| 1. |
|
|
| 2. |
|
|
| 3. |
- Axner, Ove, et al.
(författare)
-
Authors’ reply
- 2004
-
Ingår i: Spectrochimica Acta, Part B. ; 59:3, s. 390-392
-
Tidskriftsartikel (refereegranskat)
|
|
| 4. |
|
|
| 5. |
- Baskaran, Karthikeyan, et al.
(författare)
-
Benefit of Adaptive Optics Aberration Correction at Preferred Retinal Locus
- 2012
-
Ingår i: Optometry and Vision Science. - 1040-5488 .- 1538-9235. ; 89:9, s. 1417-1423
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE.: To investigate the effect of eccentric refractive correction and full aberration correction on both high- and low-contrast grating resolution at the preferred retinal locus (PRL) of a single low-vision subject with a long-standing central scotoma. METHODS.: The subject was a 68-year-old women with bilateral absolute central scotoma due to Stargardt disease. She developed a single PRL located 25 degrees nasally of the damaged macula in her left eye, this being the better of the two eyes. High- (100%) and low-contrast (25 and 10%) grating resolution acuity was evaluated using four different correction conditions. The first two corrections were solely refractive error corrections, namely, habitual spectacle correction and full spherocylindrical correction. The latter two corrections were two versions of adaptive optics corrections of all aberrations, namely, habitual spectacle correction with aberration correction and full spherocylindrical refractive correction with aberration correction. RESULTS.: The mean high-contrast (100%) resolution acuity with her habitual correction was 1.06 logMAR, which improved to 1.00 logMAR with full spherocylindrical correction. Under the same conditions, low-contrast (25%) acuity improved from 1.30 to 1.14 logMAR. With adaptive optics aberration correction, the high-contrast resolution acuities improved to 0.89/0.92 logMAR and the low-contrast acuities improved to 1.04/1.06 logMAR under both correction modalities. The low-contrast (10%) resolution acuity was 1.34 logMAR with adaptive optics aberration correction; however, with purely refractive error corrections, she was unable to identify the orientation of the gratings. CONCLUSIONS.: Correction of all aberrations using adaptive optics improves both high- and low-contrast resolution acuity at the PRL of a single low-vision subject with long-standing absolute central scotoma
|
|
| 6. |
- Baskaran, Karthikeyan, et al.
(författare)
-
Effects of Optical Defocus on Resolution Acuity in Preferred Retinal Locus
- 2011
-
Ingår i: <em>Invest Ophthalmol Vis Sci</em> 2011;52: E-Abstract 1900..
-
Konferensbidrag (refereegranskat)abstract
- PurposeResolution acuity in the peripheral visual field is primarily limited by retinal sampling. In healthy eyes, the correction of peripheral refractive errors does not produce significant visual benefits other than improved detection and low contrast acuity. However, studies (Lundstrom L et al, Optom Vis Sci, 2007;84:1046-52) have shown that peripheral refractive corrections improve resolution acuity in subjects with central visual field loss (CFL) who have an established preferred retinal locus (PRL). The aim of this study was to evaluate the effect of optical defocus on high contrast resolution acuity in the PRL. MethodsResolution acuity was evaluated under spherical defocus in the PRL of three low vision subjects (mean age 75 years) with long standing CFL (due to age-related macular degeneration). Off-axis refractive error at the PRL was measured by an open-field COAS-HD VR aberrometer and was corrected accordingly. The PRL for subject 1 was located at 10{degrees} in the temporal visual field (left eye), subject 2 at 20{degrees} in the nasal visual field (right eye) and subject 3 at 15{degrees} in the inferior visual field (left eye). Stimuli consisting of high-contrast Gabor patches with a visible diameter of 3{o} were presented on a CRT monitor situated 1.0 meter from the subject. Resolution thresholds for static visual acuity (SVA) and dynamic visual acuity (DVA) were obtained using an adaptive Bayesian algorithm. Fixation was aided using illuminated concentric rings covering {+/-}25{degrees} in the visual field. Defocus was altered in 1D steps up to {+/-}4D. When measuring DVA, the sine-wave gratings drifted within the Gaussian envelope at an angular velocity of 1{degrees}/sec. ResultsResolution thresholds for both SVA and DVA in the PRL varied significantly with the amount of optical defocus. The results show a 2 - 3 line decrease (logMAR) in SVA and DVA with 4 D positive and negative defocus. There was no significant difference between SVA and DVA with increasing defocus. In the absence of defocus, SVA was significantly better than DVA in the PRL. ConclusionsDefocus as low as one dioptre has an impact on both static and dynamic high contrast resolution acuity for CFL subjects using a PRL. The results of this study suggest that, for CFL subjects using a PRL, resolution acuity is not only sampling limited but also influenced by the optics of the eye.
|
|
| 7. |
- Baskaran, Karthikeyan, et al.
(författare)
-
Influence of age on peripheral aberration
- 2010
-
Konferensbidrag (refereegranskat)abstract
- The purpose of this study is to compare peripheral higher order aberrations in young and old emmetropic eyes across the horizontal (±40°) and inferior (–20°) visual field. Introduction People with central visual field loss use eccentric fixation for various visual tasks. Recently studies have shown that the correction of lower order aberrations (defocus & astigmatism) can improve eccentric vision in subjects with central visual field loss (CFL)[1]. The CFL subjects mostly correspond to older age groups who use eccentric fixation angles up to 20°–30°. While there have been studies comparing the off-axis lower order aberrations in normal young and old subjects[2], there is only one recent study, which has compared off-axis higher order aberrations in normal young and old emmetropic eyes up to 20° (horizontal and vertical) eccentricity[3]. In this study we have measured off-axis aberrations in a group of 10 young (23 ± 3 years) and 10 old (57 ± 4 years) emmetropes. The aberrations of the right eye were measured using COAS-HD VR Hartmann-Shack aberrometer in steps 10° out to ± 40° horizontally and –20° inferiorly in the visual field. Subjects rotated the eyes to view the fixation targets, which were red light emitting diodes, placed at 3 meter from the eye. The aberrations were quantified for a pupil area 5 mm in diameter. Discussion Mixed between-within subject’s analysis of variance of the horizontal coma C13 showed that there was a statistically significant difference between age groups (p<0.05). The coma increased linearly in both groups from nasal to temporal visual field. The rate of change was greater in the old (slope = –0.027 μm/deg) compared to the young (slope = –0.012 μm/deg) emmetropes. In the inferior visual field, vertical coma C-13 changed linearly in both groups with higher values in old (slope = 0.015 μm/deg) compared to young (slope = 0.006 μm/deg). The mean spherical aberration was positive in older emmetropes (0.053 μm) compared to young emmetropes (-0.030 μm). The HO RMS showed a quadratic increase in the periphery for both age groups. The HO RMS was greater in older emmetropes but it was not statistically significant (p>0.05) when compared to young emmetropes. Conclusions Our results show that there is an increase in coma, spherical aberration, and HO RMS with age in the periphery.
|
|
| 8. |
- Baskaran, Karthikeyan, et al.
(författare)
-
Influence of age on peripheral ocular aberrations.
- 2011
-
Ingår i: Optometry and Vision Science. - 1040-5488 .- 1538-9235. ; 88:9, s. 1088-1098
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE.: To compare peripheral lower and higher order aberrations across the horizontal (±40°) and inferior (-20°) visual fields in healthy groups of young and old emmetropes. METHODS.: We have measured off-axis aberrations in the groups of 30 younger (24 ± 3 years) and 30 older (58 ± 5 years) emmetropes. The aberrations of OD were measured using the COAS-HD VR Shack-Hartmann aberrometer in 10° steps to ±40° horizontally and -20° inferiorly in the visual field. The aberrations were quantified with Zernike polynomials for a 4 mm pupil diameter. The second-order aberration coefficients were converted to their respective refraction components (M, J45, and J180). Mixed between-within subjects, analysis of variance were used to determine whether there were significant differences in the refraction and aberration components for the between-subjects variable age and the within-subjects variable eccentricity. RESULTS.: Peripheral refraction components were similar in both age groups. Among the higher order coefficients, horizontal coma (C3) and spherical aberration (C4) varied mostly between the groups. Coma increased linearly with eccentricity, at a more rapid rate in the older group than in the younger group. Spherical aberration was more positive in the older group compared with the younger group. Higher order root mean square increased more rapidly with eccentricity in the older group. CONCLUSIONS.: Like the axial higher order aberrations, the peripheral higher order aberrations of emmetropes increase with age, particularly coma and spherical aberration.
|
|
| 9. |
- Baskaran, Karthikeyan, et al.
(författare)
-
Measurement of Off-axis Refraction with a Commercial Open Field Aberrometer
- 2010
-
Konferensbidrag (refereegranskat)abstract
- Purpose: People with central visual field loss (CFL) use their remaining peripheral vision in order to see better when performing various visual related tasks. At large off-axis angles, the eccentric vision can be limited both by the low resolution capacity of the peripheral retina and by the optical aberrations caused due to oblique angles. Previous work has shown that eccentric correction of induced off-axis astigmatism can improve vision in a preferred retinal location (PRL) for people with CFL. However, the eccentric refraction is often difficult to determine with traditional refractive methods. This work therefore shows the use of a commercially available wavefront sensor to measure fast and reliable off-axis refraction. Data on off-axis refraction is also of interest in the field of myopia research. Methods: We used the new open-field high-definition complete ophthalmic analysis system, COAS HD -VR, to evaluate off-axis refraction. Using the special Vision Research tool in this system stimulus (fixation objects) can be presented in a large part of the visual field. The instrument can measure out to 40 degrees in the horizontal visual field and 20 degrees in the vertical visual field with a range from sphere +7 D to − 17 D. It measures astigmatism up to 10 D. This instrument also allows natural binocular viewing without obstacles. Aberrations of the right eye of 30 emmetropes (24 ± 4 years) were studied. Off-axis refraction and higher order (HO) aberrations were measured in steps of 10° out to ± 30° in the horizontal visual field Results: The first data on young emmetropic eyes with this new instrument showed promising results for low (LO) and higher order (HO) aberrations in the peripheral visual field. Of the LO aberrations, astigmatism increased significantly with the off–axis angle, from 0.25 D at 10° Nasal to 1.65 D at 30° Nasal. In the HO aberrations, coma (C13) showed a linear increase across the horizontal visual field (p < 0.05) Conclusions: The COAS HD-VR shows promising results and good usability for future research in evaluation of off-axis refraction. In future we believe the aberrometer can be used clinically to measure off-axis refractions in low vision patients.
|
|
| 10. |
- Baskaran, Karthikeyan, et al.
(författare)
-
Ocular Aberrations in the Peripheral Visual Field With a Commercial Open-View Aberrometer
- 2010
-
Ingår i: Investigative Ophthalmology and Visual Science. - 0146-0404 .- 1552-5783. ; 51:5
-
Tidskriftsartikel (refereegranskat)abstract
- PurposeThe interest in off-axis aberrations has increased with the discovery of a possible link between myopia development and peripheral optics. The most common technology to measure the off-axis aberrations is a Shack-Hartmann wavefront aberrometer. This is the first study to report peripheral aberrations in a large sample of emmetropic population with a commercial open-view Shack-Hartmann aberrometer. MethodsThe commercial open-view Shack-Hartmann aberrometer COAS-HD VR was used to measure the aberrations in the peripheral vision. Aberrations of the right eye of 30 emmetropes (24 {+/-} 4 years) were studied. Off-axis aberrations were measured in steps of 10{degrees} out to {+/-} 30{degrees} in the horizontal visual field. The subjects turned their eye to view the off-axis fixation target (light emitting diode placed at 3 meters) during the measurement. The resulting wavefront aberrations were parameterized with Zernike coefficients for a 5 mm diameter pupil. All analyzes are reported according to optical society of America (OSA) recommended standards. ResultsAberrations from the 2nd to 6th order and the total higher-order root-mean-square (HO RMS) were analyzed using one-way ANOVA. The defocus C02 was significantly myopic in the nasal visual field (+20{degrees}, +30{degrees}) whereas there was no significant difference in the temporal visual field. Astigmatism C22 increased quadratically from {+/-}10{degrees} in the periphery and coma C13 showed a linear increase across the horizontal visual field (p < 0.05). The spherical aberration C04 and the total HO RMS showed a significant change at {+/-}30o. ConclusionsOur results showed that in young emmetropes there was a significant increase of HO RMS at {+/-}30{degrees}, which is expected. Astigmatism, horizontal coma, and spherical aberration vary systematically across the horizontal visual field in agreement with Seidel theory. The findings of our study with a large sample of emmetropic population agree with the previous studies done with laboratory built aberrometers.
|
|
