Distance, near, computer vision: why a single measurement isn't enough anymore

The classic measurement protocol for a progressive lens cross-checks two positions: distance vision (straight gaze, at infinity) and near vision (lowered gaze, reading distance, typically 33 to 40 cm). This protocol still holds — but it was designed at a time when "near vision" mostly meant reading a book or a newspaper.

For a good number of wearers today, the position used most in daily life is neither one: it's the computer screen, at an intermediate distance (often 50 to 70 cm) and with a gaze angle noticeably less pronounced than for reading a book held in the hand.

Why this changes centering

The pupil drops progressively as the gaze moves from distance to near vision — this is known as pupil lowering. The closer the fixation distance and the more pronounced the gaze angle, the greater this drop. A client who spends their day in front of a screen at 60 cm doesn't have the same pupil drop as when reading a book at 35 cm: calibrating the progression corridor on the reading measurement alone can shift the intermediate vision zone away from where the gaze actually rests all day long.

What a third measurement adds

Adding a measurement taken in the client's actual screen-work posture — same distance, same gaze angle as at their usual workstation — provides an extra reference point for determining the corridor height best suited to their dominant use, in addition to (not instead of) the classic distance and near measurements.