First, let me explain what intermediate vision means. Based on the distance between the object we see and our eyes, we use terms such as ‘distance vision’ and ‘near vision’. An example of distance vision is watching the television and example of near vision is reading something (printed material/phone) in your hand at a distance of about 12-18 inches.
Intermediate vision is something between near and distance vision. For example, the distance between your eyes and a desktop computer on your table is usually more than your near vision but closer than distance vision.
The information provided in this article is for those who use reading glasses, or in other words, glasses for near work. Most of us need glasses for near work around the age of 40 years and later. This condition is called as presbyopia. Generally the power of lenses in the glasses increases with the age. For example, if you are using +0.75 diopter for near work (including reading), after some months/years, you would need to change to +1.00 or +1.25 diopter for clear vision and comfort. If you don’t change, you won’t see close objects clearly and you may develop eye strain and headache.
Read this post for more details on presbyopia.
Here is an example of how the power of reading glasses increases with age (in reality, this pattern is highly variable among users of reading glasses):
40 years of age: +0.50 Diopter
45 years of age: +1.00 Diopter
50 years of age: +1.50 Diopter
55 years of age: +2.25 Diopter
60 years of age: +3.00 Diopter
In the above example, a person of 50 years of age will not be able to see objects at 12-18 inches clearly with +0.50 Diopter glasses. It is important to understand that the above person (if using +0.50 Diopter glasses) will have to increase the distance between the eyes and the object to see it clearly.
Most of the people don’t understand the importance of intermediate vision. They see distant objects without glasses (if their distance vision is good) and use reading glasses for the near objects. They don’t see objects, especially fine print, at intermediate distance clearly. Such people subconsciously resort to some workarounds. For example, the person who cannot see the screen of the computer on the table clearly, she or he would do any of the following:
- Use the reading glasses and go closer to the screen or bring the screen closer to the eyes. This could involve abnormal posture such as bending forward which itself may cause neck pain and lower backache, if prolonged.
- Remove the reading glasses and increase the distance between the screen and the eyes. However, most of the people are not psychologically comfortable with the increased distance between them and the screen.
An easy solution for this problem is using the power of glasses less than the power of your reading glasses. Going back to the above example, a person of 50 years of age would see near objects clearly with +1.50 Diopter glasses and would see objects at intermediate distance clearly with +0.50 or +0.75 Diopter glasses. Such powers can be found in older reading glasses if the person has been using and changing glasses in the past.
So if you have old reading glasses, you can use them for intermediate vision. A more popular solution nowadays is progressive lens. Progressive glasses help you see near objects, distant objects and everything in between clearly. Read this post to know more about progressive glasses.[Image by Travis Isaacs / CC BY 2.0]