This sounds obvious — but many buyers either use an old prescription or order based on a rough recollection of their power. Your eyesight can change meaningfully year to year, and ordering glasses with an outdated prescription means you'll be wearing the wrong correction from day one.

A good prescription should be no more than 1–2 years old. It should clearly mention your SPH (sphere), CYL (cylinder), AXIS, and ADD values (for bifocal or progressive lenses). If you haven't had an eye test recently, most cities in India have walk-in optometry clinics where you can get checked in under 30 minutes — often for free or for a nominal fee.

Frames that look beautiful on a model may sit entirely differently on your face. The three numbers printed on the inside of most frames — for example, 52-18-140 — tell you the lens width, bridge width, and temple (arm) length in millimetres. If you have a pair of glasses you already love the fit of, find those numbers and use them as your baseline.

Separately, know your Pupillary Distance (PD) — the measurement in millimetres between the centre of your pupils. This is critical for optical accuracy; a PD that's even 2mm off-centre can cause eye strain and distorted vision. Your optometrist will usually have it on file. Alternatively, there are free mobile apps that can measure it using your phone's front camera.

Reputable online optical stores give you several lens choices when you enter your prescription — and the differences between them genuinely matter for your daily comfort. Here are the main options you'll typically encounter:

Lens index (1.5, 1.56, 1.61, 1.67, 1.74) determines thickness. Higher prescriptions — anything above ±4.00 — benefit significantly from a higher-index lens, which is thinner and lighter. For low prescriptions, a standard 1.5 index is usually fine.

Coatings are where most buyers under-invest. An anti-reflective (AR) coating is nearly non-negotiable if you spend time on screens or drive at night. A UV coating protects your eyes from sun damage. Blue light blocking lenses reduce eye strain for heavy screen users. Photochromic lenses darken automatically in sunlight — great if you move between indoors and outdoors frequently.

Prescription glasses are a medical device — if they're wrong, you can't simply ignore it. Before you pay, make sure you understand the seller's policy on three things:

Power guarantee: Does the store offer a free remake if the prescription is dispensed incorrectly? Reputable sellers do. This is your most important protection.

Frame exchanges: What if the frame doesn't suit you as well as you hoped? Look for stores that allow a trial period or offer at least one free exchange. Some stores in India also offer a home trial service in select cities.

Lens warranty: Scratches happen. A basic warranty against coating peel or manufacturing defects (usually 6–12 months) is a sign the seller stands behind their product quality.

Prescription eyewear isn't a commodity purchase — you're trusting a store to accurately manufacture a medical product to your exact specification. It's worth spending two minutes checking a few signals of reliability before you buy.

Look for a store that has qualified opticians or optical technicians available — either via chat, phone, or email. If you have doubts about your prescription or which lenses to choose, you should be able to ask a real expert, not a chatbot. Also check customer reviews specifically for prescription accuracy and post-sales support, not just frame aesthetics.

A GST-registered business, a clear physical address, and visible contact information are baseline signals of a legitimate operation in India's growing online eyewear market.