Prism Power Calculation — Feature Guide

Module: got2_lens_prism Works together with: got2_lens_slaboff (Vertical Imbalance / Slab-Off Advisor) Menu: Inventory → Configuration → Lens Power Pricing → Prism Power Calculation

This guide explains, in plain language, what this feature does, how every setting on the configuration screen changes what a patient gets charged, and exactly what happens on a Sale Order the moment someone clicks Update Prices. It is written for opticians, billing staff, and managers — no programming knowledge required. Technical readers will find exact file/line references in the companion engineering notes; this document deliberately leaves those out in favor of plain explanations and diagrams.

Table of Contents

1. The problem this solves
2. The big picture
3. Three ideas you need before anything else makes sense
4. Screen 1 — The Rule: every setting explained
5. Screen 2 — The V-Code List
6. Screen 3 — On the Sales Order (preview)
7. The Matrix, in detail
8. What actually happens when you click "Update Prices"
9. The Slab-Off Advisor partnership
10. Worked example, start to finish
11. Troubleshooting — "why does this line look wrong?"
12. Glossary
13. A note on the sibling "Add Power" feature

1. The problem this solves

Prism is a correction added to a lens to help the eyes work together — it is written on a prescription as an amount (in prism dioptres, the symbol Δ) and a base direction (which way the thick edge of the correction points: In, Out, Up, or Down).

Billing prism is not like billing sphere or cylinder power, for two reasons:

1. The amount does not decide the billing code — the way the lens is made does. A lens with prism ground straight into its surface bills one code (V2715). The same amount of prism achieved by grinding two lens halves at different angles and joining them ("slab-off") bills a completely different code (V2710). A stick-on plastic prism membrane bills a third code (V2718). None of those three codes says how much prism it covers — the description of V2715 is simply "Prism, per lens." So a price list built as "if the amount is X, charge Y" can never pick the right code, because the amount was never what decided the code.

2. Horizontal and vertical prism combine into one number, not two. If an Rx has 2.00Δ pointing outward and 2.00Δ pointing upward, that is one diagonal correction of about 2.83Δ — not two separate 2.00Δ corrections added together. Billing them as if they were separate would overcharge the patient by more than a third.

This feature replaces an older, simpler price list that got both of these wrong — it summed horizontal and vertical prism instead of combining them properly, and it only ever knew how to bill one code (V2715), so slab-off and Fresnel press-on prism could never be billed correctly, and their price could end up going to the patient as an unexplained $0 that nobody was actually on the hook for.

2. The big picture

There are two screens you configure, and one thing opticians do on every order:

• Prism Power Calculation (this module) — the price matrix. You set this up once per pricing scheme and rarely touch it again.
• Vertical Imbalance / Slab-Off Advisor (the partner module) — decides when slab-off is medically appropriate. It never sets a price itself; it hands its decision to the Prism rule, which is the only place money is calculated.
• On the order itself, nothing manual is required beyond entering the prescription and clicking Update Prices — the correct line(s), at the correct price, appear automatically.

3. Three ideas you need before anything else makes sense

3.1 "The amount picks the price step. The method picks the code."

Think of the price matrix as a table with rows and columns:

• Each row is a range of prism amounts (e.g. "1.12Δ to 2.00Δ"). This is purely a pricing decision you make — HCPCS billing codes don't define these ranges anywhere.
• Each column is a production method — how the lab actually put the prism in the lens. This is what the billing code cares about.

This is the schedule the system ships with. You can edit every number, add rows, add columns, or change which code a column bills — see Screen 1.

3.2 A blank cell is not a $0 cell

Look at the table above again: Slab-off has no price for 0.25Δ–1.00Δ, and Ground-in has no price above 6.00Δ. Those cells are intentionally empty — they are not zero. Nobody bicentric-grinds a quarter-dioptre of vertical imbalance, and no lab can grind 7Δ of prism straight into a surface without the lens edge becoming impractically thick. If a patient's numbers land on one of those empty cells, the system does not silently charge $0 — it charges nothing and tells you why (see Troubleshooting).

3.3 Horizontal + vertical = one diagonal number, not a sum

2.00Δ Out plus 2.00Δ Up is not 4.00Δ. It is one diagonal correction of 2.83Δ, exactly the way a 3-4-5 triangle's long side is 5, not 7. The system always does this combination correctly (unless you deliberately turn it off — see the Prism measured as setting), then rounds the result to the nearest quarter-dioptre before looking it up in the price table, because prescriptions are always written in quarters.

4. Screen 1 — The Rule: every setting explained

Open Inventory → Configuration → Lens Power Pricing → Prism Power Calculation and open (or create) a rule. The form is in three parts: header settings, matching-behavior settings, and the matrix itself (on its own tab).

4.1 Header — what this rule is and when it runs

4.2 Matching behavior — how an Rx becomes a price

This is the part of the form that actually decides how the math works, not just what the prices are.

4.3 Applies To — narrowing which orders use this rule

Three optional filters, all empty by default (meaning "every order"):

• Lens Type Categories — restrict to specific lens designs (Single Vision, Progressive, Bifocal, etc.). Leave empty; prism is billed the same regardless of lens design, so narrowing this is rarely useful.
• Lens Material / Index — restrict to specific materials. Leave empty unless a specific high-index material genuinely needs a different price schedule (note that very thin, high-index blanks can physically limit how much prism can be ground in — this setting exists for exactly that kind of exception).
• Lab / Supplier — restrict to orders going to a specific lab. Useful if different labs quote different slab-off/Fresnel prices.

Whatever you fill in here is checked against the specific lenses selected on the order — if none match, this rule is skipped for that order and, if no other Active rule applies, prism pricing doesn't happen at all.

5. Screen 2 — The V-Code List

A flat, read-only list view of the exact same matrix, one row per priced cell: Code · Method · Band · Descriptor · Price · Post as. This exists purely so you (or an auditor) can see every price at a glance without reading the grid — nothing here is editable; edit the matrix on Screen 1 instead.

6. Screen 3 — On the Sales Order (preview)

A live preview showing exactly what the built-in tester's numbers (on Screen

1. would produce on a real order: the base lens line, followed by one line per eye for whatever prism was priced, with the running order total. Use this to sanity-check a schedule change before it goes live — type a test prescription into the tester on Screen 1 and watch this preview update.

7. The Matrix, in detail

7.1 Reading and editing the grid

• Add Prism Band adds a new row (amount range).
• Add Method adds a new column (production method).
• Click into any cell's code or price to edit it directly.
• A hatched, greyed-out cell means "not offered" — click add inside it if you want to start pricing that combination.
• The small ✕ on a priced cell removes it — turning it back into "not offered," not into "free."
• Reset to Prism Schedule restores the original six-band, three-method schedule this system ships with, discarding any edits.
• Clear Prices sets every existing cell's price to $0.00\ast \ast without\ast \ast removingthecells—usefulifyouwanttokeeptheshapeoftheschedulebutre-priceeverythingfromscratch.Thisisdifferentfromdeletingcells:a$0 cell still means "offered, but currently free," while a deleted cell means "not offered at all."
• Post As, set per row: Line adds its own separate charge line on the order (the normal choice); Base instead rolls the amount straight into the price of the lens line itself, with no separate prism line appearing. Use Base if your practice prefers prism to be invisible inside the lens price rather than itemized.

7.2 What happens when a prescription is matched against the grid

Important: a Gap or an Unmatched result never "rounds up" to the next band that does have a price. If slab-off isn't offered below 1.12Δ, a patient at 0.50Δ genuinely gets no slab-off charge — the system will never invent one from a neighboring row.

8. What actually happens when you click "Update Prices"

This is the part most worth understanding if you're ever wondering "why does this number look different than I expected."

8.1 The order of operations

Several different pieces of pricing logic run, one after another, every time Update Prices is clicked. Prism pricing is deliberately the very last thing that runs, so nothing that happens earlier can accidentally overwrite or erase it.

One practical consequence worth knowing: because the insurance deductible/co-pay math runs before the fresh prism line exists, a prism charge that's large enough to change how much deductible room is left won't be reflected in that math until you click Update Prices a second time. This is a deliberate trade-off — prism has to run last so nothing can silently undo its price — but it does mean one click isn't always the final word if prism materially changes the insurance math.

8.2 Deciding which eyes get charged, and how

Every time prices are updated, each eye is resolved independently:

A small Prism Method field appears on the order, right next to each eye's prism entry, whenever an Active rule applies. Leaving it on the placeholder ("Auto") lets the system decide using the logic above — this is correct for the overwhelming majority of orders. Set it explicitly only when an optician needs to override the automatic choice (for example, choosing a Fresnel press-on for a temporary post-operative pair even though the amount would normally qualify for Ground-in).

8.3 Insurance vs. self-pay

By default, only insured orders are priced for prism — a legacy behavior this system deliberately preserved. If your practice wants to charge self-pay patients for prism too, that is a single site-wide technical setting (prism_price_cash_pay) that a system administrator can turn on; it is off out of the box precisely because switching it on changes what self-pay patients are billed, and that deserves a deliberate decision rather than happening automatically on install.

9. The Slab-Off Advisor partnership

Slab-off is different from every other kind of prism: it is never written directly on a prescription. It's a correction the lab has to add because the two eyes' lens powers are different enough that reading through them naturally creates unwanted vertical prism — nobody prescribes it as a number, it's detected.

That detection is a completely separate screen — Vertical Imbalance / Slab-Off Advisor — which watches the Rx and, when the imbalance crosses a clinical threshold, shows the optician an amber banner on the order:

The division of labor is strict and deliberate:

• The Advisor only ever detects and asks. It is never allowed to invent a price.
• This module is the only place slab-off actually gets priced — the moment the optician clicks Add, the placeholder charge is immediately repriced using whatever the Slab-off column of the active matrix says for that amount of imbalance.
• If the matrix's Slab-off column has no cell covering that specific amount (a real Gap, per §3.2), the charge stays at its fallback price and a note is logged — the schedule genuinely doesn't offer that amount of slab-off, and the system doesn't invent a number to fill the space.
• On the Advisor's own configuration screen, a small read-only panel shows which rule and which price currently apply to whatever the built-in tester's numbers work out to — purely informational, so whoever is reviewing the Advisor's settings can see at a glance whether prism pricing is actually wired up to catch what it detects.

10. Worked example, start to finish

A patient's prescription:

Step 1 — combine each eye's prism into one number (§3.3):

• OD: 2.00Δ Out + 2.00Δ Up → 2.83Δ, diagonally, at 45°
• OS: 0.50Δ In alone → 0.50Δ

Step 2 — round to the nearest quarter-dioptre:

• OD: 2.83Δ → 2.75Δ
• OS: 0.50Δ → 0.50Δ (already exact)

Step 3 — decide the production method for each eye (§8.2):

• No manual override, no slab-off accepted for either eye, neither amount is above the Ground-in ceiling → both eyes use Ground-in.

Step 4 — match each amount against the matrix:

• OD 2.75Δ falls in the 2.12Δ–3.00Δ row → Ground-in column → V2715, $24.00
• OS 0.50Δ falls in the 0.25Δ–1.00Δ row → Ground-in column → V2715, $18.00

Step 5 — the order:

The two prism lines total **$42.00\ast \ast ,and—thisisthepartthatmattersforbilling—bothlinescarryareal\ast \ast Patient\ast \ast amount,not$0.00, so the correct tax gets calculated and the charge is actually collectible from the patient rather than sitting in the order total unexplained.

11. Troubleshooting — "why does this line look wrong?"

"There's no prism line on the order at all, even though prism is on the Rx."

Walk through, in order:

1. Is there an Active rule? Check Screen 1 — if the status shows Draft, Archived, or Reference, nothing prices. Only Active rules price anything.
2. Does the rule's Effective From/To cover the date the order was placed (not today's date — the order's own date)? A rule that starts "today" will not price an order placed yesterday.
3. If you just changed the Effective From/To to fix #2 — that alone is often not enough for an already existing order. The system needs to be told to re-check that specific order (ask a system administrator to run a recalculation on it) — otherwise it stays stuck with its old, blank answer indefinitely, even though a brand-new order created right now would match the rule correctly.
4. Is the order cash-pay (no insurance carrier)? By default, prism only prices on insured orders — see §8.3.
5. Does the amount land on a Gap (§3.2)? Check the Matrix tab for a hatched cell at that amount/method combination — if so, this isn't a bug, the schedule genuinely doesn't offer that combination.

"The prism line is there, but it shows $0.00 for the patient."

This was the exact problem this module was built to fix. If you're still seeing it, it almost always means the old pricing path fired instead of this one — which happens only when no Active rule matched the order (see the checklist above). Once an Active rule genuinely covers the order, every prism line this system creates carries a real patient amount, not $0.

"I got a technical error message (RPC_ERROR) when changing a setting on the Rule screen."

This was a real bug in an early version of the Matrix editor — changing an unrelated setting (like Rx states) while band/method rows already existed could trigger a server error. It has been fixed; if you see it again, it's worth reporting rather than working around.

"The grid on Screen 1 looks read-only — I can't type into it or see the Add buttons."

This was also a real, now-fixed bug — an internal permissions flag was accidentally locking the whole grid. If a specific rule still shows this, its Status may be Archived or Reference — those are intentionally read-only. An Active or Draft rule should always be fully editable.

12. Glossary

13. A note on the sibling "Add Power" feature

Under the same Lens Power Pricing menu you will also find Add Power Calculation — a separate feature that prices the reading add (bifocal, trifocal, and progressive add-power surcharges) using a similar row/column matrix idea. It is not covered by this document and has no functional relationship to prism pricing — the two features share only the same parent menu and the same underlying "round to the nearest quarter" logic. If you need to configure add-power pricing, look for its own guide.