Frame and lens are different sales
A frame is stock you hold; lenses are made to a prescription and ordered in. Billing them as one line hides the margin on each and makes a later query awkward. Separate lines show the customer what they are paying for, and let you see which side of the business actually earns — which in most optical shops is not the side owners assume.
The prescription belongs on the record
Power, axis, cylinder, addition and pupillary distance decide what is ordered, and a slip that goes missing means a remake at your cost. Recording the prescription against the customer means it is there when they return in a year, when the lens supplier queries an order, or when the customer wants a second pair to the same power.
Order, advance and collection
Between choosing and collecting there is an order with a date and an advance. Recording the advance against the party means the balance due on collection is correct and visible, rather than being reconstructed from a slip. The customer collecting also gets an invoice showing both, which prevents the conversation about what was already paid.
The number to watch
Remakes as a share of orders. Every remade lens is your cost, and the causes are few — a prescription transcribed wrongly, a measurement taken hastily, a supplier error. Recording orders properly makes the pattern visible, and it usually turns out to be one step in the process rather than bad luck.
Repeat business is the whole model
An optical customer returns — for a second pair, for a change of power, for the family. That makes the customer record more valuable here than in most retail, because it holds their prescription history, what frame they chose, and when. A shop that can open a returning customer and see all of it converts a routine visit into a considered sale, and it can prompt a recall when a prescription is a year or two old. Shops working from slips lose that entirely.