Real-world tasks like reading a menu may be the best way to evaluate monovision and multifocal contacts.
Though visual acuity testing with an eye chart is the hallmark of vision testing during routine eye exams, it may not be the best way to evaluate the performance of bifocal contact lenses, according to an international expert.
Instead, Eric Papas, PhD, says many researchers have turned to occupation-based tasks and other “real-world” activities to evaluate the performance of monovision and multifocal contacts for the correction of presbyopia.
Dr. Papas is executive director of research & development and director of post graduate studies at the Brien Holden Vision Institute, affiliated with the School of Optometry and Vision Science at the University of New South Wales in Sydney, Australia.
One basic measure of visual performance is simply the ease with which a person moves around a room, according to Dr. Papas. Recent studies using this criterion have shown that subjects wearing monovision contact lenses show subtle changes in gait when walking indoors compared to when wearing contacts with full distance correction, suggesting some degree of visual compromise associated with monovision for this task.
But assessing visual performance for other real-world tasks can be tricky, he says. Judging a person’s ability to drive safely when wearing presbyopia-correcting contact lenses is especially difficult because it is virtually impossible to duplicate constantly changing environmental and traffic conditions in a testing lab or exam room, even with sophisticated driving simulators.
To overcome these limitations, some researchers have conducted studies of contact lens wearers driving real cars on closed driving circuits. In one such study, subjects who wore monovision or multifocal contact lenses had to get significantly closer to signboards posted along the roadway to read them, compared with drivers who wore eyeglasses: Those wearing monovision lenses had to get 10 meters closer; those wearing multifocal lenses had to get 20 meters closer, Dr. Papas said.
Other researchers have conducted real-world vision tests that include activities such as driving to a local coffee shop at dusk, reading a menu or newspaper, and using a computer while wearing different types of eyewear. In at least once such study, subjects reported being more satisfied with their vision with multifocal contacts than with monovision, according to Dr. Papas.
Because outcomes of many of these real-world studies tend to show performance of monovision and multifocal contact lenses is poorly predicted by conventional visual acuity testing with an eye chart, Dr. Papas recommends that eye doctors assess the performance of these lenses in environments consistent with the wearers’ normal daily lives rather than relying solely on vision testing performed in an exam room.
Resource: Presbyopic lens performance and the “real world.” Contact Lens Spectrum. November 2010.