prescribing
for presbyopia
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 |
|
|
Aspheric
Multifocal |
Translating
Bifocal |
|
Computer User |
X |
|
|
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.
Contact Lens Spectrum, Issue: May 2006