Contrast sensitivity with silicone and poly(methyl methacrylate) intraocular lenses.

PURPOSE: To compare the optical performance of silicone intraocular lenses (IOLs) with that of conventional poly(methyl methacrylate) (PMMA) IOLs. SETTING: University hospital outpatient cataract clinic. METHODS: Ninety-one patients were randomly assigned to receive a PMMA IOL (n = 48 eyes) or a silicone IOL (n = 43 eyes). Contrast sensitivity was evaluated 4 months after surgery using the Vistech sinusoidal-grating chart and the Pelli-Robson letter sensitivity chart. RESULTS: No between-group differences were found using the Vistech test. Using the Pelli-Robson test, mean uncorrected contrast sensitivity was 1.59 log units +/- 0.13 (SD) in the PMMA group and 1.53 +/- 0.15 log units in the silicone group. Mean best corrected contrast sensitivity was 1.67 +/- 0.11 and 1.63 +/- 0.16, respectively. The differences between groups using the Pelli-Robson test were statistically significant (P < .05). No correlation was found between reduced contrast sensitivity and brownish discoloration or thickness of silicone IOLs or posterior capsule fibrosis. CONCLUSION: Contrast sensitivity was lower in patients with silicone IOLs than in those with conventional PMMA lenses.

Corneal versus scleral tunnel incision in cataract surgery: a randomized study.

PURPOSE: To compare the induced regular and irregular astigmatism after scleral and corneal tunnel incision. SETTING: University hospital outpatient cataract clinic. METHODS: One hundred phacoemulsification patients with less than 1.0 diopter (D) of preoperative astigmatism were randomly assigned to have a clear corneal incision (50 patients) or a scleral tunnel incision (50 patients). All incisions were 3.5 to 4.0 mm wide and were made in the steepest axis of the corneal astigmatism. The surgically induced astigmatism was analyzed by vector analysis from keratometric data, as well as by Fourier harmonic series analysis of the topographic data. RESULTS: One day after surgery, the surgically induced astigmatism (vector analysis, keratometry) was 1.41 D +/- 0.66 (SD) and 0.55 +/- 0.31 D in the corneal incision group and the scleral incision group, respectively (P < .01). Six months after surgery, the induced astigmatism was 0.72 +/- 0.35 D and 0.36 +/- 0.21 D in the two groups, respectively (P < .01) The corneal topography data confirmed the regular astigmatism changes found by conventional keratometry. However, in addition, Fourier harmonic series analysis of the topography data showed significantly more irregular induced astigmatism with the corneal approach than with the scleral approach. CONCLUSION: The clear corneal incision induces significantly more regular as well as irregular astigmatism than the scleral tunnel incision.

Induced astigmatism after 4 and 6 mm scleral tunnel incision. A randomized study.

PURPOSE: To study the surgically induced astigmatism after phacoemulsification through either a 4 or a 6 mm scleral tunnel incision by using multiple analyses of astigmatism. METHODS: 197 eyes from 186 patients scheduled for phacoemulsification between October 1992 and March 1994 were randomly assigned two different-sized incisions with follow-ups at 1 day, 1 week, 2 weeks, 1 month and 4 months after surgery. The surgically induced astigmatism was evaluated using at each follow-up: 1) The subtraction method, 2) vector analysis, 3) vector decomposition, 4) Cravy's vertical vector, 5) Naeser's polar values, and 6) the algebraic method. RESULTS: By subtraction, without regard to axis, the induced astigmatism 4 months after surgery was +0.04 D and +0.18 D in the 4 mm and the 6 mm incision group, respectively. By vector analysis, the numerical value of the induced cylinder was stable one month after surgery at 0.61 D and 0.77 D in the 4 mm and in the 6 mm group, respectively. However, cylinder orientation was not found stable until 4 months after surgery, where 94% and 96% of the surgically induced astigmatism (vector decomposition) was against-the-wound in the two groups, respectively. By Cravy's method, the mean induced astigmatism changed from -0.08 D to -0.32 D and from -0.42 D to -0.60 D between 1 and 4 months in the 4 mm and the 6 mm group, respectively. Similar values were found with Naeser's method and with the algebraic method. CONCLUSION: We conclude the mean cylinder of the surgically induced astigmatism (vector analysis) to be stable 1 month after phacoemulsification with both the 4 mm and 6 mm scleral tunnel incision. However, the direction of the induced axis (vector decomposition) was still drifting between 1 and 4 months in both groups. These astigmatic changes were adequately described using vector analysis and vector decomposition.

Evaluating surgically induced astigmatism by Fourier analysis of corneal topography data.

PURPOSE: To evaluate surgically induced astigmatism using Fourier harmonic series analysis of corneal topography data. SETTING: Aarhus Kommunehospital, Aarhus University, Denmark. METHODS: We evaluated the results of 46 phacoemulsifications with a 4 or 6 mm scleral tunnel sutureless incision based on the axis of the steepest meridian. We performed conventional keratometry and corneal topography before and up to 1 month after surgery. Using Fourier analysis, the corneal topographic images were broken into spherical power, regular astigmatism, and nonregular astigmatism for individual or aggregate analysis of surgically induced astigmatism. The induced refractive change (average of the difference between preoperative and postoperative corneal topographies) was analyzed and normalized according to the surgical meridian and to right/left eye. RESULTS: Regular astigmatism calculated by Fourier analysis of mires from the keratometer zone correlated well with conventional keratometry readings. Surgery induced a localized flattening in the superior region and a with-the-rule regular astigmatism component in the central area. CONCLUSION: Surgically induced corneal topography changes can be analyzed by Fourier series harmonic analysis, allowing aggregate data to be broken into optically meaningful quantities.

Evaluating surgically induced astigmatism.

Using a modification of vector analysis for calculating surgically induced astigmatism, we describe a simple method that divides the induced cylinder into two orthogonal components. This decomposition allows with-the-rule and against-the-rule astigmatic changes to be calculated for individual case analysis, as well as for statistical analysis of aggregate data. Because it is based on the true induced cylinder, as determined by optical principles, this method overcomes some of the problems associated with earlier methods of evaluating surgically induced astigmatism.

[Cataract surgery using phacoemulsification]. / Operation af grå staer med phacoemulsifikation.

Clinical results are reported in a consecutive series of 111 patients undergoing cataract surgery by phacoemulsification. On the first day after surgery, 69% of all cases had a visual acuity of 20/40 or better without any spectacle correction. Four months later this percentage had increased to 79%. Compared with a series of patients, operated by conventional extracapsular extraction, the corneal astigmatism was found to be significantly reduced in the phacoemulsification series (p < 0.001). The decrease in surgically induced astigmatism together with tailoring of the power of the intraocular lens (IOL) accounted for the good unaided visual acuity in the phacoemulsification group. Phacoemulsification is concluded to offer good optical control of the postoperative refraction in cataract patients.

Refractive results after phacoemulsification and ECCE. A comparative study.

The refractive results were evaluated in 79 patients undergoing cataract extraction by phacoemulsification using a 6-7 mm tunnel incision, and compared with a group of 77 patients undergoing planned extracapsular cataract extraction (ECCE) by the same surgeon. A mean increase in the keratometric cylinder of 0.05D and 0.52D was found in the phacoemulsification and the extracapsular cataract extraction group, respectively. This was significantly different from zero for the extracapsular cataract extraction group (p < 0.05) but not for the phacoemulsification group (p > 0.05). By vector analysis, the mean surgically induced astigmatism was 0.91D and 1.36D in the phacoemulsification and the extracapsular cataract extraction group, respectively (p < 0.01). The IOL power prediction error (spectacle plane) was found to be 0.17D (+/- 0.69 SD) in the phacoemulsification group and 0.02 D (+/- 0.79 SD) in the extracapsular cataract extraction group, respectively. We conclude that phacoemulsification improves the surgical control of the refractive outcome of cataract surgery.