Eye Prescription

Why do my glasses prescriptions differ between clinics?

Many patients are dissatisfied with the differences in prescription lenses from one clinic to the next. It is upsetting to a person for a variety of reasons:

  1. Did I use the incorrect prescription?
  2. Has my vision deteriorated as a result of my incorrect prescription?
  3. Is there a problem with my vision?
  4. Does this issue have any medical or legal ramifications?

We’ll begin by recognizing that the goal of corrective lenses is to provide a person with clear and comfortable vision. Airlines pilots, IT experts, welders, microprocessor assembly workers, drivers, teachers, farmers, students, and others all have different visual requirements. A farmer may never realize he needs distance corrective eyeglasses since his vision is so poor!

“Cycloplegic Refraction” is the initial stage in evaluating the power of prescription lenses. Eye drops are used to temporarily disable the ability to focus. This gives an understanding of the eyes’ “objective” baseline refractive state. These drugs have an entirely reversible effect.

When cycloplegia occurs, the patient experiences increased glare from lights and is unable to focus at close range. Tropicamide and Cyclopentolate have short-term effects, while Atropine has a longer-term effect.

Atropine is required in children under the age of ten, especially if they have a concurrent squint condition. After the cycloplegic effect has been completely reversed, a post cycloplegia test (PCT or PMT) is performed. Acceptance and prescription are finalized in this way, which is also known as “subjective” acceptance. Objective Refraction guides Subjective Acceptance, but the two aren’t necessarily the same.

A practitioner would usually prescribe the highest power with which a client may achieve comfortable 20/20 vision in the case of Hypermetropia (plus power for distance). In the case of myopia (lack of distance vision), the lowest power is usually suggested, resulting in 20/20 vision. To avoid eye strain, students and IT professionals may be slightly under corrected. To determine an acceptable remedy for astigmatism, a practitioner will use a red/green, Worth’s 4 dot test.

The important element to remember is that a person might have 20/20 vision in a variety of ways, and a practitioner must choose the best one! Although accuracy in measuring power is crucial since it leads a practitioner, there are various additional factors to consider when selecting adequate power.

Presbyopia is an age-related condition in which the ability to alter focus for close objects is impaired due to lens changes caused by aging. Around the age of 42 to 45, reading glasses or glasses for close work are required. The amount of power added varies depending on the occupation, working distance, ambient light conditions, a person’s height, and so on.

Practitioners can now use automated refraction instruments to accurately assess power, but it’s just as crucial to keep their optics in good shape and calibrate them on a regular basis. Inaccuracy can be caused by misalignment of prisms, dust deposits, fungus growth, or a weak Infrared light source. Many instruments have a fogging mechanism that reduces the ability to focus; any issue with this can result in a mistake.

What Exactly Do You Mean When You Say “Eye Prescription”?

If you’ve never been to an eye doctor before, you’ve probably had a basic eye exam (only to discover that you don’t have eagle eyes!). You were probably also perplexed by abbreviated terminology like OD, OS, OU, CYL, and SPH. What exactly do these terms imply?

You’ll see these abbreviations next to numerical numbers on your eyeglass prescription. And deciphering what these letters, numbers, and plus and minus signs represent is difficult.

OD and OS are the first abbreviations you’ll notice. The Latin words oculus dextrus (OD) and oculus sinister (OS) relate to the right and left eyes, respectively. We use the abbreviation OU, which stands for oculus unitas, to refer to both eyes (oculus uturque). As many optometrists and ophthalmologists now designate LE (left eye) or RE (right eye), your doctor may no longer use these abbreviations (right eye).

Where do the plus and minus signs go in? These terms refer to the sphere (SPH or simply S), which denotes your nearsightedness (–) or farsightedness (+).

CYL, or just C, refers to the cylinder or lens power required for astigmatism, which is measured in diopters. The higher the CYL, the greater the astigmatism.

So, if you have significant astigmatism, a sample prescription would say -5.25, which means you’re nearsighted by 5 and 14 diopters. This can result in blurry or distorted vision. As a result, don’t be surprised if you’re advised to wear bigger lenses.

AXIS refers to the direction of astigmatism correction, which ranges from 0 to 180 degrees. Consider superimposing a protractor scale (yep, the one your ninth-grade trigonometry teacher made you use) on the center of your eye. The vertical meridian is represented by 90 degrees in the centre, whereas the horizontal equivalent is represented by 180 degrees. Knowing these angles can assist your eye doctor in determining the proper cylindrical power for your eyeglass lenses.

Other terms you might hear include DV (distance vision), NV (near vision), ADD (added power for multifocal and bifocal lenses to correct presbyopia), and PRISM (presbyopia reduction in multifocal and bifocal lenses) (amount of prismatic power used to correct eye alignment issues).

Are My Prescriptions For Eyeglasses And Contact Lenses The Same?

No, they aren’t the same. While both prescriptions show farsightedness, nearsightedness, and astigmatism (if applicable), a contact lens prescription contains additional information due to the lenses’ location on the eye’s surface. Your eyeglasses, on the other hand, are roughly 10 to 12 millimeters (mm) from your eye surface.

So, What Exactly Does “20/20 Vision” Imply? Is It Still Possible For Me To Attain That?

You can comprehend an image from 20 feet away if you have 20/20 vision. Using the Snellen chart (the well-known eye chart with the big letter “E” on top), the image must be visible from that minimal distance.

The rule of thumb is that the lower the second number, the clearer and sharper the picture of distant things will be. Yes, it is typically feasible to restore your vision to 20/20.

How Often Does Your Prescription For Glasses Or Contacts Change?

If you obtained glasses for the first time before graduating from high school, you may have puzzled why your prescription keeps changing.

Changing eye prescriptions is such a routine occurrence that it hardly seems remarkable. I’m going to guess that the correct term for this situation is a “nomenon,” but I don’t have time to look it up. We’re going to talk about eyeglass prescriptions.

The majority of this article will focus on the pressing issue of why your eye prescription fluctuates.

However, determining whether or not your eyes are becoming worse is a lot easier.

If you graduated from high school before 2016 and were born after Gerald Ford, the answer is almost certainly “no.”

What Factors Influence The Frequency With Which My Eye Prescriptions Change?

Your eye prescription is likely to have altered by the time you see your eye doctor again. Apart from disorders that cause eye difficulties, aging is a big factor.

Because of the following reasons, your vision issues may worsen:

Macular degeneration is a condition that affects the eyes.

What Exactly Is Macular?

According to the American Macular Degeneration Foundation, macular degeneration is the main cause of vision loss (AMDF). The macula is a tiny region in the center of the retina that aids in straight-ahead vision. When pigment changes occur in the retina, it can lead to either intermediate dry macular degeneration (which affects light-sensitive cells over time) or wet macular degeneration (which damages light-sensitive cells all at once) (where abnormal blood vessels appear and leak blood).

Macular degeneration can be influenced by genetics, race, and smoking. While you may not be able to manage the first two, you may always choose to stop smoking.


As you become older, your chances of developing cataracts rise. Blurred vision with cloud-like obstructions, faded colors of objects, excessive brightness of headlights when driving at night, and even double vision are all possible symptoms. Certain factors, like as diabetes, high myopia, heavy smoking and drinking, and even continuous exposure to UV light, have been linked to the formation of cataracts, according to doctors.


The optic nerve is composed of about a million nerve fibers that link to the brain. One’s vision is impacted when it is harmed as a result of elevated eye or blood pressure. Patients may experience eye pain, nausea, and reddening of the eyes in addition to blurred vision.

Glaucoma can be treated using certain eye drops. In addition, some treatments, including as Refractive Lens Exchange (RLE), can reduce the risk of getting the condition.


If your blood sugar levels are uncontrolled and irregular as a result of diabetes, your vision will most certainly decline if it goes unnoticed. When diabetes is left uncontrolled and untreated, diabetic retinopathy, or damage to the retina caused by diabetes, can result in vision loss. This happens when weak blood vessels expand but leak, causing retinal injury.

So, before it’s too late, cut back on the sugar.


This normally happens in your early forties. You lose your ability to focus on small objects as you get older. Even with your glasses on, you find it difficult to see your daughter’s cellphone text message clearly. As a result, you adjust by holding your phone further away from your eyes to reduce blurriness.

But don’t get too worked up. Because presbyopia is a natural aspect of the aging process, we will most likely experience visual tiredness. If you’re still not having symptoms, try taking a vacation from playing on your phone 24 hours a day, seven days a week.

Why Is It That My Vision Worsens Year After Year?

Isn’t it true, though, that your prescription constantly changing? It appears that a prescription can vary while the shape of an eye does not alter. But it’s not just possible; it’s quite prevalent.

We associate changing prescriptions with changing eyes since this is true for the first few alterations. You are born with an eye that is roughly 80% of the size it will be when you reach adulthood. This means that your refractive error will alter as your eye grows during your childhood. Your prescription is determined by your refractive error. Every millimeter that the eye grows increases the prescription by -3.00.

When they stare up at the whirling mobile over their cot, little babies with a prescription of 0 have a prescription of +6.00 (!). There are numerous buffers to allow the eye to develop without becoming nearsighted. Nearsightedness is indicated by a negative prescription, indicating poor distance vision.

What happens if you’re born with insufficient buffer (pretty much anything less than a +6.00 prescription)? When your eye grows old enough to become nearsighted, you get glasses. You go into a prescription that starts with a minus sign too soon after hitting 0 refractive error.

As your eye grows larger, your refractive error will increase. Like a result, a child who receives his first pair of glasses in fourth grade (as I did) will require new spectacles every few years as his eyes develop. However, eyes stop developing at a particular age; for 95% of people, this is 18 years old, and for everyone else, it is 21 years old. In the same way that the inseam of your jeans does not alter in your twenties, neither does the shape of your eye.