Influence of corneal biomechanical properties on surgically induced astigmatism in cataract surgery

Corneal Biomechanics and Other Factors Associated with Postoperative Astigmatism after Cataract Surgery

This study aimed to investigate the impact of the cornea's biomechanical properties, corneal hysteresis (CH), and corneal resistance factor (CRF) on postoperative astigmatism after cataract surgery and determine the other factors that influence it. Forty eyes of 40 patients (13M/27F; the median age of 74) were included in this prospective study, underwent 2.75 mm incision cataract surgery, and were followed for 30 days. Visits were scheduled at baseline before surgery (V0), the 1st (V1), the 7th (V2), and the 30th (V3) postoperative days. The main parameters estimated and analyzed with Statistica® 14.0.1 were CH, CRF, astigmatism diopter, and axis. Following the cataract surgery, the CH did not significantly change during the study visits (p = 0.109). However, there was a significant change in the CRF from baseline during the study visits (per protocol set) (p = 0.002). After a slight but insignificant increase from V0 to V1, post hoc analysis found a significant decrease in the mean CRF from V1 to V2 (p = 0.049) with no substantial change from V2 to V3. According to the post hoc analysis, the median astigmatism diopter increased significantly only from V0 to V1 (p = 0.001) and slightly but not significantly decreased to the end of the study with the achievement of a near-baseline value. The main predictors for the final astigmatism diopter (R2 = 0.898) obtained by stepwise regression analysis were its values at V0, V1, and V2 (p < 0.001). The CRF at V1 was marginally significant, with a negative parameter estimate of -0.098303 (p = 0.0623). In conclusion, there was no correlation between preoperative CH and CRF and postoperative astigmatism using 2.75 mm incision cataract surgery. However, the final astigmatism diopter's main predictors were its baseline values before cataract surgery, the first, and the seventh postoperative days.

Double safe suture during cataract surgery on post radial keratotomy patients using clear corneal incisions

PURPOSE

the aim of this study is to find a safer surgical approach in cataract surgery on eyes previously treated with radial keratotomy using clear corneal incisions.

SETTING

Department of Biomedical and Dental Sciences and Morphofunctional Imaging, Ophthalmology Clinic, University of Messina, Messina, Italy.

DESIGN

Prospective study.

METHODS

A prospective study was conducted on a group of 20 patients, 21 eyes with 16 RK incisions were evaluated for cataract phacoemulsification. Samples were divided into two groups: Group 1 underwent surgery with pre-operative one corneal stitch along radial keratotomy incisions near the main access site whereas Group 2 underwent modified surgery with two corneal stitches.

RESULTS

After surgery, visual acuity, corneal hysteresis and corneal strength was evaluated. In all cases, an increased visual acuity was observed. Group 1 showed an UCVA of logMAR 0.22 ± 0.14, while group 2 presented a logMAR of 0.1 ± 0.07. Data did not show a statistically significant difference in UCVA after surgery between the two groups (P = 0.133). Instead, a significant difference in corneal hysteresis (CH), respectively with values of 8.65 ± 1.6 mmHg in group 1 and 9.2 ± 1.8 in group 2 (P = 0.031), and a corneal resistance factor (CRF) with values of 7.87 ± 1.4 mmHg in the first group and 8.65 ± 1.6 mmHg in the second one (P = 0.039) was observed.

CONCLUSIONS

Double safe suture technique offers better stabilization of corneal structure during surgery in patients preventively treated with 16 incisions RK.

Effect of Central Corneal Thickness on Corneal Higher Order Aberrations After Cataract Surgery

PURPOSE

To investigate the changes of corneal higher order aberrations (HOAs) before and after phacoemulsification in patients with different central corneal thickness (CCT).

METHODS

In this retrospective non-randomized, non- comparative cases series, 51 eyes of 51 patients who underwent phacoemulsification were enrolled. The corneal total HOAs and Zernike coefficients (3rd and 4th order) over the 3- and 4-mm zones were measured by the iTrace aberrometer (Tracey Technologies). Participants were divided into three groups (528 µm or less, 529 to 550 µm, and greater than 550 µm) depending on the CCT tested by the LenStar LS900 (Haag Streit AG). The corneal aberrations between groups were compared with analysis of variance, the variation of corneal aberrations before and after phacoemulsification was analyzed by the paired-samples t test, and generalized linear models were used to compare postoperative aberrations between groups.

RESULTS

Significant differences were found in oblique trefoil at 3 mm and vertical trefoil, oblique trefoil, and HOAs at 4 mm in the 528 µm or less group; vertical trefoil, oblique trefoil, oblique quadrafoil, and oblique secondary astigmatism at 3 mm and oblique trefoil and oblique secondary astigmatism at 4 mm in the 529 to 550 µm group; and vertical quadrafoil at 3 mm in the greater than 550 µm group. After corrected deviation of preoperative aberrations, there were significant differences in postoperative vertical coma and oblique secondary astigmatism at 4 mm when compared to the 528 µm or less and greater than 550 µm groups.

CONCLUSIONS

The lower the CCT, the greater the change in corneal aberrations in patients with cataract after phacoemulsification. Surgeons should be aware of the potential for worse visual quality related to surgically induced aberrations in patients with thin corneas. [J Refract Surg. 2021;37(12):842-847.].

Effect of corneal incision features on anterior and posterior corneal astigmatism and higher-order aberrations after cataract surgery

PURPOSE

To evaluate the influence of 2.2 mm clear corneal incision (CCI) features in surgically induced astigmatism (SIA) and higher-order aberrations (HOAs) after cataract surgery.

METHODS

Right eyes of 92 subjects receiving 2.2 mm incision cataract surgery were involved. A total of 38 eyes were categorized as the intact incision group, and 54 eyes were the defective incision group. Pre- and postoperative (1 month and 6 months) corneal astigmatism and HOAs on anterior and posterior corneal surfaces, corneal volume, and corneal thickness (CT) were measured using Pentacam. The CCI features including incision length (IL), incision angles, distance from incision to central cornea (Dis-En/Ex), and CT at incision site were quantified using AS-OCT.

RESULTS

The defective incision group showed shorter IL and larger incision angles [false discovery rate (FDR) - p < 0.05]. Changes in CT at incision site were more pronounced for the defective incision group (FDR - p < 0.05). Some SIA parameters were related to the certain specific CCI features, especially IL (FDR - p < 0.05). Both groups exhibited significant increased 6 mm posterior corneal tHOAs at 1 month (Bonferroni corrected - p < 0.01) and the defective incision group showed increased 6 mm posterior tHOAs at 6 months (Bonferroni corrected - p = 0.023). There were characteristic correlations between Zernike terms and CCI features including IL, CT, Dis-En/Ex, and incision angles at 1 month, especially over 6 mm zone.

CONCLUSION

The CCI deformities can affect corneal recovery and induce more HOAs at 1 month postoperatively. Such effects became minor, but could persist until 6 months. The IL combined with Angle-En/Ex was important factor influencing CCI integrity and corneal optical quality.

Comparison of penetrating femtosecond laser-assisted astigmatic keratotomy and toric intraocular lens implantation for correction of astigmatism in cataract surgery

This study tried to compare the clinical outcomes of femtosecond laser-assisted astigmatic keratotomy (FSAK) and toric intraocular lens (IOL) implantation for astigmatism correction and identify factors affecting the efficacy of FSAK and toric IOL implantation in astigmatism correction. This retrospective case series comprised patients with corneal astigmatism ranging between 0.5 D and 4.5 D. Patients underwent FSAK or toric IOL implantation for cataract treatment and correction of astigmatism at the Samsung Medical Center, a tertiary surgical center, between April 2016 and December 2018. All patients underwent examination before and at three months after the surgery for comparative evaluation of refractive astigmatism, corneal high order aberrations and irregularity index. The astigmatism correction was analyzed by the Alpins method. Subgroup analysis of preoperative factors was based on the extent of target-induced astigmatism (TIA), the degree of astigmatism, and astigmatism classification based on topography. Thirty-one eyes underwent toric IOL implantation and 35 eyes underwent FSAK. The refractive astigmatism was significantly decreased in both toric IOL (P = 0.000) and FSAK group (P = 0.003). The correction index (CI) of refractive astigmatism was 0.84 ± 0.39 in the toric IOL and 0.71 ± 0.60 in the FSAK group. There was no difference between the two groups (P = 0.337). The CI of the FSAK group was significantly lower than in the toric IOL group when TIA was more than 1.5 D (P = 0.006), when correcting against-the-rule (P = 0.017), and limbus-to-limbus astigmatism (P = 0.008). In conclusion, toric IOL implantation is an effective and safe procedure for correcting preoperative astigmatism in cataract surgery in the short-term observation.

Advances in Imaging Technology of Anterior Segment of the Eye

Advances in imaging technology and computer science have allowed the development of newer assessment of the anterior segment, including Corvis ST, Brillouin microscopy, ultrahigh-resolution optical coherence tomography, and artificial intelligence. They enable accurate and precise assessment of structural and biomechanical alterations associated with anterior segment disorders. This review will focus on these 4 new techniques, and a brief overview of these modalities will be introduced. The authors will also discuss the recent advances in research regarding these techniques and potential application of these techniques in clinical practice. Many studies on these modalities have reported promising results, indicating the potential for more detailed comprehensive understanding of the anterior segment tissues.

Femtosecond laser-assisted arcuate keratotomy at the time of cataract surgery for the management of preexisting astigmatism

PURPOSE

To evaluate the outcomes of femtosecond laser-assisted arcuate keratotomy combined with cataract surgery in eyes with low-to-moderate corneal astigmatism.

SETTING

Eyes of York Private Practice Ophthalmology Clinic, York, Pennsylvania, USA.

DESIGN

Retrospective case series.

METHODS

This retrospective analysis included case records of patients with preexisting corneal astigmatism ranging from 0.5 to 2.0 diopter (D). Study parameters included corneal astigmatism, refractive astigmatism, and uncorrected (UDVA) and corrected (CDVA) distance visual acuities. The results, which were analyzed at 3 months postoperatively, included frequency distribution histograms, vector analysis, and single-angle polar plots.

RESULTS

The study comprised case records of 189 eyes of 143 patients (56 men and 87 women). The postoperative refractive astigmatism was reduced significantly compared with preoperative corneal astigmatism to 0.14 D ± 0.23 (SD) from 0.92 ± 0.34 D (P < .001). One hundred eighty-one eyes (95.8%) demonstrated postoperative refractive astigmatism of 0.5 D or less. The mean surgically induced change along the preoperative steep axis was -0.59 ± 0.56 D, and the change along the orthogonal axis was 0.01 ± 0.35 D. Postoperatively, 171 eyes (90.5%) had astigmatism angle of error of 15 degrees or less. The postoperative mean UDVA and CDVA were 0.09 ± 0.16 logarithm of the minimum angle of resolution (logMAR) and 0.02 ± 0.05 logMAR, respectively. One hundred seventy eyes (90%) had a postoperative UDVA of 20/30 or better. The results demonstrated stability at 12 months postoperatively. No intraoperative or postoperative arcuate keratotomy-related events were observed.

CONCLUSION

The results suggest that femtosecond laser-assisted arcuate keratotomy represents a safe and effective method for astigmatism correction at the time of cataract surgery with demonstrated stability of correction for at least 1 year postoperatively.

Site of clear corneal incision in cataract surgery and its effects on surgically induced astigmatism

Clear corneal incision (CCI) is a commonly used surgical approach in cataract surgery. In this prospective study, we evaluated the effect of CCI site on surgically induced astigmatism (SIA) and other postoperative astigmatic changes. CCIs were constructed based on the steep meridian of the total corneal refractive power in the 4.0-mm-zone (TCRP_4.0), and patients were divided into four groups: temporal, superotemporal, superonasal, and superior according to the site of the incision. TCRP_4.0 analysis demonstrated a statistically significant reduction of astigmatism with superior incisions (P < 0.001), and the combined mean polar values for SIA changed significantly in the temporal (Hotelling T² = 1.977), superotemporal (Hotelling T² = 0.544), superonsal (Hotelling T² = 1.066), and superior incision groups (Hotelling T² = 1.134) (all P < 0.001). The posterior axis alignment should be considered in cataract surgery with CCI, and the SIA is affected by axis rotation, and incision orientation.

Comparative evaluation of corneal incision enlargement after intraocular lens delivery of new preloaded and manual implantation systems

PURPOSE

To determine whether total corneal incision enlargement after implantation of an intraocular lens with a new preloaded delivery system is comparable to a standard-of-care manual delivery system using an in vitro human cadaver eye model, despite having a smaller initial incision size.

METHODS

Human cadaver phakic whole eye globes were used for these studies (n = 16 per group). Each pair of eyes was randomly assigned to a new preloaded delivery system (UltraSert^TM) or a manual delivery system (MONARCH^® III D). The surgical procedure included creating a 2.2- and 2.4-mm corneal incision for the preloaded and manual delivery systems, respectively, measuring intraocular pressure and pre-implantation corneal incision size, delivering the intraocular lens into the anterior chamber, and measuring the post-implantation incision size.

RESULTS

The final corneal incision enlargement after intraocular lens delivery using the preloaded delivery system was 2.33 ± 0.04 mm, compared to 2.54 ± 0.05 mm after intraocular lens delivery with the manual delivery system. The mean corneal incision enlargement was comparable between the two systems, being 0.13 ± 0.04 mm using the preloaded delivery system and 0.14 ± 0.05 mm using the manual delivery system (p = 0.432).

CONCLUSION

In a human cadaver eye model, the preloaded delivery system demonstrated an intraocular lens delivery performance on cornea incision enlargement was noninferior to the manual, standard-of-care intraocular lens delivery system despite a smaller initial incision size.

TRANSLATIONAL RELEVANCE

Smaller incision sizes for cataract surgery improve patient outcomes via faster visual and wound recovery and decreased risk of complications such as postoperative inflammation and surgically induced astigmatism.

Astigmatic correction by intrastromal astigmatic keratotomy during femtosecond laser-assisted cataract surgery: Factors in outcomes

PURPOSE

To evaluate the 6-month outcomes of femtosecond laser astigmatic keratotomy (AK) combined with femtosecond laser-assisted cataract surgery and identify factors affecting the efficacy of astigmatic correction.

SETTING

Seoul St. Mary's Hospital, Catholic University of Korea, Seoul, South Korea.

DESIGN

Retrospective case series.

METHODS

Femtosecond laser AK was performed during femtosecond laser-assisted cataract surgery. The keratometric astigmatism, refractive cylinder, corneal hysteresis (CH), and corneal resistance factor (CRF) were measured preoperatively and postoperatively at 1 week, 2 months, and 6 months. Vector analysis to evaluate the 6-month outcomes of femtosecond laser AK and univariable regression analysis to determine the factors influencing the correction index were performed.

RESULTS

The study enrolled 89 eyes of 89 patients. The stigmatism type, CH, CRF, and absolute angle of error showed significant correlations with the correction index (P = .041, P = .029, P = .044, and P < .001, respectively). There was a significant difference in the correction index and no difference in keratometric astigmatism between with-the-rule (WTR), against-the-rule (ATR), and oblique astigmatism (P = .044). The keratometric astigmatism with ATR and oblique astigmatism (0.66 diopter [D] ± 0.42 [SD] and 0.46 ± 0.27 D, respectively) was significantly lower than the refractive cylinder (0.92 ± 0.56 D and 0.78 ± 0.43 D, respectively) (P < .05); this was not the case for WTR astigmatism.

CONCLUSIONS

The efficacy of femtosecond laser AK was affected by the biomechanical properties of the cornea and astigmatism type. Further studies incorporating the individual biomechanical properties of the cornea and total corneal astigmatism in a nomogram are recommended.

Spatially-resolved Brillouin spectroscopy reveals biomechanical abnormalities in mild to advanced keratoconus in vivo

Mounting evidence connects the biomechanical properties of tissues to the development of eye diseases such as keratoconus, a disease in which the cornea thins and bulges into a conical shape. However, measuring biomechanical changes in vivo with sufficient sensitivity for disease detection has proven challenging. Here, we demonstrate the diagnostic potential of Brillouin light-scattering microscopy, a modality that measures longitudinal mechanical modulus in tissues with high measurement sensitivity and spatial resolution. We have performed a study of 85 human subjects (93 eyes), consisting of 47 healthy volunteers and 38 keratoconus patients at differing stages of disease, ranging from stage I to stage IV. The Brillouin data in vivo reveal increasing biomechanical inhomogeneity in the cornea with keratoconus progression and biomechanical asymmetry between the left and right eyes at the onset of keratoconus. The receiver operating characteristic analysis of the stage-I patient data indicates that mean Brillouin shift of the cone performs better than corneal thickness and maximum curvature respectively. In conjunction with morphological patterns, Brillouin microscopy may add value for diagnosis of keratoconus and potentially for screening subjects at risk of complications prior to laser eye surgeries.

Influence of preoperative astigmatism on corneal biomechanics and accurate intraocular pressure measurement after micro-incision phacoemulsification

AIM

To define the corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann-correlated intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) prior to and following coaxial micro-incision phacoemulsification in patients with corneal astigmatism.

METHODS

Of 97 patients with cataracts were enrolled in the study. Group 1 included patients with corneal astigmatism (K1-K2) values of K1-K2<+1.0 D, and group 2 with values of K1-K2 ≥+1.0 D and ≤+2.25 D. Coaxial micro-incision phacoemulsification of a corneal incision of 2.0 mm with intraocular lens (IOL) implantation was performed. CH, CRF, IOPg, IOPcc, waveform score (WS) were measured preoperatively and one week, one month postoperatively using an Ocular Response Analyzer. Axial length (AXL) was calculated by Tomey Optical Biometer OA 2000.

RESULTS

Group 1 consisted of 51 patients with mean corneal astigmatism value of +0.49±0.25 D. Group 2 included 46 patients with astigmatism of +1.43±0.43 D. In group 1, CRF (t=2.68, P<0.05), CH (t=2.64, P<0.05) and WS (t=3.51, P<0.05) were significantly lower one week postoperatively, when compared to the preoperative values. CRF significantly decreased (t=3.61, P<0.05) when measured one month following the surgery. In group 2 CH (t=5.92, P<0.05), and WS (t=3.96, P<0.05) were significantly lowered one week after cataract surgery. Moreover, we observed a significant decrease in IOPg (t=2.24, P<0.05), CRF (t=5.05, P<0.05) and CH (t=2.31, P<0.05) one month after phacoemulsification. There was no statistically significant (t=-0.83, P=0.41) difference in AXL between study groups.

CONCLUSION

CRF, CH and IOPg are reduced in patients with preoperative corneal astigmatism equal or higher than +1.0 D and lower than +2.25 D. Hence, bias of IOPg measurement in these patients may cause underestimation of the real IOP both before and after cataract surgery. The measurement of IOPcc allows the precise assessment of IOP pre- and postoperatively, independently on corneal astigmatism, CH and CRF values.

Brillouin microscopy: assessing ocular tissue biomechanics

PURPOSE OF REVIEW

Assessment of corneal biomechanics has been an unmet clinical need in ophthalmology for many years. Many researchers and clinicians have identified corneal biomechanics as source of variability in refractive procedures and one of the main factors in keratoconus. However, it has been difficult to accurately characterize corneal biomechanics in patients. The recent development of Brillouin light scattering microscopy heightens the promise of bringing biomechanics into the clinic. The aim of this review is to overview the progress and discuss prospective applications of this new technology.

RECENT FINDINGS

Brillouin microscopy uses a low-power near-infrared laser beam to determine longitudinal modulus or mechanical compressibility of tissue by analyzing the return signal spectrum. Human clinical studies have demonstrated significant difference in the elastic properties of normal corneas versus corneas diagnosed with mild and severe keratoconus. Clinical data have also shown biomechanical changes after corneal cross-linking treatment of keratoconus patients. Brillouin measurements of the crystalline lens and sclera have also been demonstrated.

SUMMARY

Brillouin microscopy is a promising technology under commercial development at present. The technique enables physicians to characterize the biomechanical properties of ocular tissues.

[Is Holladay 2 formula acurate enough for calculating intraocular lens power in non-standard eyes?]

PURPOSE

To evaluate the benefit of the Holladay 2 formula versus the 3rd generation formulae in calculating the IOL power in eyes with non-standard axial length or keratometry before cataract surgery.

PATIENTS

Retrospectiv study from January to December 2015. The inclusion critaeria were axial length (AL) <22mm or >26mm, or average keratometry <42 D or >46 D, dividing the patients in 4 groups respectively. The 7 parameters required to calculate the Holladay 2 formula were collected. The final refractive result was turned into spherical equivalent to calculate the optimal power retrospectively. Then, the results obtained using the other formulae were compared with the optimal IOL power.

RESULTS

One hundred and twenty-six eyes operated by two surgeons were included. In the high AL group (n=32), the SRK/T was the most accurate formula; regarding the low AL group (n=36), the Hoffer Q and Holladay 2 formulae performed better; for the steep cornea group (n=27), the Hoffer Q, Haigis, Holladay 1 and 2 formulae were not different; last, the Holladay 1 and 2 were more accurate in the flat cornea group (n=33).

CONCLUSION

In our study, the Holladay 2 formula does not seem to be better than the others for calculating IOL power in non-standard eyes. Preoperative eye features in such non-standard cases should be taken into account before the surgery to choose the more suitable formula.

Corneal Biomechanical Properties after FS-LASIK with Residual Bed Thickness Less Than 50% of the Original Corneal Thickness

Background

The changes in corneal biomechanical properties after LASIK remain an unknown but important topic for surgical design and prognostic evaluation. This study aims to observe the postoperative corneal biomechanical properties one month after LASIK with amount of corneal cutting (ACC) greater than 50% of the central corneal thickness (CCT).

Methods

FS-LASIK was performed in 10 left rabbit eyes with ACC being 60% (L60) and 65% (L65) of the CCT, while the right eyes (R) were the control. After 4 weeks, rabbits were executed and corneal strip samples were prepared for uniaxial tensile tests.

Results

At the same strain, the stresses of L65 and L60 were larger than those of R. The elastic moduli of L60 and L65 were larger than those of R when the stress was 0.02 MPa, while they began to be less than those of R when stress exceeds the low-stress region. After 10 s relaxation, the stress of specimens L65, L60, and R increased in turn.

Conclusion

The elastic moduli of the cornea after FS-LASIK with ACC greater than 50% of the CCT do not become less under normal rabbit IOP. The limit stress grows with the rise of ACC when relaxation becomes stable.

Surgically induced astigmatism following trabeculectomy

PURPOSE

Surgically induced astigmatism (SIA) has attracted much interest in recent times because changes in corneal astigmatism can lead to decreased uncorrected visual acuity and patient discomfort. This study aimed to evaluate SIA and to identify factors correlated therewith after trabeculectomy.

METHODS

We retrospectively reviewed medical charts of patients who were treated with trabeculectomy at 120° meridian (superotemporal area on right eye and superonasal area on left eye) by the same surgeon. Preoperative keratometric data were compared with data collected from 2 months to 12 months postoperatively. SIA was evaluated using Naeser's polar value analysis.

RESULTS

Using Naeser's method, ΔKP(120) was calculated as 0.7 ± 0.7 (0.82@104°), which indicates a with-the-rule change. After surgery, the combined mean polar values changed significantly (Hotelling T² = 22.47; p < 0.001). Multivariate analysis of variance indicated that postoperative intraocular pressure and location of surgery were independent factors that were significantly associated with SIA (p = 0.002 and 0.03, respectively).

CONCLUSIONS

Trabeculectomy at the 120° meridian was not astigmatically neutral. In addition, the SIA after trabeculectomy appears to be greater in eyes with low postoperative intraocular pressure and a superonasal surgical wound rather than a superotemporal wound.

Precision and agreement of higher order aberrations measured with ray tracing and Hartmann-Shack aberrometers

BACKGROUND

To assess the precision and agreement of measurements of higher order aberrations (HOAs) obtained with a ray tracing aberrometer (iTrace) and a Hartmann-Shack aberrometer (Topcon KR-1 W).

METHODS

Prospective evaluation of the diagnostic test. Data from the right eyes of 92 normal subjects obtained using the two devices were included in this study. Two observers performed 3 consecutive scans to determine the intraobserver repeatability and interobserver reproducibility. About one week later, one observer performed an additional 3 consecutive scans to obtain the intersession reproducibility. The within-subject standard deviation (Sw), test-retest repeatability (TRT) and intraclass correlation coefficient (ICC) were used to assess the precision, while Bland-Altman plots were performed to assess the agreement.

RESULTS

For intraobserver repeatability of the ocular, corneal and internal HOAs, Topcon KR-1 W showed a 2.77Sw of 0.079 μm or less and ICCs of 0.761 or more; and iTrace showed a 2.77Sw of 0.105 μm or less and ICCs of 0.805 or more. The ICCs of the internal HOAs of interobserver reproducibility were less than 0.75 except for spherical aberration (SA) (0.862), and interobserver reproducibility of the counterpart showed similar but lower results. For the ocular, corneal and internal HOA measurements, statistically significant differences existed between the Topcon KR-1 W and iTrace (all P < 0.05). No significant differences were observed in the ocular SA and internal coma.

CONCLUSIONS

The ray tracing and Hartmann-Shack method aberrometers provided excellent repeatability but less reliable reproducibility in the measurement of HOAs (except for SA). The two aberrometers should not be interchangeable in clinical application because of the significant differences in HOA measurements between them.

Comparison of astigmatism prediction error taken with the Pentacam measurements, Baylor nomogram, and Barrett formula for toric intraocular lens implantation

Background

To evaluate and compare the astigmatism prediction errors taken with the Pentacam measurements, Baylor nomogram, and Barrett formula for toric intraocular lens (IOL) implantation.

Methods

Phacoemulsification with toric Precizon IOL implantation was performed in 41 eyes with corneal astigmatism (range, 1 to 5 diopters (D)) determined by IOLMaster and SimK on Pentacam. Preoperative corneal astigmatism measurements were obtained from IOLMaster readings (IOLMaster, Baylor-IOLMaster, and Barrett-IOLMaster) and Pentacam readings (SimK, Baylor-SimK, Barrett-SimK, wavefront, true net power, total corneal refractive power, and vector derived by manual vector summation using corneal front and back astigmatism). Prediction error and intraclass correlation coefficient (ICC) between the measured (or calculated) astigmatism by IOLMaster and Pentacam and the estimated corneal astigmatism estimated by IOL toricity power and residual astigmatism were determined.

Results

The centroid errors in prediction error with IOLMaster, SimK, Baylor-IOLMaster, Baylor-SimK, Barrett-IOLMaster, Barrett-SimK, wavefront, true net power, total corneal refractive power, and vector were 0.59@103, 0.61 @103, 0.37@161, 0.41@162, 0.24@171, 0.36@162, 0.42@106, 0.04@8, 0.07@82, and 0.03@82, respectively, in with-the-rule (WTR) astigmatism eyes at postoperative 3-month. They were 0.22@87, 0.20@74, 0.16@21, 0.54@10, 0.43@3, 0.33@19, 0.51@25, 0.31@58, 0.29@50, and 0.14@50 in against-the-rule (ATR) astigmatism eyes. Of the ten modalities, vector showed the lowest WTR astigmatism prediction error and the highest ICC between the predicted and the estimated corneal astigmatism for both WTR and ATR eyes.

Conclusion

Vector summation using anterior and posterior corneal surface power taken with the Pentacam yields the least astigmatism prediction error and is a promising tool for determining toric IOL cylinder power.

Change in Anterior and Posterior Curvature After Cataract Surgery

PURPOSE

To analyze the change in anterior and posterior corneal curvature after cataract surgery using a Placido-dual rotating Scheimpflug device.

METHODS

In a prospective cross-sectional study, corneal curvature was measured using the Galilei G4 device (Ziemer Ophthalmic Systems, Port, Switzerland) preoperatively and 1 week and 1, 3, and 6 months after cataract surgery with a temporal limbal self-sealing 2.2-mm incision. The surgically induced astigmatism (SIA) was determined on the anterior and posterior surfaces.

RESULTS

Fifty-nine patients (68 eyes) were assessed. Based on the anterior corneal surface, 16 (23.5%) eyes had a vertically steep meridian (with-the-rule [WTR] astigmatism), 32 (47.1%) had a horizontally steep meridian (against-the-rule [ATR] astigmatism), and 20 (29.4%) had oblique astigmatism. Based on the posterior corneal surface, 2 (2.9%) eyes had a horizontally steep meridian (ATR astigmatism), 62 (91.2%) had a vertically steep meridian (WTR astigmatism), and 4 (5.9%) had oblique astigmatism. SIA of the anterior and posterior corneal surfaces was 0.61 ± 0.33 and 0.20 ± 0.17 diopters (D), respectively. However, there was no significant difference between the preoperative and the 6-month postoperative data in the Jackson coefficient orthogonal coordinate system for the anterior and posterior corneal surfaces. SIA of WTR astigmatism of the posterior cornea was 0.19 ± 0.16 D at 6 months. Sixty-one of 62 eyes with WTR astigmatism in the posterior corneal surface still showed WTR astigmatism after cataract surgery.

CONCLUSIONS

The tendency of SIA of the posterior cornea may not be uniform, but type of posterior corneal astigmatism did not change in most cases after the 2.2-mm temporal limbal incision cataract surgery. [J Refract Surg. 2016;32(11):754-759.].

Effects of optical diameter of intraocular lenses with intrascleral fixation on higher-order aberrations

Background

Intrascleral fixation of an intraocular lens (IOL) is used in eyes that lack capsular support. The aim of the study is to determine whether a larger optical diameter IOL will decrease the higher-order aberrations (HOAs) when the haptics are extended for intrascleral fixation than a smaller diameter IOL.

Methods

Three-piece acrylic IOLs with 6.0 mm optics (X-60, VA-60BBR) and 7.0 mm optics (X-70, VA-70 AD) were fixed at lengths of 13, 14, 15, 16, or 17 mm. A wavefront analyzer was used to measure the HOAs within the central 3.0 and 5.2 mm optic diameter.

Results

The astigmatic aberration within the central 5.2 mm was greater than that within the central 3.0 mm for all IOLs. The HOAs increased significantly with an extension of the IOLs with both optical diameters (P < 0.001). The coma aberration within the central 5.2 mm was greater than that within the central 3.0 mm but it did not increase with an extension of the haptics. The astigmatic aberration of the X-60 IOL was significantly greater than that of the X-70 only at an extension of 17 mm. The astigmatic aberration of the VA-70 AD was not significantly different from that of the VA-60BBR. The cylindrical power changed from 0.047 D in the X-60 to 0.118 D in the VA-70 AD when the IOLs were extended from 13 to 17 mm.

Conclusion

When three-piece IOLs are highly extended for intrascleral fixation, the astigmatic aberration increases significantly. However, IOLs with 7 mm optics do not have less astigmatic and coma aberrations than IOLs with 6 mm optics.

Relationship between Corneal Biomechanical Properties and Optic Nerve Head Changes after Deep Sclerectomy

Purpose

To evaluate corneal biomechanical properties and optic nerve head (ONH) changes following deep sclerectomy (DS) and the relation to each other.

Methods

Forty-nine eyes with primary open-angle glaucoma that underwent DS were studied. Corneal biomechanical properties were assessed using the Ocular Response Analyzer and the ONH was evaluated by Spectralis optical coherence tomography with enhanced depth imaging technology before surgery and 3 months postoperatively. Changes in corneal hysteresis (CH), corneal resistance factor (CRF), optic nerve cupping, prelaminar tissue thickness, and lamina cribrosa depth and thickness were registered. A correlation matrix and multiple linear regression models were used to determine predictors of ONH changes.

Results

At 3 months after surgery, mean corneal compensated intraocular pressure (IOPcc) significantly decreased by 27.9% (p<00.001) and mean Goldmann-correlated IOP (IOPg) decreased by 30.52% (p<00.001). Mean CH increased and CRF decreased by 18.4% and 10.1%, respectively (p<00.001). There was a significant reversal of ONH cupping mainly due to a prelaminar tissue thickening (p<00.001). Significant associations were found between ONH cupping reversal and prelaminar tissue thickening with preoperative IOPcc (p = 0.046), IOPg (p = 0.02), and CRF (p = 0.002) and with changes in IOP, CH, and CRF (p<00.001, p = 0.004, p = 0.018, respectively) after surgery.

Conclusions

Corneal hysteresis increased and CRF decreased significantly 3 months after DS. Corneal resistance factor was the single largest preoperative factor influencing cupping reversal changes. Despite the influence of preoperative variables, postoperative IOP reduction was the only independent factor influencing changes observed in the ONH after surgery.

Intraocular lens alignment methods

PURPOSE OF REVIEW

This article reviews current concepts in intraocular lens alignment strategies to maximize intraocular lens (IOL) positioning.

RECENT FINDINGS

A variety of strategies has been developed to maximize toric IOL position, including preoperative calculators to determine the appropriate IOL power and orientation, intraoperative alignment devices, and postoperative software to determine if IOL rotation would be beneficial for refractive outcomes.

SUMMARY

The combination of using multiple toric IOL calculators and intraoperative alignment devices has improved toric IOL outcomes. The relationship of the posterior corneal power and its effect on outcomes remains to be fully elucidated. Postoperative IOL rotation may be necessary even when the IOL is aligned as planned because of surgically induced astigmatism.

Corneal biomechanical properties changes after coaxial 2.2-mm microincision and standard 3.0-mm phacoemulsification

AIM

To compare the changes in corneal biomechanics measured by ocular response analyzer (ORA) after 2.2-mm microincision cataract surgery and 3.0-mm standard coaxial phacoemulsification.

METHODS

The prospective nonrandomized study comprised eyes with cataract that had 2.2-mm coaxial microincision or 3.0-mm standard incision phacoemulsification. The corneal hysteresis (CH), corneal resistance factor (CRF), corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOPg) were measured by ORA preoperatively and at 1d, 1-, 2-, 3- and 4-week postoperatively. Results were analyzed and compared between groups.

RESULTS

In both groups, CH decreased in the immediate postoperative period (P<0.05), returned to the preoperative level at one week (P=0.249) in the 2.2-mm group, and at two weeks in the 3.0-mm group (P=0.264); there was no significant change in CRF values. In 2.2-mm group, mean IOPcc and IOPg increased at 1d postoperatively (both P<0.05), and returned to preoperative level at one week (P=0.491 and P=0.923, respectively). In 3.0-mm group, mean IOPcc and IOPg increased at 1d and 1wk postoperatively (P=0.005 and P=0.029, respectively), and returned to preoperative level at 2wk (P=0.347 and P=0.887, respectively).

CONCLUSION

Significant differences between preoperative and postoperative corneal biomechanical values were found for CH, IOPcc and IOPg. But the recovery time courses were different between the two groups. The 2.2-mm coaxial microincision cataract surgery group seemed recovery faster compared to the 3.0-mm standard coaxial phacoemulsification group.

Coaxial Microincision Cataract Surgery versus Standard Coaxial Small-Incision Cataract Surgery: A Meta-Analysis of Randomized Controlled Trials

BACKGROUND

We conducted this meta-analysis to compare the outcomes of coaxial microincision cataract surgery (C-MICS) and standard coaxial small incision cataract surgery (C-SICS).

METHODS

The outcomes of randomized controlled trials (RCTs) reporting C-MICS and C-SICS were collected from PubMed, Web of Science, and The Cochrane Library in May 2015. The final meta-analysis was conducted on the following intraoperative and postoperative outcomes: ultrasound time (UST), effective phacoemulsification time (EPT), balanced salt solution use (BSS use), cumulative dissipated energy (CDE), mean surgery time, endothelial cell loss percentage (ECL%), best corrected visual acuity (BCVA), increased central corneal thickness (CCT), laser flare photometry values and surgically induced astigmatism (SIA).

RESULTS

A total of 15 RCTs, involving 1136 eyes, were included in the final meta-analysis. No significant between-group differences were detected in EPT, BSS use, CDE, BCVA, laser flare photometry values or increased CCT. However, the C-MICS group showed less SIA (at postoperative day 7: p<0.01; at postoperative day 30 or more: p<0.01) and greater ECL% (at postoperative day 60 or more: p<0.01), whereas the C-SICS group required a shorter UST (p<0.01).

CONCLUSIONS

The present meta-analysis suggested that the C-MICS technique was more advantageous than C-SICS in terms of SIA, but C-MICS required a longer UST and induced a higher ECL%. Further studies should be done to confirm our results.

The Correlation Analysis between Corneal Biomechanical Properties and the Surgically Induced Corneal High-Order Aberrations after Small Incision Lenticule Extraction and Femtosecond Laser In Situ Keratomileusis

Background. To investigate the correlation between corneal biomechanics and the surgically induced corneal high-order aberrations (HOAs) after small incision lenticule extraction (SMILE) and femtosecond laser in situ keratomileusis (FS-LASIK). Methods. A total of 150 right myopic eyes that underwent SMILE or FS-LASIK surgery were included in this retrospective study, 75 eyes in each group. The corneal hysteresis (CH) and the corneal resistance factor (CRF) with the corneal HOAs of the anterior, posterior, and total cornea were assessed preoperatively and three months postoperatively. Multivariate linear regression was applied to determine the correlations. Results. The preoperative CRF was significantly correlated with the induced 3rd–6th-order HOAs and spherical aberration of the anterior surface and the total cornea after SMILE and FS-LASIK surgeries (P < 0.05), postoperatively. The CRF was significantly correlated with the induced vertical coma of the anterior and posterior surfaces and the total cornea after SMILE surgery (P < 0.05). There was a significant correlation between the CRF and the induced posterior corneal horizontal coma after FS-LASIK surgery (P = 0.013). Conclusions. The corneal biomechanics affect the surgically induced corneal HOAs after SMILE and FS-LASIK surgery, which may be meaningful for screening the patients preoperatively and optimizing the visual qualities postoperatively.

Long-term outcomes of limbal relaxing incisions during cataract surgery: aberrometric analysis

PURPOSE

To compare the final changes in corneal wavefront aberration by limbal relaxing incisions (LRIs) after cataract surgery.

METHODS

This prospective cumulative interventional nonrandomized case study included cataract and astigmatic patients undergoing LRIs and phaco with intraocular lens implantation. LRIs were planned using Donnenfeld nomogram. The root mean square of corneal wave aberration for total Z(n,i)(1≤n≤8), astigmatism Z(2,±1), coma Z(3-5-7,±1), trefoil Z(3-5-7,±2), spherical Z(4-6-8,0), and higher-order aberration (HOA) Z(3≤n≤8) was examined before and 3 years after surgery (optical path difference-Scan II [OPD-Scan II)]. Uncorrected distance visual acuity and best-corrected distance visual acuity (CDVA) for distance, keratometric cylinder, and variations in average corneal power were also analyzed.

RESULTS

Sixty-four eyes of 48 patients were included in the study. Age ranged from 42 to 92 years (70.6±8.4 years). After LRIs, uncorrected distance visual acuity and best-corrected distance visual acuity improved statistically (P<0.01). The keratometric cylinder value decreased by 40.1%, but analysis of KP90 and KP135 polar values did not show any decrease that could be statistically confirmed (P=0.22 and P=0.24). No significant changes were detected in root mean square of total (P=0.61) and HOAs (P=0.13) aberrations. LRIs did not induce alteration in central corneal power confirming a 1:1 coupling ratio.

CONCLUSION

LRIs determined a nonsignificant alteration of corneal HOA. Therefore, LRIs can be still considered a qualitatively viable mean in those cases where toric intraocular lenses are contraindicated or not available. Yet, the authors raise the question of nonpersonalized nomograms, as in the present study, LRIs did not reach the preset target cylinder.

Clinical utility of femtosecond laser-assisted astigmatic keratotomy after cataract surgery

PURPOSE

To examine the clinical utility of femtosecond laser-assisted astigmatic keratotomy (FSL-AK) for eyes after cataract surgery.

METHODS

Eight eyes of 6 patients with an intraocular lens and corneal astigmatism of 2.0 diopters (D) or more underwent FSL-AK. The mean preoperative manifest cylindrical refraction was 2.88 ± 0.64 D and the mean corneal astigmatism was 2.84 ± 0.83 D. Paired symmetrical arcuate incisions were created with the same settings, except for the incision depth. Uncorrected distance visual acuity (UDVA), manifest cylindrical power, and surgically induced astigmatism (SIA) were measured at 1 day, 1 week, and 1 month postoperatively. Fourier analysis of corneal topography and incision depths measured with anterior-segment optical coherence tomography were evaluated 1 month postoperatively.

RESULTS

In all eyes, the UDVA improved at 1 week and 1 month postoperatively, and the manifest cylinder also decreased postoperatively, while the SIA showed overcorrections in 6 eyes. Fourier analysis showed decreases in spherical and regular astigmatic components and increases in higher-order irregularity. The mean incision depth was measured as 60 µm deeper than the intended depth.

CONCLUSION

The FSL-AK effectively reduced corneal astigmatism and improved the UDVA, although it was demonstrated that the deeper incisions led to overcorrection.

Surgical options for correction of refractive error following cataract surgery

Refractive errors are frequently found following cataract surgery and refractive lens exchange. Accurate biometric analysis, selection and calculation of the adequate intraocular lens (IOL) and modern techniques for cataract surgery all contribute to achieving the goal of cataract surgery as a refractive procedure with no refractive error. However, in spite of all these advances, residual refractive error still occasionally occurs after cataract surgery and laser in situ keratomileusis (LASIK) can be considered the most accurate method for its correction. Lens-based procedures, such as IOL exchange or piggyback lens implantation are also possible alternatives especially in cases with extreme ametropia, corneal abnormalities, or in situations where excimer laser is unavailable. In our review, we have found that piggyback IOL is safer and more accurate than IOL exchange. Our aim is to provide a review of the recent literature regarding target refraction and residual refractive error in cataract surgery.

Corrective Techniques and Future Directions for Treatment of Residual Refractive Error Following Cataract Surgery

Postoperative residual refractive error following cataract surgery is not an uncommon occurrence for a large proportion of modern-day patients. Residual refractive errors can be broadly classified into 3 main categories: myopic, hyperopic, and astigmatic. The degree to which a residual refractive error adversely affects a patient is dependent on the magnitude of the error, as well as the specific type of intraocular lens the patient possesses. There are a variety of strategies for resolving residual refractive errors that must be individualized for each specific patient scenario. In this review, the authors discuss contemporary methods for rectification of residual refractive error, along with their respective indications/contraindications, and efficacies.

Technology and Intraocular Lenses to Enhance Cataract Surgery Outcomes-Annual Review (January 2013 to January 2014)

PURPOSE

This article is aimed to provide a clinical update on recent developments in cataract surgical techniques, with specific focus on femtosecond laser technology. The article also focuses on recent improvements in the technology used in implanting intraocular lenses (IOLs).

DESIGN

Literature review.

METHODS

The authors conducted a review of literature available in the last 12 months in the English language using PubMed. The period used to conduct the literature search was from January 1, 2013, to December 31, 2013. The following search terms were used during the PubMed search: phacoemulsification, femtosecond laser, toric IOLs, multifocal IOLs, multifocal toric IOLs, manual small-incision cataract surgery, outcomes, surgically induced astigmatism, rotational stability, trifocal IOLs, laser cataract surgery, safety, and efficacy.

RESULTS

This review incorporates selected original articles that provide fresh insights and updates on the fields of toric and multifocal IOLs, femtosecond laser cataract surgery, and manual small-incision cataract surgery. Particular attention has been paid to observational, randomized controlled clinical trials, experimental trials, and analyses of larger cohorts with prospective and retrospective study designs. Letters to the editor, unpublished works, and abstracts do not fall under the purview of this review.

CONCLUSIONS

This review is not designed to be all-inclusive. It highlights and provides insights on literature that is most useful and applicable to practicing ophthalmologists.

Biomechanics of the cornea evaluated by spectral analysis of waveforms from ocular response analyzer and Corvis-ST

PURPOSE

In this study, spectral analysis of the deformation signal from Corvis-ST (CoST) and reflected light intensity from ocular response analyzer (ORA) was performed to evaluate biomechanical concordance with each other.

METHODS

The study was non-interventional, observational, cross-sectional and involved 188 eyes from 94 normal subjects. Three measurements were made on each eye with ORA and CoST each and then averaged for each device. The deformation signal from CoST and reflected light intensity (applanation) signal from ORA was compiled for all the eyes. The ORA signal was inverted about a line joining the two applanation peaks. All the signals were analyzed with Fourier series. The area under the signal curves (AUC), root mean square (RMS) of all the harmonics, lower order (LO included 1st and 2nd order harmonic), higher order (HO up to 6th harmonic), CoST deformation amplitude (DA), corneal hysteresis (CH) and corneal resistance factor (CRF) were analyzed.

RESULTS

The device variables and those calculated by Fourier transform were statistically significantly different between CoST and ORA. These variables also differed between the eyes of the same subject. There was also statistically significant influence of eyes (left vs. right) on the differences in a sub-set of RMS variables only. CH and CRF differed statistically significantly between the eyes of subject (p<0.001) but not DA (p = 0.65).

CONCLUSIONS

CoST was statistically significantly different from ORA. CoST may be useful in delineating true biomechanical differences between the eyes of a subject as it reports deformation.

Management of residual refractive error after cataract surgery

PURPOSE OF REVIEW

To provide a review of the recent literature on the management of residual refractive error after cataract surgery.

RECENT FINDINGS

Laser in-situ keratomileusis (LASIK) is the most accurate procedure to correct residual refractive error after cataract surgery. Lens-based procedures, such as intraocular lens (IOL) exchange or piggyback lens implantation, are also possible alternatives in cases with extreme ametropia, corneal abnormalities, or in situations where excimer laser is not available. In this review, we found that Piggyback IOL were safer and more accurate than IOL exchange.

SUMMARY

Emmetropia is our main target today in modern cataract surgery. Accurate biometric analysis, selection and calculation of the adequate IOL, and modern techniques for cataract surgery all help surgeons to move toward the goal of cataract surgery as a refractive procedure free from refractive error. However, in spite of all these inputs, residual refractive error still occasionally occurs after cataract surgery and LASIK seems to be the most accurate method for its correction.