Leif Corydon

Intraocular lens power calculation with an improved anterior chamber depth prediction algorithm

Abstract The accuracy of intraocular lens (IOL) power calculation was evaluated in a multicenter study of 822 IOL implantations using the Binkhorst II, Sanders/ Retzlaff/Kraff (SRK I™, SRK II™, SRK/T™), Holladay, and Olsen formulas. All but the first of these were optimized in retrospect with calculation of the SRK A‐constant, the Holladay surgeon factor, and the Olsen pseudophakic anterior chamber depth (ACD) for each lens style. The ACD prediction of the Olsen formula was based on a previously described regression formula incorporating preoperative ACD, corneal height, axial length, and lens thickness. Among the optical IOL power calculation formulas, the highest IOL power prediction error was found with Binkhorst’s and the lowest with Olsen’s, which was more accurate than the SRK/T and the Holladay formulas (P < .05). The SRK/T formula was significantly more accurate than the original SRK regression formulas (P < .001). When analyzed for axial length dependence, all formulas showed the least error in the normal range. Error of the Olsen formula was lower than that of the others in the axial length interval 20 mm to 26 mm. No differences in accuracy were found between the optical IOL calculation formulas in eyes with an axial length above 26 mm (P < .05). The accuracy of IOL power calculation can be improved with optical formulas using newer‐generation ACD‐prediction algorithms.

Effect of a plano-convex posterior chamber lens on capsular opacification from Elschnig pearl formation

ABSTRACT Opacification of the posterior capsule occurs most commonly from Elschnig pearl migration or fibrosis. The physical contact of a posterior chamber lens, particularly one with a reverse optic, has been postulated to decrease the rate of capsular opacification by creating a barrier to Elschnig pearl migration. This randomized prospective clinical study comparing the 3M style 34S convex‐plano optic and style 34R plano‐convex (reverse) optic posterior chamber lens demonstrated a statistically significant reduction in capsular opacification by Elschnig pearls at one year in the reverse optic lenses (18.2% versus 7.6%, P = .03). No statistically significant difference in capsular fibrosis rates was noted (2.5% versus 4.5%, P = .48). The reverse optic implant also demonstrated greater iris to implant optic clearance.

Accuracy of the newer generation intraocular lens power calculation formulas in long and short eyes.

ABSTRACT The accuracy of two newer generation theoretical intraocular lens (IOL) power calculation formulas and of the empirical SRK I and II formulas was evaluated in a series of 500 IOL implantations including a series of unusually long and short eyes. The prediction error of the theoretical formulas was found to be largely unaffected by the variation in axial length and corneal power, while the prediction of the SRK I formula was less accurate in the short and long eyes. The prediction of the SRK II formula was more accurate than the SRK I in that no systematic of Tset error with axial length could be demonstrated. However, because of a relatively larger scatter in the long eyes and a significant bias with the corneal power, the absolute error of the SRK II formula was higher than that of the theoretical formulas in the long eyes. The higher accuracy of the newer generation theoretical formulas was attributed to their improved prediction of the pseudophakic anterior chamber depth.

New multifocal intraocular lens design

ABSTRACT The first clinical experience with a new diffractive multifocal intraocular lens implanted in 55 eyes of 53 patients is reported. Excluding four patients with preoperative senile macular degeneration, the best corrected visual acuity was 20/40 or better and the near vision without any add to the best distance correction was J2 or better in all cases three, six, and 12 months postoperatively.

Contrast sensitivity as a function of focus in patients with the diffractive multifocal intraocular lens

ABSTRACT Contrast sensitivity as a function of focus and visual acuity as a function of contrast were investigated in 19 patients with a diffractive multifocal intraocular lens and compared with 19 control patients with a conventional monofocal implant. The contrast sensitivity of the multifocal patients followed a bimodal curve with a maximum sensitivity at the far focus and a second peak at the near focus, corresponding to about +3 diopters in the spectacle plane. The maximum sensitivity of the multifocal group was 0.14 log units lower than the control group (PÅ.05). In the near region, the contrast sensitivity of the multifocal patients exceeded that of the control group from + 2 diopters and inward. No difference in distance visual acuity was found with high contrast letters. With intermediate contrast letters, the visual acuity of the multifocal patients was lower than that of the control group (PÅ.05).

Posterior capsule fibrosis and intraocular lens design

ABSTRACT Four different posterior chamber lens designs were used in 1,845 consecutive, unselected extracapsular cataract extractions performed over a 31‐month period in Vejle, Denmark. Ninety‐seven eyes (5.3%) required a posterior capsulotomy during a postoperative observation period ranging from two to 32 months. At 16 months postoperatively, the cumulative capsulotomy rate was 7.1% with plano‐convex anterior lenses, but only 1.7% with meniscus lenses and 1.8% with continuous ridged lenses. These results suggest that close contact between the posterior capsule and the optic could induce early posterior capsule opacification.

Diathermic capsulotomy versus capsulorhexis: a biomechanical study.

Purpose: To compare the mechanical quality of a capsulotomy opening performed by diathermy with that made by capsulorhexis (tearing). Setting: Department of Ophthalmology, Vejle Hospital, Denmark. Methods: This study included 12 pairs of human cadaver eyes and 20 pairs of pig eyes. One in each pair was randomly selected for one capsulotomy technique. The capsulotomy edge was stretched in a materials testing machine until break; force and elongation values were continuously recorded. Results: In humans, the extensibility of the diathermic capsulotomy edge was approximately half that of the capsulorhexis edge (mean 38% ± 4 [SD] versus 68% ± 6), and the force required to break the edge was reduced by a factor of five (26 ± 8 mN versus 134 ± 36 mN). Conclusion: The mechanical quality of the diathermic capsulotomy edge is significantly less than that of the capsulorhexis edge, which indicates that the diathermic capsulotomy edge would withstand less surgical manipulation.

Theoretical versus SRK I and SRK II calculation of intraocular lens power

ABSTRACT The predictability of a theoretical, computerized (PC‐assisted) intraocular lens (IOL) power calculation method and of the Sanders‐Retzlaff‐Kraff [SRK] I and II methods was evaluated from preoperative and postoperative biometry in 202 cataractous patients who had extracapsular cataract extraction (ECCE). The theoretical method resulted in the lowest range and standard deviation of the error, and the highest correlation coefficient between the observed and the predicted refraction (P < .05). The superiority of the theoretical approach was most clearly demonstrated when the postoperative measurements were used in the predictions (P < .001). This demonstrated the potential accuracy of the formula used and the importance of incorporating methods to predict the IOL position after surgery. If the prediction of the IOL chamber depth was properly corrected for the axial length dependence, a high prediction accuracy could be obtained in short as well as in long eyes.

Contrast sensitivity in patients with a new type of multifocal intraocular lens

ABSTRACT Contrast sensitivity was measured in 13 pseudophakic eyes of ten patients who had a new type of diffractive multifocal intraocular lens (IOL) and compared with an age‐matched control group with a conventional monofocal IOL. All selected cases had a postoperative follow‐up of four to six months and a corrected visual acuity of 20/20 or better. For distance vision, no significant difference in contrast sensitivity could be found between the two groups, indicating an uncompromised distance focus of the multifocal IOL. For near vision, an overall decrease in the contrast sensitivity of 0.19 log units (mean value across the tested frequency from 1.5 to is cycles/deg) was found in the multifocal group when these patients were tested without near addition and compared with the controls with near addition (P < .05). This indicated the near focus of the nitiltifocal IOL to be somewhat less efficient than the far focus. We find these results promising for the new diffractive multifocal IOL.

Prediction of postoperative intraocular lens chamber depth

ABSTRACT The postoperative intraocular lens (IOL) chamber depth was predicted using a multiple linear regression analysis of the postoperative chamber depth as a function of the corneal height, the preoperative chamber depth, and the axial length in 279 patients with a posterior chamber lens implant. Based on a linear regression formula incorporating these preoperatively defined parameters, the postoperative IOL chamber depth could be predicted with a correlation coefficient of 0.71 and an error of ± 0.30 mm (SD). It is concluded that an individual prediction of the IOL chamber depth will improve the accuracy in IOL calculation.