Lens Inventory for an Optical Shop: What 4,619 Eyes Say About What to Stock

Every optical shop has money sitting in lenses that will not sell this year. Nobody knows exactly which ones, because the question is never asked in a form that has an answer.

So I asked it of our own data. Four years of prescriptions at our own shop — 2,951 prescriptions, 4,619 eyes, September 2022 to September 2026. Here is what actually walked through the door.

Where the powers actually are

Sphere, both eyes pooled:

Two numbers matter.

85.4% of eyes sit between −3.00 and +2.00. Half the shop's work is in one narrow myopic band, and nearly a quarter is low plus — reading adds and early presbyopes.

0.5% of eyes are beyond ±4.00. Twenty-three eyes in four years. That is roughly one every nine weeks.

Now the cylinder:

86.5% of eyes need 1.00 of cylinder or less. Above 2.00, you are at 3.3% — and above 4.00, eight eyes in four years.

And the add, which decides how much of your stock needs to be bifocal or progressive:

36.9% of eyes carry an add, and three-quarters of those sit in the 1.75–2.50 band.

What this means for money

Take the naive approach: stock every sphere from −6.00 to +4.00 in 0.25 steps, cross it with cylinder 0.00 to −2.00, and you are holding something like 350 combinations per index-and-coating. Do that for four index/coating pairs and you have 1,400 lines of stock.

Now overlay the distribution. Roughly 85% of your fittings land in maybe 15% of that grid. The rest is capital in a drawer.

The practical read from this data:

• Stock deep in −0.25 to −3.00 with cylinder up to 1.00. That single rectangle covers most of what you will fit. Run out here and you lose same-day delivery on your most common job.
• Stock thin above ±4.00. One eye every nine weeks does not justify shelf stock. Order it per job and quote the lab turnaround honestly.
• Cylinder above 2.00 is order-to-job. 3.3% of eyes, and the customer is already expecting a wait.
• Roughly a third of your lens value should be add-capable. Not half, not a tenth — measure it, because this is where the ticket size is.

Why the stock module gets abandoned

Now the part that has nothing to do with distribution and everything to do with software.

A frame is easy. One model, one colour, one size, one SKU, one unit. Any billing package handles it.

A lens needs four attributes before you have identified it:

1. Index — 1.50 (CR-39), 1.56, 1.60, 1.67
2. Coating — uncoated, AR, blue-cut, photochromic
3. Power — sphere and cylinder, in 0.25 steps
4. Type — single vision, bifocal, progressive

If your software models lenses as items, you must create one item per combination. One index crossed with one coating already runs past a hundred entries. Four index/coating pairs and you are staring at four figures.

This is the single most common reason an optical shop's stock module is abandoned three months after go-live. Not because the owner lost interest — because nobody can maintain four thousand item masters by hand, and a stock count that is wrong is worse than no stock count.

Software built for opticals treats index, coating and power range as fields on one item, not as separate items. You enter the power at billing and the right stock decrements. The master list stays in the dozens.

When you evaluate software, this is the question: show me lens stock displayed by power range. Not a list of items — a view of powers. If the answer is a scrolling item list, the module will be dead by March.

Running this on your own data

The whole point is that my distribution is not yours. If your prescriptions are in a system, the query is straightforward — pool both eyes, band the sphere, count.

What you are looking for:

• Which band holds half your volume. Stock that one deep.
• Where the tail starts. Find the point past which you see fewer than one fitting a month, and stop stocking beyond it.
• What fraction carries an add. That sets your progressive and bifocal buy.
• Cylinder above 2.00 as a percentage. Almost certainly small enough to be order-to-job.

If your prescriptions are in a register rather than a system, that is the finding: you cannot answer the question at all, and you are buying stock on memory.

The second-order benefit

Once powers are structured data rather than handwriting, a second thing becomes possible: you can see which powers have not moved. Not "what is in stock" — every system does that — but "what has been in stock for eleven months."

That is the number that changes buying behaviour, and it is invisible in a register.

FAQ

How many lens powers should an optical shop stock? Fewer than most shops do. In four years of our own data, 85% of eyes fell between −3.00 and +2.00 sphere with cylinder of 1.00 or less. Stock that rectangle deep and order the rest per job — but measure your own distribution first, because it varies by locality.

Should I stock lenses above +4.00 or below −6.00? Probably not. Those bands together were 1.6% of eyes in our data — roughly one fitting every few weeks. The customer is expecting a wait on an unusual power anyway.

How do I stop my lens item master running to thousands of entries? Do not create one item per power. Index, coating and power range should be fields on a single item, with the power entered at billing. Software that forces one SKU per combination is why most optical stock modules get abandoned.

What percentage of lenses need a near add? In our data, 36.9% of eyes carried an add, and 25.7% of all eyes sat in the 1.75–2.50 band. That is roughly a third of your lens buying that has to be add-capable.

Does coating change how I categorise a lens? For stock purposes it is an attribute, not a separate product line. For GST it changes nothing either — an AR, blue-cut or photochromic lens is still a spectacle lens under HSN 9001 50. Full rate reference here.

Figures are aggregate counts from 2,951 prescriptions recorded at one Indian optical shop between September 2022 and September 2026. No customer information is published — only totals by power band.