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Can H2O2 pass through the cornea?
Monday, Sep 21, 1992 Des Iles Borromees 4
X ICER Abstracts 15
CAN H,O, PASS THROUGH THE CORNEA? Graeme S. Wilson’ and Michael V. Rile$. ‘School of Optometry, The University of Alabama at Birmingham, Alabama, USA; ‘Eye Research Institute, Oakland University, Rochester, Michigan, USA. The use of H,O, for the disinfection of hydrogel contact lenses has raised concerns that it could diffuse through the cornea into the aqueous humor and raise the concentration of H,O, enough to interfere with lens metabolism. To test the threshold at which H202 can diffuse through the cornea, 600 ul was placed on the rabbit eye for 10 min. This volume was considered to provide a wide safety margin, as it is at least ten times the volume contained in a contact lens. The lowest threshold for trans-cornea1 diffusion in viva was 300 to 600 ppm H,O,, and was obtained using a cup which prevented the solution from touching the palpebral or bulbar conjunctiva. Without the cup, the threshold rose to greater than 2000 ppm. This demonstrated the importance of the conjunctival surfaces in the eye’s defenses against H,O,. In an in vitro preparation it was possible to measure the total amount of H,O, diffusing across the cornea in the absence of the conjunctiva and aqueous humor. With 400 ppm on the comeal surface the total H,O, measured in the endothelial superfusate as a result of the 10 min exposure was 4.04Q.13 nanomcles (N=6). If all of this entered the anterior chamber instantaneously it would raise the concentration by 20 pM. This is reduced in the in viva eye by the ability of the ssnjunciival epithelium and the aqueous humor to destroy H,O,. The destruction occurs within minutes. The tenfold safety factor in the above experiments shows that residual H,O, in a contact lens as high as 300 ppm will not raise the concentration in the aqueous humor. In reality the residual H,O, is usually less than 100 ppm.
5 EFFECTS OF pH ON CORNEAL FUNCTION.-‘. et. School of Optometry1 & School L!Ja&W’ of Public Health2, University of California at Berkeley, CA. An eatbnate of overall comeal hydration control can be obtained by measuring the rate of thiclmess recovery following induced cornea1 swelling. This recovery, which can be expressed as the wrcent recovery per hour (PRPH), was fmt reported to be exponential; however, more recdni analysis indicates that the moverv has an initial slow phase lastine about 30-40 min. that cotreswnds to the time wien comeal pH is re&ced secon&uy to the contact lens-ind&d swelling. The initial slower recovery suggests the possibility that suomal acidosis may retard the comeal deswelliog process. In this study we explored the effects of comeal acidosis on hydration control by measuring the PRPH while the cornea was exposed to diierent pH levels. Comeal pH was monitored using a slit lamp fluompbototneter and controlled by using air tight goggles and exposing the eyes to one of 4 levels of CO,. Each subject provided PRPH and pH data for 4 CO* doses: 0.3.5, and 7% CO,. The fluorometric data cortespondiog to these gas mixtures showed that the average stmmal pHflSD resulting from exposure to either the 0, 3, 5, and 7% CO, was 7.65M.11, 7.3Ofo.09, 7.1.5f0.08, and 7.04f0.07 (p
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X ICER Abstracts 15
CAN H,O, PASS THROUGH THE CORNEA? Graeme S. Wilson’ and Michael V. Rile$. ‘School of Optometry, The University of Alabama at Birmingham, Alabama, USA; ‘Eye Research Institute, Oakland University, Rochester, Michigan, USA. The use of H,O, for the disinfection of hydrogel contact lenses has raised concerns that it could diffuse through the cornea into the aqueous humor and raise the concentration of H,O, enough to interfere with lens metabolism. To test the threshold at which H202 can diffuse through the cornea, 600 ul was placed on the rabbit eye for 10 min. This volume was considered to provide a wide safety margin, as it is at least ten times the volume contained in a contact lens. The lowest threshold for trans-cornea1 diffusion in viva was 300 to 600 ppm H,O,, and was obtained using a cup which prevented the solution from touching the palpebral or bulbar conjunctiva. Without the cup, the threshold rose to greater than 2000 ppm. This demonstrated the importance of the conjunctival surfaces in the eye’s defenses against H,O,. In an in vitro preparation it was possible to measure the total amount of H,O, diffusing across the cornea in the absence of the conjunctiva and aqueous humor. With 400 ppm on the comeal surface the total H,O, measured in the endothelial superfusate as a result of the 10 min exposure was 4.04Q.13 nanomcles (N=6). If all of this entered the anterior chamber instantaneously it would raise the concentration by 20 pM. This is reduced in the in viva eye by the ability of the ssnjunciival epithelium and the aqueous humor to destroy H,O,. The destruction occurs within minutes. The tenfold safety factor in the above experiments shows that residual H,O, in a contact lens as high as 300 ppm will not raise the concentration in the aqueous humor. In reality the residual H,O, is usually less than 100 ppm.
5 EFFECTS OF pH ON CORNEAL FUNCTION.-‘. et. School of Optometry1 & School L!Ja&W’ of Public Health2, University of California at Berkeley, CA. An eatbnate of overall comeal hydration control can be obtained by measuring the rate of thiclmess recovery following induced cornea1 swelling. This recovery, which can be expressed as the wrcent recovery per hour (PRPH), was fmt reported to be exponential; however, more recdni analysis indicates that the moverv has an initial slow phase lastine about 30-40 min. that cotreswnds to the time wien comeal pH is re&ced secon&uy to the contact lens-ind&d swelling. The initial slower recovery suggests the possibility that suomal acidosis may retard the comeal deswelliog process. In this study we explored the effects of comeal acidosis on hydration control by measuring the PRPH while the cornea was exposed to diierent pH levels. Comeal pH was monitored using a slit lamp fluompbototneter and controlled by using air tight goggles and exposing the eyes to one of 4 levels of CO,. Each subject provided PRPH and pH data for 4 CO* doses: 0.3.5, and 7% CO,. The fluorometric data cortespondiog to these gas mixtures showed that the average stmmal pHflSD resulting from exposure to either the 0, 3, 5, and 7% CO, was 7.65M.11, 7.3Ofo.09, 7.1.5f0.08, and 7.04f0.07 (p
S.6