DRAFT: clinical wording pending Dr van der Westhuizen review
Dr Dean van der Westhuizen
Ophthalmologist · Mbombela

Central Distortion Screen

A clinic screening aid for metamorphopsia, inspired by published dot-chart (D-chart) methods. It maps where in the central field the patient sees distortion, and how coarse a pattern still looks distorted.

How to use this

You (clinician) do:

  1. Set up the laptop once: match the green bar to a bank card (step 1 below).
  2. Seat the patient about 40 cm from the screen (roughly a forearm's length), wearing their reading glasses. Room lights on, no glare.
  3. Choose the eye to test. Ask the patient to cover the other eye with their palm.
  4. Read the instruction on screen to the patient. Click the segments they point out, or let them click.
  5. Press Next (or Enter) after each pattern. When the eye is finished, test the other eye, then save the PDF.

The patient does:

  1. Keeps one eye covered and keeps the head still, at the same distance.
  2. Looks only at the red centre the whole time. Does not look around at the pattern.
  3. While looking at the red centre, notices any part of the pattern that looks wavy, bent, missing, blurred or fainter, and points to it (or clicks it).
  4. Says "all even" if everything looks regular. Then the next pattern appears.

Each eye takes about 2 to 4 minutes. There are three rings (near the centre, middle, outer). The squares start close together and spread out if distortion is still seen.

1. Set up this laptop (once only)

Hold any bank card flat against the screen, over the green bar. Drag the slider until the green bar is exactly as wide as the card. This lets the pattern show at the correct size on this screen. The laptop remembers it, so you only do this once per laptop (redo it if you change screen or zoom).

Viewing distance: 40 cm is about a forearm's length from the eye to the screen. Keep the patient at this distance for the whole test. If the outer ring does not fit on a small screen, sit the patient a little closer and change the number below to match.

Room lights on, screen brightness high, glare-free. Patient wears near correction. Nothing entered here is stored or sent.

2. Choose the eye to test

Start with either eye. Ask the patient to cover the other eye with their palm (not pressing on it).

Results

How to read these results (draft)

  • 0 means the patient did not report any distortion.
  • Higher scores mean distortion was seen in more segments, or was still seen when the squares were spread out (more marked distortion).
  • Total score adds all 24 segments equally. Centre-weighted score counts the central ring three times and the middle ring twice, so changes close to fixation stand out more.
  • Heat map: pale means none reported, yellow means distortion only with closely packed squares, orange to red means distortion even with widely spaced squares.
  • Over time: compare the same eye from visit to visit, on the same laptop calibration, at the same viewing distance and with the same fixation target. A rising score or a heat map that spreads or reddens may suggest change and is worth a closer look. Small changes can come from attention, fixation or lighting.
  • These numbers are not comparable with licensed D-chart software results, and this screen is not a diagnosis. Please interpret alongside the clinical examination and imaging such as OCT.

Score bands (none, mild, moderate, marked) are provisional and pending Dr van der Westhuizen's review.

Please note

This is an independent educational and clinic screening aid. It approximates published D-chart methods on a general-purpose screen. It is not equivalent to licensed D-chart software or a regulated home monitoring device, and it is not a diagnosis. Results depend on screen size calibration, viewing distance, fixation and lighting. Interpret alongside clinical examination and imaging (e.g. OCT).

How scoring works: each ring is split into 8 segments. Patterns run from fine (densely packed squares) to coarse. For each segment we record the coarsest spacing (in degrees) still marked as distorted. The total score is the sum across all segments; higher means more widespread or more marked distortion. Zero means no distortion was reported.