Ocular surface parameters

To remain safe and efficacious on the eye, contact lenses must maintain clear and wetted surfaces, provide an adequate supply of atmospheric oxygen to and adequate expulsion of carbon dioxide from the cornea, allow adequate flow of the eye s tear fluid, and avoid excessive abrasion of the ocular surface or eyeflds, all under a variety of environmental conditions. The clinical performance of a contact lens is controlled by the nature of the lens material the lens design the method and quaUty of manufacture the lens parameters or specifications prescribed by the practitioner and the cleaning, disinfection, and wearing procedures used by the patient. 

Whereas the dosage form most widely used in topical ocular treatment are the eye drops (conjunctivitis, dry eye syndrome, glaucoma, iritis (anterior uveitis), keratitis) there are other parameters of ocular surface that affect pharmacotherapy, including lower conjunctival sac capacity, blinking, tear secretion and tear drainage. 

Current density was calculated from the current applied and the surface contact area of the iontophoretic probe, if mentioned in this chapter. It is clear from this summary that the two major parameters influencing drug penetration are the current density and iontophoretic duration. Ocular iontophoresis can be delivered by two approaches transcorneal and trans-scleral iontophoresis. 

The dose of chemicals applied to filter paper may be modified to view concentration-dependent parameters of test substances. By establishing the dose response to ocular irritancy, comparisons can be made to the mild, moderate and severe grading systems previously validated (Stokes 2003). An alternative exposure of test chemicals may be performed by direct application of test solution dropwise onto the center surface of the comeal (Xu et al. 2000). The test solution then dissolves into the culture media. 

Various lecithin-based MEs were also characterized by Hasse and Keipert [131]. The formulations were tested in terms of their physicochemical parameters (pH, refractive index, osmolality, viscosity, and surface tension) and physiological compatibility (HET-CAM and Draize test). In addition, in vitro and in vivo evaluations were performed. The tested MEs showed favorable physicochemical parameters and no ocular irritation as well as a prolonged pilocarpine release in vitro and in vivo. 

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