Bilateral symmetry in vision and influence of ocular surgical procedures on binocular vision: A topical review

Stereoacuity and Aniseikonia: Evaluation Before and After Bilateral Implantation of Three Types of Presbyopia-Correcting Intraocular Lenses in Uncomplicated Phacoemulsification with Due Consideration of Interocular Differences in Higher Order Aberrations, Axial Lengths, Refractive Errors, and Acuities

Purpose

To determine if the changes in stereoacuity and aniseikonia, following bilateral implantation of presbyopia correcting intraocular lenses could be predicted from preoperative measurements of higher order aberrations (HOAs), axial lengths (AL), refractive errors (RE) and corrected visual acuities (CVAs).

Patients and Methods

Stereoacuity (Randot tests, @6m & 40cm, in steps of 20 arcsecs") vertical and horizontal aniseikonia (Awaya test @6m, in steps of 1%) with best correction and HOAs (Shack-Hartmann aberrometer) were measured before, 3 and 6 months after uncomplicated bilateral phacoemulsification. Twenty patients (I) underwent a mix-and-match procedure (Tecnis MF, ZKB00 in one eye and ZLB00 in the other), 17 (II) were implanted with a trifocal (AT LISA 839 triMP) and 18 (III) with a one-piece diffractive (Synergy OU) intraocular lens. The resultant aniseikonia (AR) of vertical and horizontal pairs of aniseikonia measurements was calculated using the Pythagorean theorem. Twenty untreated age/gender matched cases were recruited as controls (IV).

Results

The key results (p < 0.001) were a) stereoacuity at distance (SAD) and near (SAN) improved, AR reduced in groups I, II & III remaining unchanged in group IV; b) some significant intergroup differences in SAD, SAN & AR were detected at postop; c) at 6 months postop, changes (Δ=pre- minus postoperative value) correlated with preoperative values (x). Linear regression revealed, I ΔSAD=0.66x-57.47 [0.832, ±66.4], ΔSAN=0.96x-34.59 [0.821, ±16.9], ΔAR=0.93AR-2.12 [0.795, ±1.4] II ΔSAD=0.79x-62.91 [0.916, ±38.1], ΔSAN=0.96x-31.49 [0.892, ±8.0], ΔAR=0.91AR-0.91 [0.839, ±1.3] III ΔSAD=0.67x-35.50 [0.991, ±23.7], ΔSAN=0.88x-38.51[0.988, ±10.6], ΔAR=0.86AR-0.96 [0.900, ±1.3]. Figures in parentheses are the corresponding rs and ±limits of agreement between actual and estimated values. Definitive overarching associations connecting interocular differences in HOAs, AL, RE, and CVAs with SAD, SAN and AR were not found.

Conclusion

Changes in stereoacuity and aniseikonia can be predicted using preoperative values. ΔSAN can be predicted within ±1, and ΔAR within ±2, scale divisions. In group III ΔSAD can be predicted within ±1, and in group I ±3, scale divisions.

Prediction of total corneal power in keratoconus using anterior surface data

CLINICAL RELEVANCE

Keratoconus results in an increase in anterior and posterior curvatures and a reduction in corneal thickness. Anterior corneal ectasia is partially compensated by remodelling the corneal epithelium. Therefore, there is an alteration in the relationship between corneal surfaces and variation in corneal power. The variation in corneal power is one of the sources that induces errors in IOL power calculation.

BACKGROUND

This study aimed to assess a method for predicting total corneal power in keratoconus using several anterior surface parameters at 3 mm and 4 mm.

METHODS

    Tomographic data obtained using Pentacam (Oculus, Germany) were analysed from 280 eyes of 140 patients with keratoconus using anterior and posterior keratometry, anterior Q-value at 8 mm, central corneal thickness, Kmax location and value, and true net power at 4 mm (TNP). Calculated total corneal power (TCPc) at 3 mm was obtained using the Gauss formula. Predicted total corneal power at 3 mm (TCPp3) and 4 mm (TCPp4) was obtained from univariate (TCPp3u and TCPp4u) and multivariate linear regression formulae (TCPp3m and TCPp4m). SimK, anterior Q-value, vertical location, and Kmax value were used in the multivariate formulae. Mean absolute error (MAE) and median absolute error (MedAE) were also calculated. Absolute frequencies within dioptric ranges of all formulas divided for keratoconus grading were evaluated.

RESULTS

TCPc and TNP exhibited a good correlation (R2 = 0.58, p < 0.05) with a higher dispersion above 50 D of corneal power. Highly significant correlations were observed between TCPp3u and TCPc (R2 = 0.978, p < 0.05) and TCPp3m and TCPc (R2 = 0.989, p < 0.05). Lower but significant correlations were observed between TCPp4u and TNP (R2 = 0.692, p < 0.05) and between TCPp4m and TNP (R2 = 0.887, p < 0.05). The best results for TCP prediction at 3 and 4 mm were obtained with TCPp3m and TCPp4m as follows: MAE of TCPp3m was 0.24 ± 0.20 (SD) D with MedAE of 0.20 D, while MAE of TCPp4m was 0.96 ± 0.77 D with MedAE of 0.80 D. The 3 mm multivariate regression formula results in higher absolute frequencies of prediction errors in the total eyes within 0.5 D (93%) than the univariate formula (81%). At 4mm, the multivariate regression formula has a lower percentage within 0.5 D (32%) than the univariate formula (41%), but the percentage of the multivariate formula is higher within 1 D (63%) than the univariate formula (56%).

CONCLUSION

All formulas show a decrease in accuracy with increasing grades of keratoconus. Multivariate linear regression formulae using only anterior surface data can predict TCP with good approximation in eyes with keratoconus in cases where posterior surface parameters are unavailable. The vertical location of Kmax and the anterior asphericity could play a relevant role in the prediction of total corneal power in keratoconus.

Comparison between IOL MASTER 500 and MYAH with vector analysis in low and mild anterior corneal astigmatism

PURPOSE

Evaluate the agreement between IOL Master 500 (Carl Zeiss Meditec AG, Germany) and MYAH (Topcon EU, Visia Imaging, Japan) in measuring axial length, keratometry, and anterior corneal astigmatism.

SETTING

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

METHODS

In this prospective study, 40 eyes (right eye 25, left eye 15) of 40 patients were included. Axial length (AL), keratometry (K1, K2), and anterior corneal astigmatism (ACA) were measured. AL, mean K (Kavg) and magnitude of ACA were compared using Bland - Altman plot analysis, parametric and nonparametric statistical analysis. The difference vector and angle of error of the ACA measured by the two devices were evaluated by vector analysis using polar diagrams.

RESULTS

Mean and standard deviation with IOL Master and with MYAH device was for AL 24.25 ± 1.22 mm and 24.25 ± 1.22 mm (p = .99), for Kavg 42.75 ± 1.53 D and 42.85 ± 1.52 D (p = .78), for Magnitude of ACA 1.00 ± 0.58 D and 0.89 ± 0.56 D (p = .38) respectively. High correlations were found for AL (R² = 0.999), Kavg (R² = 0.996), and ACA Magnitude (R² = 0.889). Bland-Altman analysis of the two devices found high agreement and absence of proportional bias (MYAH-IOL MASTER) were found between the two assessments for AL (bias = -0.0005 mm, p = .93), Kavg (bias = 0.0955 D, p = .76) and ACA (bias = 0.11 D, p = .41). Limit of agreement (upper/lower LoA, 95%CI) were respectively +0.057/-0.058 mm for AL, + 0.29/-0.09 D for Kavg and +0.49/-0.27 D for ACA. No statistical difference was found between the x-component and y-component of the ACA vector (p > .01), the difference vector (IOL MASTER-MYAH) was +0.14 D axis 159 with an absolute mean angle of error of 7.2 ± 7.5 degree.

CONCLUSIONS

The instruments appear to be interchangeable for measurements of AL, keratometry, and magnitude of ACA with high agreement between the two devices. Also, in the presence of low astigmatism, the two instruments give the same results in terms of ACA.

Method to determine the centration of a lenticule of tissue extracted from a cornea

A simple and novel method to analyse the centration of a lenticule of tissue extracted from a cornea has been developed, in which the centre of "mass" of the individual differences between post and preoperative maps of several corneal metrics represents the lenticule centration and its spatial distance to a reference point (aimed centration) determines the decentration. Different parameters have been evaluated to weight the centre of "mass". The robustness of the methods has been evaluated using perturbation analysis (adding white-noise to the data) based on realistic uncertainties. A clipped analysis has been performed to prevent large, localised areas of lacking/missing data from affecting the centre of "mass". The method has been tested on a pilot cohort of clinical data showing 30% and 63% of the treatments within 200 µm of decentration for corneal thickness and refractive equivalent power, respectively. Except for anterior elevation with a total standard deviation of 17 µm, all other metrics show excellent precision of ∼5 µm. The method provides a reliable and objective way to determine the centration of a lenticule of tissue extracted from a cornea and it can be applied to any topo- or tomographic derived metric.

Impact of Degraded Optics on Monocular and Binocular Vision: Lessons from Recent Advances in Highly-Aberrated Eyes

PURPOSE

Optical imperfections of the eye, characterized by higher-order wavefront aberrations, are exaggerated in corneal disease (e.g., keratoconus) and iatrogeny (e.g., keratorefractive surgery for myopia correction, keratoplasty for optical clarity restoration). This article reviews the recent advances on this topic for a comprehensive understanding of how optical degradations in disease models impact retinal image quality and monocular and binocular visual performance.

METHODS

Published literature over the last decade on retinal image quality and/or monocular and binocular visual functions with corneal irregularity was reviewed based on their relevance to the current topic, study population and strength of study design. The literature was summarized into four themes: 1) wavefront errors and retinal image quality of highly aberrated eyes, 2) monocular and binocular vision loss consequent to degraded optics and visual strategies to optimize performance, 3) impact of optical correction modalities on visual performance and 4) implications for clinical management of patients.

RESULTS

Across the 46 articles reviewed, the results clearly indicated that an increase in higher-order aberrations across these conditions had a significant negative impact on the patient's retinal image quality, and monocular and binocular visual functions. Interocular differences in retinal image quality deteriorated visual performance more than an overall worsening of image quality bilaterally. Minimizing optical degradation using rigid contact lenses and adaptive optics technology significantly improves retinal image quality and monocular and binocular vision, but performance remains sub-optimal relative to age-similar healthy controls.

CONCLUSION

Corneal disease and iatrogeny are useful models to understand the impact of optical degradation on retinal image quality and visual performance. Clinical management will greatly benefit from equalizing retinal image quality of both eyes of these patients. Future studies that deepen our understanding of the structure-function relation in these conditions are desirable for advancing vision science in this area and for developing novel clinical management strategies.

Sutureless Amniotic Membrane Transplantation in Inflammatory Corneal Perforations

Introduction: The aim of this study was to evaluate the efficacy of sutureless amniotic membrane transplantation (SAMT) in patients with corneal perforation secondary to ocular surface inflammatory diseases. Methods: Twelve eyes of eleven patients with corneal perforation associated with Sjögren’s syndrome and ocular cicatricial pemphigoid were included. Surgical procedure consisted in the application of two layers of amniotic membrane covering the corneal perforation and a therapeutic contact lens placed above the two layers, followed by sutureless tarsorrhaphy with Steri-strip applied for 15 days to immobilize the eyelids. All patients underwent slit-lamp examination, fluorescein corneal staining, and anterior segment optical coherence tomography (AS-OCT), preoperatively and post-surgery, weekly for one month, and then every two weeks for three months. Results: All 12 eyes had complete resolution of corneal perforation. Pachymetry measurements improved in all eyes, and complete healing of the corneal ulcer was obtained following treatment and maintained up to 3 months follow-up in all patients. Conclusions: SAMT was proven to be a safe and effective option for the management of inflammatory corneal perforation. The procedure is non-traumatic and easy to perform since the surgical technique is sutureless and does not require topical therapy because it takes advantage of the intrinsic properties of the membrane itself.

Theta burst stimulation in adults with symmetric and asymmetric visual acuity

PURPOSE

Theta Burst Stimulation can influence adult neuro-visual response in imbalanced visual pathways, possibly by influencing cortical excitability. Our objective was to compare suppressive imbalance (SI) and visual acuity (VA) after applying repetitive Transcranial Magnetic Stimulation between groups of subjects with normal binocular vision, visual asymmetry, and amblyopia.

METHODS

Thirty-five volunteers between 19 and 51 years of age were split into three groups: 6 volunteers with asymmetric VA (group A); 19 amblyopes (group B); and 10 subjects with normal binocular vision (group C). VA and SI of all groups were evaluated before and after a single session of continuous Theta Burst Stimulation (cTBS) or placebo stimulation over the right occipital cortex.

RESULTS

In both groups A and B, we found a significant VA improvement in the non-dominant eye after cTBS (p = 0.04 and p = 0.01, respectively). In SI evaluation, group A and group B also revealed a significant improvement after the cTBS session (p = 0.03 and p = 0.01, respectively). Finally, in the group of volunteers with normal binocular vision and for placebo groups A and B, there were no significant differences in VA and SI after cTBS.

CONCLUSIONS

Amblyopic and visually asymmetric individuals improved VA and SI of the non-dominant eye after cTBS when compared to baseline and to placebo stimulation. These enhancements were not found in the group of volunteers with normal binocular vision. We can therefore reasonably assume that cTBS may interfere with the visual system of subjects that present some kind of asymmetry, possibly by improving neuronal imbalances.

Differences in Image Quality after Three Laser Keratorefractive Procedures for Myopia

SIGNIFICANCE

Psychophysical estimates of spatial and depth vision have been shown to be better after bilateral ReLEx small-incision lenticule extraction (SMILE) refractive surgery for myopia, relative to photorefractive keratectomy (PRK) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). The present study provides the optical basis for these findings using computational image quality analysis.

PURPOSE

This study aimed to compare longitudinal changes in higher-order wavefront aberrations and image quality before and after bilateral PRK, FS-LASIK, and SMILE refractive procedures for correcting myopia.

METHODS

Wavefront aberrations and image quality of both the eyes of 106 subjects (n = 40 for FS-LASIK and SMILE and n = 26 for PRK) were determined pre-operatively and at 1-week, 1-month, 3-month, and 6-month post-operative intervals using computational through-focus analysis for a 6-mm pupil diameter. Image quality was quantified in terms of its peak value and its interocular difference, residual defocus that was needed to achieve peak image quality (best focus), and the depth of focus.

RESULTS

The increase in root mean squared deviations of higher-order aberrations post-operatively was lesser after SMILE (1-month visit median [25th to 75th interquartile range], 0.34 μm (0.28 to 0.39 μm]) than after PRK (0.80 μm [0.74 to 0.87 μm]) and FS-LASIK (0.74 μm [0.59 to 0.83 μm]; P ≤ .001), all relative to pre-operative values (0.20 μm [0.15 to 0.30 μm]). The peak image quality dropped and its interocular difference increased, best focus shifted myopically by 0.5 to 0.75 D, and depth of focus widened significantly after PRK and FS-LASIK surgeries, all relative to pre-operative values (P < .001). All these changes were negligible but statistically significant in a minority of instances after SMILE surgery (P ≥ .01).

CONCLUSIONS

Although all three refractive surgeries correct myopia, the image quality and its similarity between eyes are better and closer to pre-operative values after SMILE, compared with FS-LASIK and PRK. These results can be explained from the underlying increase in higher-order wavefront aberrations experienced by the eye post-operatively.

Interocular Difference of Axial Length, Anterior Chamber Depth, Keratometry, Corneal Astigmatism According to Axial Length

Purpose: To investigate the interocular difference of axial length (AL), mean keratometry (K), corneal astigmatism and anterior chamber depth (ACD) according to AL without history of ocular surgery.Methods: This study was performed on 16,411 patients (32,825 eyes) who were measured AL, K, corneal astigmatism and ACD by IOL Master® from April 2007 to September 2016, excluding patients with missing values and extreme values in AL. After, patients were divided into four groups based on AL; AL < 24 mm, 24 mm ≤ AL < 26 mm, 26 mm ≤ AL < 28 mm, AL ≥ 28 mm, we investigated which variables were associated according to AL. To compensate for age and sex, 1:1:1:1 random matching was performed for age and sex.Results: The longer the average AL of both eyes, the greater the difference between the AL, ACD and mean corneal K of both eyes. The longer AL group had the deeper ACD, the flatter mean corneal K, the higher corneal astigmatism. The older age group had the more shallow ACD, the steeper mean corneal K, lower corneal astigmatism.Conclusions: Ophthalmologists have to be careful in setting fellow eye as control in treating or studying patients with long AL or axial myopia. Because, the longer the average AL of both eyes, the greater the difference between the AL, the ACD and the mean corneal K of both eyes.

Longitudinal Changes in Optical Quality, Spatial Vision, and Depth Vision after Laser Refractive Surgery for Myopia

SIGNIFICANCE

Laser refractive surgery procedures are efficacious at correcting myopia, but they result in long-term deterioration of optical quality that affects monocular and binocular visual performance. The study shows that the optical quality of the two eyes needs to be similar to optimize binocular visual performance after surgery.

PURPOSE

This study aimed to systematically analyze longitudinal changes in optical quality, high- and low-contrast logMAR acuity and random-dot stereoacuity before and after three refractive surgery procedures for correcting myopia.

METHODS

A total of 106 subjects (laser-assisted in situ keratomileusis, 40; photorefractive keratectomy, 26; small-incision lenticule extraction, 40) with myopia and astigmatism ≤1.5 D participated in this prospective cohort-based study. All aforementioned outcome variables were measured in both eyes pre-operatively and 1 week and 1, 3, and 6 months post-operatively.

RESULTS

Pre-operative myopic spherical equivalent of refraction (median [25th to 75th interquartile range], -6.4 D [-8.0 to -4.2 D] for laser-assisted in situ keratomileusis, -4.3 D [-5.0 to -3.5 D] for photorefractive keratectomy, -5.5 D [-6.5 to -4.3 D] for small-incision lenticule extraction) was corrected to within ±0.75 D of emmetropia in all cohorts up to 6 months post-operatively (P < .001). Higher-order wavefront aberrations, uncorrected high- and low-contrast logMAR acuity, and stereoacuity all worsened and remained so up to 6 months post-operatively, relative to pre-operative values (P < .001). Stereoacuity worsened with both interocular average and difference in the magnitude of higher-order aberrations, whereas logMAR acuities worsened only with interocular average of these aberrations (r ≥ 0.40; P < .01 for all).

CONCLUSIONS

Although the refractive surgery procedures tested here correct myopia, they result in a sustained (up to 6 months) loss of optical quality and spatial and depth-related visual functions post-operatively. Both interocular average and difference in the eye's optical quality seem to impair binocular visual functions after refractive surgery for myopia.

Topical lipoic acid choline ester eye drop for improvement of near visual acuity in subjects with presbyopia: a safety and preliminary efficacy trial

Objectives

This study evaluated the safety of topical lipoic acid choline ester (UNR844, 1.5%) ophthalmic solution and its efficacy in improving distance-corrected near visual acuity (DCNVA) in subjects with presbyopia.

Subjects and methods

This was a prospective, randomized, double-masked, and multicentre clinical trial. Subjects with a diagnosis of presbyopia (n = 75) were randomized 2:1 to UNR844 or placebo. On days 1–7, all subjects were dosed unilaterally (twice a day, b.i.d.) in their non-dominant eye to ensure safety and tolerability prior to days 8–91 when dosing was changed to bilateral (b.i.d.). Clinical assessments, including DCNVA and adverse events (AEs), were recorded at each study visit. Patients who completed the study were recruited into a non-interventional follow-up study that monitored them until 7 months after their final UNR844 exposure. The primary endpoints were safety and the mean change in DCNVA from baseline in the study eye.

Results

UNR844 administration (n = 50) produced no safety concerns and was well-tolerated, with no clinically-relevant changes in best-corrected distance visual acuity, pupil size, intraocular pressure, or discontinuations due to adverse events. DCNVA improved in the study eye in the UNR844 group compared to placebo during the 91 days of treatment [UNR844 vs. placebo, mean change in LogMAR (SD); −0.159 (0.120) vs. −0.079 (0.116)]. Bilateral DCNVA improved, with 53.1% UNR844 vs. 21.7% placebo subjects gaining ≥10 letters. Improvements in DCNVA were sustained at 5 and 7 months after UNR844 dosing ceased.

Conclusions

These results support further development of UNR844 ophthalmic solution for the treatment of presbyopia.

Direct Evidence of Symmetry between Bilateral Human Corneas in Biomechanical Properties: A Comparison Study with Fresh Corneal Tissue

Purpose. To investigate the difference between the eyes from the same human with respect to the biomechanical properties of fresh corneal tissues and investigate the assumption of similarity of the corneal biomechanical properties between the eyes. Methods. Strip specimens extracted through a small incision lenticule extraction (SMILE) surgery were tested using a uniaxial tensile test. The specimens were extracted vertically. Low-strain tangent modulus (LSTM), high-strain tangent modulus (HSTM), and tensile strength (${\sigma }_b$) were the biomechanical parameters used in the comparison of the eyes from the same human. Results. Ninety corneal specimens from 45 persons were included in this study. The LSTM of the left and right eyes were 1.34 ± 0.52 and 1.37 ± 0.46 MPa, while the HSTM were 50.53 ± 7.51 and 49.41 ± 7.01 MPa, respectively. There was no significant difference between the eyes in terms of LSTM, HSTM, and${\sigma }_b\left(P=0.813,0.335,\text{and\hspace{0.17em}}0.605,\text{resp}.\right)$. The LSTM and HSTM were significantly correlated with the spherical equivalent (SE) ($P\le 0.01,P=0.001$, resp.). Conclusions. The assumption that the corneal biomechanical properties of the eyes from the same human are similar has been confirmed for the first time using fresh human corneal tissue. This finding may be useful in further biomechanical studies.

A Geometric Theory Integrating Human Binocular Vision With Eye Movement

A theory of the binocular system with asymmetric eyes (AEs) is developed in the framework of bicentric perspective projections. The AE accounts for the eyeball's global asymmetry produced by the foveal displacement from the posterior pole, the main source of the eye's optical aberrations, and the crystalline lens' tilt countering some of these aberrations. In this theory, the horopter curves, which specify retinal correspondence of binocular single vision, are conic sections resembling empirical horopters. This advances the classic model of empirical horopters as conic sections introduced in an ad hoc way by Ogle in 1932. In contrast to Ogle's theory, here, anatomically supported horopteric conics vary with the AEs' position in the visual plane of bifoveal fixations and their transformations are visualized in a computer simulation. Integrating horopteric conics with eye movements can help design algorithms for maintaining a stable perceptual world from visual information captured by a mobile robot's camera head. Further, this paper proposes a neurophysiologically meaningful definition for the eyes' primary position, a concept which has remained elusive despite its theoretical importance to oculomotor research. Finally, because the horopteric conic's shape is dependent on the AE's parameters, this theory allows for changes in retinal correspondence, which is usually considered preformed and stable.

The Structure of the Lens and Its Associations with the Visual Quality

In humans, the lens is the organ with the ability to change morphology and refractive power, designated as accommodation, to focus light from various distances and obtain clear retinal image. The accommodative ability of the lens depends on its structure and biological parameters. The lens grows throughout the life, forming specific lens sutures and a unique gradient refractive index, and possesses regenerative ability under certain circumstances. Minimally invasive lens surgery that preserves endogenous lens epithelial stem/progenitor cells (LECs) can achieve functional lens regeneration in humans. The lens is the main source of intraocular aberration, especially intraocular higher-order aberrations (IHOAs) which is found to be binocularly symmetrical in phakic eyes. There is a compensation mechanism between corneal aberrations and lens aberrations. Therefore, the structure and the biological parameters of the lens, the binocular relationship of the lens and the correlation between the lens and cornea affect visual quality. This paper summarises the above findings and their current and potential applications in refractive surgeries, providing a comprehensive understanding of the lens as a strong determinant of visual quality in the optical system.

Profiles of intraocular higher-order aberrations in healthy phakic eyes: prospective cross-sectional study

Background

Ocular wavefront aberration is a crucial optical factor affecting retinal imaging. Internal aberrations contributed to compensation mechanism of ocular aberration. However, previous studies mainly focused on total and corneal higher order aberrations, and little is known about the profile of internal HOA (IHOA) in healthy subjects.

Methods

Participants with healthy crystalline lenses were prospective enrolled. The root mean square (RMS) of IHOAs for a pupil diameter of 4 mm were measured with an iTrace aberrometer. Lenticular parameters were measured with a swept source anterior segment optical coherence tomography (AS-OCT). Regression analyses were used to determine factors associated with logarithmic IHOAs.

Results

Sixty-six Chinese participants (132 eyes) ranging from 5 to 59 years were analyzed. Logarithmic IHOA was positively associated with axial length (AL) (coefficient =0.101, P=0.016), and negatively associated with ocular refraction (coefficient =-0.032, P=0.023). Logarithmic internal coma increased by 0.161/mm (P=0.016) as AL became longer and decreased by 0.081/diopter (P<0.001) as ocular refraction became hyperopic. Lens tilt (coefficient =-0.121, P=0.037), decentration (coefficient= 3.027, P=0.003), and radius of anterior lens surface curvature (RAL) (coefficient= 0.096, P=0.026) were associated with logarithmic internal trefoil. lens tilt was also associated with logarithmic internal spherical aberration (coefficient =-0.195, P=0.018) and second astigmatism (coefficient =-0.132, P=0.030). Binocularly, the extent of coma, trefoil was different, while that of spherical aberration, secondary astigmatism was consistent. The vectors of the same type of IHOAs were nearly paralleled.

Conclusions

IHOAs are mainly affected by ocular refraction, RAL, lens tilt and decentration. Intraocular differences and directions of higher-order aberrations follow certain rules, and their effects on visual function warrant further study.

The relationship between clinical measures of aniseikonia and stereoacuity before and after LASIK

PURPOSE

To determine the significance of changes and and inter-relationships between three markers of binocular function (aniseikonia, distance and near stereoacuity) following unremarkable LASIK at 3 and 6 months postoperatively.

METHODS

All patients underwent LASIK using the Schwind Amaris 750S and the flaps were created using Intralase 150 kHz. Patients were I, monocular myopes II, binocular myopes III, binocular hyperopes IV, binocular astigmats V, anisometropes and VI, matched age and gender control (n = 20 in each group except III where n = 18). Aniseikonia (Awaya test), distance and near stereoacuity (Randot tests) were measured before surgery, and at 3 and 6 months after surgery. At all times data were collected under constant conditions and analyzed using appropriate non-parametric statistical tests.

RESULTS

The following statistically significant changes were found after applying the Bonferroni correction (p ≤ 0.001); aniseikonia reduced (groups I, III, IV, V), stereoacuity improved at distance (groups I, III-V) and near (groups I, V). Inter-group differences in aniseikonia distance and near stereoacuity were significant preoperatively, but not postoperatively. In groups I, IV and V, the changes in aniseikonia and stereoacuity (near and distance) were significantly correlated with the preoperative value. Aniseikonia was significantly correlated with distance and near stereoacuity preoperatively but not postoperatively.

CONCLUSION

Binocular function improved in all groups after LASIK except in binocular myopes. In general, binocular function was still low compared with the control group at six months postoperatively. It is unclear why binocular function improved in the binocular astigmats.

Binocular vision alterations after refractive and cataract surgery: a review

To review binocular and accommodative disorders documented after corneal or intraocular refractive surgery, in normal healthy prepresbyopic patients. A bibliographic revision was performed; it included works published before 1st July 2017 where accommodation and/or binocularity was assessed following any type of refractive surgical procedure. The search in Pubmed yielded 1273 papers, 95 of which fulfilled the inclusion criteria. Few publications reporting binocular vision and/or accommodative changes after refractive surgery in normal subjects were found. The reduction in fusional vergence is the most frequently reported alteration. Anisometropia is an important risk factor for postoperative binocular vision-related complaints. Most diplopia-related visual complaints, irrespective of the surgical procedure, were in fact misdiagnosed preoperative disorders. The preoperative evaluation of patients seeking spectacle/contact lens independence should include a complete binocular and accommodation assessment where parameters such as the phoric posture, accommodative amplitude and facility, near point of convergence, fusional reserves and accommodative convergence/accommodation coefficient are measured. This would allow the identification of risk factors that could compromise the success of the refractive surgery and cause clinical symptoms.

Factors Associated With Ocular Cyclotorsion Detected by High-Speed Dual-Detection Eye Tracker During Single-Step Transepithelial Photorefractive Keratectomy

PURPOSE

To determine demographic, surgical, and preoperative visual factors affecting the level of static and dynamic cyclotorsion (SC and DC) in eyes undergoing single-step transepithelial photorefractive keratectomy (TransPRK).

METHODS

In this cross-sectional study, 386 patients with different types of refractive errors scheduled for single-step TransPRK were enrolled. A comprehensive profile of personal, optic, and visual characteristics of patients as surgical parameters were collected. Statistical modeling was used to explore correlates of SC and DC before and during the refractive procedure, respectively.

RESULTS

There was no difference in various indices of SC and DC between right and left eyes. Lower age (beta = -0.20), uncorrected (beta = -0.99) and corrected (beta = -0.72) visual acuities, and keratometry (beta = -0.09) were significantly associated with higher ranges of DC during the laser ablation procedure. Worse mesopic contrast sensitivity (beta = 0.24) and higher (beta = 0.002, left eyes) or lower (beta = -0.002, right eyes) kappa locus also showed significant associations with a higher range of DC. In cases of SC before the procedure, amount (beta = 0.46) and axis (beta = -0.003) of the astigmatism demonstrated notable associations.

CONCLUSIONS

Through comprehensive modeling, age, visual axis indices, visual acuity, and contrast sensitivity were found to be the main factors significantly associated with dynamic ocular globe cyclotorsions during single-step TransPRK. This could help identify eyes at higher risk of cyclotorsion and its potential complications in refractive surgery. [J Refract Surg. 2018;34(11):736-744.].

Assessment of Pattern and Shape Symmetry of Bilateral Normal Corneas by Scheimpflug Technology

Purpose: The aim of this study was to assess bilateral symmetry in normal fellow eyes by using optical and geometric morphometric parameters. Methods: All participants underwent complete biocular examinations. Scheimpflug tomography data from 66 eyes of 33 patients were registered. The interocular symmetry was based on five patterns: morphogeometric symmetry, axial symmetry at the corneal vertex, angular-spatial symmetry, direct symmetry (equal octants), and enantiomorphism (mirror octants). Results: No statistically significant differences were found between right and left eyes in corneal morphogeometric (p ≥ 0.488) and aberrometric parameters (p ≥ 0.102). Likewise, no statistically significant differences were found in any of the axial symmetry parameters analyzed (p ≥ 0.229), except in the surface rotation angle beta (p = 0.102) and translation coordinates X0 and Y0 (p < 0.001) for the anterior corneal surface, and the rotation angle gamma (p < 0.001) for the posterior surface. Similarly, no statistically significant differences were identified for direct symmetry (p ≥ 0.20) and enantiomorphism (p ≥ 0.75), except for some elevation data in the posterior surface (p < 0.01). Conclusions: The level of symmetry of both corneas of a healthy individual is high, with only some level of disparity between fellow corneas in rotation and translation references. Abnormalities in this pattern of interocular asymmetry may be useful as a diagnostic tool.