The Difference Between Long and Short Sightedness

Many people believe long sightedness to be the straightforward opposite of short sightedness. While to a certain extent this is true, the difference between long and short sightedness is a little more complex than long sightedness simply being able to see in the distance and not up close, and short sightedness being vice versa. To further complicate things, an additional condition known as presbyopia is often confused for long sightedness as people with presbyopia find an increasing difficulty with their near vision. 

Refractive Error in the Eyes and Eye Anatomy

In simple terms, refractive error refers to the mismatch of the eye’s focusing power to the length of the eyeball. Refractive error includes both long and short sightedness, as well as another condition known as astigmatism, and the previously mentioned presbyopia.

There are several points in the eye that light must pass through in order for us to see. These anatomical points serve as surfaces to bend light rays such that the rays come to a sharp point on the retina at the back of the eye, thereby providing a clear image. It’s when the refractive (focusing) power of these anatomical components doesn’t quite manage to bring the rays of light to a sharp focus on the right spot that we experience blurry vision. 

Light first passes through the tear film, which covers the cornea, before then passing through the cornea itself. The cornea is the transparent dome at the front of the eye; together with the tear film it accounts for about two-thirds of the focusing power of the eye. The crystalline lens, which sits behind the coloured iris, is responsible for the remaining one-third. The lens is suspended in place with fibres attached to a ring of muscle and can adjust its shape to bring forward the focal point of the eye to focus on closer objects in an action known as accommodation – this is particularly important for understanding long sightedness. 

The length of the eyeball, known as the axial length, plays a significant role in the presence of refractive error. As mentioned earlier, light must be refracted, or focused, through the tear film, cornea, and crystalline lens, to come to a sharp point right on the retina in order for us to perceive clear vision. If this focal point of light falls short of the retina, or falls behind the retina, we end up with blurred sight. 

The main difference between long and short sightedness, and the only straightforward part of this explanation, is that long sightedness, also known as hyperopia or hypermetropia, occurs when the eyeball is too short for the focusing power of the eye – that is, the focal point of light falls behind the retina. Short sightedness, also called myopia or nearsightedness, occurs when the length of the eyeball is too long for its focusing power, and the focal point of light falls short of the retina. Both long and short sightedness may occur in conjunction with astigmatism, which is commonly caused by an uneven cornea.

Presbyopia refers to the age-related decline in the flexibility of the crystalline lens and reduced accommodative ability, resulting in an increasing difficulty at focusing up close such as during reading. Many people confuse this with long sightedness, believing both to simply refer to an inability to see at near, but these are two different conditions. Presbyopia occurs to everyone with age, and can occur alongside both long and short sightedness. 

The Difference Between the Long and Short Sightedness Experience 

Here we come to the complicated part. 

People with long sightedness, can be quite content at both far and near distance viewing without the need for glasses or conversely, experience blurred sight for both distant and near objects, and require corrective lenses all the time. This is typically dependent on two factors – the age of the person (and therefore their ability to accommodate) and the magnitude of their hyperopia. In a young person with a flexible crystalline lens and active accommodation, a hyperopic refractive error may be compensated through accommodation, meaning the lens is able to change its shape enough to provide clear vision at both distance and near. However, the nature of hyperopia is such that the crystalline lens is working to focus even far distance objects. This means a young person who is very long sighted may find the effort to see clearly even in the distance is too great, with this effort increasing as the viewing distance comes closer, and will therefore need glasses for both long and short distances. 

On the other hand, people with short sightedness, or myopia, will always find their long-distance vision to be clearer through their corrective lenses, regardless of age. A young person with short sightedness will also be able to read clearly at near through their glasses for myopia, due to active accommodation, but may find that removing their spectacles for reading is just as clear and possibly more comfortable. An older patient with myopia and reduced accommodative ability will find they will have difficulty seeing at near unless they remove their distance optical correction or wear lenses such as multifocals or bifocals with an integrated reading prescription.  

Refractive error can be a complicated topic but the good news is that there are a multitude of options for correcting both long and short sightedness, including glasses, contacts, and laser eye surgery. Call us today at (03) 9070 3580.