Purchase this article with an account.
Babak Aghazadeh, Daozhi Wang, Paul Chamberlain; Objective assessment of toric contact lens rotational stability through digital video processing techniques. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):3091.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Conventional methods using a slit lamp to evaluate toric contact lens’ orientation and rotational stability are subjective, time-consuming, and not always precise. In this study, a novel video processing based algorithm is proposed to automatically track the standard orientation mark on contact lenses and provide an objective method to evaluate their rotational stability.
A selection of videos from clinical assessment of five subjects was performed to enable development of the processing technique. After 15 minutes of lens wear, lenses were assessed for rotational recovery after deliberate 90° mislocation (degrees/10 blinks). In a post-processing step, these videos were analyzed to firstly identify the region of interest (ROI) in each video frame containing the orientation mark. Each ROI was selected by finding the maximum normalized cross correlation between the video frame and a template of orientation mark. Next, the orientation mark was detected in each ROI using Canny edge detection algorithm, and its angle with horizontal axis was estimated using Hough transformation. A mathematical model was derived to describe the rotational recovery of lenses, and the model parameters were compared to evaluate lens rotational recovery.
Toric lens orientation angle was measured robustly with higher temporal resolution (~35 ms) through proposed video processing technique (Figure 1). Two models (Quadratic, Exponential) were found to be effective in estimating lens orientation versus time (Figure 2). Using model parameters of polynomial coefficients and exponential decay coefficient, lens’ rotational stability were evaluated and compared objectively. Furthermore, the proposed method provided means to obtain other meaningful information on lens performance. For instance, lens rotation between blinks / during blinks, and lens superior-inferior movement were also quantified for further analysis.
A video analysis-based technique suitable for the evaluation of toric contact lens rotational stability is proposed. The method provides means to better evaluate toric contact lens rotational stability and to understand the dynamics of lens on eye that may relate to variations in toric lens ballast design.
This PDF is available to Subscribers Only