Why is my Eyeglass Prescription Wrong?

Why is my Eyeglass Prescription Wrong?

by Brian Chou, OD, FAAO, FSLS

  • November 16, 2022

You just got your new eyeglasses, but something feels wrong. What is going on? Rather than jumping to conclusions, you will want to consult your eye care professional. That way, you get specific advice for your individual situation. Often, your solution is simple and does not cost more. But read on to learn some possibilities why your glasses don’t work well.

In general, there is a range of eyeglass prescriptions that each patient may accept. For that reason, it is an oversimplification to suggest that there is only one “right” eyeglass prescription and everything else is “wrong”. There are many possible reasons why your new glasses may not feel right.

Insufficient adaptation

New eyeglasses commonly take 20 to 40 cumulative hours of wear before they feel normal. In the beginning, new glasses can alter your sense of space and make objects that are normally straight appear bowed. It can take longer to acclimate if you wear the glasses sporadically rather than for extended periods.

Certain eyeglass prescriptions are notoriously difficult to adjust to, including high lens powers, certain types of astigmatic corrections, and prescriptions addressing a significant asymmetry between the two eyes. Your eye doctor should indicate if this applies to you at the time your glasses are prescribed. In some cases, it is possible to get a better outcome with necessary contact lenses because they can bypass the optical side effects of eyeglasses. Your eye doctor should indicate if contact lenses may give you an improved outcome compared to eyeglasses when your eyeglasses are prescribed.

If you are unable to adjust to new eyeglasses — even after sufficient cumulative wearing time — your eye doctor may modify the eyeglass prescription to make the glasses more comfortable, yet this often comes at the expense of clarity. This is one compelling reason for filling your eyeglass prescription at your provider’s office. If your eyeglass prescription requires a remake, you do not risk having to pay additional fees for re-evaluation as there is alignment between creation and filling your prescription.

Incorrect fabrication or prescription error

There are instances where the laboratory unintentionally makes your eyeglasses different from what your doctor specified. The prescription should be within a range provided by the ANSI Z80.1-2015 tolerances, and this should get verified by the fabricating laboratory and/or dispensing optician. There are also instances where your eye doctor may write your prescription different from what was intended. For established eye care laboratories and doctors, fabrication and prescription mistakes are uncommon. But they do occur, as humans are involved. In these cases, your eye care professional can help make things right.

Frame adjustments and proper materials needed

A skilled optician can ensure that your eyeglass prescription is filled to maximize performance and aesthetic appearance. For example, extreme powers filled with poorly matched eyeglass materials can cause poor visual quality. If the eyeglass lenses are not centered, too far away or too close to the eyes, or the lenses are tilted too much or little, the vision may be blurry and uncomfortable. If the lens design does not match what the doctor intended, this can also lead to visual problems. For example, if your eye doctor specifies that you need a “near-variable focus” design such as the Shamir Computer lens, but you receive a general progressive lens design, you will not experience the vision that your doctor intended. Some warehouse and internet eyeglass enterprises tend to substitute product which may not match the prescribed materials and lens design, and this can yield suboptimal outcomes.

Day-to-day fluctuations in vision

Some patients test out differently from one day to another. If the evaluation for eyeglasses is performed when the vision is not representative, the visual performance with glasses will be suboptimal. In other words, if you get tested for eyeglasses when your eye focusing is at a peak or trough, your prescription may not work well for most of the time.

It is not always possible to identify causes of these day-to-day or “diurnal” fluctuations. But in some cases, your doctor can trace it to fluctuating blood sugar levels, dry eyes, irregular corneas (e.g., after radial keratotomy surgery) or developing cataracts. Please consult your eye doctor if any of these underlying causes are suspected.

Undetected eye disease and amblyopia

Reduced vision even with new eyeglasses can be due to eye disease such as macular degeneration, cataract, or keratoconus. For example, with keratoconus, glasses are usually ineffective at fully restoring vision. With keratoconus, custom scleral contact lenses are the mainstay for vision restoration. Sometimes subtle eye disease is detected by your doctor only after repeated attempts to improve vision with eyeglasses.

In about 1-2% of cases, reduced vision in one eye is due to amblyopia, or undeveloped vision which occurs during early childhood. This can occur if there is a sizeable asymmetry between how the two eyes focus, or from an eye turn or blockage of vision in one eye (e.g., cataract). For amblyopia to develop, the deprivation in vision occurs during early childhood. If diagnosed during this time, eye patching therapy can minimize the enduring reduction of vision in one eye.


ReVision Optometry is a referral-based practice in San Diego providing scleral contact lens services for patients with keratoconus and other complex eye conditions. To schedule, request your examination online or call our office at 619.299.6064.