Converting existing non-prescription sunglasses into a pair with corrective lenses is often achievable. This process involves removing the original lenses and replacing them with new ones that incorporate your specific vision prescription. The feasibility of this conversion relies heavily on the physical characteristics and design of the original frame structure. Understanding these initial limitations is the first step in successfully adapting a favorite pair of shades.
Assessing Frame Suitability for Prescription Lenses
The primary factor determining a frame’s suitability is its curvature, often called the base curve or wrap factor. Frames with a flatter profile are generally easy to adapt for prescription lenses, as they minimize optical issues. High-wrap frames, common in many sports or fashion sunglasses, have a greater base curve and present significant challenges for installation.
High-wrap frames introduce distortion, especially for individuals with stronger prescriptions or high astigmatism corrections. When a corrective lens is wrapped tightly around the face, the angle at which light passes through the lens edge changes dramatically. This angular change can cause objects to appear curved or tilted, sometimes referred to as the “fishbowl effect.”
Specialized digital lens technology can compensate for this distortion, but its effectiveness decreases with very strong prescriptions or extreme curves. Experts recommend keeping the astigmatism correction (cylinder value) below +/- 1.50 for high-wrap styles to maintain sharp vision. Some manufacturers offer frames that look like wraps but utilize a flatter lens base curve to accommodate higher prescriptions without distortion.
The frame material also plays a role in the conversion process and overall durability. Metal and durable plastic frames must withstand the pressure exerted by optical lab equipment when new, custom-cut lenses are pressed into place. Frames made of thin or brittle materials risk cracking or breaking during installation. Opticians often recommend against converting frames that show signs of stress or are in poor condition.
Understanding the Conversion Process
Once the frame is suitable, the conversion requires precise technical steps performed by a professional optician or specialized optical lab. First, you must provide the lab with a current, unexpired vision prescription from your optometrist. This document must include your sphere, cylinder, and axis values to ensure the new lenses provide the correct vision correction.
Accurate measurement of the pupillary distance (PD), the distance between the centers of your pupils, is necessary. Even more critical for custom sunglass frames is determining the optical center (OC) height. The OC is the specific point on the lens that provides the clearest vision without prismatic effects.
These measurements are taken while you are wearing the specific frame to account for its unique tilt and wrap, ensuring the lens aligns perfectly with your eye. If the PD or OC is measured incorrectly, the wearer may experience eye strain or blurred vision. The physical conversion then moves to the lab, where the old lenses are removed and the new prescription lenses are cut to match the frame’s exact groove.
Essential Sunglass Lens Options
Choosing the correct lens material impacts both safety and final thickness. Polycarbonate and Trivex are popular choices because they are highly impact-resistant, making them standard for sports and safety eyewear. Trivex offers slightly better optical clarity than polycarbonate while still providing high impact protection.
For individuals with higher prescriptions, high-index plastic is recommended because it bends light more efficiently, allowing for a thinner and lighter lens edge. All quality prescription sunglass lenses should offer 100% protection against both UVA and UVB ultraviolet rays. A UV400 rating ensures the lenses block wavelengths up to 400 nanometers, covering the full spectrum of harmful radiation.
Polarization is a beneficial feature that employs a chemical filter to selectively block horizontal light waves. This filtering substantially reduces glare from flat, reflective surfaces like water, snow, or roads, improving visual comfort and clarity. While polarization enhances vision, it must be combined with a dedicated UV-blocking feature, as it does not automatically provide UV protection.
The color of the tint affects how light is filtered and is chosen based on personal preference or activity needs. Gray tints provide the most natural color perception. Brown or amber tints enhance contrast, making them suitable for driving or golf. Applying an anti-reflective coating to the back surface of the lens is also recommended, as it prevents light from reflecting into the eye, maximizing visual clarity.
Cost Factors and Warranty Implications
The final cost of converting sunglasses is influenced by several factors, often making the process more expensive than anticipated. High-powered prescriptions and the selection of specialized materials, such as high-index plastic or premium polarized lenses, are significant cost drivers. Brand-name lens designs and the advanced digital surfacing required for high-wrap frames also add to the overall expense.
The expense of the custom lenses alone can frequently be comparable to or exceed the cost of purchasing a new, complete pair of budget-friendly prescription sunglasses. A major consideration is the frame’s warranty, as using a third-party optical lab to replace the original lenses can sometimes void the manufacturer’s warranty. Manufacturers often state that any alteration to the frame voids the warranty for defects.
There is also a risk that the existing frame may break during the lens installation process, especially if the frame is old or brittle. Because the frame is customer-owned, the optical lab is typically not responsible for replacing the frame if it breaks during the custom lens cutting or mounting procedure.