective review of files of patients with a capsule complication and control patients with no complication operated on in 2003 was performed. RESULTS: The review comprised 324 patients with a capsule complication and 331 control patients. In the logistic regression analyses, preoperative conditions associated with a capsule complication were previous trauma, white and brunescent/hard cataract, and phacodonesis. The intraoperative factors of loose zonules, the use of trypan blue, and miosis were all statistically significantly overrepresented in the capsule complication group. The same was true for eyes operated on by surgeons with the least experience. CONCLUSIONS: By preoperatively identifying cataract cases with the identified risk factors and allocating them to surgeons with the longest experience, the number of capsule complications could be kept low. Operating early in the course of the disease to prevent the cataract from becoming a poor surgical risk and improving training of junior surgeons should further reduce the frequency of capsule complications.

Evaluation of aqueous outflow facility in patients with high intraocular pressure after cataract surgery.

BACKGROUND AND OBJECTIVE: To study whether patients with a marked elevation of intraocular pressure (IOP) the day after cataract surgery may have a chronically impaired aqueous outflow. PATIENTS AND METHODS: In 128 consecutive patients, IOP was measured both preoperatively and the day after phacoemulsification and intraocular lens implantation. In the late postoperative period, aqueous outflow facility (C-value) was measured with pneumatonography in patients (n = 7) who experienced a postoperative IOP increase of at least 20 mm Hg and in patients (n = 11) with a difference between preoperative and postoperative IOP of not more than 2 mm Hg. RESULTS: Aqueous outflow facility was normal in both groups. Mean C-value was 0.32 +/- 0.18 microL/min/ mm Hg in the hypertensive group and 0.23 +/- 0.10 microL/ min/mm Hg in the normotensive group. The difference was not statistically significant (P = .20). CONCLUSIONS: Patients with marked IOP elevation the day after cataract surgery do not seem to have a chronically impaired aqueous outflow facility compared with normotensive patients.

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.

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.