Narrow vs. Wide Corridor Progressive Lenses: Corridor Length, Fitting Height & Peripheral Swim

In every progressive lens, the vertical channel connecting the upper distance zone to the lower reading circle is called the Progressive Corridor. Along this channel, power gradually increases from zero addition to your full reading addition (e.g. +2.00D Add).

Corridors are engineered in specific millimeter lengths: Short/Narrow (11mm – 13mm), Regular (14mm – 15mm), and Long/Wide (17mm – 19mm).

Optical physics dictates that you cannot create a smooth power increase along a vertical corridor without generating unwanted surface astigmatism in the lateral periphery. This is governed by Minkwitz's Theorem:

$$\text{Rate of Lateral Astigmatic Growth} = 2 \times \frac{\text{Add Power}}{\text{Corridor Length}}$$

This fundamental theorem reveals that if you compress the corridor into a very short 11mm space to fit a trendy narrow frame, the rate of peripheral astigmatism doubles! The corridor becomes narrow, and any slight eye movement into the periphery triggers intense, nauseating visual 'swim'.

To ensure a wide, effortless intermediate and reading corridor:

• Choose frames with a vertical lens depth (B-measurement) of at least 30mm to 36mm.
• Ensure a minimum Fitting Height (Segment Height) of 18mm to 20mm from the center of your pupil down to the bottom inside bevel of the frame.
• Utilize wide-corridor backside freeform surfacing (ELLASUV Progressive Series), where custom digital algorithms push peripheral astigmatism into unreachable lateral frame corners.