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Rigid gas permeable lens surface evaluation
Rigid Gas Permeable Lens Surface Evaluation Jean-Charles Allary*, Veronica Mapstone, Jean-Pierre Guillont, Michel Guillon§ (Kleist, 1979; Miller, 1980; Kleist, 1984) and rigid (Backman, 1979, Kleist, 1984) contact lenses. However, this has never been done in a systematic manner or as a means of monitoring a clinical trial as in t h e present study. The advantages of dark field microscopy in clinical research are multiple: i) The technique is non destructive, hence the lens surface characteristics can be analysed at every visit; ii) The observations, that takes only a few minutes, can be made by a technician away from the consulting room, enabling the practitioner to carry out his/her clinical work; iii) The range of magnifications available (angular magnifications X 10 to x75) permit both an overall observation of contact lens surfaces and the detailed study of any anomaly that may be present; iv) The dark background makes any anomaly very obvious and hence this system enables greater resolution than conventional light microscopy at similar magnification.
Introduction The wettability of contact lenses, in particular rigid lenses has been the subject of many reports. Most of these investigations have been concerned with the wettiiag characteristics of new lenses (Madigan & Holden, 1986a; Madigan & Holden, 1986b and Benjamin, 1988) and do not consider the long term effects of wear and care. The present investigation was aimed at evaluating the systematic use of a non destructive technique that can be performed by a technician during any clinical visit to evaluate the surface characteristics of lenses and to help decide whether or not it is necessary to replace a lens because of lens surface alterations. This paper describes the technique used and gives a photographic reference scale for the various entities observed. It also reports upon the lens surface changes observed with time of wear which are indicative of the lens care efficacy.
Dark Field Microscopy The technique of dark field microscopy has been used in the past to-study contact lens surfaces with both soft *Jean-Charles Allary, OD t Jean-Pierre Guillon, BSc, FBCO §Michel Guillon, PhD, FBCO
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In this evaluation, we photographed each contact lens before issue and at each after-care visit after cleaning with Boston Cleaner. In each instance we took photographs at three different magnifications (the linear magnifications in the film plane were ×2.6, ×4.1 and X6.5). The classification for each contact lens assessed was based upon the photographs at all three magnifications.
Classification of Lens Surface Appearance Three entities were analysed to describe the appearance of the lens front surfaces: scratches, surface film and deposits. Scratches classification indicates: i) the surface quality produced by the contact lens manufacturer; ii) the surface damage produced by mechanical cleaning of rigid gas permeable lenses by the patient. Film classification is concerned with rating the appearance of the mucus film that coats rigid gas permeable contact lenses. The coating enables the aqueous part of the tear film to adequately wet the contact lens. The presence of a regular, continuous and moderate coating is therefore essential to good in vivo lens wettability. Deposit classification rates the discrete deposits that have not been removed by cleaning with Boston Cleaner and remain visible at the contact lens front surface. Each entry .was classified according to a five point scale: 0 = None or Very Slight 1 = Slight 2 = Moderate 3 = Heavy 4 = Very Heavy
Transactions of B.C.L.A. Conference Birmingham 1989
The most common classifications obtained are reproduced on Figures 1, 2 and 3 for lens scratches, films and deposits respectively.
Fig. 1= 2= 3=
1 Scratches classification Slight Moderate Heavy
Results and Discussion A study involving Silicon Acrylate lenses (Boston IV vs Paraperm EW) and Fluorosilicon Acrylates (Equalens 1) demonstrated the sensitivity of the investigational technique. In particular, analysis of the photographs showed the excellent lens surface condition before issue and the change in time during wear. The level of scratches and deposits increased, confirming that the lens surface condition is altered during use, and regular replacement of R G P lenses, possibly once a year, could be recommended. The technique described has proven to be a very useful tool for clinical research. It can also be used in routine clinical practice. In the latter case, the lens is held with tweezers and viewed through the slitlamp biomicroscope observation system. The illumination system is setto produce a dark field background against which to view the lens and any anomaly can be seen. This type of lighting is achieved by illuminating the lens from the side.
Address for further correspondence
Fig. 2 Film classification 1 --- Slight 2 = Moderate 3 = Heavy
Dr Jean-Charles Allary, Contact Lens Research Consultants, 40-44 Vauxhall Bridge Road, Pimlico, London SW1V 2RX Tel: 01 630-9124. Fax: 01 630-8927
References Bachman HA (1979). The effects of contact lens deposits. The Optician 177 (4568): 9-10. Benjamin WJ (1987). Care regime and initial wetting of Silicone/Acrylate surfaces in vivo. Tranac. Br Contact L e n s Conf." 55-56. Kleist FD (1979). Appearance and nature of hydrophilic contact lens deposits -- Part 1: protein and other organic deposits. I n t Contact L e n s Clin 6: 49-58. Kleist FD (1984). Identification prevention and removal of contact lens deposits. (Allergan Pharmaceuticals, Irvine Calif.). Madigan M & Holden BA (1986a). A new method of wetting angle measurement. Int. Eyecare 2: 45-46. Madigan M & Holden BA (1986b). Preliminary report on lens wear and its effect on wetting angle. Int. Eyecare 2: 38-44. Miller B (1980). Observations of deposits on soft contact lens by different methods of light microscopy, scanning microscopy and electron microbe proble analysis. I n t Contact L e n s Clin 7: 22-35.
Fig. 3 Deposits classification 1 = Slight 2 = Moderate 3 --- Heavy 4 = Very Heavy
Transactions of B.C.L.A. Conference Birmingham 1989
19
Introduction The wettability of contact lenses, in particular rigid lenses has been the subject of many reports. Most of these investigations have been concerned with the wettiiag characteristics of new lenses (Madigan & Holden, 1986a; Madigan & Holden, 1986b and Benjamin, 1988) and do not consider the long term effects of wear and care. The present investigation was aimed at evaluating the systematic use of a non destructive technique that can be performed by a technician during any clinical visit to evaluate the surface characteristics of lenses and to help decide whether or not it is necessary to replace a lens because of lens surface alterations. This paper describes the technique used and gives a photographic reference scale for the various entities observed. It also reports upon the lens surface changes observed with time of wear which are indicative of the lens care efficacy.
Dark Field Microscopy The technique of dark field microscopy has been used in the past to-study contact lens surfaces with both soft *Jean-Charles Allary, OD t Jean-Pierre Guillon, BSc, FBCO §Michel Guillon, PhD, FBCO
18
In this evaluation, we photographed each contact lens before issue and at each after-care visit after cleaning with Boston Cleaner. In each instance we took photographs at three different magnifications (the linear magnifications in the film plane were ×2.6, ×4.1 and X6.5). The classification for each contact lens assessed was based upon the photographs at all three magnifications.
Classification of Lens Surface Appearance Three entities were analysed to describe the appearance of the lens front surfaces: scratches, surface film and deposits. Scratches classification indicates: i) the surface quality produced by the contact lens manufacturer; ii) the surface damage produced by mechanical cleaning of rigid gas permeable lenses by the patient. Film classification is concerned with rating the appearance of the mucus film that coats rigid gas permeable contact lenses. The coating enables the aqueous part of the tear film to adequately wet the contact lens. The presence of a regular, continuous and moderate coating is therefore essential to good in vivo lens wettability. Deposit classification rates the discrete deposits that have not been removed by cleaning with Boston Cleaner and remain visible at the contact lens front surface. Each entry .was classified according to a five point scale: 0 = None or Very Slight 1 = Slight 2 = Moderate 3 = Heavy 4 = Very Heavy
Transactions of B.C.L.A. Conference Birmingham 1989
The most common classifications obtained are reproduced on Figures 1, 2 and 3 for lens scratches, films and deposits respectively.
Fig. 1= 2= 3=
1 Scratches classification Slight Moderate Heavy
Results and Discussion A study involving Silicon Acrylate lenses (Boston IV vs Paraperm EW) and Fluorosilicon Acrylates (Equalens 1) demonstrated the sensitivity of the investigational technique. In particular, analysis of the photographs showed the excellent lens surface condition before issue and the change in time during wear. The level of scratches and deposits increased, confirming that the lens surface condition is altered during use, and regular replacement of R G P lenses, possibly once a year, could be recommended. The technique described has proven to be a very useful tool for clinical research. It can also be used in routine clinical practice. In the latter case, the lens is held with tweezers and viewed through the slitlamp biomicroscope observation system. The illumination system is setto produce a dark field background against which to view the lens and any anomaly can be seen. This type of lighting is achieved by illuminating the lens from the side.
Address for further correspondence
Fig. 2 Film classification 1 --- Slight 2 = Moderate 3 = Heavy
Dr Jean-Charles Allary, Contact Lens Research Consultants, 40-44 Vauxhall Bridge Road, Pimlico, London SW1V 2RX Tel: 01 630-9124. Fax: 01 630-8927
References Bachman HA (1979). The effects of contact lens deposits. The Optician 177 (4568): 9-10. Benjamin WJ (1987). Care regime and initial wetting of Silicone/Acrylate surfaces in vivo. Tranac. Br Contact L e n s Conf." 55-56. Kleist FD (1979). Appearance and nature of hydrophilic contact lens deposits -- Part 1: protein and other organic deposits. I n t Contact L e n s Clin 6: 49-58. Kleist FD (1984). Identification prevention and removal of contact lens deposits. (Allergan Pharmaceuticals, Irvine Calif.). Madigan M & Holden BA (1986a). A new method of wetting angle measurement. Int. Eyecare 2: 45-46. Madigan M & Holden BA (1986b). Preliminary report on lens wear and its effect on wetting angle. Int. Eyecare 2: 38-44. Miller B (1980). Observations of deposits on soft contact lens by different methods of light microscopy, scanning microscopy and electron microbe proble analysis. I n t Contact L e n s Clin 7: 22-35.
Fig. 3 Deposits classification 1 = Slight 2 = Moderate 3 --- Heavy 4 = Very Heavy
Transactions of B.C.L.A. Conference Birmingham 1989
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