Is −4.00 eyesight bad?

−4.00 eye prescription, how bad is that?

On the usual scale it is moderate. That is the moderate band (−3.25 to −6.00): the sharp zone ends inside arm's reach, so lenses are part of getting dressed. The number says how far you see without lenses, nothing about how healthy the eye is: a −4.00 eye with the glasses on typically reads a full 20/20 line, and every quarter step either way moves the bare-eye horizon a little.

Where does the blur start at −4.00?

Bare-eyed at −4.00, everything closer than 25 cm is sharp edge to edge. Right at 25 cm the edges start to soften, and past it detail fades rather than disappearing. That horizon is nearer than a phone held normally (30 cm), so nothing on the everyday list is sharp without lenses.

The arithmetic is one line: 100 divided by the number gives the sharp distance in centimeters. 100 ÷ 4.00 = 25 cm. Every quarter step on the paperwork moves that horizon, which is why the pages either side of this one read differently.

What glasses number for a computer screen at −4.00?

A lens that focuses exactly at a 60 cm screen would be about −2.25 (the full number less 1.67). The EndMyopia starting point for a close-up pair is −2.75, the full number less 1.25, which leaves the screen just inside the sharp range with a little blur at the far edge.