Retinal image quality in myopic children undergoing orthokeratology alone or combined with 0.01% atropine

BACKGROUND

The retinal image quality derived from lower-order (LOA) and higher-order aberrations (HOA) for fixed 3-mm and photopic pupil diameters, in children undergoing combined 0.01% atropine and orthokeratology (AOK) versus those receiving orthokeratology alone (OK) over two years was evaluated.

METHODS

The visual Strehl ratio based on the optical transfer function (VSOTF), derived from 2nd- to 4th-order terms (LOA and HOA combined), 2nd-order terms (LOA only), and 3rd- to 4th-order terms (HOA only) for fixed 3-mm and natural photopic pupil diameters, was compared between the two treatment groups. The individual Zernike coefficients for a fixed 3-mm pupil size of 2nd- to 4th-orders, root mean square (RMS) of LOA ([Formula: see text], [Formula: see text], and [Formula: see text] combined), HOA (3rd to 4th orders inclusive), and Coma ([Formula: see text] combined) were also compared between the two groups.

RESULTS

Right eye data of 33 AOK and 35 OK participants were analysed. Under photopic conditions, significantly lower VSOTF based on HOA only was observed in the AOK group compared with that in the OK group at all post-treatment visits (all P < 0.05); however, interactions between HOA and LOA resulted in comparable overall retinal image quality (i.e., VSOTF based on LOA and HOA combined) between the two groups at all visits (all P > 0.05). For a fixed 3-mm pupil size, the VSOTF based on HOA only, LOA only, or HOA and LOA combined, were not different between the two groups (all P > 0.05). AOK participants had slower axial elongation (mean ± SD, 0.17 ± 0.19 mm vs. 0.35 ± 0.20 mm, P < 0.001), a larger photopic pupil size (4.05 ± 0.61 mm vs. 3.43 ± 0.41 mm, P < 0.001) than OK participants, over two years.

CONCLUSIONS

HOA profile related to an enlarged pupil size may provide visual signal influencing eye growth in the AOK group.

Ocular aberrations in eyes with Primary Congenital Glaucoma

PURPOSE

To highlight the magnitude of ocular higher order aberrations (HOA) and lower order aberrations (LOA), including component contributions from corneal and internal planes in Primary Congenital Glaucoma (PCG) patients.

METHODS

Consecutive treated PCG patients co-operative for ocular examination and aberrometry, were enrolled over two years for this cross-sectional, comparative, single centre, unmasked study. Best corrected visual acuity, refraction, IOP, wavefront aberrometry and topography (iTrace) were performed and results were compared with unaffected fellow eyes of unilateral glaucoma patients as well as age and sex matched controls with no ocular anomalies other than treatable refractive error.

RESULTS

Both eyes of 32 consecutive PCG patients (17 unilateral, 15 bilateral) and 39 controls were enrolled. The median LogMAR corrected distance visual acuity of PCG eyes was 0.68 (IQR: 0.2 - 1.8). Total ocular (Root mean square (RMS) 1.7µm vs 0.3µm, p = 0.014), corneal (RMS 1.1µm vs 0.3µm, p = 0.004) and internal (RMS 1.1µm vs 0.2µm, p = 0.013) aberrations, as well as HOAs and LOAs at each plane were significantly higher in PCG eyes than in controls. Component HOAs from corneal and internal planes were positively correlated with each other (p < 0.001; rs: 0.7). Total aberrations were greater in the affected eyes of PCG compared to the rest. The predominant subtype of HOAs in PCG were coma and trefoil. PCG with corneal opacity/Haab's striae had significantly higher astigmatism than the affected eyes with clear corneae at corneal plane (p = 0.02). The aberrations were not statistically associated with the corneal diameter or refractive error in PCG eyes.

CONCLUSIONS

Significantly greater aberrations (Total, HOAs and LOAs, at corneal as well as internal plane) were seen among eyes affected with PCG. Though the exact impact of these aberrations on the final visual outcome is difficult to determine, these could play a pertinent role in compromising visual function, thus impacting the management of visual rehabilitation in these patients.

Joint effect of defocus blur and spatial attention

Defocus blur and spatial attention both act on our ability to see clearly over time. However, it is currently unknown how these two factors interact because studies on spatial resolution only focused on the separate effects of attention and defocus blurs. In this study, eleven participants performed a resolution acuity task along the diagonal 135˚/315˚ with horizontal, at 8˚ eccentricity for clear and blurred Landolt C images under various manipulations of covert endogenous attention. All the conditions were interleaved and viewed binocularly on a visual display. We observed that attention not just improves the resolution of clear stimuli, but also modulates the resolution of defocused stimuli for compensating the loss of resolution caused by retinal blur. Our results show, however, that as the degree of attention decreases, the differences between clear and blurred images largely diminish, thus limiting the benefit of an image quality enhancement. It also appeared that attention tends to enhance the resolution of clear targets more than blurred targets, suggesting potential variations in the gain of vision correction with the level of attention. This demonstrates that the interaction between spatial attention and defocus blur can play a role in the way we see things. In view of these findings, the development of adaptive interventions, which adjust the eye's defocus to attention, may hold promise.

Ocular higher-order aberrations in a school children population

PURPOSE

The primary objective of the study was to explore the statistics of ocular higher-order aberrations in a population of primary and secondary school children.

METHODS

A sample of 557 children aged 10-15 years were selected from two primary and two secondary schools in Heraklion, Greece. Children were classified by age in three subgroups: group I (10.7±0.5 years), group II (12.4±0.5 years) and group III (14.5±0.5 years). Ocular aberrations were measured using a wavefront aberrometer (COAS, AMO Wavefront Sciences, USA) at mesopic light levels (illuminance at cornea was 4lux). Wavefront analysis was achieved for a 5mm pupil. Statistical analysis was carried out for the right eye only.

RESULTS

The average coefficient of most high-order aberrations did not differ from zero with the exception of vertical (0.076μm) and horizontal (0.018μm) coma, oblique trefoil (-0.055μm) and spherical aberration (0.018μm). The most prominent change between the three groups was observed for the spherical aberration, which increased from 0.007μm (SE 0.005) in group I to 0.011μm (SE 0.004) in group II and 0.030μm (SE 0.004) in group III. Significant differences were also found for the oblique astigmatism and the third-order coma aberrations.

CONCLUSIONS

Differences in the low levels of ocular spherical aberration in young children possibly reflect differences in lenticular spherical aberration and relate to the gradient refractive index of the lens. The evaluation of spherical aberration at certain stages of eye growth may help to better understand the underlying mechanisms of myopia development.

Accounting for the phase, spatial frequency and orientation demands of the task improves metrics based on the visual Strehl ratio

Advances in ophthalmic instrumentation have allowed high order aberrations to be measured in vivo. These measurements describe the distortions to a plane wavefront entering the eye, but not the effect they have on visual performance. One metric for predicting visual performance from a wavefront measurement uses the visual Strehl ratio, calculated in the optical transfer function (OTF) domain (VSOTF) (Thibos et al., 2004). We considered how well such a metric captures empirical measurements of the effects of defocus, coma and secondary astigmatism on letter identification and on reading. We show that predictions using the visual Strehl ratio can be significantly improved by weighting the OTF by the spatial frequency band that mediates letter identification and further improved by considering the orientation of phase and contrast changes imposed by the aberration. We additionally showed that these altered metrics compare well to a cross-correlation-based metric. We suggest a version of the visual Strehl ratio, VScombined, that incorporates primarily those phase disruptions and contrast changes that have been shown independently to affect object recognition processes. This metric compared well to VSOTF for letter identification and was the best predictor of reading performance, having a higher correlation with the data than either the VSOTF or cross-correlation-based metric.

Ocular aberrations in amblyopic children

PURPOSE

To study the pattern of ocular aberrations in amblyopic children, and evaluate a possible relation to etiology and treatment outcomes of amblyopia.

METHODS

The WaveScan Wavefront System (AMO, Santa Ana, CA, USA) aberrometer was used to assess 75 eyes (60 children) after instillation of 1% cyclopentolate eyedrops. There were 29 males and 31 females with a mean age of 9.23 ± 2.55 years (range, 5-14 years). The study sample was subdivided into four groups; 16 emmetropic non-amblyopic eyes (control group); 24 pre-treatment newly diagnosed amblyopic eyes; 16 eyes of treated amblyopes and; 19 eyes with refractory amblyopia.

RESULTS

Amblyopes had statistically significant greater root mean square (RMS) values for whole eye aberrations, 2nd order aberrations, defocus ([Formula: see text]) and astigmatism ([Formula: see text]) compared to emmetropes (P < 0.0001). The refractory amblyopic group showed statistically significant differences in whole eye RMS, 2nd order- aberrations, defocus ([Formula: see text]) and astigmatism ([Formula: see text]) when compared to treated amblyopic groups (P < 0.0001). Apart from a statistically significant difference in 5th order RMS of pre-treated amblyopes versus the control group, no other significant differences were found in higher order aberrations (HOAs: coma, spherical, higher-order astigmatism, trefoil, or 3rd, 4th, 5th or 6th order terms) between emmetropes and any of the amblyopic groups.

CONCLUSION

Lower order aberrations remain the major factor that affect retinal image quality and hence amblyopia development especially in ametropic eyes. This can be corrected optically. Studying HOA profile in amblyopic eyes failed to explain why refractory amblyopia does not respond to orthoptic treatments. This outcome indicates that theories of central problems in image processing and binocular interaction are likely the main cause of refractory amblyopia.