Ophthalmic lenses are used to manipulate or bend light to focus the incoming light rays correctly on the retina. There are a wide variety of ophthalmic lenses on the market, with each type having unique features and benefits.
At Charl Laäs Optometrists we are very proud to be able to offer a comprehensive range of ophthalmic lenses for our patients.
The lens categories are:
- Single vision lenses
- Accommodative support lenses
- Office lenses
- Bifocal lenses
- Trifocal lenses
- Multifocal lenses
Single vision lenses
Single vision lenses as the name implies will only focus light for a single distance. These lenses are typically used to correct distance errors like myopia (nearsightedness) or hyperopia (farsightedness), and refractive errors like astigmatism (irregular corneas).
They are also used as reading lenses in people older than 42, for the correction of Presbyopia (age-related farsightedness). The lens will provide a simplistic solution as the patient will be able to clearly focus on objects between 30 cm to 40 cm with no peripheral distortion in the lens.
Single vision lenses do however have the limitation of blurring distant objects when a person looks further away than the 30cm to 40cm reading distance. It is, therefore, necessary to regularly put on or remove the glasses, depending on the viewing distance.
Accommodative support lenses
These ophthalmic lenses are designed specifically for distance wear, with an increase of magnification towards the bottom of the lens. Popularly used patients younger than 42 with visual fatigue.
Visual fatigue is a phenomenon caused by many factors related to our lifestyle and activities with increasingly prolonged periods of intermediate or near vision use. Symptoms of eyes that sting or feeling tight, blurred vision or headaches start appearing after a long day of reading, studying or computer work, accommodative support lenses might be an option for you.
Office lenses are also known as intermediate-to-near-progressive lenses. They are specifically developed for the administrative or office worker. Important to note is that this lens is still a reading lens and will not focus clearly on objects in the distance. There is a small amount of distortion noticeable in the periphery of the lens due to the progressive nature of the lens.
As the name implies, Bifocal lenses have two (bi) focal points. These lenses have a visible line dividing the optic zones into two sections.
The top section has the distance prescription allowing a person to focus clearly on objects further than 6m away. The bottom part of the lens is focused on near work around the 30cm to 40cm mark.
Benefits of bifocal lenses:
- Focus clear for both distance and near objects
- Provide wide peripheral vision without any distortion
Disadvantages of bifocal lenses:
- Do not focus on intermediate distances like computer screens and arm’s length activities
- Severe image jump when walking and looking down
Trifocal lenses look the same as bifocal lenses except that a third intermediate zone has been added above the reading segment. This lens has the same advantages and disadvantages as bifocal lenses except that the intermediate viewing zone is now also in focus.
With the birth of multifocal lenses (discussed below), trifocal lenses have mostly become obsolete.
Multifocal lenses are also known as distance-to-near-progressive-, progressive-, varifocal- or progressive additional (PAL) lenses. The top section of the multifocal lens corrects for the distance refractive error of the patient and then gradually adds the near addition power until the maximum reading power is achieved at the bottom of the lens.
The progression of the power from distance to reading, creates a noticeable non-focus area in the periphery of the multifocal lens. There are many different multifocal designs available, for example, hard- and soft designs, short corridor designs and freeform designs.
Benefits of multifocal lenses:
- No visible lines of demarcation, hiding the fact that there is a reading zone in the lens.
- No image jump, which reduces the risk of losing your balance when looking down at steps and sidewalks.
Disadvantages of multifocal lenses
- Distortion or unclear vision when a person looks into the periphery of the lens.
- An adaption period of about 2 weeks is needed for the visual mind to adjust to the optics of the lens.