Toric, and importantly, quadrant specific corneal lens designs, and also scleral lens designs are available on some instruments.
Figure 3 shows a patient with 2.50DC against-the-rule astigmatism fitted with an RGP corneal lens with a complex toric periphery in a logical and sequential series of six 'virtual' steps.
Each small eye, known as an ommatidium, consists of a corneal lens
, a crystalline cone, and a light sensitive organ at the base.
The absence of a corneal lens
on each stemma was readily apparent when non-sclerotized internal material was removed with 15% KOH.
In case anyone gets the wrong idea a cyborg is a combination of machine and living organism, which means anyone with a pacemaker, artifical joint, limb, drug implant system, implanted corneal lens
or artificial skin is technically a cyborg.
Ordinarily, light passes through the corneal lens
and focuses images on the rear portion of the eye, known as the retina.
Firstly, fitting an irregular cornea with a corneal lens can be challenging and, despite the best efforts of the eye care practitioner, frustratingly the patient can sometimes still be disappointed with comfort, vision, or possibly even both.
As the objective with scleral contact lenses is to vault over the cornea, rather than align closely with it, as is characteristic of a corneal lens, these lenses are usually fitted by sag rather than the more familiar base curve.
An apparent shift in the position of the fourth corneal lens
to a more ventral position also supports this hypothesis.
It is essential to do this before fitting a rigid corneal lens
, but is it really necessary when fitting soft contact lenses?
Some corneas are so irregular or asymmetric that a corneal lens simply will not stay in the eye.
For patients who require the vision of an RGP lens but who cannot tolerate a corneal lens, there is now a simple solution, which was not open to us two or three years ago.