A Review of the Theoretical Concepts, Measurement Systems and Application of Contact Lens Oxygen Permeability

Abstract

The interest in rigid gas-permeable contact lenses for extended wear has promoted a re-evaluation of the theoretical and practical aspects of the oxygen transport characteristics of contact lens materials. Oxygen permeability has been considered by some authors to be a parameter which is dependent upon the measurement conditions; however, this paper demonstrates that an intrinsic permeability coefficient may be derived for a given material when the basic principles of the transport mechanisms are considered. Two basic methodologies have been described for measuring oxygen permeability--dual-chamber and electrochemical methods, the latter being the more popular. Although consistency in measured oxygen transmissibility of a given lens may be achieved among laboratories, current analytical techniques do not allow the intrinsic permeability coefficient of materials to be determined. Future research should be directed towards developing methods to fully correct for surface and edge effects, and to achieve standardization among laboratories.

Silicone Hydrogels Materials for Contact Lens Applications

“…Due to the potential impact of contact lenses on corneal physiology, oxygen diff usion through the cornea has been studied during the past 40 years and several models have been developed [41][42][43][44][45]. Th ree methods are most commonly used to measure oxygen transmissibility of contat lenses of given thickness "t" (Dk/t) of CLs: polarographic, coulometric and gas-to-gas techniques, each one having advantages and disadvantages [46][47][48]. Th e polarographic method was modifi ed and used recently by Wichterlova et al [49].…”

Synthesis and Physical Properties of Ophthalmic Copolymer Containing 4-fluorostyrene

“…렌즈는 임상적으로 편안한 착용감을 제공할 수 있으며, 최근 콘택트렌즈 재질의 물성 중 부작용 발생에 많은 영향을 주는 산소투과율(oxygen transmissibility)을 증가시킬 수 있다. [7][8][9] 이에 고굴절률을 가진 콘택트렌즈 재료는 광학적인 장점뿐 만 아니라 생리적인 면에서도 장점을 가질 수 있다. 콘택트렌 즈의 굴절률을 높이기 위해 사용되는 물질인 polystyrene은 벤젠 고리에서 수소 1개를 vinyl기로 치환한 구조를 가진 방 향족 탄화수소로 벤젠 고리를 포함하기 때문에 광학적으로 굴절률이 매우 높다.…”

Determination of Oxygen Permeability/Transmissibility and Storage of Contact Lenses Using HPLC with Reductive Electrochemical Detection in Combination with a Specifically Designed Sampling Unit

“…In recent years, considerable attention has been paid to the development of new contact lens materials with very high oxygen permeabilities that should be especially suitable for extended wear . As a consequence of these developments, not only theoretical and practical aspects of oxygen transport characteristics across contact lenses have received increased attention but also analytical methodologies to measure this intrinsic property of lens materials − have been studied. In the following section, a short review concerning the basic theoretical concepts and principles of measurement of oxygen permeability of contact lenses shall be given.…”

“…Many different methodologies have been developed to measure the oxygen transport characteristics of polymer membranes. In contact lens research, most of the Dk measurements are made with one form or other of electrochemical device, , the most popular methods being the single-chamber “polarographic” (SCP) technique developed by Fatt et al − and the coulometric carrier gas (CCG) method. − The Fatt method, which is based on the amperometric oxygen sensor (Clark electrode), has become standard for the determination of oxygen permeability of soft hydrogel lenses. Oxygen permeability of rigid contact lenses is usually determined as gas-to-gas permeability using the dual-chamber coulometric method, which is also more suited than the polarographic method for assessing lenses with oxygen permeability of over 100 barrer/cm.…”

“…In certain cases, differences between the dissolved oxygen permeability, determined with an aqueous-membrane-aqueous system, such as the Fatt method, and the gaseous oxygen permeability obtained with a gas-membrane-gas system (e.g., by the coulometric method) have been found. These discrepancies can be explained by experimental errors, known as edge effect ,, and boundary effect, ,,,, which unless corrected, will lead to an overestimation and an underestimation, respectively, of oxygen permeability of the lens material.…”