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N.A. Afshari, C. Johnson; Corneal–Scleral Contribution to Intraocular Pressure Dampening: Pressure/Volume Dynamics of the Corneal–Scleral Shell in an Artificial Anterior Chamber Model . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2722.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine if the mechanical compliance of the cornea and sclera contribute to dampening acute pressure surges caused by intraocular changes in volume. Methods: Ten fresh human globes were acquired from the North Carolina Eye Bank. A full–thickness circumferential excision of the posterior sclera was made just anterior to the vortex veins using scissors. The vitreous, retina, uvea and lens were removed. The remaining corneal–scleral shell was mounted on a two–port rigid artificial anterior chamber and secured in place. One port was attached via rigid tubing to a micro–infusion pump. The other port was attached via rigid tubing to a pressure transducer. All air was flushed from the system and the transducer was zeroed with the system open to atmospheric pressure with the eye soft. An infusion of balanced salt solution was then initiated at a rate of 10mL/hr (2.78mL/sec). As soon as the shell became inflated and the chamber pressure began to rise, the pressure was recorded every 5 seconds. The infusion pump was turned off once the recorded pressure had surpassed 100mmHg. A watertight seal was achievable in 8 out of 10 shells. As a control, the experiment was also conducted with the chamber removed from the system and the transducer connected, via the same rigid tubing, directly to the transducer. Results: In each of the control experiments, the pressure rose above 100mmHg with less than 25mL infused. The pressure–versus–volume curve approached a straight vertical line, indicating there was little compliance within the tubing, infusion pump and transducer. Conversely, the pressure–versus–volume curve of the corneal–scleral shells all had a vertical asymptotic shape, demonstrating compliance. The average infusion volume to reach a pressure of 20mmHg was 80mL (range 42 – 125mL, standard deviation 23mL); to reach 40mmHg was 116mL (range 69 – 166mL, standard deviation 29mL); to reach 60mmHg was 140mL (range 83 – 208mL, standard deviation 38mL); to reach 80mmHg was 160mL (range 111 – 236mL, standard deviation 40mL); to reach 100mmHg was 182mL (range 125 – 264mL, standard deviation 46mL). The approximate volume of the anterior chamber is 2.5mL. Therefore the range of added volume that translated to a pressure of less than 100mmHg ranged from 5% to 10% of the original volume in the eight shells tested. Conclusions: The corneal–scleral shell of human eyes is compliant rather than rigid. This compliance allows the corneal–scleral shell to dampen the pressure that is translated from changes in volume, and may play a role in protecting the optic nerve.
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