Poor Initial Vision: Edward S. Bennett, OD, MSEd, FAAO, FSLS
KE was a long-term (10 year) corneal GP wearer who was in the office to be dispensed a new pair of Dk 100 GP contact 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:
|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. Eye care practitioners can also order GP lenses with plasma treating or coatings such as Tangible’s Hydra-PEG. You can also be recommend that the patient regularly uses cleaners such as Menicon’s Progent.
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 soap to 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 corneal 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 or topography 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 by refitting the patient with a corneal 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.
- 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.
- 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.
- 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.
- 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.
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