Wavefront technology in ophthalmology

Advanced Optical Wavefront Technologies to Improve Patient Quality of Vision and Meet Clinical Requests

Adaptive optics (AO) is employed for the continuous measurement and correction of ocular aberrations. Human eye refractive errors (lower-order aberrations such as myopia and astigmatism) are corrected with contact lenses and excimer laser surgery. Under twilight vision conditions, when the pupil of the human eye dilates to 5-7 mm in diameter, higher-order aberrations affect the visual acuity. The combined use of wavefront (WF) technology and AO systems allows the pre-operative evaluation of refractive surgical procedures to compensate for the higher-order optical aberrations of the human eye, guiding the surgeon in choosing the procedure parameters. Here, we report a brief history of AO, starting from the description of the Shack-Hartmann method, which allowed the first in vivo measurement of the eye's wave aberration, the wavefront sensing technologies (WSTs), and their principles. Then, the limitations of the ocular wavefront ascribed to the IOL polymeric materials and design, as well as future perspectives on improving patient vision quality and meeting clinical requests, are described.

Predictors of Visual Acuity Improvement and Supernormal Vision After Refined Single-Step Transepithelial Photorefractive Keratectomy

PURPOSE

To investigate predicting factors of visual acuity improvement and achieving uncorrected (UDVA) or corrected (CDVA) distance visual acuity supernormal vision (⩾ 15/10; Snellen 20/13) 1 year after refined transepithelial photorefractive keratectomy (TransPRK).

METHODS

In this retrospective case series, a total of 155 eyes with myopia (mean ± standard deviation = -3.53 ± 1.81 diopters) with and without astigmatism (range = 0.25 to 4.50 diopters) were recruited and observed for 1 year. Patients underwent refined single-step TransPRK using the SCHWIND AMARIS 500 laser (SCHWIND eye-tech-solutions GmbH, Kleinostheim, Germany). The main predicting factors of postoperative supernormal vision and visual acuity improvements were sought by statistical modeling.

RESULTS

Logistic models showed mesopic contrast sensitivity, high laser fluence, and coma higher-order aberration (HOA) as predicting factors for both UDVA and CDVA super-normal vision. Myopia, astigmatism, dynamic cyclotorsion correction, optical zone, and transitional zone showed associations only in simple models and were not retained in multivariable models. According to the linear regression models, CDVA, mesopic contrast sensitivity, coma HOA, and keratometry were common predictors of both postoperative UDVA and CDVA improvement compared to preoperative UDVA. Astigmatism, optical and transitional zones, and high laser fluence were common predictors only in simple regression models.

CONCLUSIONS

Through statistical modeling, preoperative CDVA, mesopic contrast sensitivity, coma HOA, and simulated keratometry were found to be the main factors that predicted improvement of both postoperative CDVA and UDVA compared to preoperative CDVA. Furthermore, mesopic contrast sensitivity, coma HOA, and high laser fluence were the common predictors of achieving both CDVA and UDVA supernormal vision 1 year after refined single-step TransPRK. [J Refract Surg. 2019;35(12):771-780.].

Irregular Astigmatism and Higher-Order Aberrations in Eyes With Dry Eye Disease

Visual disturbances were included in the definition of dry eye disease in the 2007 Dry Eye Workshop report. As a result, quality of vision (QoV) in dry eye patients has received increased attention. Corneal topography and wavefront sensors have been used to objectively and quantitatively evaluate optical quality, with data showing increases in irregular astigmatism and higher-order aberrations (HOAs) in dry eye patients. Furthermore, ocular optical characteristics are influenced by the tear film, which constantly fluctuates over time. Therefore, dynamic quantitative assessments of optical quality with continuous measurements are essential to understanding QoV in dry eye patients. This review summarizes what is known and what advances have been made in evaluating and understanding QoV in dry eye patients. In particular, corneal topographic and wavefront analyses, conducted both overseas and in Japan, are described.

Measuring Ocular Aberrations Sequentially Using a Digital Micromirror Device

The Hartmann–Shack wavefront sensor is widely used to measure aberrations in both astronomy and ophthalmology. Yet, the dynamic range of the sensor is limited by cross-talk between adjacent lenslets. In this study, we explore ocular aberration measurements with a recently-proposed variant of the sensor that makes use of a digital micromirror device for sequential aperture scanning of the pupil, thereby avoiding the use of a lenslet array. We report on results with the sensor using two different detectors, a lateral position sensor and a charge-coupled device (CCD) scientific camera, and explore the pros and cons of both. Wavefront measurements of a highly aberrated artificial eye and of five real eyes, including a highly myopic subject, are demonstrated, and the role of pupil sampling density, CCD pixel binning, and scanning speed are explored. We find that the lateral position sensor is mostly suited for high-power applications, whereas the CCD camera with pixel binning performs consistently well both with the artificial eye and for real-eye measurements, and can outperform a commonly-used wavefront sensor with highly aberrated wavefronts.

Effects of tear film dynamics on quality of vision

The precorneal tear film is maintained by blinking and exhibits different phases in the tear cycle. The tear film serves as the most anterior surface of the eye and plays an important role as a first refractive component of the eye. Alterations in tear film dynamics may cause both vision-related and ocular surface-related symptoms. Although the optical quality associated with the tear film dynamics previously received little attention, objective measurements of optical quality using wavefront sensors have enabled us to quantify optical aberrations induced by the tear film. This has provided an objective method for assessing reduced optical quality in dry eye; thus, visual disturbances were included in the definition of dry eye disease in the 2007 Dry Eye Workshop report. In addition, sequential measurements of wavefront aberrations have provided us with valuable insights into the dynamic optical changes associated with tear film dynamics. This review will focus on the current knowledge of the mechanisms of wavefront variations that are caused by different aspects of tear film dynamics: specifically, quality, quantity and properties of the tear film, demonstrating the respective effects of dry eye, epiphora and instillation of eye drops on the quality of vision.

The impact on human visual performance when viewing 2-D and 3-D movies

BACKGROUND AND OBJECTIVE:

To examine the human visual performance (wavefront aberration) and subjective questionnaire (SQ) of visual fatigue when viewing 2-D and 3-D movies.

METHODS:

Thirty healthy adults observed 2-D and 3-D movies on the same television from a 3m distances during 2D, 3D-A (with better 3D glasses), and 3D-B (with poorer 3D glasses) viewing conditions. Visual quality index, including modulation transfer function index (MTFI), higher order aberration root mean square (RMS), vertical coma (VC), horizontal coma (HC) and spherical aberration (SA), were assessed before and after each viewing condition. One-way repeated measures ANOVA was performed to assess the changes of each test variable before and after movie viewing.

RESULTS:

Participants watching movies with 3D-B conditions experienced higher change of MTFI, RMS, VC and HC but smaller SQ, compared with 2D and 3D-A (P< 0.05). Additionally, higher MTFI but smaller SQ was found for 3D-A compared with 2D viewing condition (P< 0.05).

CONCLUSIONS:

While prolonged viewing 2-D and 3-D movies would lead to poorer visual performance, 3-D glasses with better quality can play the major role in reducing visual ability for users. The change of human eye wavefront aberration might be useful for the evaluation of visual fatigue in the future.

Clinical features of subepithelial layer irregularities of cornea

PURPOSE

To illustrate surgical outcomes of subepithelial irregularities that were identified incidentally during laser refractive surgery.

MATERIALS AND METHODS

The study group consisted of 406 patients who underwent 787 surface ablation refractive surgeries. Ophthalmologic evaluations were performed before each procedure and at 1, 3 and 6 months post-operatively. Subepithelial irregularities were evaluated by analyzing still photographs captured from video recordings. Sizes and locations were determined by a calibrated scale located at the major axis of the tracking system's reticle.

RESULTS

Subepithelial irregularities were identified in 27 eyes during 787 surface ablation refractive surgeries. Most of the subepithelial irregularities did not show any abnormalities in the wavefront aberrometer. However, one case with diameter greater than 1.00 mm and one case of clustered multiple subepithelial irregularities with moderate size were corresponded significant coma (Z31) and increased higher order aberration (HOA) in the HOA gradient map.

CONCLUSIONS

Corneal subepithelial irregularities may be related to problems that include significantly increased localized HOA and remaining permanent subepithelial opacity. Subepithelial irregularity should be considered even if the surface of the cornea is intact and there are no specific findings measured by corneal topography.

Higher-order aberrations and visual acuity after LASEK

BACKGROUND

To determine ocular higher-order aberrations (HOAs) in eyes with supernormal vision after myopic astigmatic laser subepithelial keratomileusis (LASEK) and to compare the findings with those in eyes with natural supernormal vision.

METHODS

Ocular HOAs were measured after LASEK in 20 eyes of 12 myopic astigmatic patients with postoperative uncorrected visual acuity (UCVA) of >20/16 (group 1). Patients who were included in the study had no visual symptoms like glare, halo or double vision. The measurements were taken 8.3 +/- 3 months after LASEK surgery. In group 2 ocular HOAs were examined in 20 eyes of 10 subjects with natural UCVA of >20/16 as a control. Measurements were taken across a pupil with a diameter of 4.0 mm and 6.0 mm. Root-mean-square (RMS) values of HOAs, Z(3)-1, Z(3)1, Z(4)0, Z(5)-1, Z(5)1 and Z(6)0 were analyzed.

RESULTS

The mean RMS values for each order were higher in group 1 when compared with group 2 at 4.0 mm and 6.0 mm pupil diameters. There was no statistically significant difference between groups in spherical and coma aberrations (P > 0.05). Mean RMS values for total HOAs were 0.187 +/- 0.09 microm at 4.0 mm and 0.438 +/- 0.178 microm at 6.0 mm pupil in group 1 and 0.120 +/- 0.049 microm at 4.0 mm and 0.344 +/- 0.083 microm at 6.0 mm pupil in group 2. The difference between groups in total HOAs was statistically significant at 4.0 mm and 6.0 mm pupil diameters (P < 0.05).

CONCLUSION

Ocular HOAs exist in eyes with supernormal vision. After LASEK, the amount of HOAs of the eye increases under both mesopic and photopic conditions. However the amount of HOA increase does not seem to be consistent with visual symptoms.

Comparison of higher-order aberrations between eyes with natural supervision and highly myopic eyes in Koreans

Purpose

To describe the characteristics and investigate the differences of higher-order aberrations (HOAs) between the eyes with a natural, uncorrected visual acuity (UCVA) of 20/12 and eyes with highly myopic eyes in Korean adults.

Methods

Thirty-one eyes of 20 subjects with UCVA of 20/12 (Group 1) and 54 eyes of 36 myopic patients with greater than -6 diopters (Group 2) were analyzed for type and magnitude of HOAs across a 6.0 mm pupil. HOAs were measured by Wavescan (VISX, Santa Clara, CA, USA) in natural scotopic conditions and were presented as root-mean-square (RMS:µm) in Belle aberration maps.

Results

The mean spherical equivalent (SE) of manifest refraction was -0.15±0.25 D (range: +0.37 to -0.50 D) in Group 1 and -7.25±0.78 D (range: -6.00 to -9.25 D) in Group 2. The total root-mean-square (RMS) values of HOAs for Group 1 and Group 2 were 0.28±0.09 µm and 0.27±0.087 µm, respectively (P>0.05). The mean values of coma, trefoil, and spherical aberration were 0.14±0.091 µm, 0.14±0.089 µm, 0.091±0.059 µm in Group 1 and 0.16±0.077 µm, 0.14±0.073 µm, 0.082±0.059 µm in Group 2, respectively.

Conclusions

This study helped establish ocular aberration standards for those with natural supervision and those with highly myopic eyes among Koreans. Individuals with natural supervision had significant amounts of HOAs, and there was no significant difference in the amount of HOAs between the two groups. The index of higher-order aberrations may not be a perfect predictor of the amount of refractive error.

Changes of Ocular Higher Order Aberration in On- and Off-Eye of Rigid Gas Permeable Contact Lenses

PURPOSE

To investigate ocular higher order aberration (HOA) changes caused by rigid gas permeable (RGP) contact lens (CL) wear.

METHODS

Twenty-two eyes of 22 myopic patients and 14 eyes of 14 keratoconic patients who were fitted with an RGP CL were enrolled to examine ocular HOAs using a Hartmann-Shack wavefront sensor before and after RGP wear. Root mean square (RMS) values and Zernike coefficients in RGP-on and RGP-off eyes were compared for both myopic and keratoconic eyes, or between patient groups divided according to their prefitted total HOA value (RMS<0.33 microm or>or=0.33 microm in myopic eyes and RMS<0.46 microm or>or=0.46 microm in keratoconic eyes). All HOA values were recomputed for a 4-mm pupil for comparison purposes.

RESULTS

In keratoconic eyes, RGP CL changed the direction of vertical coma from -0.185 to 0.134 microm (p=0.024). In the low HOA myopic group, total HOA increased from 0.23 to 0.35 microm (p=0.006) by RGP CL wear, mainly due to increased coma aberration from 0.0951 to 0.2146 microm (p=0.006). The direction of vertical coma changed from the inferior to superior cornea in the low HOA group (p=0.020). In the high HOA keratoconic group, total HOA decreased from 0.54 to 0.36 microm (p=0.049), and the direction of the vertical coma changed from the inferior to superior cornea (p=0.049).

CONCLUSIONS

RGP CL wear may enhance or reduce HOA based on original existing ocular aberration mainly through directional changes in vertical coma.

Phototherapeutic Keratectomy for Epithelial Irregular Astigmatism: An Emphasis on Map-Dot-Fingerprint Degeneration

PURPOSE

To study the changes in irregular astigmatism in patients with recurrent corneal erosion syndrome due to map-dot-fingerprint degeneration and to demonstrate that both symptomatic and asymptomatic map-dot-fingerprint degeneration/recurrent corneal erosion syndrome may be related to irregular astigmatism, which can effectively be corrected by phototherapeutic keratectomy (PTK) or standard spherical photorefractive keratectomy (PRK).

METHODS

Eleven eyes with irregular astigmatism related to map-dot-fingerprint degeneration/recurrent corneal erosion syndrome with and without changes at the slit-lamp microscope were treated with PTK or spherical PRK, which was performed with a VISX S2 or S4 excimer laser. All eyes underwent videokeratography performed pre- and postoperatively using either the Tomey TMS-2N Topographic Modeling System or EyeSys Technologies Corneal Analysis System 2000.

RESULTS

Mean pre- and postoperative best spectacle-corrected visual acuity (BSCVA) was -0.18 +/- 0.14 logMAR and 0.04 +/- 0.04 logMAR, respectively. This improvement in BSCVA was statistically significant. The mean gain in Snellen lines was 2.4 +/- 2.1. Preoperative corneal videokeratography showed irregular astigmatism with an elevation pattern that was corrected in all eyes despite the fact that no astigmatic photorefractive correction was performed.

CONCLUSIONS

Following PTK, eyes with irregular astigmatism related to map-dot-fingerprint degeneration showed significant improvement in BSCVA and correction of irregular astigmatism as revealed by videokeratography. This study shows that irregular astigmatism can be exclusively of epithelial origin and in some eyes abnormal corneal epithelium may create optical aberrations. This possibility should be taken into account when, for example, wavefront-guided stromal photoablation procedures are being planned.

Measurement of Contrast Sensitivity and Glare Under Mesopic and Photopic Conditions Following Wavefront-guided and Conventional LASIK Surgery

PURPOSE

To compare contrast and glare vision in a prospective study of eyes treated using conventional and wavefront-guided LASIK surgery. The reproducibility of a glaremeter device used to quantitatively measure glare and halo was also determined.

METHODS

Ninety-two eyes of 46 patients underwent conventional LASIK surgery and 104 eyes of 52 patients underwent wavefront-guided LASIK surgery. Visual acuity, glare disability measured using a glaremeter, and contrast sensitivity assessed using a Pelli-Robson chart were measured monthly for 6 months postoperatively. Glaremeter testing was performed under both mesopic (5.4 +/- 0.4 cd/m2) and photopic (78.3 +/- 4.4 cd/m2) conditions. To evaluate the reproducibility of the glaremeter, 36 eyes of 18 nonoperated myopic patients were tested.

RESULTS

The coefficient of variation and the reliability coefficient for the glare test were 13.6% and 95.2%, respectively. The glaremeter showed that glare disability under mesopic conditions differed between conventional and wavefront-guided LASIK eyes over 6-month follow-up (907.5 +/- 491.5 vs 986.1 +/- 448.0 pixels preoperatively and 1717.1 +/- 521.2 vs 1407.8 +/- 411.3 pixels at 6 months, P<.0001). At 6 months, contrast sensitivity log values were 1.62 +/- 0.31 and 1.78 +/- 0.34 for conventional and wavefront-guided LASIK eyes, respectively (P=.010). The visual complaint score was lower in the wavefront-guided LASIK group (P=.0116).

CONCLUSIONS

Compared to conventional ablation, wavefront-guided ablation provided superior outcomes in terms of postoperative glare under mesopic conditions, subjective complaints, and contrast sensitivity. In addition, it appears the glaremeter can be used for clinical quantitative evaluation of glare and halo.

Optical Factors in Increased Best Spectacle-corrected Visual Acuity After LASIK

PURPOSE

To study the factors that correlate with improved best spectacle-corrected visual acuity (BSCVA) after LASIK.

METHODS

This was a nonrandomized, prospective clinical trial of 850 eyes from 480 patients undergoing LASIK for myopia, hyperopia, and mixed astigmatism. The mean preoperative spherical equivalent refraction was -3.75+/-4.82 diopters (D) (range: -13.88 to 6.00 D). From this population, 72 eyes (including 22 amblyopic eyes) from 43 patients were found to have improved BSCVA 6 months after LASIK. All patients underwent LASIK with the NAVEX platform. These eyes were analyzed to evaluate factors that correlated with improved BSCVA. Pre- and postoperative BSCVA, refraction, pupil diameter, corneal topography, asphericity (Q value), total aberrations, and higher order wavefront aberrations were analyzed. All wavefront aberrations were measured using the NIDEK Optical Path Difference Scan aberrometer (OPD-Scan) preoperatively and at 6 months postoperatively.

RESULTS

Postoperatively, the mean sphere was -0.44 1.30 D (range: -4.50 to +2.50 D). The mean increase in BSCVA was 0.15+/-0.09 logMAR. A statistically significant negative correlation was observed between the increase in BSCVA and the preoperative BSCVA (P<.01). Mixed astigmatic and highly myopic eyes are more likely to gain BSCVA after LASIK than moderately myopic (P<.05) and hyperopic eyes (P<.001). In patients with myopia, the amount of BSCVA improvement correlated with the magnitude of the correction (P<.05). The induction of spherical aberration negatively correlated with the increase in BSCVA (P<.05). There were no significant differences between normal eyes and amblyopic eyes with respect to postoperative improvement in BSCVA (P>.05).

CONCLUSIONS

Decreased preoperative BSCVA, lower total spherical aberration induction, and preoperative mixed astigmatism and high myopia correlate with an increase in BSCVA after LASIK.

Ocular higher-order aberrations in eyes with supernormal vision

PURPOSE

To quantify ocular higher-order aberrations (HOAs) in eyes with supernormal vision, that is, natural uncorrected visual acuity (UCVA) > or = 20/15, to analyze the correlation between ocular HOAs and age in these eyes, and to investigate the correlation of HOAs between right and left eyes.

DESIGN

Observational case series.

METHODS

Ocular HOAs were examined across a naturally dilated pupil with a diameter > or = 6.0 mm in 70 eyes of 35 subjects with > or = 20/15 UCVA (mean age 24.3 years +/- 7.7 [SD]) using the Nidek OPD scan wavefront aberrometer. Root-mean-square (RMS) values of HOA, total spherical aberration (TSA), total coma (TC), and total trefoil (TT) were analyzed. Correlation analysis was performed to assess the association between ocular HOAs and age and the correlation of HOAs between right and left eyes.

RESULTS

Mean RMS values were 0.334 +/- 0.192 microm for HOA, 0.110 +/- 0.077 microm for TSA, 0.136 +/- 0.081 microm for TC, and 0.268 +/- 0.220 microm for TT. There were no significant differences in the mean values of HOA, TSA, TC, and TT between right and left eyes. The Pearson correlation coefficient between right and left eyes for TSA was 0.764 (P<.0001). No significant correlation was found between right and left eyes for HOA, TC, and TT. No significant correlation was found between each of the ocular aberrations and age.

CONCLUSIONS

The amount of ocular HOAs in eyes with natural supernormal vision is not negligible, and is comparable to the reported amount of HOAs in myopic eyes.

Measuring of ocular wavefront aberration in large pupils using OPD-scan

Wavefront analysis using a scanning slit refractometer (the OPD-Scan) was evaluated in both artificial and human eyes, in comparison with the Hartmann-Shack wavefront sensor (H-S) currently often used. Comparison of different methods and configurations carried out in the artificial eyes yielded basically the same results in moderate refractive error cases. There was a closer match between the RMS (root mean square) wavefront error obtained by OPD-Scan and H-S in the 6 mm pupils than in the 4 mm pupils of the same normal human eyes. Although OPD-Scan employs a different approach in determining aberration, the aberration value is similar to that of H-S, especially in large pupils.

Wavefront aberrations measured with Hartmann-Shack sensor in patients with keratoconus

OBJECTIVE

To compare the ocular wavefront aberrations of normal and keratoconic eyes and to describe the characteristics of the higher-order aberrations in eyes with keratoconus.

DESIGN

Prospective case control and observational study.

PARTICIPANTS

Thirty-five keratoconic eyes and thirty-eight normal controls.

METHODS

Higher-order aberrations in refraction were measured with a wavefront sensor, and those aberrations resulting from the cornea were evaluated by videokeratographic data.

MAIN OUTCOME MEASURES

Coma-like (S(3 + 5)), spherical-like (S(4 + 6)), and total (S(3 + 4 + 5 + 6)) higher-order aberrations in both refraction and the cornea.

RESULTS

The mean +/- standard deviation of S(3 + 5) (1.88 +/- 1.16), S(4 + 6) (0.70 +/- 0.55), and S(3 + 4 + 5 + 6) (2.03 +/- 1.23) in refraction (6-mm diameter, root mean square, micro m) were significantly higher in the keratoconic eyes than in normal controls (0.26 +/- 0.10, 0.19 +/- 0.10, 0.34 +/- 0.11, respectively; Mann-Whitney U test, P = 0.001). Coma-like aberrations were 2.32 times larger than spherical-like aberrations in keratoconic eyes.

CONCLUSIONS

The increase of ocular higher-order aberrations in keratoconic eyes results from an increase of corneal higher-order aberrations. Coma-like aberrations were dominant compared with spherical-like aberrations in keratoconic eyes. Wavefront sensing will enable us not only to evaluate the quality of vision but also to differentiate keratoconic eyes from normal eyes by analyzing the characteristics of the higher-order aberrations.

Effect of tear film break-up on higher-order aberrations measured with wavefront sensor

PURPOSE

To investigate whether optical wavefront aberrations vary with tear film break-up.

DESIGN

Observational case series.

METHODS

Higher-order aberrations were examined for 20 eyes of 20 normal subjects with a Hartmann-Shack wavefront sensor before and after tear film break-up.

RESULTS

Higher-order aberrations for photopic vision (central 4 mm diameter) after tear film break-up increased 1.44 fold compared to higher-order aberrations before tear film break-up (P =.001, paired t-test). Higher-order aberrations after tear film break-up for scotopic vision (central 6 mm diameter) were also 1.23 times higher than those before break-up (P =.005, paired t-test).

CONCLUSION

Wavefront sensing enabled us to evaluate the induced irregular astigmatism caused by tear film break-up quantitatively. Wavefront aberrations should be measured carefully to avoid the effects of tear film break-up, especially in wavefront-guided refractive surgery.