Myopia
What is it: Eye’s ’power’ is too high causing light to focus in front of the retina. Moving closer to the object being viewed will increase clarity.
Symptoms: Difficulty in viewing distant objects.
How it’s corrected: Eyeglasses with ‘negative power’ lenses are used, for instance -3.00.
Hyperopia
What is it: Eye’s ‘power’ is too low causing light to focus behind the retina. The eye may be able to compensate and increase the ‘power’ for tasks that require clarity.
Symptoms: When mild, there may be no symptoms; when moderate, near work can be difficult and cause eye strain; when severe, even distant objects can look blurry; it also depends on age and time spent on visually demanding tasks.
How it’s corrected: Eyeglasses with ‘positive power’ lenses are used, for instance +3.00. The amount of correction (or none) depends on various factors such as the age, symptoms, visual tasks, and amount of hyperopia.
Presbyopia
What is it: Eye’s ability to focus is reduced. This happens naturally with age and typically affects people above 40 years old.
Symptoms: Difficulty in viewing near objects when wearing a pair of eyeglasses corrected for distant vision.
How it’s corrected: Eyeglasses with a ‘power’ that is more positive than the distant eyeglasses, for instance a -3.00 for distance eyeglasses and -1.00 for near eyeglasses. Progressives, which combine both a far and near prescription within the lenses, may be considered.
Read more about the solutions for presbyopia.
Astigmatism
What is it: Eye’s ‘power’ is different along each ‘axis’, i.e. not spherical
Symptoms: Elongation of images along one direction, sometimes causing the effect of a double-vision where there there are two edges to a word or object right next to each other.
How it’s corrected: Eyeglasses with a ‘cylindrical power’ component to the lenses are used, with neutralises the ‘astigmatic power’. You often see an ‘axis’ tagged to the corrective astigmatic power, such as -1.00X180 which means an astigmatic correction of -1.00 at 180 axis. See our buying guide and prescription reading guide.
FAQs:
Isn’t hyperopia the same as presbyopia (老花)?Hyperopia is simply the eye not being ‘powerful’ enough in it’s natural state, thus having to continuously ‘focus’ in order to look at objects, far or near.
Presbyopia on the other hand is the inability to bring the eyes’ focus to near, while eyeglasses for distant vision are worn.
A child with mild to moderate hyperopia might have no symptoms at all as the eye is able to compensate, while anyone with presbyopia would most certainly complain and come in for reading glasses.
Someone recommended progressives for my child?
Is the TV causing astigmatism?
What is considered high myopia?
Are there risks to having high myopia?
If I lower my child’s myopia prescription, will it be beneficial?
[1] (Chung, Mohidin, O’Leary, 2002)
[2] (Li, Li, Zhou, et. al., 2015)
[3] (Tyler and Wagner, 2019)
