Soft contact lenses evolution
March 5th, 2009 | by zoe |The generation born just after World War 2 was able to switch from wearing glasses to contact lenses when turning into teenagers. Especially in the USA the contact lenses became very popular after Bausch & Lomb (Optical lenses manufacturer) introduced the spincasted Soflens B-serie . This particular lens was a step forward from the hard contact lens designs by removing the barrier of feeling a definite foreign object introduced onto the eye. Bausch & Lomb initially brought out the Soflens with the idea that one curvature design should fit most wearers. It turned out that this was not the case because problems started to occur after wearing these lenses for a few months or longer. The cornea in many cases started to struggle with oxygen starvation after a period of time. Initially it was unknown why this happened. In theory the contact lens material seems to breathe oxygen to the eye and also there was the “pump effect” underneath the contact lens when the wearer blinked.
What was not taken in account that this might be the case in certain diopter corrections (lens powers) but not all lens powers were behaving the same way? On top of that the cornea topography was not fully understood by the manufacturers. The surface curvature of the corneas was only measured from the apex with a maximum area of approx 3mm across by the existing keratometers. The rest of the 13 mm a-spherical area was ignored. This resulted in many cases where the sclera around the cornea became squeezed by the edge peripheral of the contact lens which resulted in a limited blood supply to the edge of the cornea.
In some cases a ring of indentation was visible after the removal of the contact lenses.
But there were more issues regarding the wearing of soft contact lenses. The breathable contact lenses materials tended to attract a build-up of proteins crystals which were produced by eyelid glands. The result was that after a few months the contact lenses became very scratchy and in the end it would cause irritation, allergies and even damage to the corneal surface. The percentage of protein excretion varied considerable among contact lens wearers.
This meant that some people got away with a minimum of lens cleaning and others could simply not keep the lenses protein free. Up to the 1990’s a contact lens replacement meant considerable cost to the wearers and the result was that contact lenses were worn till they became intolerable before replacing. In many cases the optometrist were consulted after the symptoms became very obvious and the poor optometrist had to refer quite a few cases to the ophthalmologists. Although he patient was usually to blame for not adhering to the optometrists’ wearing regime, the poor optometrist was the one who had to deal with the patient’s frustrations.