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When it comes to fitting patients with progressive addition lenses (PALs), selecting patients who are good candidates in the first place may be the most important part of the process. Jenean Carlton, BA, ABOC, NCLC, offers some pointers for PAL success.
When it comes to fitting patients with progressive addition lenses (PALs), selecting patients who are good candidates in the first place may be the most important part of the process, according to Jenean Carlton, BA, ABOC, NCLC, an industry consultant and director of communications, U.S.A., for Optometry Giving Sight.
Good candidates for progressive designs are emerging presbyopes with a low add power, Carlton said. The low add means the lens will have a minimal amount of unwanted cylinder in the periphery.
“This is the best-case scenario for a patient to be introduced to a progressive because they are not going to experience a lot of distortion in the peripheral areas of the lenses,” Carlton said. “If we wait until that patient is a moderate-to-more-advanced presbyope, then the add powers can be higher, which creates a greater degree of unwanted or unprescribed cylinder in the peripheral areas of the lens.”
Unwanted peripheral cylinder aberration is inherent in any progressive design, Carlton noted.
Patients who have worn progressive lenses are good candidates as well, because they know what to expect, but even they may have problems adjusting if their prescription is changing dramatically, Carton said. “Some patients are so used to their previous lenses and the degree of unwanted cylinder in the periphery, based on the add power that they wore originally, that they may have trouble adjusting as they become more advanced presbyopes and the add power is bumped up,” she added.
Other good candidates are patients who are motivated to wear a progressive; patients who want to wear a line-less lens are motivated, according to Carlton. She pointed out that patients who need a specific-use progressive, such a patients who use computers, are also likely to succeed with a PAL.
Presbyopes who have more than 2 D of cylinder require careful consideration as PAL candidates, again because of the negative effect that higher cylinder powers have on peripheral distortion, according to Carlton.
“Unfortunately, at 2 D cylinder power or higher, the unwanted cylinder component in the periphery can go over the 180 line and cause the patient’s distance field to narrow and can result in significant aberration for the individual,” she said. “This is where it gets really problematic. If the unwanted cylinder creeps over the 180 line, this unprescribed cylinder gives the patients a ‘swim effect’ when they are walking around. Now, patients not only have a more problematic distance zone due to the higher cylinder component in the prescription, but coupled with a high add power and patients will also experience more narrow intermediate and near zones as well.”
Patients switching from a “flat-top” segment to a progressive design can also be tough to make happy because of the reduction in the size of the near vision zone.
“Take a patient in a hard design flat top 28 (FT28),” Carlton explained. “That’s a very usable design because it gives patients 28 mm of usable near vision width, and there’s no progressive that can compete with that. So, patients going from a very wide near segment to a progressive design can have a difficult time adjusting to the narrower near field of a PAL.
“This is why it is important for early presbyopes to be fitted with progressive lenses,” she emphasized. “It’s easier to adjust to a progressive when the add power is low and also when the patient isn’t already accustomed to a larger near segment.”
In this situation, Carton said patients’ degree of success with PALs might depend on their occupations. “In a worst-case scenario, someone, such as an engineer or architect, would experience better vision for their particular occupation by being fitted with a FT28 or wider segment, or at least a ‘hard’ design PAL. These patients are not likely to benefit from other PAL designs because of the narrower near zone associated with these lenses.”
Although some in the industry think that such designs are “old technology,” Carlton said they are still useful, and this is one instance that it would be appropriate to put a patient in a harder progressive design.
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