by Juan Paolo Delos Santos, M.D
Error of Refraction (EOR) is one of the most common eye conditions in the world. Globally, it affects 2.3 billion people. It has a higher occurrence among South East Asian countries, including the Philippines, as compared to western countries. EORs can greatly affect quality of life if left uncorrected. However, it can easily be diagnosed, measured, and corrected by using corrective glasses, contact lenses, and even refractive laser surgery. Here are some important definitions you need to know:
Visual Acuity (VA)
Visual Acuity is defined as sharpness of vision, measured by the ability to discern letters or numbers at a given distance according to a fixed standard. It is usually expressed as a fraction (distance of the patient from the chart/distance the average person can see from the chart)
For example, a 20/20 vision means that a person can see an object from 20 feet away what an average person can also see from 20 feet away. If a person has a 20/40 vision, that means that he can see from 20 feet away what the average person can see from 40 feet away. It means that he has a blurry vision and needs to get nearer the object for him to see clearly.
For example, a 20/20 vision means that a person can see an object from 20 feet away what an average person can also see from 20 feet away. If a person has a 20/40 vision, that means that he can see from 20 feet away what the average person can see from 40 feet away. It means that he has a blurry vision and needs to get nearer the object for him to see clearly.
Nearsightedness or Myopia
As the name implies, a nearsighted patient can only clearly see near objects. Distant or far objects are blurry to him. These types of patients are the ones who need to get closer to the object to see it better. Patients with Myopia are given “negative” or “minus” lenses like -2.00D, -2.50D, etc. This usually happens when the length of the eyeball is anatomically longer than usual. Generally, the longer the eye ball, the higher the negative grade of the glasses. For example, a patient with a -3.00 grade has a longer eyeball than a patient with a -1.00 grade.
These are the patients who can see clearly at far but has a blurry vision at near. They are usually given “positive” or “plus” lenses like +2.00D, +2.50, etc. This happens when the length of the eyeball is anatomically shorter than the normal length. Generally, the shorter the eyeball, the higher the positive grade, i.e., a patient with a +3.00 grade has a shorter eyeball that a person with a +1.00 grade.
Astigmatism
Astigmatism is defined as a condition in which the eye is not completely round. Imagine the eyeball as having the shape of a basketball, wherein all the light that comes in converge evenly at the macula. An astigmatic eye is like a football-shaped eye where the lights that come in are bent unevenly, giving the sensation of a skewed or wavy view.
Presbyopia
Presbyopia is the condition where the eyes have a hard time accommodating to read at near. This is similar to farsightedness but has a different mechanism. It usually begins at 40 years old and is corrected also by “plus” lenses or reading glasses.
Note that all these different types can occur simultaneously together. Some people can have myopia with astigmatism and presbyopia while some can have hyperopia and astigmatism but no presbyopia.
Detection, Measurement, and Treatment of EOR
A person can easily be detected to have EOR simply by letting him read the Snellen’s chart found mostly in optical centers and doctor’s clinics. Their refraction or grade can be determined by doing a retinoscopy either manually or by machine. Once the refraction or grade is established, treatment is done by prescribing the appropriate glasses or contact lens. Hence, it is very important to test your vision thru the Snellen’s chart at least once a year to see if you are developing any Error of Refraction.
Persons With Disability
According to the National Council on Disability Affairs (NCDA), an individual is qualified to be issued a PWD card if his/her:
1. Best Corrected Visual Acuity is 20/70 or worse in the better eye
2. Field of Vision is less that 20 degrees wide in the better eye (seen on patients with glaucoma)
3. Vision cannot be improved by glasses, medications or surgery.
It is not based on the grade of your glasses but is based on your visual acuity when you are wearing glasses. Hence, a person with a grade of -8.00D but can still see 20/20 once he wears his glasses is not considered a PWD. On the contrary, a person with a grade of -3.00D but has a Best Corrected Visual Acuity of only 20/80 on both eyes is considered a PWD. These patients usually have a vision impairing condition like End-stage Glaucoma, Severe Diabetic Retinopathy, Bilateral Retinoblastoma, and the like.
Remember, have an annual check-up with your ophthalmologist so we can catch your eye diseases earlier! Now you know!
References
Hashemi H, Fotouhi A, Yekta A, Pakzad R, Ostadimoghaddam H, Khabazkhoob M. Global and regional estimates of prevalence of refractive errors: Systematic review and meta-analysis. J Curr Ophthalmol. 2017;30(1):3-22. Published 2017 Sep 27. doi:10.1016/j.joco.2017.08.009