If you’re considering contact lenses, you know there are a lot of lenses from which to choose, such as daily, weekly, monthly, tinted and multifocal. One thing you may not be thinking about is the shape of the lenses.
Spheric vs. Aspheric Contact Lenses
The shape of the contact lens and how it’s curved determine if your contact lenses fit well. This shape and curvature also ensure the lenses refract (bend) light entering your eye properly to correct your vision. The curve of the lens can be either spheric or aspheric.
Spheric contact lenses are shaped like part of a sphere. This shape resembles the surface of a baseball or a beach ball. Spheric contacts have the same curvature throughout the refracting portion of the lens. You could wear these lenses to correct refractive errors such as myopia (nearsightedness) or hyperopia (farsightedness).
Aspheric contact lenses have a more complex shape. The curve gradually changes from the center of the lens to the edge. The edge is flatter than in spheric lenses.
What Are Spheric Contact Lenses?
Spheric contacts are often referred to as a standard or conventional lens. These lenses have been around for many years and are more common than aspheric contacts.
However, spheric contacts aren’t always the best choice for people with high prescriptions. This is because the shape of the lenses can cause blurred vision due to peripheral distortions caused by spherical aberration. This is called “spherical aberration” because it only happens with spherically shaped lenses.
When light enters the eye, the cornea and lens at the front help to focus it to a point directly on the retina in the back of the eye. You wear contact lenses to help your eyes refract light so it lands in the right place.
When spheric contacts bend light, all the light doesn’t hit the retina. Instead, the light that enters through the center part of the lens’s surface converges at a different location than the light that enters through the edges. This can cause vision distortions when the wearer looks away from the center of the lens to the left, right, up or down.
Who Can Wear Spheric Contact Lenses?
Spheric lenses generally provide great optics. But they can sometimes cause blurry vision for some people. But, in some cases, spheric contact lenses are the preferred choice.
They may be better for people who have had laser eye surgery to correct hyperopia. This is because during laser eye surgery for hyperopia, the laser shapes the cornea to make it steeper. An aspheric contact lens’s flattened edges results in a disparity between the steepness of the cornea and the contact lens.
Contact Lenses To Correct Astigmatism
People with astigmatism (which results in blurry vision at all distances) wear toric contact lenses.
Toric contact lenses have a different prescription in each meridian. You can wear toric lenses if you have astigmatism, even with or without myopia or hyperopia.
A toric lens is shaped like a donut. It has different focusing powers on the vertical and horizontal orientations of the lens.
In the past, it was thought that aspheric contact lenses might be beneficial to those with low levels of astigmatism. But now, most experts think that people with astigmatism do not benefit significantly from aspheric lenses. In some cases, they may actually see better with a spheric lens design.
Rigid gas permeable lenses are a possible solution for severe cases of astigmatism. The rigid material of a spherical lens molds the front surface of the cornea so the eye can perform better. Spherical contact lenses have only one power throughout the lens. Thus, they can move around on your cornea without negatively affecting your vision.
What Are Aspheric Contact Lenses?
The main difference between aspheric contact lenses and spheric contact lenses is the shape. The different curvatures on the surface and the flat edges of an aspheric lens focus light more precisely than spheric contact lenses. This also creates a wider field of view.
Aspheric contacts are designed to better match the shape of the cornea. For these reasons, aspheric contact lenses often provide sharper vision than spheric contacts.
Who Can Wear Aspheric Contact Lenses?
Aspheric lenses may be right for you if you:
- Want overall better vision. The aspheric lens design can help you see better when you’re doing things like working on a computer, driving in the dark or spending time in poor lighting conditions. Aspheric lenses may also sharpen vision while playing sports that require you to change focus quickly.
- Have presbyopia. Aspheric lenses can help correct presbyopia, an age-related eye condition that makes it hard to see clearly up close.
- Have cataracts. Cataracts cause blurry vision, and spheric lenses can make it worse. Aspheric contact lenses are often better specifically because they reduce spherical aberration. Spherical aberration is often made worse by a cataract.
- Have severe ametropia. Ametropia is the medical term for myopia, hyperopia or astigmatism – refractive errors that prevent people from seeing clearly. Aspheric lenses’ flatter edges help focus light onto the retina, giving wearers clearer vision.
If you’re interested in contact lenses, make an appointment with your eye doctor. They’re your best resource for information and recommendations about any type of contact lenses.