Patients with high prescriptions, defined as prescriptions above +/- 4.00 diopters, require special consideration when selecting lens materials. The higher the prescription, the thicker and heavier the lenses will be. This can lead to problems with lens comfort, adaptation, and vision quality. Choosing the right lens material is essential for ensuring the best possible vision correction and quality of life for patients with high prescriptions. This article will examine the key factors to consider when selecting lens materials for high prescriptions and provide recommendations on the best options currently available.
What issues do patients with high prescriptions commonly face?
Patients with stronger prescriptions face several potential issues that need to be addressed through proper lens material selection:
- Thick, heavy lenses – As the power of the prescription increases, the edges of the lenses become thicker. This adds weight to the glasses, which can cause discomfort.
- Peripheral distortion – The increased thickness toward the edges of strong lenses can create distortion for peripheral vision.
- Aberrations – Optical aberrations like spherical aberration, chromatic aberration, and other image distortions are more likely with high power lenses.
- Adaptation issues – It may take time to adapt to the difference in weight and visual perception with new high prescription glasses. This adaptation period can cause dizziness, nausea, or headaches.
- Frame fit and cosmetic issues – The lenses may not fit well in standard size frames, being too thick to fit properly. Aesthetically, thick high power lenses are often undesirable.
Addressing these potential downsides is important for ensuring the best vision possible and good quality of life with high prescription glasses.
Key factors in choosing lens materials
Several factors should be considered when selecting an appropriate lens material:
Lens thickness
Choosing materials with low specific gravity and high refractive index can help minimize edge thickness. Lighter materials also reduce overall weight.
Optical clarity
Materials with good light transmission and low dispersion provide better optical clarity. This improves vision quality and reduces peripheral aberrations.
Scratch resistance
High index lenses can be more prone to scratches. Scratch-resistant coatings greatly improve durability.
Lens treatments
Special coatings and treatments like anti-reflective coating, oleophobic coating, tints, and photochromic options optimize lenses for each patient’s needs and environment.
Cost
Advanced lens materials and treatments add to the cost, so balancing performance and affordability is ideal.
Availability
Some specialized lens materials may not be readily available at all eye care providers. Ordering times should be considered.
Frame size and fit
Thinner, lighter lenses allow for better fit in standard frames. Smaller, rounder frames can also accommodate stronger prescriptions.
Overview of common lens materials
There is a range of lens materials available, from standard plastics to advanced high-index materials. Each has advantages and disadvantages for high prescriptions.
Plastic (CR-39)
CR-39 plastic is the most common, standard lens material. It is economical but heavier. For strong prescriptions over +/- 4.00 diopters, CR-39 is generally not recommended as the lenses become very thick and heavy. The material also suffers from higher chromatic aberration issues at high powers.
Polycarbonate
Polycarbonate plastic lenses are thinner and lighter than CR-39. They have good impact resistance, but lower scratch resistance. Optical clarity is also reduced compared to other materials. For prescriptions over +/- 6.00 D, polycarbonate may still be quite thick cosmetically. Specialty high-index lenses usually yield better optics and thinner profiles.
High-index plastics (1.67, 1.70, 1.74)
High-index plastic lenses are the most common choice for stronger prescriptions. With refractive indices from 1.67 up to 1.74, they offer a 20-40% thickness reduction over CR-39. Durability and optics are also improved. 1.67 index lenses work well up to prescriptions around +/- 6.00 D. For stronger powers, 1.70, 1.74 or glass lenses are better options.
Mid-index plastics (1.60, 1.56)
Mid-index lenses like 1.60 and 1.56 index trivex have refractive indexes between standard CR-39 and high-index plastics. They are 20-30% thinner than CR-39, but do not offer as much of a thickness reduction as higher index lenses. They have excellent impact resistance and good optics. Trivex also blocks 100% UV light. Mid-index lenses are good for prescriptions up to about +/- 4.00 D.
Glass
Glass lenses are actually the thinnest option for very high prescriptions above +/- 8-10 D. However, glass is much heavier than plastic. Extra anti-reflective treatments and scratch-resistant coatings are advised. Glass lenses are less prone to scratches and have excellent light transmission for optimal optics in strong powers.
Polycarbonate multifocals
For high prescription bifocals, lined multifocal, or progressive addition lenses, polycarbonate is often the material of choice. Lens thickness is minimized and polycarb has high impact resistance for safety. The optics are not compromised as severely in multifocals as in single vision lenses.
Recommendations for high prescriptions by power range
The best lens material options based on the range of the patient’s prescription are:
+/- 4.00 to 6.00 D prescriptions
– 1.67 high-index plastic lenses
– 1.60 or 1.56 index mid-index plastic
– Polycarbonate lenses possible but not ideal optically
+/- 6.00 to 8.00 D prescriptions
– 1.70 or 1.74 high-index plastics
– Glass lenses
Above +/- 8.00 D prescriptions
– Glass lenses
– 1.74 index plastic if available
– Polycarbonate lined multifocal or bifocal
Best options for high astigmatism
Patients with irregular astigmatism and prescriptions with cylinder values above 4.00 diopters also benefit from high-index lens materials. The best options include:
– 1.74 index plastic
– Glass lenses
– Contact lenses may also be preferable for some high/irregular astigmatism patients
Recommendations for lens treatments and coatings
Advanced lens treatments and coatings optimize vision and improve comfort. Recommended options for high prescription lenses:
- Premium anti-reflective (AR) coatings – Reduce glare and reflections, essential for strong lenses.
- UV blocking – Protect eyes from harmful UV exposure.
- Polarized lenses – Cut reflective glare, especially useful for outdoor use.
- Photochromic lenses – Change darkness in response to light levels to control brightness.
- Scratch-resistant coatings – Protect lens surfaces from scratches and wear.
- Oleophobic coating – Repels oil, smudges, fingerprints for easy cleaning.
- Tints – Can reduce outdoor glare and brightness sensitivity.
Tips for adjusting to progressive or bifocal lenses
For presbyopic patients requiring multifocal or progressive lenses, adaptation can be challenging at first. Here are some tips for easing the adjustment period:
- Start with lenses with a smaller near zone or corridor length to get used to the transition between distances.
- Practice focusing gaze just above the lower reading area when walking to avoid dizziness.
- When going down steps, keep head upright and eyes lowered to see steps clearly through the near zone.
- Turn head more deliberately toward objects at different distances to keep them in the correct viewing zone.
- Give yourself time to adapt to the feel of the lens vision – it can take days to weeks.
With practice and patience, multifocal lenses can greatly improve convenience and quality of life for those needing presbyopia correction.
Understanding pricing
Lens material and treatment choices can significantly impact the price of prescription glasses. Here are some factors affecting the cost:
- Lens material – High-index plastics cost more than lower index standard plastics.
- Treatments – Premium coatings like anti-reflective and photochromic add cost.
- Multifocals – Progressives cost more than bifocals and single vision.
- Lens size/power – Larger lens blanks for strong powers cost more.
- Brands – Brand name versus generic lenses affect prices.
- Provider – Cost can vary between different eye care practices.
Discussing budget constraints with your eye doctor is recommended to find the optimal balance of maximum vision performance at an affordable price. Prioritize key treatments like AR coating.
Frequently asked questions
Do high-index lenses have any disadvantages?
High-index lenses are less impact resistant. They also tend to be more prone to scratches and reflections without proper coatings. Cost is higher as well.
Can high astigmatism be corrected with glasses?
Yes, eyeglasses work very well for most cases of high and irregular astigmatism. Contact lenses may also be an option for severe astigmatism.
Do lens materials affect adaptation time?
Thinner, lighter lenses allow for faster adaptation typically. Polycarbonate can sometimes cause more distortion which may slow adaptation time.
How often do very strong prescriptions need to be updated?
Annual exams are important as vision can change rapidly with high myopia and presbyopia. Lens materials often need to be changed every 1-2 years with shifting prescriptions.
Can LASIK surgery help reduce dependence on glasses?
For some high myopes, LASIK can reduce dependency on glasses or contacts. However, residual refractive error often still requires correction with glasses or contacts after surgery.
Conclusion
Selecting the optimal lens material is crucial for high prescription eyeglasses. The thinnest, lightest lens that provides the clearest optics should be the priority. Glass, high-index plastics from 1.67 to 1.74, and polycarbonate multifocals are generally the best options today. With the right lenses and coatings tailored to their needs, patients with strong prescriptions can see clearly and comfortably. Consulting an eye doctor for personalized recommendations is key to successful vision correction.
