Caption: Figure 3 Unwanted corneal changes in soft lens wear, resulting in subtle corneal warpage
, imaged using a difference map with the Medmont E300 Corneal Topographer (Precision Technology Services Ltd.
Topographic changes in contact lens-induced corneal warpage
While mean power and posterior elevation maps were generated on Orbscan, TMS-1 was used to detect the corneal warpage taking advantage of its relative scale in the axial map.
Patients were excluded if corneal warpage, central corneal scarring, hydrops, and severe thinning of the cornea (300 microns or less) were present.
Contact lens wear can induce corneal warpage
and, therefore, a period of one week out of soft contact lenses and one month out of RGP contact lenses prior to refractive surgery evaluation is recommended.
However, upon removal of the lens, significant binding, corneal warpage
and persistent epithelial defects were evident (see Figure 4) which would all contribute to the reduced VA.
b) Corneal warpage
as a result of a poorly fitting RGP lens
Prior to pre-operative assessment, soft contact lens wearers need to leave their lenses out for one to two weeks and rigid lens wearers must leave lenses out for at least four weeks due to the possibility of corneal warpage
PMMA has almost no oxygen transmission and is quite inflexible and so long term wear usually causes corneal warpage
(Figure 4) and problems related to hypoxia and, therefore, these patients should be refitted with RGPs.
a) There is mild keratoconus present b) The subject is not fixating steadily c) There is corneal warpage
present d) There is regular astigmatism of over 1.