Association between soft contact lens decentration and scleral shape
Giancarlo Montani Dip.Optom FBCLA
Chiara Sicoli Dr. in Optics and Optometry
Purpose: The aim of this study was to assess the association between decentration of soft contact lenses and the scleral shape.
Method: This study included 24 REs of habitual spherical (single vision and multifocal) disposable and frequent replacement soft CLs wearers. HVID and anterior segment sagittal heights (ASSHs), for a chord of 15,00mm, were measured using a Fourier transform profilometer and the lowest and highest sagittal heights with their relative direction determinate. With the habitual CLs used fitted the images of anterior eye were acquired in primary gaze and opening the eyelids with a slit lamp and a digital images acquisition system focused on the edge of the lens. The position of the centre of lens in respect to the centre of the cornea on horizontal and vertical axes was objectively determined using the program Image J with the software measurement scale calibrated using the image of a reticule of a CL loupe. Total decentration and its direction was determined also through trigonometric analysis.
Results: On average, most of CLs evaluated were displaced in a temporal–inferior position in respect to the center of the cornea regardless of the kind of lens used (temporal decentration 0.42±0.36mm, inferior decentration 0.36±0.31mm). A significantly strong Pearson’s correlation was found comparing the differences between the lowest and highest ASSHs with the total decentration r=0,812 (p<0.01) and comparing the ratio between the total diameter of CL used and the HVID with the total decentration r=0,858 (p<0.01). A moderate Pearson’s correlation was found instead comparing the direction of highest ASSH with the direction of the total decentration r=0,589 (p<0.05)
Conclusions: In conclusion the decentration of common disposable and frequent replacement soft CLs can primarily be attributed to the asymmetry of anterior segment. A lower difference between the total diameter of CLs and the HVID can reduce this effect.
1st Author Biography: Giancarlo Montani is Professor of Clinical Contact Lens Application at the University of Salento, Italy. Involved in Optometry education since 1988, he has been Department Head of the Contact Lens Division at the Santa Chiara University Medical Centre in Pisa, Italy until 2004. In 2007 Professor Giancarlo Montani has co-founded the Centre for contact lens research of the University of Salento. Giancarlo Montani also works in private practice. He has published numerous articles in optometric journals, and has been invited as lecturer to several national and international Optometry Congresses.
*Data correct at the time of submission to BCLA by NCC.