Poor Acquired Vision: Manuel Conde, OD
JB was a 25-year-old male who had been wearing low-Dk gas permeable (GP) corneal contact lenses for the past eight years. He presented to the office complaining of decreased vision for several weeks with his current GP lenses. His lenses were approximately 1 ½ years old.
Test Procedures, Fitting/Refitting, Design and Ordering
Visual Acuities (with Contact Lenses):
|Over-refraction: -0.50 DS 20/25
|Over-refraction: -0.25 DS 20/25
Slit Lamp Examination:
Both lenses exhibited mucoprotein deposits on the anterior lens surface. In addition, both lenses had scratches on the anterior lens surface. Also, both lenses decentered superiorly on the eye.
With verification of the lenses there was no evidence of base curve toricity or power change.
Patient Consultation and Education
Patient was re-instructed about lens care and possibility of re-fitting with new higher Dk GP lens material. Several procedures were used to solve JB’s complaints. First the lens was cleaned with a laboratory cleaner.
Second, in-office polishing of the anterior lens surface was used to reduce mild lens scratches. Third, a re-fitting with a higher Dk GP lens material was performed. It is also important in these cases for patients to be educated to clean the lenses in an up and down/back and forth manner in the palm of the hand immediately upon removal in the evening.
Follow-Up Care/Final Outcome
With the combination of patient education and in-office polishing, the surface problems noticeably improved. Visual acuity was improved to 20/20 OD and OS. He was able to wear these lenses comfortably until his new lenses arrived. With long-term wear of the F-S/A lenses, this problem did not recur.
Discussion, Alternative Management Options
Reduced visual acuity with GP wear is commonly caused by muco-protein film or haze on the anterior lens surface. Temporary relief can often be provided via the use of in-office laboratory cleaning. In-office GP lens polishing is often not necessary although it may be beneficial when a laboratory cleaning is unable to remove the entire muco-protein film. You can also recommend that the patient regularly uses cleaners such as Menicon’s Progent to remove lens deposits and increase lens wettability. Another option is to order new GP lenses with plasma treating or coatings such as Tangible’s Hydra-PEG.
Another common cause of acquired reduction in vision in corneal GP wearing patients is lens warpage. It can be problematic with patients accustomed to cleaning their lenses digitally (i.e., between the fingers) as opposed to in the palm of the hand. More flexible GP lenses such as high Dk GP lens materials exhibit more potential for both on-eye flexure and lens warpage than low Dk lens materials.
GP lens warpage and GP lens flexure result in the same changes to lens fit and over-refraction (OR). Warpage is generally due to heat generated by aggressive rubbing while cleaning a lens or storing the lens in a hot environment such as a car in Summer. Flexure is an on-eye situation caused by a thin profile high Dk lens, on a toric cornea, and with tight eyelids. In both cases, the OR cylinder changes by the amount of the warp/flexure. If the cornea is with-the-rule (W-T-R) and the OR is with-the-rule, the amount of W-T-R cylinder in the OR increases by the amount of warp/flexure. If the cornea is W-T-R and the OR is against-the-rule, the amount of cylinder in the OR decrease by the amount of the warp/flexure.
1) Edrington TE and Barr JT. Bend me, shape me: lens flexure. Contact Lens Spectrum 2002;17(2):48
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