Short Sighted Symptoms And Correction
Short Sighted Symptoms And Correction
Short sighted means your vision is good generally within arms length, where beyond this and into the distance the vision is blurry.
The exception to this is a condition that develops with most individuals usually from middle age where we have trouble seeing close up to read, so whether short sighted or longsighted we would need either reading glasses, bifocals or varifocals and these details are covered in other articles.
To explain what causes being short sighted and what you need to correct this condition with glasses we need to understand the main components of the eye.
Structure of The Eye
Eye – is made up of the cornea, the crystalline lens, the retina and optic nerve.
Cornea – is the transparent front part of the eye that covers the pupil, iris and anterior chamber. The refractive power of the cornea is approximately 43 dioptres which is most of the eyes focusing power but its focal point is fixed unlike the crystalline lens.
Crystalline lens – is a transparent structure that sits behind the cornea in the eye where together they help to refract light to be focused on the retina.
Retina – is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, similar to the film in a camera.
As light strikes the retina it initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses. These are sent to various visual centres of the brain through the fibres of the optic nerve.
Optic Nerve – is considered to be part of the central nervous system and transmits visual information from the retina to the brain. Any nerve damage produces irreversible blindness.
How The Eye Works
Rays of light pass through the cornea and into the lens, both of which focus the rays onto the retina to create an image. The image is converted into an electric signal, which
is transmitted to the brain via the optic nerve. This in effect allows the brain to see.
Short-sightedness is a refractive eye condition. It happens when the eye continues to grow and becomes too long from front to back. The result is light rays do not reach the retina at the back of the eye only focus in front of it so objects in the distance appear blurred.
The medical term for short sighted is myopia. There are varying degrees of myopia or being short sighted that range from mild where treatment may not be required to moderate and high which can significantly affect the way we see.
Symptoms of being Short Sighted (Myopia)
Symptoms can start around puberty when the eye measures around 19mm and becomes worse with age because the eye grows longer. Short sightedness normally stabilises around the mid to late 20s when a person is fully grown and the eye measures around 24 – 25 mm.
It’s very important even at a young age to have regular eye examinations, particularly if your child struggles to see the blackboard at school or comments that distant objects seem fuzzy or blurred.
Age related eye conditions like cataracts may also influence short sightedness
Following your eye examination the optician will discuss their results and findings with you and provide you with a written prescription.
On your optical prescription are numbers and these are units of measurement. Numbers between – 0.50D and – 3.00D are most common for a short-sighted person and corrective lenses are often recommended for activities such as watching television or driving.
The letter (D) refers to the term dioptre which is a unit of measurement of the optical power of a lens or curved mirror. It’s equal to the reciprocal of the focal length which is
measured in metres. A prescription lens of minus (-) 3.00D brings parallel rays of light to focus at one third of a metre so correcting the distance vision to help with driving and make road signs clearer.
A short sighted person will require a minus (-) prescription lens to correct the vision, the higher the number the thicker the lens on the outer edge.
Moderate myopia is a measurement of between -3.00D and -6.00D and will require a person to wear glasses full-time. The edges of the lens will appear thick so choice of frame is critical to the overall appearance of the glasses.
A minus (-) 1.00D lens is thinner on the outer edge than a high minus (-) 6.00D lens. Depending on your optical frame when a standard optical lens is fitted or (glazed) into the frame it can feel heavy uncomfortable to wear and often ugly in appearance.
To reduce the weight and enhance the appearance many people with a high minus (-) prescription choose a higher index Lens which are thin, light and more attractive.
High myopia is a measurement of -6.00D and above so people will only see close objects clearly without glasses if they hold them very close to their eye.
Glasses made from standard plastic lenses such as the CR39 material will appear very thick on the outer edge and heavy. High index lenses are strongly recommended for this type of prescription as they have the same optical power and are thinner.
Short Sighted (Myopia) & Eye Examination
There is no substitute for a full eye examination in the consulting room to detemine how Short Sighted you are with a thorough diagnosis however, what ever the outcome, you are totaly free to take your optical prescription to the supplier of choice.
Compliments of the Reglaze Glasses Team