While oxygen flux does a better job of illustrating the amount of oxygen entering the anterior cornea, it still falls short as a measure of corneal metabolism because oxygen can also enter through the posterior cornea as well.1 It is important to be able to model corneal metabolism to understand the amount of energy that the cornea is generating to carry out its normal functions. The amount of oxygen available for these processes is the rate limiting step1 and so by understanding the oxygen consumption needs of the cornea we can in turn understand if a contact lens placed on it’s surface is compromising that process or not.
The work of Noel Brennan shown here depicts the results of this corneal modelling as a colour map. Where no lens is worn and hence no compromise to corneal oxygenation is present, the colour map is a uniform blue across the entire cornea. His results show, irrespective of Dk/t, prescription or design, all of the silicone hydrogel tested in the study provide adequate oxygen to the eye to enable it to continue to metabolise without compromise.
The learning from this work, and the point to remember when selecting a lens, is that all currently available silicone hydrogel contact lenses provide adequate oxygen to the eye for daily wear irrespective of their Dk/t.
Read on to find out more about the material properties of silicone hydrogels and how through better understanding of their contribution to contact lens comfort the most appropriate contact lenses can be selected for patients.
Oxygen consumption plots for various toric soft CLs. Courtesy Prof. Noel Brennan.
1. Brennan, N and Morgan, P. Part I: Clinical Highs & Lows of Dk/t. Has oxygen run out of puff? Optician, 2009, Vol 238, No 6209, 16–20.