Refraction and Aberration Across the Horizontal Central 10?? of the Visual Field

Atchison, David A.; Lucas, Stephen D.; Ashman, Ross A.; Huynh, Michael A.; Schilt, David W; Ngo, Phuc Q

doi:10.1097/01.opx.0000214382.75847.c4

Cited by 18 publications

(22 citation statements)

References 38 publications

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“…The fovea, located in the center of the macula and the seat of sharp central vision, is routinely imaged in OCT. Because it measures just 1 mm in diameter by 120 μm in depth (Atchison et al 2006), it cannot generally be visualized with pulse/echo ultrasound. The use of a focused laser as detailed in this study may allow PAI to resolve this clinically important structure, especially if PAI, as is generally the case with ophthalmic OCT scanners, could be coupled with scanning laser ophthalmoscopy to provide simultaneous real-time imaging of the retinal surface.…”

Section: Discussionmentioning

confidence: 99%

High-Resolution Photoacoustic Imaging of Ocular Tissues

Silverman

Kong

Chen

et al. 2010

Ultrasound in Medicine & Biology

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Optical coherence tomography (OCT) and ultrasound (US) are methods widely used for diagnostic imaging of the eye. These techniques detect discontinuities in optical refractive index and acoustic impedance respectively. Because these both relate to variations in tissue density or composition, OCT and US images share a qualitatively similar appearance. In photoacoustic imaging (PAI), short light pulses are directed at tissues, pressure is generated due to a rapid energy deposition in the tissue volume, and thermoelastic expansion results in generation of broadband US. PAI thus depicts optical absorption, which is independent of the tissue characteristics imaged by OCT or US. Our aim was to demonstrate the application of PAI in ocular tissues and to do so with lateral resolution comparable to OCT. We developed two PAI assemblies, both of which used single-element US transducers and lasers sharing a common focus. The first assembly had optical and 35-MHz US axes offset by a 30° angle. The second assembly consisted of a 20-MHz ring transducer with a coaxial optics. The laser emitted 5-ns pulses at either 532-nm or 1064-nm, with spot sizes at the focus of 35-μm for the angled probe and 20-μm for the coaxial probe. We compared lateral resolution by scanning 12.5-μm diameter wire targets with pulse/echo US and PAI at each wavelength. We then imaged the anterior segment in whole ex vivo pig eyes and the choroid and ciliary body region in sectioned eyes. PAI data obtained at 1064 nm in the near infrared had higher penetration but reduced signal amplitude compared to that obtained using the 532-nm green wavelength. Images were obtained of the iris, choroid and ciliary processes. The zonules and anterior cornea and lens surfaces were seen at 532 nm. Because the laser spot size was significantly smaller than the US beamwidth at the focus, PAI images had superior resolution than those obtained using conventional US.

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Section: Discussionmentioning

confidence: 99%

High-Resolution Photoacoustic Imaging of Ocular Tissues

Silverman

Kong

Chen

et al. 2010

Ultrasound in Medicine & Biology

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“…It is assumed that the angular subtense of the stimuli in the experiments lies within the isoplanatic area of the eye, and therefore, the convolution is performed using a spatially invariant PSF. In the human eye, the changes in astigmatism are small across the central 10 degrees (Atchison et al, 2006; Atchison, Scott, & Charman, 2003). However, as a result, the computationally blurred stimuli did not include the (small) astigmatic distortion produced when principal powers are unequal (i.e., meridional differences in magnification).…”

Section: Methodsmentioning

confidence: 99%

Adaptation to astigmatic blur

et al. 2010

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Adapting to blurred or sharpened images alters the perceived focus of subsequently viewed images. We examined whether these adaptation effects could arise from actual sphero-cylindrical refractive errors, by testing aftereffects in images simulating second-order astigmatism. Image blur was varied from negative (vertical) through isotropic to positive (horizontal) astigmatism while maintaining constant blur strength. A 2AFC staircase was used to estimate the stimulus that appeared isotropically blurred before or after adapting to images with astigmatism. Adaptation to horizontal blur caused isotropically blurred images to appear vertically biased and vice versa, shifting the perceived isotropic point toward the adapting level. Aftereffects were similar for different types of images and showed partial selectivity so that strongest effects generally occurred when testing and adapting images were the same. Further experiments explored whether the adaptation depended more strongly on the blurring or “fuzziness” in the images vs. the apparent “figural” changes introduced by the blur, by comparing how the aftereffects transfer across changes in size or orientation. Our results suggest that strong selective adaptation can occur for different lower order aberrations of the eye and that these may be at least partly driven by the apparent figural changes that blurring introduces into the retinal image.

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“…As eccentric retinoscopy is thought to produce a hyperopic refractive shift 9,10 because of the peripheral corneal flattening and testing along the shorter, off the visual axis, axial length, 11 he cited previous work on intraocular lenses showing the induction of myopic and astigmatic errors when light strikes a lens obliquely 12 to support his findings. A subsequent study examining refraction across the central 101 of the horizontal visual field in dilated subjects with a Hartmann-Shack wavefront sensor found a maximum change of 0.5 D in mean sphere, 13 supporting Jackson's findings of retinoscopic changes occurring within a few degrees of central fixation.…”

Section: Rempt Et Almentioning

confidence: 59%

The impact of off the visual axis retinoscopy on objective central refractive measurement in adult clinical practice: a prospective, randomized clinical study

Tay

Mengher

et al. 2011

Eye

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Purpose The objective of this study was to examine the effect of the off axis retinoscopy on objective central refractive measurement in adult clinical practice. Methods In all, 40 subjects underwent undilated retinoscopy in a randomly selected eye both on and off the visual axis by a single masked examiner. Off axis retinoscopy was defined as retinoscopy performed with the testing eye of the examiner aligned with the contralateral (non-test) eye of the subject resulting in an off axis deviation in the nasal horizontal visual field. Retinoscopy was performed in negative cylinder only and spherocylindrical measurements were converted to power vectors for analysis. Paired t-test was used to assess differences in M, J 0 and J 45 power vectors including differences between mean aided and unaided LogMar acuities. Results In all, 14 subjects were myopic (SErÀ0.5 D), 13 subjects were emmetropic (SE between À0.49 and 1.0 D) and 13 subjects were hyperopic (SE 41.0 D). Mean angle of deviation was 5.581 in the nasal horizontal visual field. J 0 showed a significant negative shift in those with myopia (Po0.001) and emmetropia (P ¼ 0.049) following off axis retinoscopy. No significant differences in M, J 0 and J 45 were found in the hyperopes. Mean aided LogMar acuities after on and off axis retinoscopy were both significantly better than mean unaided LogMar VA (Po0.001 in both cases). Conclusion Small degrees of off axis retinoscopy encountered in everyday clinical practice can induce errors in objective central refractive measurement.

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Refraction and Aberration Across the Horizontal Central 10?? of the Visual Field

Abstract: Subtle changes in cycloplegic refraction exist across the horizontal central 10 degrees of the retina. The results indicate the need for correct alignment when measuring objective refraction.

Cited by 18 publications

References 38 publications

High-Resolution Photoacoustic Imaging of Ocular Tissues

High-Resolution Photoacoustic Imaging of Ocular Tissues

Adaptation to astigmatic blur

The impact of off the visual axis retinoscopy on objective central refractive measurement in adult clinical practice: a prospective, randomized clinical study

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