Bifocal RGP Contact Lenses for Progressive Myopia
Clinically, we have known for years that rigid contact lenses retardrefractive changes, especially throughout the teen-age years. During thesecond semester of school, especially in northern regions, myopic changesare more prevalent due to increased educational demands and inclementweather that keeps people indoors doing near activities. A convergenceexcess posture of the eyes often results, but RGP bifocal contact lensescan supplement reading comfort and help slow the myopic shift.
THE VALUE IN BINOCULAR EVALUATION
Most of us learned that the clinical evaluation should consist of threeparts: evaluation of ocular and systemic health, refraction and correctionof the optical system, and assessment of the binocular components. But inthis day of managed care within a litigious society, it seems we focus onthe first two components and neglect the third.
Phorias and ductions give a simple yet thorough evaluation of the patient'sbinocularity and can be performed in just a few minutes. I'm finding moreand more convergence excess in the pediatric population, so these testsare important for a lifetime visual treatment program.
Most lateral alignment of the eye posturing should be between 4 and 6exophoria. When there's more esophoric posture for near, plus lenses andespecially bifocals will reduce the accommodative stress. The therapeuticvalue of bifocal RGP contact lenses makes them more beneficial than spectacles.
CORRECTING TWO PROBLEMS WITH ONE DESIGN
The following patient demonstrates the advantages of using RGP multifocalsto aid binocular vision, improve comfort and help retard myopic progression.
A On January 12, 1989, J.G., a 13-year-old girl, demonstrated:
- OD -2.00D +0.25 x 165; 20/20
- OS -2.00 +0.50 x 170; 20/20
- Distance phoria: orthophoric
- Near phoria: 5 esophoric
- K's: OD 44.75/44.50 @104;
We prescribed single vision RGP lenses.
A On February 13, 1990, she demonstrated:
- OD -2.25 +0.25 x 170; 20/20
- OS -2.25 +0.50 x 175; 20/20
- Distance phoria: 1 exophoria
- Near phoria: 16 esophoria
- K's: OD 44.62/44.37 @ 91;
OS 45.00/44.50 @ 53
On March 12, 1991, J.G. was still wearing rigid contact lenses, but losingmotivation. We prescribed Softperm lenses (combination RGP/soft lens), alsoa single-vision modality. During this time, we were concerned about theconvergence excess.
A On April 15, 1991, J.G. returned with significant changes in the subjectiveexam:
- OD -3.50 +0.50 x 105; 20/20
- OS -3.75 + 0.25 x 105; 20/20
- Near lateral phoria: 15 esophoria
J.G. wanted to continue with single-vision contact lenses.
A On September 10, 1992, subjective examination was:
- OD -4.50 +0.50 x 75; 20/20
- OS -4.00 +0.75 x 105; 20/25+
- Near esophoria: 22 diopters
Due to the increased myopia and the increased convergence excess, weprescribed an aspheric multifocal RGP design (Conforma's VFL-3). J.G. wasvery comfortable with the lenses, wearing them 15-16 hours per day.
A On May 24, 1995, there were no overrefractive changes; her visual acuitywith contact lenses was 20/20 in each eye.
- Near phoria: 8 esophoria
- K's: OD 43.50/44.37@91;
A On December 19, 1996, the subjective examination was:
- OD -4.00 +0.25 x 115; 20/20
- OS -4.75 +0.50 x 70; 20/20
- Near phoria: 14 esophoria
- K's: OD 43.37/44.12@112;
In four years of RGP multifocal contact lens wear, there was minimalchange in J.G.'s myopic progression and an improvement in esophoric posturefor near through the distance lens. With the +2.00D add effective power,she is orthophoric for near.
Now a senior in college, J.G. represents a population of young peoplewith progressive myopic changes as well as visual accommodative problemsthroughout their adolescent and young adult years. I feel that RGP bifocalcontact lens wear in these patients helps reduce both myopic shift and functionalvision symptoms such as headaches. CLS
Dr. Hansen, a cornea and contact lens diplomate and fellow of theAmerican Academy of Optometry, is in private practice in Des Moines, Iowa.