When viewing demands, be it from books or more recently from digital display devices, on the visual system exceed the capacity of our accommodative and vergence systems to maintain clear and comfortable vision, eye strain occurs. The muscles of our eyes, the ciliary and extra-ocular muscles, must work constantly to maintain the proper focus and alignment. With constant near visual tasks, this demand, like repetitive strain injury, causes dysfunctions. The resulting visual strain can lead to tension in the facial muscles and cause headaches.
Our amplitude of accommodation and accommodative facility (ability of our eyes to change accommodation quickly in response to changes in our viewing distance) reduces after prolonged near viewing. As well, sustaining clear vision at near increases the tonic level of our accommodation, causing a period of blurred distance vision after near work.
How can we as optometrists help an increasing subset of our patients who are suffering from this digital eye strain? The answer lies in lenses designed for a digital work. They are offered by all the labs we deal with such as HOYA (1), Zeiss (2) , Nikon and Essilor. Digital lenses use a low addition power (over the distance correction) to treat a complex of vision problems associated with symptomatic pre-presbyopes (those who don’t need bifocal or progressive glasses yet) with lots of near vision tasks. Since they are young (in their 20’s and 30’s), these patients are used to getting unrestricted clear (disturbance free) distance vision with their habitual glasses. With these digital lenses, the progression of power and the accompanying peripheral blur is lowered so as not to interfere with the distance vision. But the near zone still needs to be reached with minimal head and eye movement because these patients can still read fairly clearly without any additional power. The corridor is shortened and the optics and position of the near zone calculated to optimize the viewing of mobile devices at about 30 cm relatively easily. Essentially, these lenses give just enough additional power to offset the load on the accommodation, while maintaining good distance vision. And the additional power is easily reached without having to adopt awkward position that can cause musculoskeletal strain.
Come visit us at Dr. Mei-Ling Chan in Optometry (3) in Barrie and ask us about these digital lenses.
