GP Lens Case Grand Rounds Troubleshooting Guide – 08

Poor Initial Vision: Ed Bennett, OD, MSEd

Background

KE was a long-term (10 year) GP wearer who was in the office to be dispensed a new pair of fluoro-silicone/acrylate lenses.

Test Procedures, Fitting/Refitting, Design and Ordering (If Applicable)

After dispensing of the lenses, the patient commented that her vision was “not as sharp as her old lenses.”

Visual Acuities (with Contact Lens Wear):

OD: 20/25+ (fluctuates) Over-refraction: -0.25DS 20/25+
OS: 20/25 (fluctuates) Over-refraction: Pl -0.25 x 170 20/25

Slit Lamp Examination:

OU: Good centration and an alignment lens-to-cornea fitting relationship with fluorescein
Front surface exhibits poor wettability (break-up of tears on the front surface of the lens

Patient Consultation and Education

The key factor with this patient is to remediate the problem as soon as possible to minimize patient dissatisfaction.

Follow-Up Care/Finale Outcome

With KE, simply using a laboratory cleaner (available from your CLMA member laboratories) was sufficient to solve the problem. In addition, after cleaning the lens, the wetting solution was rubbed onto the lens surface to assist in optimizing the on-eye surface wettability. The aided visual acuity improved to 20/20+ OD, OS, OU and the patient left the office satisfied with her new lenses.

Discussion, Alternative Management Options

Poor initial wettability is most often caused via the polishing process used by laboratories – specifically, pitch polish – which, when left on the lens surface, can result in extremely poor wettability. Fortunately, this problem has been reduced recently as many manufacturers have changed to water soluble compounds during the deblocking and lens cleaning manufacturing steps which has eliminated the need for harsh solvents.

This form of nonwetting can also result from the use of lanolin-based hand creams and soft soaps. Therefore, patients need to be advised not to handle their GP lenses immediately after use of such a cream or soft or ensure that it has been removed from the
hands prior to handling.

Another cause of poor initial vision would be lens flexure. Flexure can result when a GP lens changes shape with the blink and fails to correct all of the anterior corneal astigmatism. This is most likely to occur with an ultrathin GP lens fit steeper than “K” on a moderate (≥ 1.50D) corneal astigmatic patient. In addition, the use of a larger than average optical zone diameter (i.e., > 8.0mm) will create a steeper (increased sagittal depth) profile and increase the likelihood for bending of the lens with the blink.

Diagnosis of flexure results from keratometry performed over the lenses. If these values are not spherical, the lens is flexing. In addition, the base curve radius will be spherical when verified with the radiuscope. It is managed via refitting the patient with a GP lens with a standard thickness and a flatter base curve radius.

Of course another cause of poor initial vision was the use of a lens with an incorrect power. This is easily diagnosed via over-refraction and then selecting a lens with the corrected power. Of course, if significant refractive cylinder (often ≥ 0.75D) is present via over-refraction, the selection of a front surface toric or soft toric lens would be indicated.

Supplemental Readings

  1. Bennett ES. Problem Solving. In Bennett ES, Hom MM. Manual of Gas Permeable Contact Lenses (2nd ed.). Elsevier Science, St. Louis, MO, 2004:190-211.
  2. Bennett ES, Wagner H. Rigid lens care and patient education. In Bennett ES, Weissman BA. Clinical Contact Lens Practice (2nd ed.) Lippincott Williams & Wilkins, Philadelphia, PA, 2005: 277-294.
  3. Herman JP. Flexure of rigid contact lenses on toric corneas as a function of base curve fitting relationship. J Am Optom Assoc 1983;54(3):209-213.
  4. Hom MM. Rigid gas-permeable lens care and patient education. In Hom MM: Manual of Contact Lens Prescribing and Fitting with CD-ROM (2nd. Ed.) Butterworth-Heinemann, Woburn, MA, 2000:167-176.

Back to Table of Contents