Avoid Choking the Cornea

Contact lenses have been worn for many decades and have improved substantially over the years. Along with this change in lens technology has been a dramatic improvement testing and diagnostic capabilities. While many contact lens wearers do so with out incident, there are many perils that may inflict damage to the eyes that can result in devastating complications.

Proper contact lens fitting and follow ups should include not only the basic refraction, cornea readings and corneal health evaluation, but also corneal topography and endothelial cell count measurements. The topography examines the outer most layer of the cornea for irregularities, curves and pathology. The Endothelial cell count measures the actual cells in the inner most layer of the cornea. This layer is one cell layer thick and when damaged does NOT regenerate. Thus, proper care must be taken when considering both contact lens wear and any ocular surgery. The ECC evaluates the number of cells per unit area and the quality of the cells. In an otherwise healthy normal individual one would expect to see about 2400 cells per unit area and the actual cells should be uniform, regimented, equal in size and shape and similar in color. Any alteration in their appearance could indicate a negative change resulting in death to the cells and a gap in this cell layer. The endothelium has the responsibility of pumping water out of the cornea. Any damage to it will result in increased corneal swelling, thickness, glare and a decrease in correctable vision.

An ECC should be performed on all contact lens patients to make sure that this very important tissue component is functioning properly. Certain changes in the endothelium should result in major changes in contact lens wearing.

Polymegathism is a change in the cell size and appearance within the endothelial layer. Studies have suggested that Polymegathism demonstrates a compromise in the endothelial cell's ability to pump water out of the cornea. This can, and often does result in corneal opacification (cloudy cornea). The etiology of the change is the increase of lactate in the cells, changes in PH, and an elevation in CO2. As a result, there is a decrease in cellular ATP and an increase in endothelial hypoxia.

The reason for these changes is often contact lens over wear, poor fitting contact lenses, and poor contact lens compliance. The resultant changes occur because the endothelium is over worked and breaks down under the stress. These cells appear as huge irregular cells and may number as few as several hundred per unit area in severe cases.

In patients with moderate to severe Polymegathism contact lens wear must either be completely terminated or substantially reduced to less then 10 hours per day. In addition, the only lens that would permit enough oxygen through to the cornea would be a high DK (allowing a good deal of oxygen) rigid gas permeable contact.

With regard to refractive surgery, this condition is a contra-indication. During the normal course of any corneal procedure there is a possibility of endothelial cell loss. Therefore, any corneal surgery that is not required must be avoided. In addition, future cataract surgery may pose a problem since there is always loss of endothelial cells during that procedure.

In summary, before wearing contact lenses a complete exam should be performed including an ECC to make sure that the entire cornea is healthy and that it is not being put at risk by wearing the lens. Of course the same rules apply prior to LASIK.