Vint and York's Comprehensive Guide to Glasses Prescriptions
Eye dysfunction is a common affliction and many people have experienced going to the eye doctor and receiving a glasses prescription. This prescription is characterized by symbols and abbreviations representing the degree of the condition and the lens power needed to correct the issue. It can be a confusing piece of paper and illegible for most people. This article will help you learn how to understand eyeglasses prescriptions, common eye conditions that require them, and frequently asked questions relating to eyeglasses prescriptions.
Common Eye Conditions That Require Glasses-Prescription
Below are the most common eye conditions that you might be diagnosed with that would require you to wear eyeglasses.
Myopia is a condition that affects your distance vision; it is also referred to as nearsightedness. People with myopia experience difficulty seeing distant objects, but they can see objects that are close clearly. It is an eye focus disorder easily rectified with eyeglasses, contact lenses, or surgery. The exact cause of myopia has not been established yet, but it is believed to be a result of environmental and hereditary factors.
Myopia is a refractive error, which means the shape of the eye does not allow light to focus correctly on the retina. The cornea and the lens work together to bend light onto the retina to affect clear vision. Myopia can be explained using three main errors; when the eyeball is too long from front to back, the cornea is too curved, or there is an issue with the shape of the eye's lens.
The common symptoms of myopia include blurred vision of distant objects, eye strain, headaches, squinting, tiredness when looking more than a foot away, for example, when driving.
In rare cases, myopia develops into severe disorders such as high and degenerative myopia.
Presbyopia can be defined as the loss of the eye’s ability to see objects clearly from a near distance; it is also referred to as farsightedness. It becomes noticeable as people age. The term presbyopia comes from a Greek word meaning old eye. In most people, presbyopia is identified shortly after they reach 40. The eye lens is soft and flexible and thus quickly changes its shape - however as you age, it becomes more rigid and cannot change shape easily. Presbyopia is easily rectified using eyeglasses, contact lenses, or surgery.
The symptoms of presbyopia include blurred vision at average reading distance, a tendency to hold reading material farther to make letters clearer, headaches or eye strain after doing close-up work or reading.
Several factors increase the possibility of presbyopia, such as age; other medical conditions, for example, cardiovascular diseases, multiple sclerosis, and diabetes. Such diseases have been confirmed to cause premature presbyopia. Other factors include drugs such as diuretics, antihistamines, and antidepressants.
Astigmatism refers to an eye problem where the curvature of the eye causes blurred close and distant vision. It occurs when the cornea or the lens inside the eye has mismatched curves. In most cases, astigmatism is diagnosed at birth and may occur in combination with myopia or presbyopia, but it is not severe enough to require rectification. When it becomes serious, it is corrected by eyeglasses or surgery.
Astigmatism is a refractive error that occurs when the lens or cornea is curved more steeply in one direction than in another. In cases where the cornea has mismatched curves, the condition is defined as corneal astigmatism, while in cases where the lens has mismatched curves, it is defined as lenticular astigmatism.
Apart from being present from birth, the condition may develop after surgery, eye injury, or disease. You should also be aware that astigmatism is not caused or worsened by sitting too close to the television, reading in poor light, or squinting.
The main symptoms include blurred vision, distorted vision, eye strain and discomfort, difficulty with night vision, headaches, and squinting.
Diplopia is an eye problem where the individual sees two images of a single object. It is also known as double vision. In most cases, it is a temporary condition, or it could be a symptom of more severe health conditions. It occurs in four primary forms, namely, monocular, binocular, horizontal, and vertical. Monocular is present when you use only one eye at a time, binocular is when both eyes are open simultaneously, and the double vision disappears when you cover one eye. Horizontal diplopia is when the binocular diplopia appears from side to side, while vertical diplopia is when binocular diplopia appears from top to bottom.
Double vision depends on the cause and how or why your eyes are not aligned. However, it is important to note that this condition is most common in adults older than 60.
Eyeglasses-prescription charts are given to guide the type of corrective lens a patient needs. A corrective lens can be defined as a lens worn on or in front of the eye to rectify refractive errors in the eye, such as presbyopia, astigmatism, hyperopia, and myopia. They are designed to help the eyes to focus light properly onto the retina to affect clear vision. Corrective lenses bend light rays to the required degree before entering the eye. The main types of glasses fitted with corrective glasses include the following.
- Monofocal lenses- a monofocal lens has one focal point that allows the wearer to see things near or far.
- Bifocal lenses- a bifocal lens is divided into two parts: near vision on the smaller lower part and distance vision on the top. The lens has visible lines that divide the two parts.
- Trifocal lenses- A trifocal lens accommodates three different visions; near, middle, and far sight.
- Progressive lenses- A progressive lens is similar to the bifocal and trifocal lens, but it is made in a way that enables a smooth transition between the focal points. The lines separating the different focal points are not visible in progressive lenses.
Contents of Glasses Prescription Charts
An eye prescription chart contains many numbers and abbreviations. The contents of glasses-prescription charts include the sphere, cylinder, axis, addition, prism, acuity, and vertex divided into specific measurements for each eye, the right and left, abbreviated as O.D. and O.S., respectively.
O.D. versus O.S.
O.D. is the abbreviation for oculus dexter, Latin for the right eye. O.S. is the abbreviation for oculus sinister, Latin for the left eye. Your glasses-prescription may also be labeled O.U., the abbreviation for oculus uterque, Latin for both eyes. However, some clinics and doctors use RE and L.E. in the prescriptions to represent the right and left eye, respectively.
You also need to note that the prescription for your right eye; O.D., always comes before the information for your left eye; O.S., the prescription is arranged this way because when the doctor faces you, they see your right eye on their left first and your left eye on their right second.
N.V. versus DV
NV means near vision, while DV means distance vision.
Pupillary Distance (P.D.)
Pupillary distance is the distance between your pupils measured in millimeters. This measurement helps align the center of the lens with the center of your pupils to impact the most accurate vision possible. It is measured manually or using a pupilometer. Most eye doctors include your pupillary distance on every prescription.
Opticians use the term sphere to mean that the correction for presbyopia or myopia is equal in all eye meridians. This crucial section in the glasses-prescription chart indicates the lens power required to correct myopia or presbyopia. Lens power is measured in diopters indicated by the letter (D).
There is a negative or positive sign before the figure written under the sphere column. The sign is an indication of whether you are nearsighted or farsighted. Minus sign (-) means you have been diagnosed with myopia/nearsightedness, while a plus sign (+) means you are farsighted.
As used in glasses-prescriptions, the term cylinder means that the particular lens power added to correct astigmatism is not spherical. It is shaped in a way that one eye meridian has no added curvature and the meridian perpendicular to this meridian contains the lens curvature and maximum power to rectify astigmatism.
The cylinder specification follows the sphere power on the glasses-prescription chart. It indicates the amount of lens power needed to correct astigmatism. The number under the cylinder (CYL) column has a minus or plus sign. The plus sign indicates correction for farsighted astigmatism, while a minus sign indicates correction for nearsighted astigmatism.
The column might be blank in some prescription charts, meaning that you have not been diagnosed with astigmatism or the degree of astigmatism is too small to need any correction.
Axis specifications come after the cylinder prescription. It is used in glasses-prescriptions to describe the lens meridian that does not contain cylinder power to correct astigmatism. All glasses-prescriptions that include cylinder power need to include an axis prescription. The axis is assigned with angle degrees from 1 to 180. The vertical meridian of the eye corresponds with the number 90, while the horizontal meridian corresponds with 180. If the cylinder section was blank, the axis column should also be blank since the two work together as the axis neutralizes the difference in power in the eye with the power in the lens.
Add refers to the added magnifying power applied to the bottom section of multifocal lenses to rectify presbyopia. Multifocal lenses are also known as progressive lenses. They have multiple focusing powers to improve vision at different distances. The different sections of focusing power are blended in these lenses to rectify farsightedness, nearsightedness, and intermediate distances.
The number under this column is always preceded by a plus sign (+) even when it is not indicated. It ranges between +0.75 and +3.00 D . Note that the figure specified is the same for both eyes.
Prism is the amount of prismatic power prescribed to rectify eye alignment problems. Prism is measured in prism diopters (p.d. or a free handwritten triangle), and it is not common in most prescriptions.
Prism correction glasses are used to fix double vision problems. Diplopia, as mentioned earlier, is a condition where a person sees two identical images using both eyes.
The amount of the prism is indicated in fractional English or metric units, for example, 0.25 or ¼. The direction of the prism is indicated by noting the relative position of its base. You might note the following abbreviations used for direction; B.U., B.D., B.I., and B.O. B.U. Indicates base up, B.D. Indicates base down, B.I. Indicates base in or towards the patient's nose, and B.O. indicates base out, which means towards the patient's ear.
FAQs About Eye Glasses-Prescriptions
Do the Eye Glasses-Prescriptions Have an Expiry Date?
Eyeglasses-prescriptions are usually valid for a year or two. The exact period the prescription is valid depends on state laws, after which you need to schedule an eye exam to renew it. You should go for regular examinations to ensure that you are seeing as well as possible.
Is My Contact Lens Prescription The Same As My Glasses Prescription?
Not in all cases. Eyeglasses are designed to sit short distances away from your eyes, while contact lenses rest directly on the cornea. That difference in position of the lenses translates to unmatching prescriptions. Even if the figures on your glasses and contact lens prescription are similar, the contact lens prescription has additional content such as the brand name of the contact lens that you have been recommended to use, for example, DAILIES, clarity, Acuvue, etc.
This comprehensive guide will be handy in understanding prescription and general information about the eye conditions that mostly require eye glasses-prescriptions.