Article

Eyelid pressure: Inferences from corneal topographic changes

Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Australia.
Cornea (Impact Factor: 2.36). 02/2009; 28(2):181-8. DOI: 10.1097/ICO.0b013e31818a7d61
Source: PubMed

ABSTRACT It is known that eyelid pressure can influence the corneal surface. However, the distribution of eyelid pressure and the eyelid contact area and the biomechanics of the changes are unknown. Although these factors are difficult to directly measure, analysis of eyelid-induced corneal topographic changes and eyelid morphometry enables some inferences to be drawn.
Eighteen subjects, aged between 19 and 29 years, with normal ocular health were recruited. Corneal topographic changes were measured after 4 conditions consisting of 2 downward gaze angles (20 and 40 degrees) and 2 types of visual tasks (reading and steady fixation). Digital photography recorded the width of Marx line, the assumed region of primary eyelid contact with the cornea.
Significantly larger corneal changes were found after the 40-degree downward gaze conditions compared with 20-degree conditions because of the upper eyelid contact (P < 0.001). For the 40-degree downward gaze tasks, the lower eyelid changes were greater than those because of the upper eyelid (P < 0.01). The upper eyelid Marx line width was associated with the amplitude of corneal change (R = 0.32, P < 0.05).
Analysis of the corneal topographic changes gives insight into the pressure applied by the upper and lower eyelids in different situations. These include greater upper eyelid pressure with increasing downward gaze and greater lower eyelid pressure compared with the upper eyelid in 40-degree downward gaze. There was some evidence that supports Marx line as the primary site of contact between the eyelid margins and the cornea.

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    • "Using the calibration equation for a pressure cell assumes that the entire cell is loaded by the eyelid margin (i.e., over a width of more than 1.14 mm). Current evidence suggests that the area of primary contact between the upper eyelid and eye surface is likely to be less than 1 mm [3], [12]. Once the contact area between the cornea and upper eyelid has been confirmed, eyelid pressure measurements can be scaled based upon this contact area. "
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