Optic designs

Single Vision

Single vision lenses have the same focal power throughout (top to bottom) and can be used to correct nearsightedness, farsightedness, astigmatism, or a combination of these disorders. Most people who wear glasses before the age of 40 have single vision lenses.

Bifocal Lenses

Bifocal lenses have two parts: the upper part normally used for distance vision and the lower part used for near-vision tasks such as reading. Many people after reaching age 45 develop a condition called presbyopia, which is deterioration in the ability of the eye's natural lens to expand or contract in order to focus on close objects. People with presbyopia need a special lens for reading and may need a different lens for seeing in the distance. Benjamin Franklin invented bifocals so he wouldn't need to switch glasses when reading. They serve that same purpose today.

Until recently, bifocal eyeglasses had a line going across the entire length of the lens. Now there are a number of variations on the theme. All work the same way, by reserving part of the lens for near-vision correction. The rest of the lens can be used for distance vision correction or can have no correction at all.

The segment for near-vision correction can have one of several shapes:

• Half-moon, or flat-top segment
• Round segment
• Narrow rectangular area called a ribbon segment
• The entire bottom half of the lens, in what is called variously the Franklin, Executive, or Ribbon style

Progressive Addition Lenses

Progressive Addition Lens (PAL) is the lens that increases in power from top to bottom for excellent optics at all distances. Progressive lenses have no clear dividing lines as the focus changes from bottom to top. They have become popular in recent years because they look like single vision glasses.

Computer Lenses

Computer lens is the special purpose lens designs suitable for efficiency from the near vision zone, such as with reading, computer keyboard zone, into the middle vision zone, such as at computer monitor distance. For distances over 80 cm, computer lens may be used, but definition of vision is dependant on individual prescriptions.

Computer lens is suited to continuous work over long periods of time or when a wider zone for reading is needed.

Sports Single Vision Lenses

Certain fashion sunglasses or sports eyewear frames are designed for aesthetic and/or aerodynamic purposes, highly curved to wrap around the face. This results in the convex surface of the lens required being tilted and not perpendicular to the vertical view, unlike conventional frame designs, and therefore new lens design principles apply in order to avoid distortion, caused by both SPH-CYL error and prismatic error, particularly evident around outside of the lens center. Also, in case of high minus powers, lenses may be too flat to fit into curved frames. Excelite Sports SV was conceived especially for strongly curved frames.

Sports Single Vision Lens is designed by compensating for SPH-CYL and prismatic error. With FFA (Face Form Angle) measurement and Sports Tech software calculations, the lens produced is accurate to the prescription required with a curved frame, which would be distorted with a conventional lens design in the same frame. Vision is more comfortable, clear and natural, even in fashion sunglasses or highly curved sports eyewear.