Patient Selection Tips for Presbyopic GP Lenses
BY CRAIG W. NORMAN, FCLSA
In my September 2004 column "Play Matchmaker for Your Patients and their CLs," I discussed how to decide between a soft or GP presbyopic lens system. Within each of these categories we have have additional decisions to make even before we choose a particular brand or manufacturer regarding which style of lens best meets each patient's needs.
Ocular Metrics and Choice of GP Presbyopic Lens Style
|Add 1.75D or less||X||?|
|Add between 1.75D and 2.25D||?||X|
|Add 2.25D or greater||X|
|Distance power up to +/- 0.75D||?||?|
|Distance power up to =/-6.00D||X||X|
|Distance power >=/-6.00D||?||X|
|Refractive and corneal toricity similar||X||X|
|Refractive and corneal toricity different||?||?|
|Lower lid at the limbus||X||X|
|Lower lid>1mm below/above the limbus||X||?|
|Pupil size 3mm to 5mm||X||X|
|Pupil size >5mm||X|
GP Design Options
For example, there are two primary lens style categories for GP presbyopic lenses aspheric multifocals and translating bifocals. Other GP designs exist, but they too will fit into one of these two categories.
You'll notice I didn't use the term simultaneous vision. Because all GP presbyopic designs move during the blink cycle, vision typically occurs out of specific parts of these lenses rather than simultaneously as with soft multifocal lenses.
So how do you decide which GP design to use? We can almost always correct two of the three primary viewing distances (distance, intermediate and reading) with presbyopic contact lenses, so begin by asking patients which of these are most important to them. For example, patients who have strong intermediate needs usually do best in aspherics while those who have critical driving and reading desires will fare better with one of the bifocal designs available.
This "two out of three" philosophy is helpful, but you also need to take additional factors into account. Table 1 demonstrates some of the metrics that will aid the lens selection process.
General Selection Guidelines
Aspheric designs can usually easily correct lower add powers, but consider bifocals for higher adds.
Most distance powers do well with either style, but patients who have little distance correction may not like their distance vision with either if any blurring occurs during driving or other tasks.
Both aspherics and bifocals perform well when the refractive and corneal astigmatism are similar. If the astigmatism is dissimilar, try either style in a toric design.
Two key measurements to always consider are lid position and pupil size. When the lower lid comes to rest at the inferior limbus, either style can work quite well. It's problematic for translating bifocals though, if the lower lid is either above or below the limbus. If too low the lens has no support; too high and the seg will interfere with distance vision and may necessitate truncation.
Craig Norman is director of the Contact Lens Section at the South Bend Clinic in South Bend, Indiana. He is a fellow of the Contact Lens Society of America and is an advisor to the GP Lens Institute. He is also a consultant to B&L.