Accuracy of Intraocular Lens Power Calculation Using Anterior Chamber Depth from Two Devices with Barrett Universal II Formula

Expected vs. Actual Refractive Error in Patients Presenting With Phacomorphic Glaucoma

Aim

Phacomorphic glaucoma (PG) is a rare but clinically significant presentation requiring emergent cataract surgery. We chose to investigate whether the expected refractive error based on the intraocular lens (IOL) calculations differed from the expected refractive outcome post-surgery.

Materials & Methods

A retrospective analysis of patients with PG between 2009 to 2018 who underwent cataract surgery and had postoperative refraction was included. Information collected included presenting and postoperative best-corrected visual acuity (BCVA), intraocular pressure (IOP) pre­ and postoperatively, and the presence of corneal edema. Predicted spherical equivalence (SphEq) data was collected from IOL calculations, and postoperative SphEq was calculated from postoperative manifest refraction.

Results

Twenty patients with PG who underwent cataract surgery were identified; of these, 10 patients and 10 eyes who underwent manifest refraction post­op were included. Mean BCVA at presentation was 20/544 [Logarithm of Minimal Angle of Resolution (LogMAR) 1.44], and mean pre-op IOP was elevated at 24.6 ± 14.2 mmHg. Mean BCVA measured at one month post-op improved to 20/192 (LogMAR 0.983). Mean IOP decreased to 19 ± 8.8 mmHg at one month post-op. The mean difference between the predicted and actual refractive error, as calculated by SphEq was ­0.088 (p=0.570).

Conclusion

The study shows an improvement in visual acuity and IOP post-cataract surgery in patients with PG, as would be expected. The study also demonstrates that patients ended up with a slightly more myopic refractive error than expected postoperatively, and illustrates the clinical variability in postoperative refractive outcomes from a large standard deviation. This is a new and clinically important finding, although not statistically significant, that has not been previously published.

Effect of eyedrops and applanation tonometry on optical biometry

PURPOSE

To determine whether eyedrops (phenylephrine, tropicamide, and fluorescein-proparacaine) and Goldmann applanation tonometry (GAT) have an effect on optical biometry measurements for preoperative cataract surgery workup.

SETTING

George Washington University, Washington, DC.

DESIGN

Nonrandomized controlled trial.

METHODS

Participants older than 18 years with no contraindications to eyedrops or tonometry were recruited. Optical biometry measurements were obtained on a single eye using the Lenstar LS900. One drop each of phenylephrine, tropicamide, and fluorescein-proparacaine was applied to the same eye, and measurements were repeated. GAT was performed, and measurements were repeated. For controls, the contralateral eye was also measured at each interval.

RESULTS

There was no statistically significant difference in mean predicted postoperative refraction (PPOR) keratometry (K) 1, K2, or axis postdrops and post-GAT 62 eyes (n = 62). After drops were applied, mean central corneal thickness increased from 540 to 542 µm (P = .0002), mean anterior chamber depth (ACD) increased from 3.68 to 3.70 mm (P < .0001), and lens thickness (LT) decreased from 3.66 to 3.65 (P = .001). After GAT, ACD increased to 3.76 mm (P < .0001), and LT increased to 3.60 mm (P < .0001). There was no statistically significant difference in PPOR or other parameters for the control eyes (n = 5).

CONCLUSIONS

GAT and phenylephrine, tropicamide, and fluorescein-proparacaine drops did not affect the primary outcome of PPOR. This suggests that cataract surgery candidates do not need to return for a separate preoperative visit for optical biometry.

High Agreement between Barrett Universal II Calculations with and without Utilization of Optional Biometry Parameters

Purpose: To examine the contribution of anterior chamber depth (ACD), lens thickness (LT), and white-to-white (WTW) measurements to intraocular lens (IOL) power calculations using the Barrett Universal II (BUII) formula. Methods: Measurements taken with the IOLMaster 700 (Carl Zeiss, Meditec AG, Jena, Germany) swept-source biometry of 501 right eyes of 501 consecutive patients undergoing cataract extraction surgery between January 2019 and March 2020 were reviewed. IOL power was calculated using the BUII formula, first through the inclusion of all measured variables and then by using partial biometry data. For each calculation method, the IOL power targeting emmetropia was recorded and compared for the whole cohort and stratified by axial length (AL) of the measured eye. Results: The mean IOL power calculated for the entire cohort using all available parameters was 19.50 ± 5.11 diopters (D). When comparing it to the results obtained by partial biometry data, the mean absolute difference ranged from 0.05 to 0.14 D; p < 0.001. The optional variables (ACD, LT, WTW) had the least effect in long eyes (AL ≥ 26 mm; mean absolute difference ranging from 0.02 to 0.07 D; p < 0.001), while the greatest effect in short eyes (AL ≤ 22 mm; mean absolute difference from 0.10 to 0.21 D; p < 0.001). The percentage of eyes with a mean absolute IOL dioptric power difference more than 0.25 D was the highest (32.0%) among the short AL group when using AL and keratometry values only. Conclusions: Using partial biometry data, the BUII formula in small eyes (AL ≤ 22 mm) resulted in a clinically significant difference in the calculated IOL power compared to the full biometry data. In contrast, the contribution of the optional parameters to the calculated IOL power was of little clinical importance in eyes with AL longer than 22 mm.