Ophthalmic lenses
Lenses are used to correct the principal refractive errors by either concentrating or diverging light to focus on the retina:
 |
Myopia (Near sighted ness); |
|
Hyperopia (Short sightedness); |
|
Presbyopia (Lack of near vision focus making it difficult to read and do close work) fous due e |
|
Astigmatism |
| |
|
|
| |
| Refractive Errors |
| |
|
Single vision |
| |
|
Bifocal lenses |
| |
|
Progressive lenses |
| |
|
|
| Lens materials |
| |
|
Glass |
| |
|
Plastic |
| |
|
Polycarbonate |
| |
|
|
| Lens coatings |
| |
|
Anti-reflective coating |
| |
|
Scratch resistant coating |
| |
|
Hydrophobic coating |
| |
|
Photochromic lenses |
| |
| Other |
| |
|
High index |
| |
|
Aspheric lenses |
|
|
|
|
|
|
|
|
| |
|
|
Refractive Errors
Best vision through ophthalmic lenses:
Single vision lenses for short-sighted and long-sighted persons:
If you have difficulty seeing distant objects, you are myopic and require concave (minus) lenses to improve your vision.
If you cannot see close objects but can focus on distant objects, you are hyperopic and require convex (plus) lenses to help you focus clearly.
Bifocal lenses:
provide two points of focus — usually one for distance and one for near vision. Generally, you look up and through the distance portion of the lens when focusing on points farther away, and you look down and through the near vision segment of the lens when focusing on reading material or close work up to about 18 inches away.
The segment that is devoted to near-vision correction can be in one of several shapes:
A half-moon, also called a flat-top, straight-top or D segment. These lenses provide a greater near vision area and can be fitted to smaller frames.
A round segment.
A full bottom half of a lens, called the Franklin, Executive or E style.
Progressive lenses
Progressive lenses sometimes referred to as no-line bifocals, not only provide visual correction for distances that traditional bifocals can't, but they also hide the fact that you even need reading glasses. Progressive lenses are the closest to how natural vision is before the onset of presbyopia that you can get in a pair of prescription eyeglasses. They are more than just a defined near and distance correction in one lens. Rather, progressives provide a smooth transition from distance through intermediate to near, with all the in-between corrections included as well. This constant graduation of the prescription means that you can look up to see in the distance, look ahead to view things such as the computer in the intermediate zone, and drop your gaze downward to read and do fine work comfortably close up.
This illustration of a progressive lens shows the configuration of distance, intermediate and near zones.
Reading glasses Bifocal lenses Progressive lenses
Back surfacing, wave front technology and individualised measurements through digital surfacing are some of the innovative methods used today.
Advantages of Progressive Addition Lenses
- Continuous field of clear vision
- Comfortable intermediate vision
- Continuous perception of space
A progressive lens is designed not only to restore a presbyope’s ability to see clearly at all distances but also to optimally respect all physiological visual functions
Lens materials: Glass, plastic, polycarbonate
Mineral (glass) -The original material for lenses.
Organic (plastic) – Plastic lenses today (CR39) are the most widely marketed for their light weight comfort.
Polycarbonate – These unbreakable lenses are ideal for rimless frames due to their high impact resistance. They are thinner and lighter than plastic lenses. This extra toughness makes them the lenses of choice for children's glasses, sports eyewear and safety glasses. They have the added benefit of protecting against UV rays.
TRIVEX - The Tri-Performance Lens Material
Lens coatings
Anti-reflective coating
Light travelling through lenses are reflected obscuring the wearer’s eyes or creating disturbing reflections. Anti Reflective coating provides the front and back surfaces of the lens with layers that ensure that the reflected light rays interfere and cancel each other out. Visually, the spectacles then do not seem to have any lenses in them.
Solitaire TopCoat®
Scratch resistant coating
Hydrophobic coating
Photochromic lenses
Photochromic lenses change from light to dark depending on the amount of ultraviolet light they are exposed to. They are the ideal solution for those with prescription lenses who want to wear one pair of spectacles both indoors and outdoors.
ColorMatic® - comfortable vision day and night |
 |
 |
|
Reduce lens thickness with high index lenses:
For high corrections (both plus and minus) the corrective lens is considerably thick and therefore, heavy. The best solution for such prescriptions is high index lenses that are thinner and lighter than the average lens. High index material bends light more than the conventional plastic lenses. As a result less lens material can be used to correct the same amount of refractive error
. 
Aspheric lenses
Flatter, thinner, lighter!:
In an aspheric design, the lenses have flatter curves; this means lenses do not bulge out of the frame as much as regular lenses. The side profile of aspheric lenses is thinner, which greatly enhances the appearance of finished eyewear.
|
