Convergence Test (Near Point)

What it measures

This test estimates your near point of convergence (NPC) — the closest distance to your nose at which your eyes can keep a single target single before it splits into two. A receded (more distant) near point is the hallmark of convergence insufficiency, a common cause of eye strain, blurred or double vision, and difficulty when reading at close range.

How it works

You focus on a small, high-contrast target on the screen and slowly bring the screen straight toward the bridge of your nose, keeping the target as a single image for as long as you can. As the target gets very close your eyes can no longer converge enough to fuse the two images, so the single target suddenly splits into two — this is the 'break' point. You note how far the screen is from your eyes at that instant and set a slider to that distance. Optionally, you can pull the screen back out and mark the 'recovery' point where the two images merge back into one. The break distance is then compared with typical NPC values used in eye care.

Tips for an accurate result

• 1Use the calibration card as a ruler — The on-screen card is 85.6 mm wide, about 8.6 cm. Holding a real bank card alongside the screen gives you a quick physical reference for estimating the break distance.
• 2Keep the target small and sharp — A fine detail is easier to see double than a large blob. Focus on the smallest feature of the target so the split is unmistakable.
• 3Repeat a few times and average — Clinicians take several measurements because the break distance drifts a little with fatigue and concentration. Retake the test a few times and use a typical value rather than your single best try.