Reading the letters is not always seeing well: cataract and contrast

1 · The familiar eye chart

The letters from the eye test can still be read

This is the letter chart from any eye test: black on white, each row smaller. Switch on the simulated cataract: the letters lose some crispness, but they can still be read. That is why someone with a cataract can “see the letters well” and still notice that their vision is worse.

Eye chart with black letters on white, from larger to smaller. Every row reads clearly.

Approximate simulation: the veil mimics the light scattered by a cloudy lens.

2 · Same size, less contrast

Seeing well is not just reading small letters

Here everything is the same size: only the contrast changes, row by row. This is what contrast sensitivity tests measure, and it is closer to what daily life demands.

Four rows of letters and of circles with lines, all the same size and each row with less contrast. Without the veil all four rows can be told apart.

Approximate simulation: the veil mimics the light scattered by a cloudy lens.

3 · Oncoming headlights

That is why night driving is often the first thing to become difficult

At night contrast is already low. When headlights approach, a cataract turns their light into a veil and halos that cover everything around them. Try the three states and watch the pedestrian.

A road at night with an oncoming car and a pedestrian in dark clothes crossing: the pedestrian can be seen.

Approximate simulation: the veil mimics the light scattered by a cloudy lens.