Ocular wavefront aberrations in patients with macular diseases

Analysis of the impact of optical aberrations in en-face full-field OCT microscopy

Optical coherence tomography (OCT) is a powerful technique for cross-sectioning imaging. However, the lateral resolution may be degraded by optical aberrations originating from the sample or the setup. We present an extensive quantitative study of the impact of aberrations in time-domain en-face full-field OCT (FFOCT). Using an adaptive optics loop integrated in an FFOCT setup, a deformable mirror is used to introduce low-order calibrated aberrations. The experimental analysis of both the line spread functions (SF) and the complex object images has allowed us to measure the loss in contrast and the impact on lateral spatial resolution. We demonstrate that the frequency content of FFOCT image spectra in terms of signal-to-noise ratio and cutoff frequency is degraded by aberrations but remains much higher than in conventional incoherent images. Line SF profiles in conventional imaging display widening, whereas in FFOCT they display oscillations, leading to the possible perception of preserved resolution. Nevertheless, for complex objects, the aberration image blurring is strong due to the convolution process by the point SF, resulting in a significant filtering of the image spatial spectrum.

HIGHER-ORDER ABERRATIONS IN EYES WITH SILICONE OIL TAMPONADE

PURPOSE

To investigate the changes in higher-order aberrations (HOAs) after silicone oil removal and to evaluate their associations with visual acuity.

METHODS

Fifty-nine eyes of 58 patients who underwent SO removal were included. Total, corneal, and internal optic HOAs, and best-corrected visual acuity were measured before and 1 month after SO removal, and changes were compared between phakic and pseudophakic eyes.

RESULTS

Total ocular and internal optic HOAs decreased significantly after SO removal both in pseudophakic (n = 40, all P < 0.001) and phakic eyes (n = 19, P = 0.017, P = 0.004). Preoperative HOAs (P < 0.001) and changes in HOAs (P = 0.006) were greater in pseudophakic eyes than in phakic eyes. Best-corrected visual acuity was significantly improved after SO removal, from 20/105 to 20/78 (P < 0.001) in pseudophakic eyes, whereas there was no difference in phakic eyes (P = 0.714). Preoperative HOAs and the reduction in HOAs after SO removal were greater in best-corrected visual acuity-improved eyes than best-corrected visual acuity-unchanged eyes (P < 0.001).

CONCLUSION

Silicone oil tamponade induced an increase in HOAs, and these increases were greater in pseudophakic eyes than in phakic eyes. Silicone oil may cause additional visual impairments because of HOAs, beyond those caused by retinal diseases, particularly in pseudophakic eyes.

Biometric and refractive changes after orbital decompression in Korean patients with thyroid-associated orbitopathy

PURPOSE

To determine the biometric and refractive changes after orbital decompression in Korean patients with thyroid-associated orbitopathy (TAO).

METHODS

Retrospective, observational study (between October 2012 and September 2014) was performed. Patients with TAO undergoing orbital decompression for stable proptosis received ophthalmic examinations, including Hertel exophthalmometry, A-scan biometry, autorefraction measures, corneal topography, and wavefront aberration measures, before orbital decompression and again 2 months after surgery.

RESULTS

Included in the study were 43 eyes from 23 patients. The mean exophthalmometric value decreased by 4.1 mm 2 months after orbital decompression (P<0.001). On average, axial length (AL) increased significantly by 0.08 mm (P<0.001); specifically, 37 (86%) of the 43 eyes had increased AL. Whereas anterior chamber depth and lens thickness showed no significant changes (P=0.086 and P=0.905, respectively), the mean spherical refraction and spherical equivalent (SE) decreased by 0.35 and 0.48 D, respectively (P=0.008 and P<0.001, respectively). However, cylindrical refraction and axis showed no significant changes (P=0.057 and P=0.218, respectively). The changes in AL and SE were significantly correlated (R=-0.411, P=0.009). Notably, there were no changes in corneal topography or wavefront aberration after orbital decompression.

CONCLUSIONS

TAO patients who underwent orbital decompression showed myopic refractive change via increase in AL. Possible refractive changes should be considered in cases of TAO complaining of decreased visual acuity after orbital decompression.

OCULAR WAVEFRONT ABERRATIONS AND OPTICAL QUALITY IN DIABETIC MACULAR EDEMA

PURPOSE

To evaluate optical quality and internal aberrations in patients with diabetic macular edema.

METHODS

In this prospective study, 33 eyes of patients with diabetic macular edema were scanned with a ray-tracing wavefront device. As a control group, wavefront aberrometry was performed in 31 patients. Ocular and internal aberrations and visual quality metrics were evaluated separately to determine whether the source of aberrations was ocular or internal. Main outcome measures included corrected visual acuities, ocular and internal aberrations, Strehl ratio, and modulation transfer function.

RESULTS

There was a statistically significant difference between the groups in internal higher order (HO) root mean square (0.34 ± 0.24 vs. 0.16 ± 0.05), HO Strehl ratio (0.08 ± 0.05 vs. 0.18 ± 0.09), and modulation transfer function (0.29 ± 0.1 vs. 0.4 ± 0.1). There was no statistically significant difference in Strehl ratio and HO root mean square between phakic and pseudophakic patients. Height of cystoid spaces was a significant predictor (P < 0.001) of Strehl ratio. Besides inner and outer segment integrity, HO Strehl ratio significantly determined best-corrected visual acuity.

CONCLUSION

In eyes with macular edema, internal HO wavefront aberrations were greater than in control eyes. This increase in HO wavefront error seems visually relevant. This study results suggest increased intraretinal edema as the source of HO aberrations.

Wavefront error correction with adaptive optics in diabetic retinopathy

PURPOSE

To determine the effects of diabetic retinopathy (DR), increased foveal thickness (FT), and adaptive optics (AO) on wavefront aberrations and Shack-Hartmann (SH) image quality.

METHODS

Shack-Hartmann aberrometry and wavefront error correction were performed with a bench-top AO retinal imaging system in 10 healthy control and 19 DR subjects. Spectral domain optical coherence tomography was performed and central FT was measured. Based on the FT data in the control group, subjects in the DR group were categorized into two subgroups: those with normal FT and those with increased FT. Shack-Hartmann image quality was assessed based on spot areas, and high-order (HO) root mean square (RMS) and total RMS were calculated.

RESULTS

There was a significant effect of DR on HO and total RMS (p = 0.01), and RMS decreased significantly after AO correction (p < 0.001). Shack-Hartmann spot area was significantly affected by DR (p < 0.001), but it did not change after AO correction (p = 0.6). High-order RMS, total RMS, and SH spot area were higher in DR subjects both before and after AO correction. In DR subgroups, HO and total RMS decreased significantly after AO correction (p < 0.001), whereas the effect of increased FT on HO and total RMS was not significant (p ≥ 0.7). There were no significant effects of increased FT and AO on SH spot area (p = 0.9).

CONCLUSIONS

Diabetic retinopathy subjects had higher wavefront aberrations and less compact SH spots, likely attributable to pathological changes in the ocular optics. Wavefront aberrations were significantly reduced by AO, although AO performance was suboptimal in DR subjects as compared with control subjects.

Changes in ocular monochromatic higher-order aberrations in the aging eye

PURPOSE

To characterize corneal, internal, and total ocular monochromatic higher-order aberration (MHOA) changes that occur in the aging eye.

METHODS

Prospective observational case series including 300 eyes of 167 patients (mean age = 63.8 years) attending the ophthalmology service at University Hospital Ayr, Scotland. Corneal, internal, and total ocular aberrations were measured over a 6-mm dilated pupil. Zernike coefficients were obtained to the sixth order. Changes in MHOA between age groups and inter-eye correlations between right and left eyes were analyzed.

RESULTS

A significant inter-eye correlation was found for refractive mean spherical equivalent and cylinder. A significant inter-eye correlation for the whole eye, corneal, and internal MHOA was found (p < 0.001). Right eye analysis found a significant positive correlation between age and the root mean square of whole eye MHOA (p = 0.012), with an increase from 0.517 μm in the fifth decade to 0.824 μm in the ninth. Total internal MHOA increased from 0.411 to 0.704 μm. A significant positive correlation was found between age and internal fourth- (p = 0.007), fifth- (p = 0.029), and sixth-order (p = 0.025) root mean square aberrations. There were no significant age-related changes in corneal MHOA or corneal spherical aberration. Overall mean (SD) corneal SA was 0.203 (0.082) μm.

CONCLUSIONS

A strong correlation between the right and left eyes exists for MHOA. Whole eye MHOA increases with age. Such changes can be attributed to age-related changes in the internal optical quality of the eye. Such normative data are useful to the cataract surgeon when considering the use of an aspherical IOL to counteract corneal-induced SA during cataract surgery.