Single vision eyeglasses correct one field of vision. These glasses distribute focus evenly over the entire surface area of the lens. They are the most common type of glasses prescribed. Single vision eyeglasses are an all-purpose lens that correct distance vision, specifically myopia (nearsightedness).
Myopia is a refractive error caused by an eyeball that is too long. The long eyeball causes the light to focus slightly in front of the retina instead of on the very surface of the retina. Myopia can also be the result of the cornea or lens being too curved to focus the light correctly. The effect is that an individual has near good vision but poor distance vision. Eyeglasses are usually prescribed to treat myopia. With the correction, one can indulge in activities such as driving, watching a movie, seeing the classroom board, etc. Choosing to wear single vision eyeglasses all the time or only when there is need depends on the degree of the myopia.
Some people may not require correction for long distances. They can obtain reading glasses over the counter. The power contained in these lenses is the same in both eyes. Reading glasses can also be prescriptive.
Types of Material
The lenses in single vision eyeglasses are made from various kinds of materials:
- Glass - Glass was the most popular material in the past. It, however, came with several disadvantages such as being too heavy, less flexible and unsafe since it is more likely to break and cause harm. Sometimes, when the lens breaks inside the eye, it can cause serious injury or even loss of the eye.
- Plastic - Most lenses today are made of plastic. Plastic has more advantage over glass. The lenses made from plastic are lighter, more flexible and safer to use because they are not likely to break. Plastic lenses also come with the advantage of being able to block the harmful ultraviolet (UV) light.
- Polycarbonate lens - These lenses are made of safety lens material that is profoundly impact- resistant. This means that the lenses are ideal for those who engage in activities which make them prone to injuries.
- Trivex lens - The lens can be made of Trivex, a similar but newer version of the polycarbonate lenses. Even though Trivex meets the same safety standards as polycarbonate, it is less distorting.
- High-index lens - The high-index lens is thin and made of plastic. It is ideal for individuals in need of high visual correction. It has the advantage of less distortion since it does not leave a ‘coke bottle’ appearance on the wearer. The ‘coke bottle’ appearance is common with individuals who wear eyeglasses with thick lenses.
Types of Protective Coating on Glasses
The eye needs protection to keep it healthy, hence the inclusion of a protective coating on the lens. There are several types of coatings which include:
- Prescription sunglasses fitted with UV protection.
- There is a type of coating that helps to protect the eye against the dangerous UV light rays. However, some plastic lenses do not have this type of coating because these lenses block UV light on their own.
- Photochromic lenses suitable for both the indoors and outdoors. These lenses are made of a tint that changes according to the amount of light present. When there is sunlight, the darker tint is used while the lighter tint works indoors. However, photochromic lenses do not work well in all environments. For instance, in a car or airplane, the windows may block the light rays that cause the tint change. It may take some time for the tint of the lens to adjust from dark to light.
- Anti-reflective coatings which lessen reflections off the eyeglass surface. The result is that the wearer has an improved appearance. The eyeglass wearer also experiences better and effective eye contact with others. Coated lenses carry several more advantages. The wearer experiences reduced eye strain because of less glare and reflections which happen when the lenses allow more light to pass through them. This action improves contrast, sensitivity and visual acuity. For individuals who are specifically affected by glare from headlights while driving at night, these coatings can be extremely beneficial.