Contents lists available at ScienceDirect Contact Lens and Anterior Eye journal homepage: www.elsevier.com/locate/clae Semi-automatic measurement of rigid gas-permeable contact lens movement in keratoconus patients using blinking images Hassan Rezazadeh a , Hossein Arabalibeik b, ⁎ , Fateme Alipour c , Pezhman Pasyar a , Vahid Sadeghi a a Department of Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran b Research Center of Biomedical Technology and Robotics (RCBTR), Tehran University of Medical Sciences, Tehran, Iran c Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran ARTICLE INFO Keywords: Circular Hough transform Fluorescein pattern Keratoconus Lens movement RGP contact lens ABSTRACT Purpose: To introduce a method for estimation of the rigid gas-permeable contact lens (RGP) movement. Materials and methods: Videos captured from normal blinking of keratoconus patients while wearing RGP lenses were used for this study. The videos are recorded using the CCD camera of a smart phone attached to the eyepiece of the slit lamp. The algorithm starts with extracting two frames of the video related to the highest and lowest positions of the lens during blinking, followed by an appropriate edge detection method. In the next step circular Hough transform is used to find the center of lens and to segment it in each image. Finally the lens movement is estimated by measuring vertical displacement of the lens center between these two frames. Results: Mean and standard deviation of the difference between real movement and results of the algorithm for 20 cases are -8.66% and 10.71% respectively. The results are highly correlated with Pearson coefficient 0.986 P < 0.001. Bland-Altman plot with 95% levels of agreement (LoA) shows an agreement between exact manual measurement method and the proposed algorithm. Conclusion: The proposed algorithm shows a relatively high accuracy as the first attempt and compared to the routine qualitative visual estimation. Considering the importance of the lens movement, although this system was not tested on a series of RGP fitting patients yet, semi-automatic measurement may potentially help prac- titioners decide the appropriate RGP lens fit and reduce the fitting time. 1. Introduction Keratoconus is a degenerative ecstatic disorder of the eye in which structural changes within the cornea makes it thin and turns it into a more conical shape than its normal gradual curve [1]. Despite pre- valence differences in diverse parts of the world, it is estimated that 1 out of 2000 in the general population is suffering from keratoconus [1]. The etiology of the disease is unknown but genetic factors play a role in its development [1,2]. The cone shape of the cornea causes image distortion as a result of the increased higher order aberrations, de- creased visual acuity and sensitivity to light [3]. In early stages of keratoconus, glass or soft contact lens may correct the distortion. As the condition progresses, these may no longer provide the person with a satisfactory degree of visual acuity, and most prac- titioners will move to manage the condition with rigid contact lenses known as rigid gas-permeable (RGP) contact lenses [4,5]. Different surgical procedures are available for improving the visual outcome, which are usually performed for more advanced cases, who cannot tolerate or gain good visual acuity using RGPs [1,2]. Experts believe that almost 99% of patients could be managed by RGPs [2]. RGP lenses provide a thin layer of tears behind the lens, which substitutes the irregular corneal shape by a regular shape of the back surface of the lens (considering the fact that refractive index of the tear is very close to the cornea) and by correcting the resultant regular refractive error in the front surface of the lens, visual acuity would be corrected [6–8]. Other advantages of RGP contact lens are safety, long term comfort and ease of care [9]. Appropriate fitting of contact lens in keratoconus is difficult [10]. Many factors affect fitting considerably, among which BOZR, lens dia- meter, lens design and manufacturer, patient comfort and centration worth mentioning [11]. Studies also show that lens movement during blinking is of fundamental importance in wear comfort [12]. Small lens movements cause tear trapping and leads to reduced vision while large movements may cause the lens to fall out or be uncomfortable. Therefore this parameter should be kept within an appropriate range. Currently, this parameter is estimated visually by practitioners – a https://doi.org/10.1016/j.clae.2018.07.002 Received 19 August 2017; Received in revised form 15 May 2018; Accepted 7 July 2018 ⁎ Corresponding author at: Research Center of Biomedical Technology and Robotics (RCBTR), IK Hospital Complex, Keshavarz Blvd., Tehran, Iran. E-mail address: arabalibeik@tums.ac.ir (H. Arabalibeik). Contact Lens and Anterior Eye xxx (xxxx) xxx–xxx 1367-0484/ © 2018 Published by Elsevier Ltd on behalf of British Contact Lens Association. Please cite this article as: Rezazadeh, H., Contact Lens and Anterior Eye (2018), https://doi.org/10.1016/j.clae.2018.07.002