Tired Eyes? Understanding Aspheric Optics and Why You'll Love Biofinity Energys10:53 AM
The average American spends more than 10.5 hours a day on digital devices like computers and smart phones, so is it any wonder our eyes are tired at the end of the day? We're actively using them to look at small print from a lit screen for over 60% of our waking hours!
If you are a contact lens wearer, you may have noticed that your eyes feel more tired when you wear contact lenses than when you wear your glasses. This is not in your head - it's a scientific fact. Because contact lenses physically sit on your eye, the amount of work and energy your eye muscles use to focus on near objects (like computers and cell phones) is greater than when you wear glasses that sit a few millimeters off your face. In eyecare lingo we call this accommodative demand: the amount of work muscles have to do to focus up close. But happy contact lens wear is not lost; meet Biofinity Energys.
Demystifying Aspheric Optics
Let's start with some basic optics. Our cornea is curved, so when light enters the eye it immediately gets distorted or bent by the fact it passed through a curved plane. The result is the object you're looking at also looks curved (even if it's not). This is called spherical aberration - the distortion to vision that occurs simply as a result of the fact our eye is a curved sphere and not flat.
|Our cornea is a curved surface, so when light enters, it also gets bent and curved. The result is an imperfect image entering our eye - one that is bent just like our corneal shape. This is spherical aberration. via|
Knowing that we have spherical aberration-caused visual distortions inherent to the eye itself, CooperVision has mapped out the "average" cornea and designed a contact lens to negate the spherical aberrations that are naturally present. The power profile of the contact lens will change gradually from the central cornea to the peripheral cornea to match the bend and curvature change of the average corneal shape. The result is a lens that's designed to correct your vision perfectly at each point of the contact lens -- not just a -4.00 throughout the whole lens like most contact lens designs, but a -4.00 right in the center and then maybe a -3.93 right outside, and a -3.87 out at the periphery for example. The goal is that your eye gets only the correction it needs at each point in space, and not more correction than necessary, which would increase the amount of work your eye has to do when looking at something up close like a cell phone or computer (the accommodative demand).
|A spherical contact lens will match the optics of our spherical cornea, giving everything a curved or bent shape; aspheric contact lenses are designed to prevent this curved distortion and keep the true dimensions and shape of the objects we are looking at. via|
If you are an astute reader, you may have noticed there are some potential shortcomings of this design. It does assume an "average" cornea, so if your cornea is far from average then you may not get any visual benefit, or potentially even feel like vision is worse (though you'd have to be pretty far off from average for this). Some people will notice a vision difference (presumably those that are very average), and some people may notice nothing at all with an aspheric lens design. CooperVision reports from their own study that 8 out of 10 digital device users (using devices at least 4 hours a day, 5 days a week) report Biofinity Energys made their eyes feel less tired.
What About Astigmatism?
Some doctors have tried to use aspheric contact lenses to mask low amounts of astigmatism, There is data to support this! A 2004 study comparing aspheric contact lenses to spherical contact lenses (in this case CooperVision's Frequency 55 lenses) found that aspheric optic designs can mask 66% of the astigmatism in patients with an average astigmatism amount of 0.69D. If your patient has -0.75D of astigmatism or more, they'll likely need a toric lens for statistically significant improved visual correction, but for low astigmatism amounts there is evidence you can mask over half of it with an aspheric design. Spherical lenses only masked 21% of low amounts of astigmatism in the same study.
Who Is This Lens For?
The key to fitting success with Biofinity Energys is to understand what the lens does and what the lens doesn't do. It won't give a reading boost to people needing reading glasses. There is no reading power anywhere in this contact lens. But if you have teens, millennials, or even pre-presbyopes that aren't needing reading glasses yet but are feeling end of day eye strain and fatigue, this lens is a perfect recommendation. Patients usually won't see any differently reading letters on a chart, but how their eyes feel when they adjust to look up close - that's what the difference will be if they are having issues with eye fatigue in their previous contact lens brand.
When I fit Biofinity Energys, this is what I tell my patients:
"Mr. Jones, you told me your eyes were feeling really tired at the end of the day. There's a new contact lens design I want you to try that can relieve some of the strain on your eyes when you're looking at computers or your phone. Most people don't notice that they see any differently, but how your eyes feel at the end of the day -- that's what this lens can improve. I can keep your vision clear and sharp like what you're experiencing in your lenses right now, but just help them work less as you go through your day."
Replacement Schedule: Monthly
Material: Comfilcon A (silicone hydrogel, same material as Biofinity)
Base Curve: 8.6
Power Ranges: +8.00 to -12.00D (0.50D steps after +/- 6.00D)
I'd love to hear your feedback on the lens! Please comment below if you've tried it out or what your patients are saying!