Hydrogel Lens-related Corneal Distortion
The material characteristics of hydrogel contact lenses are generally more forgiving than those of GP lenses. Yet the wearing of virtually any type of contact lens including a soft lens can result in undesired effects on the cornea.
Corneal surface distortion associated with hydrogel lens wear isn't common in clinical practice, and consequently you may miss it if you don't include it as a possibility while working through a clinical differential diagnosis. The following represents just such a case of hydrogel lens-related corneal distortion.
A 24-year-old male who wore Acuvue 2 (Vistakon) lenses on a daily wear basis for his -6.25DS of myopia presented with a complaint of double vision in his right eye only. The patient reported that the diplopia was mild, the onset occurred sometime during the previous three weeks, it wasn't getting worse and it wasn't associated with any event or activity. The visual disturbance was present with or without his contact lenses. He had no general health problems and was not taking any medications.
His vision was slightly reduced in the affected eye, with best correction and preliminary tests indicating full versions and vergences, no tropia and no significant phorias. I performed topography OU (Figure 1a) and noted some distortion of each eye at this initial visit.
Figure 1a and 1b. Axial maps OU at the initial presentation (top) and after one month daily wear of higher-Dk, silicone hydrogel lenses.
Schornack (2003) recommended using lenses with higher oxygen transmissibility to alleviate the relative hypoxia that may be associated with hydrogel contact lens-induced corneal warpage. With this in mind, I dispensed Acuvue Advance (Vistakon) lenses (Dk = 60) of identical design to the patient's Acuvue 2 (Dk = 28) lenses.
The patient returned one month later reporting that his double vision was gone and that he had no continuing problems. His corrected visual acuity was now 20/20 in his right eye and topography indicated a more regular corneal surface (Figure 1b).
Corneal distortion of some degree is expected in lens wearers, and its effects on corneal surface regularity are typically sub clinical and insignificant. Even so, it's one reason why a lens wearer must cease lens wear for a period of time before undergoing evaluation as a refractive surgery candidate.
This case reminds us that corneal distortion associated with hydrogel lens wear can progress to a level at which it affects vision. Fortunately, the effects seem reversible over time by increasing oxygen delivery to the cornea. But do remember the value of assessing the regularity of the corneal surface when contact lens wearers present with visual disturbances that are unusual or unexplained by more routine causes.
Dr. Snyder is an adjunct professor of optometry at the University of Alabama at Birmingham. Since submitting this article he has joined Bausch & Lomb as Director of Professional Relations.
For references, please visit www.clspectrum.com/references.asp and click on document #136.