FOR DOCTORS

The Foundation’s Boston Ocular Surface Prosthesis offers a unique solution for patients who suffer from many corneal diseases that have been inadequately addressed by all other available low-risk options. Unlike conventional intralimbal contact lenses, this device, about the size of a nickel (17 23mm), rests entirely on the sclera and immerses the cornea in a pool of bubble-free oxygenated artificial tears that masks irregular astigmatism and, by protecting it from the desiccating effects of air exposure and the friction of blinking, nurtures corneal surface healing in ocular surface diseases including severe dry eye, neurotrophic cornea, stem cell-deficient cornea and exposure.

The Boston Ocular Surface Prosthesis design
This device is the first fluid-ventilated gas-permeable Ocular Surface Prosthesis that maintains an oxygenated aqueous corneal environment free of air bubbles. Lens suction is avoided by incorporating a series of radial channels in the posterior haptic surface that facilitates the aspiration of tears (while excluding air). The lenses are fabricated from oversized discs of Equalens II (Bausch & Lomb) and were approved by the FDA for managing corneal disorders in 1994.

The bearing surface of the peripheral zone (haptic) is defined by spline functions that offer unequalled flexibility for creating seamless, non-conic shapes needed to achieve a more precise relationship with the underlying sclera to avoid occluding the channels or allow the intrusion of air bubbles. Another unique feature of this device is the transitional zone, itself a flexible and elastic spline, that can be elongated or compressed to raise or lower the optic in micron increments while maintaining a smooth transition between the optic and haptic. This vault-control mechanism extends its range to accommodate the most ectatic corneas, including advanced keratoglobus. Moreover, by functioning independently of the base curve radius, it enables the fitter to choose that parameter to provide a more uniform fluid layer and minimize spherical aberrations.

Designing the Boston Ocular Surface Prosthesis is a trial-and-error process of evaluating the fitting characteristics of a series of diagnostic lenses. A model of the chosen trial lens is displayed on a desktop computer and its shape is manipulated by a proprietary spline-based computer-aided design/manufacturing program (U.S. patent #5,452,031) developed by the Foundation over the past 15 years. A lens file is created which is transmitted to the operating system of the high precision Nanoform Lathe capable of generating non-symmetrical rotating surfaces. The fitting characteristics of the lens are evaluated and the procedure is repeated if necessary until the optimal design is created. This on-site technology has been an essential resource for advancing the development of the Foundation's lenses and enabling us to reach a success rate exceeding 90%.

The oxygen tension of the corneal liquid bandage is maintained by the oxygen permeable polymer (Equalens™ II) from which the devices are fabricated. Specially manufactured discs of this material are made for the foundation as a gift of Bausch & Lomb.

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