Recently, a trending topic on Weibo has caught the public’s attention: “Is there really a difference between glasses that cost 300 RMB and those that cost 3000 RMB?” The underlying concern seems to stem from fears that improper eyewear could harm our eyes.
To sum it up: cheap glasses aren’t necessarily a problem, but poorly fitted prescriptions can indeed cause harm.
The crux of the matter lies not in the price of the glasses but in the accuracy and appropriateness of the eye examination and prescription. Choosing glasses goes beyond just matching the degree; improper fitting can have long-term and far-reaching effects on eye health, potentially worsening nearsightedness and even triggering other eye diseases.
In this discussion, we will explore what to pay attention to during the fitting process, the risks of poor fitting, and how to minimize those risks through scientifically-backed fittings.
**Inaccurate Prescription Parameters**
One common issue with eye exams is that the measurements taken can be skewed, particularly during accommodation spasm when the eyes haven’t adequately relaxed. Generally, after a well-deserved break or a reduction in prolonged near-distance activities, nearsightedness levels can return to their authentic state. However, consistently wearing inappropriate lenses (like overcorrected ones) while accustomed to a stressed accommodative state can lead to pseudo-nearsightedness becoming true nearsightedness or an increase in nearsightedness.
Incorrect correction of farsightedness—such as undercorrection—can easily lead to conditions like esotropia and visual fatigue from near tasks. Similarly, improper astigmatism correction, such as inadequate power or wrongly oriented axes, can degrade visual quality.
In some cases, the precise prescription may not be the best parameter for fitting glasses. One must consider factors like the wearer’s adaptability, differences from previous lenses (if applicable), eye alignment (whether there’s strabismus), visual function (accommodation and convergence abilities), and reading habits to appropriately adjust the prescription for optimal comfort.
**Incorrect Pupil Distance and Optical Center Height**
When wearing glasses, it’s essential that the eyes look through the optical centers of the lenses. This demands accuracy from optometrists in measuring pupil distance and optical center height. If these measurements are off, it could misalign the optical center with the visual axis, potentially leading to strabismus in severe cases.
For nearsighted lenses:
– A pupil distance that’s too wide may result in exotropia.
– A pupil distance that’s too narrow can cause esotropia.
If one side of the lenses is higher than the other, or if the frame is warped leading to uneven heights, it may result in abnormalities in eye positioning and habitual tilting of the head while viewing.
**Improper Frame Tilt Angle**
Generally, individuals of East Asian descent have a frame tilt angle between 8° and 10°. If the tilt angle is too steep, it can create a situation where the actual optical power exceeds the prescribed degree, leading to overcorrection and subsequent visual fatigue. Additionally, lens tilt may create a cylindrical effect, causing images to appear “flattened,” especially pronounced with higher prescriptions.
The main culprits behind excessive tilt are mismatched frames and nose bridges. If a nose bridge is small or flat, larger frames might not stabilize well, causing the lenses to tilt forward. Loose or overly tight temple arms can also contribute to this issue.
**Inappropriate Lens Curvature**
The lens curvature angle typically ranges from 170° to 180°. Excessive curvature can cause vertical astigmatism, negatively impacting visual quality. Some trendy and aesthetically pleasing frames may not align with facial features and cause discomfort in wear.
**Improper Eye-to-Lens Distance**
If the eye-to-lens distance is too small, eyelashes may touch the lenses, potentially smearing oil on the inner surface or damaging the lenses. Conversely, too large a distance can disrupt the optical effect, impairing vision. In some cases, due to deformation or improper fitting of the temple arms, one lens may be closer to the eye than the other, causing blurriness, distortion, or eye fatigue.
Choosing adjustable nose pads rather than one-piece ones can help alleviate many of these distance issues.
**Improper Assembly Resulting in Lens Deformation**
Sometimes, due to production processes or improper assembly, lenses can become distorted, resulting in additional aberrations and even double vision, causing discomfort.
**Lens Wear and Tear**
Different brands of lenses have varying dispersive coefficients, refractive indices, and coatings. If lenses are severely worn, their light transmittance decreases, darkening vision. Higher dispersion levels can also degrade image quality, potentially causing visual blurriness or rainbow effects.
While high refractive index lenses can be thinner, they often come with lower Abbe numbers or increased dispersion. Fortunately, some manufacturers now offer materials that provide both high refractive rates and lower dispersion, offering thinner, clearer lenses.
What’s worse, our eyes have a certain degree of adaptability, which means we might quickly acclimate to discomfort, masking the long-term damage that ill-fitting prescriptions can inflict on our visual health.
In conclusion, whether one opts for 300 RMB or 3000 RMB lenses, price alone does not equate to professionalism. To obtain a pair of glasses that are “clear, durable, and comfortable,” it’s advisable to visit a reputable medical institution for a comprehensive exam. Accurate and suitable fittings combined with personal needs and expectations will yield the best results.
