Su Yeon Kang

Comparison of Hoffer Q and Haigis Formulae for Intraocular Lens Power Calculation According to the Anterior Chamber Depth in Short Eyes

PURPOSE To compare the accuracy of the Hoffer Q and Haigis formulae according to the anterior chamber depth (ACD) in cases of short axial length (AL). DESIGN Retrospective cross-sectional study. METHODS A total of 75 eyes from 75 patients with an AL of less than 22.0 mm implanted with an Acrysof IQ intraocular lens (IOL) were enrolled. The median absolute errors (MedAEs) predicted by the Hoffer Q and Haigis formulae were compared. The correlations between ACD and the predicted refractive error calculated using the 2 formulae were analyzed. RESULTS There were no significant differences in the MedAEs predicted by the Hoffer Q and Haigis formulae (0.40 and 0.40 diopter [D], respectively). The difference between the refractive errors predicted by the Hoffer Q and Haigis formulae increased significantly as the ACD decreased (R(2) = 0.644, P < .001). The MedAE predicted by the Haigis formula (0.40 D) was significantly smaller than that predicted by the Hoffer Q formula (0.66 D) in eyes with an ACD of less than 2.40 mm (P = .027). There were no significant differences found between the MedAEs predicted by the Hoffer Q and Haigis formulae in eyes with an ACD of 2.40 mm or more. CONCLUSIONS The differences between the predicted refractive errors of the Hoffer Q and Haigis formula increased as ACD decreased in short eyes. Therefore, ACD should be taken into consideration when evaluating the accuracy of the IOL power calculation formulae in short eyes.

Use of corneal power-specific constants to improve the accuracy of the SRK/T formula.

PURPOSE To evaluate the effect of average corneal power (K) and axial length (AL) in a data-adjusted A-constant for improving the refractive outcome in the Sanders-Retzlaff-Kraff (SRK)/T formula. DESIGN Retrospective, consecutive, case series. PARTICIPANTS A total of 637 patients (637 eyes) who underwent uncomplicated phacoemulsification with implantation of the Acrysof IQ (IQ; Alcon, Fort Worth, TX; 314 eyes) or Akreos AO (AO; Bausch & Lomb, Rochester, NY; 323 eyes) intraocular lens (IOL) by a single surgeon. METHODS The correlation among the K, AL, and predicted refractive error in the SRK/T formula was analyzed. Patients were divided into 2 subgroups, the first to calculate the different data-adjusted A-constants based on the K and the second to compare the median absolute error (MedAE) based on different A-constants with the traditional A-constant in the SRK/T formula. MAIN OUTCOME MEASURES The data-adjusted A-constant and the MedAE (diopters [D]). RESULTS The data-adjusted A-constant showed a decreasing trend as K increased. The data-adjusted A-constant was 119.04 in the IQ group and 118.27 in the AO group. The calculated A-constant was 119.33 in the IQ group and 118.57 in the AO group when the cornea was flatter than 43.0 D and 43.2 D, respectively. The A-constant was 118.71 in the IQ group and 117.96 in the AO group when the cornea was steeper than or equal to 44.7 D and 45.0 D, respectively. The MedAE decreased from 0.29 D to 0.23 D in the IQ group (P = 0.001) and from 0.44 D to 0.38 D in the AO group (P < 0.001) when different A-constants were used. The MedAE further decreased from 0.36 D to 0.24 D in the IQ group (P = 0.005) and from 0.58 D to 0.37 D in the AO group (P < 0.001) when subjects with K 1.00 D or more above or 1.00 D below the most accurate K in each group were compared. CONCLUSIONS For a steep cornea, the calculated A-constant was smaller than that of the entire K, but for a flat cornea, a larger A-constant was calculated. Using different A-constants based on the K improved the refraction outcomes relying on the SRK/T formula.

Which Keratometer is Most Reliable for Correcting Astigmatism with Toric Intraocular Lenses

Purpose To evaluate the accuracy of preoperative keratometers used in cataract surgery with toric intraocular lens (IOL). Methods Twenty-five eyes received an AcrySof toric IOL implantation. Four different keratometric methods, a manual keratometer, an IOL master, a Pentacam and an auto keratometer, were performed preoperatively in order to evaluate preexisting corneal astigmatism. Differences between the true residual astigmatism and the anticipated residual astigmatism (keratometric error) were compared at one and three months after surgery by using a separate vector analysis to identify the keratometric method that provided the highest accuracy for astigmatism control. Results The mean keratomeric error was 0.52 diopters (0.17-1.17) for the manual keratometer, 0.62 (0-1.31) for the IOL master, 0.69 (0.08-1.92) for the Pentacam, and 0.59 (0.08-0.94) for the auto keratometer. The manual keratometer was the most accurate, although there was no significant difference between the keratometers (p > 0.05). All of the keratometers achieved an average keratometric error of less than one diopter. Conclusions Manual keratometry was the most accurate of the four methods evaluated, although the other techniques were equally satisfactory in determining corneal astigmatism.

Comparison of meibomian gland loss and expressed meibum grade between the upper and lower eyelids in patients with obstructive meibomian gland dysfunction

Purpose: The aim of this study was to compare meibomian gland loss (MGL) and expressed meibum grade between upper and lower eyelids in patients with obstructive meibomian gland dysfunction (MGD) and to evaluate the correlation between these 2 parameters and other clinical measurements. Methods: Twenty-six eyes of 26 patients with obstructive MGD were enrolled. Upper and lower MGLs were evaluated using noncontact meibography. Expressed meibum quality was assessed in 8 glands of the central third area of the upper and lower eyelids on a scale of 0 to 3 for each gland (total score range, 0–24). Tear film stability was evaluated based on tear break-up time (TBUT), and corneal staining was graded according to the National Eye Institute scale (range, 0–15). Results: The mean MGL in the lower eyelids (24.1% ± 10.8%) was significantly greater than that of the upper eyelids (11.2% ± 5.2%) (P < 0.001). The mean expressed meibum grade in the lower eyelids (16.5 ± 5.1) was also significantly larger than that of the upper eyelids (11.2 ± 5.2) (P < 0.001). MGL was significantly correlated with expressed meibum grade in both eyelids (r = 0.451, P = 0.021 in the upper eyelids; r = 0.626, P = 0.001 in the lower eyelids). The meibum grades of both the upper and lower eyelids were negatively correlated with TBUT and positively correlated with corneal staining score. However, the MGL in both the eyelids was not correlated with TBUT or with corneal staining score. Conclusions: In patients with obstructive MGD, MGL and meibum grade in the lower eyelids were significantly greater than those of the upper eyelids. Although MGL and meibum quality showed a positive correlation with each other, TBUT and corneal staining score were significantly correlated with only meibum grade, and not with MGL.

Effect of effective lens position on cylinder power of toric intraocular lenses

OBJECTIVE To evaluate the effects of effective lens position (ELP) on the corneal plane effective cylinder power of toric intraocular lenses (IOLs). DESIGN Retrospective cross-sectional study. PARTICIPANTS Ninety-four eyes from 78 patients who underwent uncomplicated phacoemulsification with implantation of an AcrySof toric IOL (1.50- to 3.00-D cylinder). METHODS The amount of corneal plane effective cylinder power of toric IOLs given by the manufacturer (target-induced astigmatism vector [TIA]) was compared with the postoperatively achieved cylindrical correction (surgically induced astigmatism vector [SIA]). The theoretical corneal plane cylinder power of toric IOLs was calculated according to ELP and corneal power using a refractive vergence formula. RESULTS The TIA (1.59 ± 0.43 D) was significantly smaller than the SIA (1.78 ± 0.65 D; p < 0.001). The difference between the magnitudes of SIA and TIA demonstrated a significant negative correlation with ELP (r = -0.219 and p = 0.034). The theoretical corneal plane cylinder power of toric IOLs demonstrated a decreasing trend as the ELP and corneal power increased. The range of changes in corneal plane effective cylinder power according to ELP and corneal power was greater in toric IOLs with high toricity. CONCLUSIONS The cylinder power of AcrySof toric IOLs should be adjusted according to ELP. For eyes with small ELP, the cylinder power should be reduced, and for eyes with large ELP, the cylinder power should be increased. The amount of reducing or increasing cylinder power of toric IOLs should be increased as the toricity increases.

Toric Intraocular Lens Calculations Using Ratio, of Anterior to Posterior Corneal Cylinder Power

PURPOSE To evaluate the accuracy of toric intraocular lens (IOL) calculation using estimated total corneal astigmatism based on the anterior-to-posterior corneal cylinder power ratio according to the axis orientation of anterior corneal astigmatism. DESIGN Retrospective cross-sectional study. METHODS Nine hundred twenty-eight eyes of 928 reference subjects and 20 cataract patients (20 eyes) implanted with a toric IOL were enrolled. Linear regression analysis parameters (β0 and β1) of relationship between the simulated keratometry cylinder (CylSimK) and posterior corneal cylinder power of reference subjects were used to calculate the estimated posterior corneal astigmatism (-[β1 × CylSimK + β0] @ 90). When regression analysis was not significant, estimated posterior corneal astigmatism was defined as the negative value of the mean posterior corneal cylinder power @ 90. Estimated total corneal astigmatism was defined as the vectorial sum of anterior corneal astigmatism and estimated posterior corneal astigmatism. Residual astigmatism error, predicted using SimK, was compared with that predicted using estimated total corneal astigmatism. RESULTS Estimated posterior corneal astigmatism was determined to be -(0.15 × CylSimK + 0.22) @ 90 in eyes with with-the-rule astigmatism, -(0.05 × CylSimK + 0.27) @ 90 in oblique astigmatism, and -0.27 @ 90 in against-the-rule astigmatism. The median magnitude of the predicted residual astigmatism error calculated using estimated total corneal astigmatism (0.30 cylinder diopters) was significantly smaller than that calculated with SimK (0.50 cylinder diopters). CONCLUSIONS Toric IOL calculations using estimated total corneal astigmatism based on the anterior-to-posterior corneal cylinder power ratio provided a more appropriate toric IOL cylinder power than calculations using SimK astigmatism.

Comparison of the actual amount of axial movement of 3 aspheric intraocular lenses using anterior segment optical coherence tomography

Purpose To compare the mean effective lens position (ELP) and actual amount of axial movement of 3 aspheric intraocular lenses (IOLs) using anterior segment optical coherence tomography (AS‐OCT). Setting Department of Ophthalmology, Korea University College of Medicine, Seoul, South Korea. Design Retrospective comparative study. Methods Consecutive patients had phacoemulsification with aspheric IOL implantation. The ELP measurements by AS‐OCT were taken 1 week and 1, 3, and 6 months postoperatively. The ELPRMS was defined as the root mean square (RMS) of the change in ELP at each follow‐up timepoint. Results An XL Stabi ZO 3‐plate IOL was implanted in 30 eyes, an Acrysof IQ C‐loop IOL in 22 eyes, and an Akreos MI‐60 4‐plate IOL in 17 eyes. The 4‐plate IOL showed significant changes in the mean ELP from 1 week to 1 month and from 3 to 6 months postoperatively (P=.005 and P=.028, respectively). The changes of the other 2 IOLs were insignificant during the 3 postoperative visits. However, the mean ELPRMS of the C‐loop IOL (0.06 mm ± 0.31 [SD]) was smaller than that of the 3‐plate IOL (0.14 ± 0.28 mm) and the 4‐plate IOL (0.20 ± 0.35 mm) (P=.014 and P=.023, respectively) during the 3 timepoints. Conclusion An appropriate method based on the actual amount of axial IOL movement, such as the ELPRMS, is needed to assess the axial positional stability of IOLs. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Change in Efficiency of Aspheric Intraocular Lenses Based on Pupil Diameter

PURPOSE To measure the effect of spherical aberration correction by aspheric intraocular lenses (IOLs) based on pupil diameter, and to determine the minimum pupil diameter for each aspheric IOL. DESIGN Retrospective cross-sectional study. METHODS Eight-six patients (169 eyes) who were implanted with a HOYA AF-1 NY-60 (HOYA Corporation) or Tecnis ZCB00 1-piece IOL (Abbott Medical Optics Inc) were enrolled. Ocular, corneal, and internal spherical aberrations were measured at the 1-month postoperative visit using the Wavefront Analyzer KR-1W (Topcon). Minimum pupil diameter, which is required for each aspheric IOL to be effective, was calculated using a regression equation. RESULTS The mean value of internal spherical aberration of the Tecnis ZCB00 group (-0.09 ± 0.094 μm) was lower than that of the HOYA NY-60 group (-0.05 ± 0.072 μm) (P = .005). The original negative spherical aberrations of the HOYA NY-60 (-0.18 μm) were measured at a pupil diameter of 5.6 mm, and for the Tecnis ZCB00 (-0.27 μm) at a pupil diameter of 6.1 mm. The aspheric IOL efficiency dropped to 0% when the pupil diameter was 3.47 mm for the Tecnis ZCB00 group and 3.71 mm for the HOYA NY-60 group. CONCLUSIONS When the pupil diameters of patients are smaller than 3.4 mm for the Tecnis ZCB00 and 3.7 mm for the HOYA NY-60, the spherical aberration correction using these aspheric IOLs seems to be ineffective. Approximately 10% of the eyes showed smaller pupil size than the minimum effective diameter under mesopic conditions.

A simple method to shorten the unfolding time of prehydrated hydrophobic intraocular lens

OBJECTIVE To evaluate the effect of warm ophthalmic viscosurgical devices (OVDs) on the unfolding time of prehydrated hydrophobic acrylic intraocular lenses (IOLs). DESIGN Experimental study and human trial. PARTICIPANTS Three foldable hydrophobic acrylic IOLs (enVista MX60, AcrySof SN60AT, and Tecnis 1 ZCB00). METHODS The unfolding times of 3 kinds of IOLs were measured according to temperature from 26°C to 32°C in a transparent container filled with a mixture of OVDs and balanced salt solution. The unfolding time of each IOL was measured 4 times for each temperature. Unfolding time was defined as the time required for the folded IOL to recover ≥ 90% of its overall optic diameter before folding. In human trials, the unfolding time of the MX60 in a capsular bag filled with 30°C OVDs was compared with that filled with room temperature OVDs for 4 cases in each group. RESULTS The unfolding time of the MX60 (215 ± 25 seconds) was significantly longer than that of the SN60AT (28 ± 7 seconds) and the ZCB00 (29 ± 7 seconds) at 26°C (p = 0.013). However, there were no differences in the unfolding time of 3 IOLs at 32°C. In human trials, the unfolding time of the MX60 was shorter in a capsular bag filled with 30°C OVDs (32 ± 13 seconds) than if filled with OVDs kept at room temperature (127 ± 27 seconds; p = 0.029). CONCLUSIONS When fast and complete unfolding characteristics are needed, filling the anterior chamber and capsular bag with OVDs warmed to 30°C before IOL implantation is recommended.

Differences in corneal astigmatism between partial coherence interferometry biometry and automated keratometry and relation to topographic pattern.

PURPOSE: To compare the corneal astigmatism values obtained with a partial coherence interferometry (PCI) biometer and an automated keratometer and to evaluate the association between these differences and corneal topographic patterns. SETTING: Department of Ophthalmology, Guro Hospital, Korea University College of Medicine, Seoul, Korea. DESIGN: Comparative case series. METHODS: Corneal astigmatism was measured by PCI biometry (IOLMaster) and automated keratometry (RK‐F1 autorefractor). Eyes were divided into 3 groups based on the difference in absolute astigmatism values between PCI biometry and automated keratometry (ie, PCI biometry − automated keratometry) as follows: Group 1, more than 0.25 diopter (D); Group 2, within ±0.25 D; Group 3, less than −0.25 D. The topographic maps were grouped into patterns of round, oval, symmetric bow tie, asymmetric bow tie, and irregular. Distributions of topographic patterns according to group and astigmatism values by topographic patterns were evaluated. RESULTS: The study enrolled 312 eyes. The most common pattern was the asymmetric bow tie (34.6%) followed by symmetric bow tie (20.5%), round (18.9%), irregular (16.3%), and oval (9.6%). The asymmetric bow‐tie pattern was the most common in Group 1 and Group 2 (36.1% and 50.0%, respectively); however, in Group 3, the symmetric bow‐tie pattern was the most common (32.8%). The distribution of topographic patterns by groups was statistically significantly different (P=.015, Pearson chi‐square test). CONCLUSION: The difference in corneal astigmatism between the PCI biometer and automated keratometer may depend on the corneal topography pattern. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.