Controlling rigid lens centration though specific gravitiy

Quinn, Thomas G. & Carney, Leo G. (1992) Controlling rigid lens centration though specific gravitiy. International Contact Lens Clinic, 19, pp. 84-88.


The recent availability of a wide range of gas permeable contact lens materials improves the clinician's ability to more precisely meet the unique demands of each contact lens wearing eye. Most attentions has focussed on differences in material oxygen permeability, dimensional stability, surface wetting, and deposit resistance. One parameter that also varies but has received little attention, is specific gravity. Most of the first generation gas permeable materials had specific gravity values that varied only slightly. However, with the introduction of the newer generations of materials, this range has nearly doubled (see fig 1). It is conceivable that, in addition to manipulation of other design features, centration of a lens on a patients eye could be influenced by selecting a lens material based on its specific gravity. A low riding lens can cause dryness and irritation. The incidence and severity of 3-9 o'clock staining may be exacerbated by a chronically low riding lens.1 Lebow2 suggested that a low riding lens could be raised if switched to a material of lower specific gravity. Conversely, a chronically high riding lens, which can compromise vision and potentially irritate the superior limbal region,3 could be lowered by a lens fabricated with a high specific gravity material. Lens decentration, in general, has been implicated as a risk factor for inducing corneal warpage. It is apparent then that optimal lens centration significantly reduces complication rates with gas permeable contact lens wear. Cornstock and Carney5 reported that individual patient ocular characteristics have a greater on vertical lens positioning than do lens design features. However, if specific gravity does allow the clinician to more effectively control lens centration, complication rates would decrease and chair time would be reduced. the purpose of this study was to determine if the specific gravity differences among today's materials significantly affects vertical lens positioning, specifically in those patients whose current contact lenses do not centre well. If so an additional tool would be added to the clinicians armamentarium in providing optimum lens performance for their contact lens wearing patients. Patient satisfaction, safety and economy may all benefit.

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ID Code: 3154
Item Type: Journal Article
Refereed: Yes
Additional Information: For more information, please refer to the journal's website (see link) or contact the author. Author contact details:
Additional URLs:
Keywords: Rigid Gas Permeable, RGP, contact lenses, specific gravity, fitting
ISSN: 0892-8967
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 1992 Elsevier
Deposited On: 30 Jan 2006 00:00
Last Modified: 15 Jan 2009 06:54

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