Objective analysis of contact lens fit.
OBJECTIVE
To assess the validity and repeatability of objective compared to subjective contact lens fit analysis.


METHODS
Thirty-five subjects (aged 22.0±3.0 years) wore two different soft contact lens designs. Four lens fit variables: centration, horizontal lag, post-blink movement in up-gaze and push-up recovery speed were assessed subjectively (four observers) and objectively from slit-lamp biomicroscopy captured images and video. The analysis was repeated a week later.


RESULTS
The average of the four experienced observers was compared to objective measures, but centration, movement on blink, lag and push-up recovery speed all varied significantly between them (p<0.001). Horizontal lens centration was on average close to central as assessed both objectively and subjectively (p>0.05). The 95% confidence interval of subjective repeatability was better than objective assessment (±0.128 mm versus ±0.168 mm, p=0.417), but utilised only 78% of the objective range. Vertical centration assessed objectively showed a slight inferior decentration (0.371±0.381 mm) with good inter- and intrasession repeatability (p>0.05). Movement-on-blink was lower estimated subjectively than measured objectively (0.269±0.179 mm versus 0.352±0.355 mm; p=0.035), but had better repeatability (±0.124 mm versus ±0.314 mm 95% confidence interval) unless correcting for the smaller range (47%). Horizontal lag was lower estimated subjectively (0.562±0.259 mm) than measured objectively (0.708±0.374 mm, p<0.001), had poorer repeatability (±0.132 mm versus ±0.089 mm 95% confidence interval) and had a smaller range (63%). Subjective categorisation of push-up speed of recovery showed reasonable differentiation relative to objective measurement (p<0.001).


CONCLUSIONS
The objective image analysis allows an accurate, reliable and repeatable assessment of soft contact lens fit characteristics, being a useful tool for research and optimisation of lens fit in clinical practice.
Optics Department, Faculty of Physics, University of Valencia, Spain.
Lurdes
L
Belda-Salmerón
Ophthalmic Research Group, Aston University, Birmingham, UK.
Tom
T
Drew
Ophthalmic Research Group, Aston University, Birmingham, UK; Visioncare Research, Farnham, UK.
Lee
L
Hall
Ophthalmic Research Group, Aston University, Birmingham, UK. Electronic address: j.s.w.wolffsohn@aston.ac.uk.
James Stuart
JS
Wolffsohn
D000328:Adult; D001767:Blinking; D003263:Contact Lenses, Hydrophilic / Q000592:standards*; D003315:Cornea / Q000033:anatomy & histology*; D004311:Double-Blind Method; D004867:Equipment Design; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000503:physiopathology / Q000628:therapy*; D015203:Reproducibility of Results
Fitting characteristics; Lens evaluation; Objective repeatability; Soft contact lens; Validity