Higher Order Aberrations Of Eye Research Articles

Ray-tracing-guided myopic LASIK: real-world clinical outcomes.

To assess effectiveness of individualized ray-trace based laser in situ keratomileusis (LASIK) for correction of myopia in everyday clinical practice. Single-site private practice. Retrospective nonrandomised unmasked chart review. Consecutive, myopic eyes (range ≤-8.25 diopters [D] sphere; astigmatism 0 to -4.25 D) treated with ray-trace based LASIK were included. Patients underwent wavefront, tomography, and biometry assessment using the InnovEyes Sightmap diagnostic device. The ray-trace based algorithm (InnovEyes algorithm) then generated an individualized 3D eye model and calculated a customized LASIK ablation profile. Postoperative visual acuity, refractive error and whole eye higher-order aberrations (HOAs) were evaluated over 3 months. The procedure was performed on 400 eyes (200 patients). Mean preoperative manifest refraction spherical equivalent was -3.39 ± 1.58 D (right eye -3.84 ± 1.63 D, left eye -3.98 ± 1.75 D). At month 3, uncorrected distance visual acuity (UDVA) was ≥20/20 in all eyes, ≥20/16 in 89% (right eye 90%, left eye 89%), ≥20/12 in 51% (54% right eye; 47% left eye), and 20/10 in 8% (right eye 8%; left eye 9%) of eyes respectively. UDVA was within 1 line of preoperative corrected distance visual acuity in 98% of eyes (right eye 98.5%; left eye 98%) and 39% of eyes (right eye 38%; left eye 39%) gained 1 line improvement. There was a statistically but not clinically significant increase in total HOAs (right eye 0.06 ± 0.133 μm; left eye 0.057 ± 0.125 μm; P < .001). The spherical aberration decreased (right eye -0.047 ± 0.095 μm, P < .001; left eye -0.051 ± 0.091 μm, P < .001). Ray-trace based LASIK was safe and effective for correction of myopia with and without astigmatism. Approximately, half the eyes achieved ≥20/12.5 UDVA and 8% achieved 20/10. There was no clinically significant increase in total whole eye HOAs.

Impact of Scleral Lens Front Surface Eccentricity on Visual Acuity, Contrast Sensitivity, and Higher-Order Aberrations in Eyes With Keratoconus.

To investigate the effect of front surface eccentricity (FSE) of scleral lenses (SLs) on corrected distance visual acuity (CDVA), contrast sensitivity (CS), and higher-order aberrations (HOAs) in keratoconic eyes. Fifteen keratoconic eyes fitted with BostonSight SCLERAL lenses of different eccentricity values (FSE0=0, FSE1=0.30, and FSE2=0.60). CDVA, CS, and HOAs were measured at baseline and after 30 min of SL wear. CDVA and CS were measured with the Early Treatment Diabetic Retinopathy Study and Pelli-Robson chart, respectively, and iTrace aberrometer was used to evaluate the HOAs. Baseline CDVA was 0.30±0.29, which significantly improved to 0.10±0.11, 0.05±0.06, and 0.05±0.08 logMAR with FSE0, FSE1, and FSE2, respectively ( P <0.05). The post hoc showed no significant difference between eccentricities. Baseline CS was 1.19±0.47, which improved to 1.54±0.12, 1.59±0.10, and 1.60±0.11 with FSE0, FSE1, and FSE2, respectively ( P <0.01), but post hoc showed no significant difference between eccentricities. A statistically significant reduction was found in HOAs when compared with baseline ( P <0.01). Comparison between eccentricities showed a significant difference only between FSE0 and FSE1 for RMS coma ( P =0.01) and RMS spherical aberrations ( P =0.004) where FSE1 showed better performance in reducing HOAs compared with FSE0. HO-RMS, RMS secondary astigmatism, and RMS trefoil showed no significant difference between eccentricities, but FSE1 and FSE2 performed superior to FSE0. BostonSight SCLERAL lenses with varying eccentricities corrected a significant amount of HOAs and improved CDVA and CS in keratoconus patients. Practitioners should be aware of this distinct feature of SLs and use it as needed to improve visual performance.

Visual outcomes and higher-order aberrations in eyes implanted with hybrid extended depth of focus intraocular lens

Visual outcomes and higher-order aberrations in eyes implanted with hybrid extended depth of focus intraocular lens

Management of Anterior Stromal Necrosis After Polymethylmethacrylate ICRS: Explantation Versus Exchange With Corneal Allogenic Intrastromal Ring Segments.

To evaluate management of keratoconic eyes with anterior stromal necrosis overlying the intracorneal ring segment (ICRS), by either ICRS explantation alone or exchange with corneal allogenic intrastromal ring segments (CAIRS). Among 643 Intacs SK (Additional Technology, Inc) inserted at one institutional center, 16 eyes (15 patients) with overlying spontaneous anterior stromal necrosis were identified. Data included size of stromal defect and refractive and topographical findings before ICRS insertion, before anterior stromal necrosis, and 6 months after intervention. The 10-year incidence of anterior stromal necrosis after femtosecond laser-assisted ICRS insertion was 5.5%. Eight eyes underwent ICRS removal only and 8 eyes had ICRS exchanged with CAIRS. In the first group, CDVA worsened from 0.14 before melt to 0.28 logMAR after removal (P = .10), simulated keratometry (SimK) and maximum axial keratometry (Kmax) increased from 44.73 to 46.34 diopters (D) (P = .14) and from 49.23 to 52.26 D (P = .14), respectively, and coma worsened from 0.87 to 1.52 D (P = .02). In the CAIRS group, CDVA of 0.16 before melt improved to 0.11 logMAR postoperatively (P > .99), and topographic indices stabilized with SimK, Kmax, and coma mildly altering from 45.31 to 45.44 D (P > .99), from 49.25 to 49.64 D (P > .99) and from 0.87 to 0.81 D (P > .99), respectively. Whether the ICRS were explanted or exchanged, the visual and topographic mean values were better than those reported before ICRS implantation, whereas higher order aberrations in eyes without CAIRS regressed to levels before ICRS insertion. At the site of melt, thinnest residual stromal thickness averaged 327 µm with ICRS removal and 490 µm with CAIRS. Eyes with larger melt areas resulted in less optimal results with CAIRS implantation. Early experience in the management of anterior stromal necrosis by exchange of polymethylmethacrylate ICRS with CAIRS seems to avoid stromal thinning and confer better visual and topographic results, which were more pronounced with thicker segments. The benefit of CAIRS in large stromal melts needs to be investigated. [J Refract Surg. 2022;38(4):256-263.].

Impact of asteroid hyalosis on internal higher-order aberrations in eyes with cataract accompanied by acoustic shadows on swept-source optical coherence tomography examination.

Increased internal higher-order aberrations (HOAs) have been reported in eyes with asteroid hyalosis, which is usually asymptomatic. This report describes 2 patients with cataract and concurrent asteroid hyalosis. In the first case, internal HOAs were within the normal range, and swept-source optical coherence tomography (SS-OCT) did not show acoustic shadows. After cataract surgery, visual acuity improved and internal HOAs remained within normal limits. However, in the second case, SS-OCT revealed multiple acoustic shadows, presumably due to asteroid hyalosis, and internal HOAs increased in both eyes. After combined vitrectomy and cataract surgery, visual acuity and the internal HOA values improved in both eyes, and acoustic shadows disappeared on SS-OCT. Phacovitrectomy should be considered if the cause of visual impairment is cataract and asteroid hyalosis. Objective assessment of internal HOAs by a wavefront sensor and checking for acoustic shadows on SS-OCT might be useful in detecting this combination of ophthalmic conditions.

Wavefront aberrations in children with different types of amblyopia

Purpose. To quantify and characterize higher-order aberrations in eyes of children with amblyopia caused by different etiology factors; to evaluate the relationship between the wavefront profile and the effectiveness of the amblyopia treatment. Material and methods. This study involved 26 children (52 eyes) from 3 to 9 years old (average age 6.2±3 years) with different types of amblyopia: unilateral amblyopia due to impaired binocular vision and anisometropia, as well as unilateral or bilateral amblyopia caused by hyperopia. Patients were divided into four groups depending on the effectiveness of pleoptic treatment: 14 children (24 eyes) – with positive treatment results, 8 children (12 eyes) – with refractory amblyopia, 4 pre-treatment newly diagnosed patients (6 eyes) without previous history of optical correction, and 10 non-amblyopic contralateral eyes (control group). All patients had central fixation and didn`t have any severe systemic diseases. Higher-order aberrations were measured with iTrace Visual Function Analyzer (Tracey Technologies, Houston, TX) after instillation of 1% cyclopentolate eyedrops. Results and discussion. Wavefront profiles were significantly different in the studied groups. Total spherical aberrations and astigmatism were significantly higher in group with refractory amblyopia (-0.53±1.19 and 2.25±1.07, p=0.02) compared with all the other groups: the group of patients before pleoptic treatment (-0.17±0.23 and 1.79±1.47), group treated with high efficiency (-0.31±0.81 and 1.04±0.13) and with control group (-0.13±0.17 and 1.38±0.11). Total coma-like aberrations didn`t show statistically significant differences in all studied groups (р=0.06). The level of corneal higher-order aberrations (total, coma, spherical) in all three amblyopic groups was higher than in the control group without amblyopia. Conclusion. We revealed statistically significant differences in the wavefront profiles in children with amblyopia of various etiologies in comparison with the control group, including higher-order aberrations. The data obtained indicate that an amblyopic eye with hyperopia has higher level of spherical aberrations and astigmatism due to higher level of internal HOAs, particularly spherical aberrations and astigmatism, which is typical for patients with unsuccessful treatment. Therefore, that type of aberrations is likely to be the main cause of refractory amblyopia.

Corneal higher-order aberrations in eyes with chronic ocular graft-versus-host disease

PurposeChronic ocular graft-versus-host disease (GVHD) is a long-term complication after hematopoietic stem cell transplantation (HSCT) and leads to irreversible visual morbidity due to severe ocular surface impairments including visual disfunction. However, knowledge about the optical function in chronic ocular GVHD is limited because it is difficult to assess quantitative optical function objectively. The development of anterior segment optical coherence tomography has allowed objective quantification of optical function by evaluating corneal higher-order aberrations (HOAs). Therefore, we applied this quantification in chronic ocular GVHD patients and verified the correlation between corneal HOAs and visual acuity. MethodsWe retrospectively reviewed chronic ocular GVHD patients and the recipients after HSCT. Then, analyzed the relationship between visual function and the severity of chronic ocular GVHD. ResultsThe eyes of patients with chronic ocular GVHD had higher corneal HOAs than those of non-GVHD patients (HOAs; 0.481 ± 0.306 vs 0.254 ± 0.084, and 0.917 ± 0.609 vs 0.529 ± 0.130. P < 0.001, and 0.002. 4-mm and 6-mm diameters respectively. Corneal HOAs were correlated with the severity of chronic ocular GVHD (r = 0.436. P < 0.001). Moreover, corneal HOAs were correlated with visual acuity, especially in eyes with severe chronic ocular GVHD cases (HOAs; 4-mm r = 0.636. P = 0.036. Total 6-mm r = 0.871. P =<0.001). ConclusionsWe succeed to assess the objective value in the optical function of the chronic ocular GVHD. Quantification of corneal HOAs could be an objective evaluation to assess optical function in eyes with chronic ocular GVHD.

Effects of a semi-scleral contact lens on refraction and higher order aberrations

PurposeTo investigate effects of Rose K2 XL semi-scleral contact lenses (Menicon Co.) on visual acuity and higher-order aberrations in eyes with irregular corneas. Methods: One hundred and twelve eyes of 84 patients fitted with Rose K2 XL lenses were analysed. Participants were in 4 clinical groups: keratoconus, intra-corneal ring segments, radial keratotomy, and penetrating keratoplasty. Corrected distance visual acuity and ocular aberrations were determined before lens wear and 60 min into lens wear. The i-Trace aberrometer was used to determine aberrations at 4.5 mm pupil size. ResultsThere were 55, 22, 19 and 16 eyes in keratoconus, intra-corneal ring segments, radial keratotomy and penetrating keratoplasty groups, respectively. Before lens wear, eyes had poor corrected distance vision acuity (mean and standard deviation +0.55 ± 0.33 logMAR), high negative spherical equivalent refraction (−6.4 ± 3.7 D), high cylindrical errors (4.5 ± 2.2 D), large higher-order root-mean-squared (HO-RMS) aberration (1.5 ± 1.3 μm) and large higher-order aberration components. Cylinder was particular high for the penetrating keratoplasty group (mean 5.9 ± 2.5 D), root-mean-squared third-order coma was lowest for the radial keratotomy group (0.7 ± 1.0 μm), and fourth-order spherical aberration was highly negative for the intra-corneal ring segment group (co-efficient –0.4 ± 0.7 μm). With lens wear, the values changed considerably. Corrected distance visual acuity improved by 0.51 ± 0.31 logMAR, cylinder decreased by 3.6 ± 2.1 D, HO-RMS aberration reduced by 1.1 ± 1.2 μm, and higher-order aberration components decreased considerably. Magnitudes of group changes reflected the magnitudes before lens wear. ConclusionsRose K2 XL semi-scleral contact lenses were effective in improving vision and reducing ocular aberrations for eyes with irregular corneas.

Corneal Higher-Order Aberrations in Eyes With Corneal Scar After Traumatic Perforation.

To evaluate corneal higher-order aberrations (HOAs) in eyes with corneal scar after traumatic perforation and their correlation with visual acuity. This retrospective consecutive case study included 40 eyes of 40 consecutive patients (mean age, 39.2±21.6 years), treated for traumatic corneal perforation at Tokyo Dental College, and 18 normal control eyes. Higher-order aberrations of anterior and posterior corneal surfaces and total cornea were analyzed by swept-source optical coherence tomography. Correlations between corneal HOAs and visual acuity were analyzed. Higher-order aberrations within 4-mm diameter were significantly larger in eyes with corneal perforation (anterior surface, 0.51±0.54 μm; posterior surface, 0.20±0.14; and total cornea, 0.52±0.50) as compared to normal controls (0.10±0.02, 0.02±0.01, and 0.09±0.02, respectively; all P<0.001). Higher-order aberrations within 6-mm diameter were significantly larger in eyes with corneal perforation (anterior surface, 1.15±1.31; posterior surface, 0.31±0.23; and total cornea, 1.09±1.28) as compared to normal controls (0.21±0.06, 0.06±0.01, and 0.19±0.06, respectively; all P<0.001). The most common topography pattern observed was the minimal change pattern (37.5%), followed by asymmetric pattern (30.0%). Visual acuity significantly correlated with corneal HOAs (anterior surface: R=0.646, P<0.001; posterior surface: R=0.400, P=0.033; and total cornea: R=0.614, P<0.001). Corneal scar after traumatic perforations not only induces corneal opacity, but also increases corneal HOAs, which indicates a direct effect on visual acuity.

Comparison of topographic indices and corneal higher order aberrations in eyes with an extreme asymmetry of keratoconus with control eyes

Purpose: To compare topographic indices and anterior corneal higher order aberrations (HOAs) of forme fruste keratoconus (KC) (fellow eyes) with clinical KC and control eyes. Setting: Tertiary Eye Hospital, India. Materials and Methods: This study retrospectively reviewed 298 patients with KC. Patients were evaluated with placido-based topographer. KC was diagnosed according to Rabinowitz and McDonnell criteria and clinical sign. Twenty-one patients with clinical KC in one eye (Group A), fellow eye (Group B) with normal topography with no clinical sign, and 21 control eyes (Group C) were included in the study. Topographic indices (keratometry, inferior superior ratio, irregularity, shape factor, and eccentricity) and HOAs (trefoil, coma, spherical aberration, total root mean square [RMS], HOAs RMS of third to seventh order for 6 mm diameter) were obtained. Group B was compared with Groups A and C. Results: The prevalence of an extreme asymmetry of KC in our study population is 7.04% with mean age of 21.98 ± 7.39 years. All topographic indices were higher in Group A compared to Group B (P

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.

Immediate effect of a tear enhancer and meibomian gland expression on the corneal surface and whole eye higher order aberrations

PurposeTo investigate changes in higher order ocular aberrations (HOA) induced by the administration of 0.15% sodium hyaluronate tear enhancer (TE) and meibomian gland expression (ME) on the tear film of normal subjects. MethodsHOA values were obtained from the corneal surface (CS) and whole eye (WE), using a corneal topographer and Shack–Hartmann aberrometer, from both eyes of 50 subjects (25 females, mean age±sd 32.5±11.0 years, and 25 males, 33.88±11.2 years) for two pupil sizes (3 and 6mm) in a dark environment. One drop of Blink Contacts™ (Abbott Medical Optics) was instilled into the right eye and HOA measurements repeated after 30s. After 1h, the meibomian glands of the left lower eyelid were gently squeezed and HOA measurements repeated after 30s. ResultsThere was no significant difference for CS and WE root mean square (RMS) HOAs between right and left eyes before (both pupil sizes) and after TE use or ME (3mm pupil). For 6mm pupil, TE use significantly reduced the WE RMS HOA (p<0.05, mean±sd) for Z40 (0.297±0.136 to 0.053±0.069), and Z55 (0.221±0.372 to 0.098±0.121) while ME significantly increased CS RMS HOA (p<0.05, mean±sd) for Z3−3 (0.799±1.178 to 1.302±1.991) and Z44 (0.594±1.184 to 0.988±1.463). In general, the change in HOA was significantly correlated with the initial value before TE use or ME (p<0.05). ConclusionThere were no detectable differences between right and left eyes. For the 6mm pupil, the tear enhancer tended to improve optical performance of the WE and meibomian gland expression tended to reduce the optical performance at the CS.

Changes in meibomian gland morphology and ocular higher-order aberrations in eyes with chalazion.

PurposeTo examine the changes in meibomian gland morphology and ocular higher-order aberrations (HOAs) in eyes with chalazion and its excision.MethodsSeven male patients with previous history of chalazion excision and seven control male subjects were enrolled. Changes in meibomian gland morphology (meiboscores, gland dropout, and shortening) were evaluated by using meibography equipped in a wavefront analyzer KR-1W and in a slit-lamp device BG-4M. Ocular HOAs were measured sequentially with KR-1W. The tear film breakup time (BUT) was measured.ResultsBoth KR-1W and BG-4M visualized meibomian gland as clear similar images. The tear film BUT (mean ± SD, 5.6±3.0 vs 9.4±2.3 seconds, P=0.025), the total meiboscore (median [interquartile range], 2 (2−3) vs 0 (0−1), P=0.007) as well as the meibomian gland dropout rate (86% vs 14%, P=0.008) and shortening rate (100% vs 29%, P=0.031) differed significantly between the patient and control groups. The first total ocular HOAs (0.142±0.063 vs 0.130±0.015, P=0.80) were similar in both groups, whereas the stability index of the total HOAs over time (0.0041±0.0048 vs −0.0012±0.0020, P=0.030) differed significantly between the patient and control groups.ConclusionsChalazion and its excision were associated with dropout and shortening rate of meibomian glands. The morphological changes of meibomian glands in chalazion may be associated to instability of the tear film, which was suggested by the tear film BUT and the stability of ocular HOAs.

Evaluation of the True Wavefront Aberrations in Eyes Implanted With a Rotationally Asymmetric Multifocal Intraocular Lens.

Standard evaluation of aberrations from wavefront slope measurements in patients implanted with a rotationally asymmetric multifocal intraocular lens (IOL), the Lentis Mplus (Oculentis GmbH, Berlin, Germany), results in large magnitude primary vertical coma, which is attributed to the intrinsic IOL design. The new proposed method analyzes aberrometry data, allowing disentangling the IOL power pupillary distribution from the true higher order aberrations of the eye. The new method of wavefront reconstruction uses retinal spots obtained at both the near and far foci. The method was tested using ray tracing optical simulations in a computer eye model virtually implanted with the Lentis Mplus IOL, with a generic cornea or with anterior segment geometry obtained from custom quantitative spectral-domain optical coherence tomography in a real patient. The method was applied to laser ray tracing aberrometry data at near and far fixation obtained in a patient implanted with the Lentis Mplus IOL. Higher order aberrations evaluated from simulated and real retinal spot diagrams following the new reconstruction approach matched the nominal aberrations (approximately 98%). Previously reported primary vertical coma in patients implanted with this IOL lost significance with the application of the proposed reconstruction. Custom analysis of ray tracing-based retinal spot diagrams allowed decoupling of the true higher order aberrations of the patient's eye from the power pupillary distribution of a rotationally asymmetric multifocal IOL, therefore providing the appropriate phase map to accurately evaluate through-focus optical quality. [J Refract Surg. 2017;33(4):257-265.].

Effect of Light Scattering and Higher-order Aberrations on Visual Performance in Eyes with Granular Corneal Dystrophy.

This study was aimed to assess the relationship of intraocular forward scattering, corneal backward scattering, and corneal higher-order aberrations (HOAs) with corrected distance visual acuity (CDVA) in eyes with granular corneal dystrophy (GCD). We retrospectively examined forty two eyes of 42 consecutive patients who diagnosed GCD, and age-matched 20 eyes of 20 healthy subjects. We assessed objective scattering index (OSI) using the double-pass instrument (OQAS II, Visiometrics), corneal densitometry (CD) using the Scheimpflug rotating camera (Pentacam HR, Oculus), and corneal HOAs using the Hartmann-Shack aberrometry (KR-9000, Topcon). The OSI, CD, and corneal HOAs were significantly larger in the GCD group than those in the control group (Mann-Whitney U test, p < 0.001). We found significant correlations of logMAR CDVA with the OSI (Spearman correlation coefficient r = 0.577, p < 0.001), and with the CD (r = 0.340, p = 0.028), but no significant association with corneal HOAs (r = 0.061, p = 0.701). Intraocular forward scattering, corneal backward scattering, and corneal HOAs in eyes with GCD were higher than that in normal eyes. The CDVA was significantly correlated with intraocular forward scattering, but not with corneal HOAs in eyes with GCD, suggesting that light scattering, especially forward scattering, plays a more vital role in visual performance than corneal aberrations in eyes with GCD.

Visual Function and Higher-Order Aberrations in Eyes After Corneal Transplantation: How to Improve Postoperative Quality of Vision.

An understanding of corneal optics is important to optimize the visual outcome after eye surgery. Recent advances in the surgical techniques of lamellar keratoplasty have changed the strategies used for corneal transplantation. Lamellar keratoplasty has the advantage of having a lower rate of graft rejection, superior biomechanical properties, and reduced higher-order aberrations (HOAs) compared with penetrating keratoplasty; thus, the use of lamellar keratoplasty has increased over the last 15 years. However, some patients have poor postoperative visual acuity despite a clear cornea, and the reasons for the poor visual outcome are poorly understood. By combining corneal imaging technologies and the latest optical software, we proposed the concept of "parallelism of anterior and posterior surfaces in lamellar keratoplasty." In physiologically normal eyes, in which the anterior and posterior surfaces are parallel to each other, the posterior surface of the cornea compensates the HOAs of the anterior surface, and this is also true in eyes after penetrating keratoplasty. However, after lamellar keratoplasty, in which the anterior and posterior surfaces are independent and not parallel, irregularities in the posterior surface increase the HOAs of the anterior surface. This article introduces this concept to enhance our understanding of visual optics in eyes after penetrating and lamellar keratoplasties and how to apply this concept to surgery to improve and optimize patient visual outcomes.

Design of eye models used in quantitative analysis of interaction between chromatic and higher-order aberrations of eye

Special kinds of eye models are constructed by means of optical system design to quantitatively investigate impacts of longitudinal chromatic aberration (LCA), transverse chromatic aberration (TCA) and LCA+TCA on retina image quality and on depth of focus (DOF), as well as interaction between chromatic and higher-order aberrations. Results show that LCA plays a main role in enhancement of DOF and higher-order aberrations further increase DOF. For most of the eyes the impact of higher-order aberrations on vision is much smaller than that of LCA+TCA and the presence of LCA+TCA further reduces the impact of higher-order aberrations. The impact of LCA approximates to that of LCA+TCA, and the impact of TCA approximates to that of normal level of higher-order aberrations and is negligible.

Topographic, Corneal Wavefront, and Refractive Outcomes 2 Years After Collagen Crosslinking for Progressive Keratoconus

The aim was to report the corneal higher-order aberrations (HOA), the topographic metrics, and the visual and refractive outcomes 2 years after performing collagen crosslinking (CXL) for progressive keratoconus. The correlation among corneal HOAs, topographic metrics, and visual acuity changes was also investigated. This is a prospective case series involving 42 eyes from 32 patients with progressive keratoconus treated with CXL. The main outcomes measured at baseline and 6, 12, and 24 months after treatment were uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refractive changes, topographic data, and corneal aberrations. Two years after CXL treatment, the UDVA (P < 0.001), CDVA (P < 0.001), and spherical equivalent (P = 0.048) improved significantly. The corneal topographic data revealed significant decreases in apical keratometry (P < 0.001), differential keratometry (P = 0.031), and central keratometry (P = 0.003) compared with the baseline measurements. Aberration analyses revealed a significant reduction in coma (P = 0.016), trefoil (P = 0.018), secondary astigmatism (P < 0.001), quatrefoil (P = 0.031), secondary coma (P < 0.001), and secondary trefoil (P = 0.001). Corneal HOA (except quatrefoil) demonstrated a significant correlation with postoperative CDVA; the highest correlations were for coma (rho = 0.703, P < 0.001), secondary astigmatism (rho = 0.519, P = 0.001), and total HOA (rho = 0.487, P = 0.001). However, the corneal HOA changes were not statistically associated with improved visual acuity. After treatment, the reduction in apical keratometry was the only variable that correlated with the improvement in the CDVA (rho = 0.319, P = 0.042). After 2 years, CXL was found to be effective in improving the UDVA, CDVA, topographic metrics, and most corneal HOAs in eyes with progressive keratoconus. A significant reduction was observed in apical keratometry, and this reduction directly correlated with an improvement in visual acuity.

Retinal image quality during accommodation

We asked if retinal image quality is maximum during accommodation, or sub-optimal due to accommodative error, when subjects perform an acuity task. Subjects viewed a monochromatic (552nm), high-contrast letter target placed at various viewing distances. Wavefront aberrations of the accommodating eye were measured near the endpoint of an acuity staircase paradigm. Refractive state, defined as the optimum target vergence for maximising retinal image quality, was computed by through-focus wavefront analysis to find the power of the virtual correcting lens that maximizes visual Strehl ratio. Despite changes in ocular aberrations and pupil size during binocular viewing, retinal image quality and visual acuity typically remain high for all target vergences. When accommodative errors lead to sub-optimal retinal image quality, acuity and measured image quality both decline. However, the effect of accommodation errors of on visual acuity are mitigated by pupillary constriction associated with accommodation and binocular convergence and also to binocular summation of dissimilar retinal image blur. Under monocular viewing conditions some subjects displayed significant accommodative lag that reduced visual performance, an effect that was exacerbated by pharmacological dilation of the pupil. Spurious measurement of accommodative error can be avoided when the image quality metric used to determine refractive state is compatible with the focusing criteria used by the visual system to control accommodation. Real focusing errors of the accommodating eye do not necessarily produce a reliably measurable loss of image quality or clinically significant loss of visual performance, probably because of increased depth-of-focus due to pupil constriction. When retinal image quality is close to maximum achievable (given the eye's higher-order aberrations), acuity is also near maximum. A combination of accommodative lag, reduced image quality, and reduced visual function may be a useful sign for diagnosing functionally-significant accommodative errors indicating the need for therapeutic intervention.

Impact of positive coupling of the eye’s trefoil and coma in retinal image quality and visual acuity

When the eye's higher-order aberrations are measured and reported, as important as the magnitude of each individual term are the possible combinations between them, which may change the overall retinal image quality and therefore visual performance. We have evaluated the relationships among different aberration terms in the human eye-coma, trefoil, and spherical aberration-and their effects on both retinal image quality and visual acuity (VA). In a group of normal young subjects with normal to excellent vision, we measured the eye's aberrations and high contrast VA under natural conditions after carefully correcting defocus and astigmatism. Among the different combinations of aberration terms, we only found a significant negative correlation (r2=0.30) between the vertical coefficients of trefoil C(3,-3) and coma C(3,-1). This is a positive coupling that produces a better retinal image quality than any of the other possible combinations of these terms. However, this improvement in image quality is limited by the presence of other aberrations. Only in a few eyes that presented the larger values of coupled vertical trefoil and coma appeared a significant improvement of image quality. Although we did not find a clear correction between the coma-trefoil vertical coupling and VA, most eyes with large amounts of aberrations (RMS>0.4 μm) have these terms coupled, keeping decimal acuity around 1.2 or higher.