By Dr. Bob Grohe
A 35-year-old male presents with both gas permeable extended wear contact lenses recently either sliding off the cornea or popping out of the eye. This has also been complicated by difficulty removing the lenses when they decenter and become stuck on the conjunctiva.
Due to the unpredictable nature of lens sliding or popping out, he has recently replaced three lenses. He also notices more difficulty reading with the computer or newspaper. He knows it is nothing he is doing wrong, because he cleans his lenses by vigorously rubbing the lens between his fingers until the lens is “squeaky-clean.”
Since his lenses are “obviously defective” and only three months old, he is here today to get his new free pair of lenses. His medical history is not significant for any medical condition, although he does use his computer off and on seven to 10 hours a day between work and home. He is a previous 10-year PMMA and nine-year low Dk RGP wearer.
Clinical evaluation, including a review of comparative available eye examination information from the previous practitioner, revealed:
Current Exam Data (1995) Previous Exam Data (1993)
|Vision with CLs||Over refraction||Old spectacles|
|OD 20/25-2||+0.50 = 20/20-1||OD -4.00 -1.00 x 170|
|OS 20/30-2||+1.00 = 20/20-1||OS -4.25 -0.75 x 180|
|OD 41.62 x 41.87 mires clear||OD 42.50 x 44.12|
|OS 41.75 x 41.87 mires clear||OS 42.50 x 44.25|
|OD -3.25 sphere||= 20/20- J1||OD -4.00 -0.75 x 170 = 20/25+|
|OS -3.50 -0.25 x 175||= 20/20- J1||OS -4.50 -1.00 x 180 = 20/20-|
CLs Verified As Cls Designed and Accepted
|Base Curve||OAD||F||Base Curve||OAD||F|
|OD 8.09 x 8.19mm||9.4mm||-5.75||OD 7.94mm||9.4mm||-4.25|
|OS 8.14 x 8.01mm||9.4mm||-5.50||OS 7.94mm||9.4mm||-4.75|
Slit Lamp Evaluation of CLs:
1. Radical base curve flattening
A pair of lenses was redesigned for the patient with an alignment fitting approach:
Base CurveOADPowerVisual Acuity
This case demonstrates short term and long-term clinical problems to address. For the short term, the plan consisted of refitting the patient with a pair of lenses with a base curve 0.25 D. flatter than the flattest current K reading using the same OAD and appropriate power compensation. It was also important to convince the patient of the immediate need to change his multi-year habits with his previous lenses. Radical base curve flattening is a problem somewhat unique to PMMA and low Dk RGP wearers. To correct the habits it is necessary to emphasize to the patient that his/her new lenses are safer but require a slightly kinder, gentler way of handling. Old habits to discontinue specifically include any “squeaky-clean” ritual of between the fingers rubbing while cleaning.
When cleaning the lenses, it should be done in the evening, every day and by placing several drops of abrasive cleaner in the palm of the hand and rubbing the lens with the fifth finger in a back and forth motion for 3-5 seconds. Circular motion should be avoided as this can mimic the minus-creating polishing effect of a modification repowering. Since abrasive cleaners are very effective, only a mild amount of digital pressure should be used while cleaning. A regression to old handling and cleaning habits is very common. Therefore, practitioners and staff need to verify patient compliance with the new habits indefinitely until three consecutive office visits reveal ongoing compliance.
The long-term problem occurred from sphericalization over a two-year period as a result of the progressive radical flattening of the base curves. Sphericalization and corneal molding have been noted among both daily and extended wear RGP use. The consequences of corneal molding can be either disruptive for near vision or deceptive as manifested by a general instability of visual acuity. To clinically corroborate, corneal topography will graphically reveal a sphericalized cornea with single color homogeneity and very little power variation.
When combined with rough handling and vigorous cleaning techniques, this created an ortho-K like curvature and power change of the cornea and lenses. The increased, overminused lenses caused the patient to begin noticing a decrease in his near point vision. Refitting allowed the patients’ cornea to restabilize over a six month period beginning with a quick return of his near point ability within two weeks but a prolonged, unstable refraction that did not provide a stable 20/20 endpoint until nine months later. Spectacles were then prescribed that could be interchanged with the contact lenses to provide clear vision at far and near.