1. Epidemiology and refractive determination of astigmatism at near sight
C. Anders, B.Sc. 1; O. Kolbe, B.Sc.1; Prof. Dr. S. Degle1
1University of Applied Sciences Jena, Germany
Introduction:
Results:
A connection between the subjectively measured amount of near astigmatism and pupil decentration (t-test, p=0.002) was found
Increasing visual requirements at close range and the establishment of advanced lens manufacturing technologies have led to a new focus on the issue of near astigmatism. The phenomenon of astigmatism at near sight has been discussed controversially in the past 15 years1-7.
Subjective Near Astigmatism
43% of the subjects showed an amount of near astigmatism of at least D
42% showed a change in axis axis change of at least 3°.
In the group with a pupil decentration of ≥0.24 mm the amount of near astigmatism is significantly higher than in the group with a decentration of <0.24 mm (see Fig. 4)
Purpose:
This study investigated the prevalence of astigmatism with accommodation and the comparability of subjective and objective results. It is to determine whether and how the maximum amplitude of accommodation (MAA), the amount of distance astigmatism (DA) and pupil decentration affect near astigmatism. Furthermore, the reliability of a specially developed screening figure was tested.
Figure 4: Correlation of subjective amount of near astigmatism and decentration of the pupil
Conclusion:
Figure 2: left change in the amount of astigmatism in subjective refraction right change in the axis of astigmatism in subjective refraction (N=72)
Objective Near Astigmatism
47% of the subjects showed an amount of near astigmatism of at least D
53% showed a change in axis axis change of at least 5°.
Near astigmatism is not rare but needs to be investigated concerning its impact on the visual acuity and visual perception. There is also a need to examine why subjective and objective measurements were not connected. It has to be acknowledged that there is test-retest variability in measuring astigmatism by either subjective or objective methods.
To confirm the assumption that near astigmatism is caused by the crystalline lens, additional assessments of the data regarding the amount of the cylinder are necessary. Further studies can point out the representativeness of the influence of a decentrated pupil. We have to be critical of the outcomes of near astigmatism screening figures.
Methods:
This prospective cross-sectional study was performed at the Department of SciTec, major optometry, of the University of Applied Sciences Jena, followed the tenets of the Declaration of Helsinki. After subjects received a verbal and written explanation of the character and risks of the study, informed consent was obtained.
The refraction of 72 subjects (32 males; 47 females), aged between 20 and 55 years (median 25), was measured at distance and close range. The measurements were made subjectively with a cross cylinder and objectively with an aberrometer (WASCA Analyzer G200), Carl Zeiss Meditec AG, Jena - Germany).
Figure 3: left change in the amount of astigmatism in objective refraction right change in the axis of astigmatism in objective refraction (N=64)
References:
Correlations
Subjective and objective results were not significantly correlated
the change of the amount of astigmatism (r= , p=0.735)
the change of axis (r=-0.204, p=0.159)
There is no dependence of MMA on the near astigmatism (Kruskal-Wallis-H, p=0,145 (subjective), p=0.857 (objective))
The objective axis-change is attached to the amount of the distance astigmatism (Mann-Whitney-U, p=0.002)
The group with distance astigmatism less than -0.5 D showed a significant higher change of axis than the group with -0.5 D and more
There is no dependence between the results of the screening test (Figure 1) and the subjectively and objectively measured near astigmatism of at least D (Chi-square, psub=0.538, pobj=0.807)
[1] Tsukamoto, M. et al Accommodation causes with-the-rule astigmatism in emmetropes. Optometry and vision science : official publication of the American Academy of Optometry, 77 (3).
[2] Mutti, D. O., Enlow, N. L. & Mitchell, G. L Accommodation and induced with-the-rule astigmatism in emmetropes. Optometry and vision science : official publication of the American Academy of Optometry, 78 (1)
[3] Cheng, H. et al A population study on changes in wave aberrations with accommodation. Journal of vision, 4 (4)
[4] Radhakrishnan, H. & Charman, W.  2007b. Changes in astigmatism with accommodation. Ophthalmic & physiological optics : the journal  of the British College of Ophthalmic Opticians (Optometrists), 27 (3)
[5] He, J. C. et al Change in corneal shape and corneal wave-front aberrations with accommodation. Journal of vision,
[6] Yang, Y., Thompson, K. & Burns, S. A Pupil location under mesopic, photopic, and pharmacologically dilated conditions. Investigative ophthalmology & visual science, 43 (7).
[7] Lemm, D. et al Aberrationen höherer Ordnung bei Blickbewegungen. Der Ophthalmologe : Zeitschrift der Deutschen Ophthalmologischen Gesellschaft, 107 (8)
Furthermore, a novel ray figure was developed and used to screen for astigmatic change in close range. It consists of 36 concentric arranged lines, in equal gaps of 10 degrees and two small central rings with different line widths, based on the Verhoeff Circles, see Figure. 1. The clinical designation of astigmatism (cylinder power and axis) was converted to power vectors, the near astigmatism
Figure 1: Novel ray figure for the subjective
measurement of the astigmatism at near sight
astigmatism calculated using the change in the J180 and J45 vectors, and afterwards reconverted to determine a change in cylinder power.
contact:
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