- Email: [email protected]
Controlling myopia progression with Ortho-K
S2
Abstracts of the 2011 BCLA Annual Clinical Conference / Contact Lens & Anterior Eye 34, Supplement 1 (2011) S1–S43
Oxygen; my view Nathan Efron E-mail address: [email protected] Oxygen has been the “holy grail” of contact lens wear for over 100 years, but it is just one piece of a complex jigsaw puzzle. Clearly, high oxygen transmissibility (Dk/t) silicone hydrogel lenses meet the oxygen needs of the cornea. The Dk/t of these lenses is over 75 Dk units, which is far above that of the “best” hydrogel lenses (30 Dk units). Clinical trials have failed to reveal any hypoxic problems with silicone hydrogel lenses. Thus, conditions such as epithelial microcysts, limbal redness, hypoxic staining, stromal neovascularisation, oedema and endothelial polymegethism do not occur with these lenses. My view is that – looking at the “big picture” – we are far better off now that we have silicone hydrogel lenses.
Oxygen; my view Noel Brennan E-mail address: [email protected] Dk/t does not provide an unambiguous measure of the corneal physiological state during contact lens wear. Consumption is a better index as it directly relates to the metabolism of oxygen and thus to the energy produced. In daily wear, switching to silicone-hydrogels from hydrogels will lead to less limbal hyperemia and less endothelial polymegethism, but not much else. For open eye wear, a Dk/t of about 30 is both predicted and has been measured to be enough to prevent peripheral corneal changes. Thus, there is essentially no difference between different silicone-hydrogels in the amount of oxygen reaching the cornea for daily wear. More oxygen does not lead to safer contact lens wear in terms of infections and infiltrates. More oxygen prevents neovascularization but the threshold is probably a Dk/t of as low as 8! Even with the silicone-hydrogel of highest Dk/t, the cornea still swells by about one percent above that observed without contact lenses during closed eye wear.
Oxygen; my view James Wolffsohn E-mail address: The cornea requires oxygen to maintain normal function and integrity. The corneal epithelium receives most of its oxygen supply in the open eye condition from the atmosphere which diffuses across the tear film to supply the epithelium. Despite the importance of oxygen measurements, techniques have been limited by their invasive nature (interrupting the normal tear flow and blinking mechanism) and small corneal area of assessment. Lens thickness varies with lens design and prescription and factors other than oxygen availability may affect corneal swelling. While oxygen consumption appears a better index of corneal physiology, current calculations are based on theoretical modelling backed up by equivalent oxygen percentage-based data. Flux models predict law of diminishing returns need to be assessed clinically. New techniques can assess the ocular consumption of the whole ocular front surface non-invasively which will improve our understanding of how much oxygen is needed for healthy physiology. A new device consisted of a transparent goggle placed over the eye and adnexia with an oxygen sensitive material located on the inner surface will be described. The material emissivity to light is dependent on the available oxygen. An external fibre optic probe is used to sample the light emissivity in real-time. As the output is affected by temperature, a second probe was inserted into the goggle to allow a compensation to be applied. The technique has been shown to differentiate between closed and open eye conditions and has good repeatability.
Oxygen; my view Brien Holden E-mail address: [email protected] One of the most contentious debates in contact lens research over the last 60-70 years relates to the supply of oxygen to the cornea during lens wear. The highest oxygen transmissible silicone hydrogel contact lenses have elim-
inated the clinical signs of hypoxia that are classically associated with conventional hydrogel lens wear. An increasing number of practitioners now see silicone hydrogel lenses as the first choice lens for their patients irrespective of wear schedule, because these lenses offer superior metabolic health. The level of oxygen in the pre-corneal tear film (pre-corneal oxygen tension) affects the maintenance of healthy corneal metabolism. If the oxygen tension is at a high level, the cornea can maintain normal “aerobic” function. To achieve this with a contact lens the lens design/material must allow oxygen to flow freely from the front to the back surface and into the tear film. A contact lens with very low oxygen flow results in the cornea becoming less sensitive. This decreased sensitivity makes the eye more prone to adverse reactions such as epithelial erosion and keratitis. Risk assessment in contact lens practice involves identifying sources of potential harm, assessing the likelihood that harm will occur and the consequences if harm does occur. Quantifiable risk assessment determines human health risks associated with exposure to products such as contact lenses and the chemical solutions used for their care and maintenance. The supply of oxygen to the cornea during contact lens wear forms a part of the overall risk assessment. This presentation examines the physiological response of the cornea to contact lens wear and assesses the clinical performance of both high and low oxygen permeability lenses. The relationship between contact lens oxygen permeability and the degree of comfort experienced by the wearer is emphasised. This presentation also looks into the future of contact lens technology and design and examines research conducted to improve and advance the clinical performance of contact lenses.
CONFERENCE SESSION 3 – Irving Fatt Lecture and Scientific Paper Session on Orthokeratology/Myopia Controlling myopia progression with Ortho-K Jacinto Santodomingo E-mail address: [email protected] The prevalence of myopia has increased substantially in recent decades and is approaching 10–25% and 60–80% in the West and East Asia, respectively. Worldwide, the condition is considered to be the leading cause of visual impairment. Several treatment therapies, including contact lenses, bifocal and multifocal spectacle lenses and pharmaceutical agents, have been used with relatively modest success to eliminate or reduce myopia progression. Overall, most therapies have small treatment benefits that last for relatively short periods of time. Recently, modern orthokeratology has been shown to be effective in slowing myopia progression in children. This presentation will review the safety and efficacy of orthokeratology for myopia progression control.
Orthokeratology for slowing myopic progression: a randomised controlled trial Pauline Cho*, Sin-Wan Cheung Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China *E-mail address: [email protected] Purpose: To confirm if orthokeratology can retard myopic progression via a randomized, single-masked study. Method: Children aged 6-10 years old with spherical equivalent refractive error −1.25D to −4.50D (with-the-rule astigmatism less than 1.50D) were recruited and randomly assigned to wear Menicon Z Night Lens and spectacles. Axial length after cycloplegia was measured using the IOLMaster. The right eye or the eye which satisfied the Rx requirement was selected for analysis. Results: A total of 81, 81, 72 and 45 children have completed the 6-, 12, 18- and 24-month timelines respectively. Progression of myopia, in terms of axial length, was consistently faster in children wearing spectacles than those wearing ortho-k lenses at each timeline and the differences were statistically significant (t-tests, p<0.01). At the 24-month timeline, the increase in axial length of children wearing spectacles (n=24) and ortho-k lenses (n=21) were 0.67±0.29 mm and 0.39±0.27 mm respectively. (The power of the study based on the 24-month’s results is 90%). Conclusions: Ortho-k significantly slowed the progression of myopia in children.
Abstracts of the 2011 BCLA Annual Clinical Conference / Contact Lens & Anterior Eye 34, Supplement 1 (2011) S1–S43
Oxygen; my view Nathan Efron E-mail address: [email protected] Oxygen has been the “holy grail” of contact lens wear for over 100 years, but it is just one piece of a complex jigsaw puzzle. Clearly, high oxygen transmissibility (Dk/t) silicone hydrogel lenses meet the oxygen needs of the cornea. The Dk/t of these lenses is over 75 Dk units, which is far above that of the “best” hydrogel lenses (30 Dk units). Clinical trials have failed to reveal any hypoxic problems with silicone hydrogel lenses. Thus, conditions such as epithelial microcysts, limbal redness, hypoxic staining, stromal neovascularisation, oedema and endothelial polymegethism do not occur with these lenses. My view is that – looking at the “big picture” – we are far better off now that we have silicone hydrogel lenses.
Oxygen; my view Noel Brennan E-mail address: [email protected] Dk/t does not provide an unambiguous measure of the corneal physiological state during contact lens wear. Consumption is a better index as it directly relates to the metabolism of oxygen and thus to the energy produced. In daily wear, switching to silicone-hydrogels from hydrogels will lead to less limbal hyperemia and less endothelial polymegethism, but not much else. For open eye wear, a Dk/t of about 30 is both predicted and has been measured to be enough to prevent peripheral corneal changes. Thus, there is essentially no difference between different silicone-hydrogels in the amount of oxygen reaching the cornea for daily wear. More oxygen does not lead to safer contact lens wear in terms of infections and infiltrates. More oxygen prevents neovascularization but the threshold is probably a Dk/t of as low as 8! Even with the silicone-hydrogel of highest Dk/t, the cornea still swells by about one percent above that observed without contact lenses during closed eye wear.
Oxygen; my view James Wolffsohn E-mail address: The cornea requires oxygen to maintain normal function and integrity. The corneal epithelium receives most of its oxygen supply in the open eye condition from the atmosphere which diffuses across the tear film to supply the epithelium. Despite the importance of oxygen measurements, techniques have been limited by their invasive nature (interrupting the normal tear flow and blinking mechanism) and small corneal area of assessment. Lens thickness varies with lens design and prescription and factors other than oxygen availability may affect corneal swelling. While oxygen consumption appears a better index of corneal physiology, current calculations are based on theoretical modelling backed up by equivalent oxygen percentage-based data. Flux models predict law of diminishing returns need to be assessed clinically. New techniques can assess the ocular consumption of the whole ocular front surface non-invasively which will improve our understanding of how much oxygen is needed for healthy physiology. A new device consisted of a transparent goggle placed over the eye and adnexia with an oxygen sensitive material located on the inner surface will be described. The material emissivity to light is dependent on the available oxygen. An external fibre optic probe is used to sample the light emissivity in real-time. As the output is affected by temperature, a second probe was inserted into the goggle to allow a compensation to be applied. The technique has been shown to differentiate between closed and open eye conditions and has good repeatability.
Oxygen; my view Brien Holden E-mail address: [email protected] One of the most contentious debates in contact lens research over the last 60-70 years relates to the supply of oxygen to the cornea during lens wear. The highest oxygen transmissible silicone hydrogel contact lenses have elim-
inated the clinical signs of hypoxia that are classically associated with conventional hydrogel lens wear. An increasing number of practitioners now see silicone hydrogel lenses as the first choice lens for their patients irrespective of wear schedule, because these lenses offer superior metabolic health. The level of oxygen in the pre-corneal tear film (pre-corneal oxygen tension) affects the maintenance of healthy corneal metabolism. If the oxygen tension is at a high level, the cornea can maintain normal “aerobic” function. To achieve this with a contact lens the lens design/material must allow oxygen to flow freely from the front to the back surface and into the tear film. A contact lens with very low oxygen flow results in the cornea becoming less sensitive. This decreased sensitivity makes the eye more prone to adverse reactions such as epithelial erosion and keratitis. Risk assessment in contact lens practice involves identifying sources of potential harm, assessing the likelihood that harm will occur and the consequences if harm does occur. Quantifiable risk assessment determines human health risks associated with exposure to products such as contact lenses and the chemical solutions used for their care and maintenance. The supply of oxygen to the cornea during contact lens wear forms a part of the overall risk assessment. This presentation examines the physiological response of the cornea to contact lens wear and assesses the clinical performance of both high and low oxygen permeability lenses. The relationship between contact lens oxygen permeability and the degree of comfort experienced by the wearer is emphasised. This presentation also looks into the future of contact lens technology and design and examines research conducted to improve and advance the clinical performance of contact lenses.
CONFERENCE SESSION 3 – Irving Fatt Lecture and Scientific Paper Session on Orthokeratology/Myopia Controlling myopia progression with Ortho-K Jacinto Santodomingo E-mail address: [email protected] The prevalence of myopia has increased substantially in recent decades and is approaching 10–25% and 60–80% in the West and East Asia, respectively. Worldwide, the condition is considered to be the leading cause of visual impairment. Several treatment therapies, including contact lenses, bifocal and multifocal spectacle lenses and pharmaceutical agents, have been used with relatively modest success to eliminate or reduce myopia progression. Overall, most therapies have small treatment benefits that last for relatively short periods of time. Recently, modern orthokeratology has been shown to be effective in slowing myopia progression in children. This presentation will review the safety and efficacy of orthokeratology for myopia progression control.
Orthokeratology for slowing myopic progression: a randomised controlled trial Pauline Cho*, Sin-Wan Cheung Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China *E-mail address: [email protected] Purpose: To confirm if orthokeratology can retard myopic progression via a randomized, single-masked study. Method: Children aged 6-10 years old with spherical equivalent refractive error −1.25D to −4.50D (with-the-rule astigmatism less than 1.50D) were recruited and randomly assigned to wear Menicon Z Night Lens and spectacles. Axial length after cycloplegia was measured using the IOLMaster. The right eye or the eye which satisfied the Rx requirement was selected for analysis. Results: A total of 81, 81, 72 and 45 children have completed the 6-, 12, 18- and 24-month timelines respectively. Progression of myopia, in terms of axial length, was consistently faster in children wearing spectacles than those wearing ortho-k lenses at each timeline and the differences were statistically significant (t-tests, p<0.01). At the 24-month timeline, the increase in axial length of children wearing spectacles (n=24) and ortho-k lenses (n=21) were 0.67±0.29 mm and 0.39±0.27 mm respectively. (The power of the study based on the 24-month’s results is 90%). Conclusions: Ortho-k significantly slowed the progression of myopia in children.