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K. Ehrmann, F. Conrad, E.B. Papas, A. Ho; Normative Ocular Parameters for Various Angles of Gaze . Invest. Ophthalmol. Vis. Sci. 2006;47(13):115.
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© ARVO (1962-2015); The Authors (2016-present)
To obtain normative data of lid, cornea and pupil anatomical parameters of different age, gender and ethnic groups for four gaze directions.
A purpose–built eye–tracker instrument was used to capture images of the eye and eyelids while the subjects’ gaze followed the pivoting CCD camera. The four camera positions were 0° (primary gaze), –15° temporal and +6° and +15° nasal. Using automated image analysis, parameters for pupil and horizontal visible iris diameters (HVID), horizontal pupil decentration (HPD), upper and lower lid distance (ULD, ULL respectively) from pupil centre and upper and lower lid angles (ULA, LLA respectively) were determined. For the lid angles, 2 points on the lid margin (2mm nasal and 2mm temporal from the pupil centre) were selected to calculate the angle against the horizontal. Both eyes from 200 subjects of three ethnic groups, aged 18 to 65 years were measured.
A positive angle indicates the lid margin is sloping upwards nasally. A positive pupil decentration indicated that the pupil is centred more nasally with respect to the visible iris. ULD and LLD remained virtually unchanged as the eye moves from temporal to nasal, whereas both lid angles changed significantly. ULA is negative for temporal gaze (–2.6°) changing to +7.6° for the +15° nasal gaze. LLA changes in the opposite direction, from +4.1° at temporal to –5.8° for the nasal gaze. Mean HPD was 0.3mm nasal. The major difference between ethnic groups is for ULA with Asian eyes sloping more nasally upwards, Caucasian downwards and Others almost horizontal. For most gaze directions these differences reached statistical significance (p< 0.05). ULD was generally smaller for Asian eyes, but was not significantly different statistically from the other groups. Results from age and gender groups showed no consistent trend in differences for any of the parameters.
The upper eyelid shows greatest variation between ethnic groups, which can have significant effects on the on–eye performance of toric contact lenses in terms of orientation and rotational stability.
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