Metropsis Visual Function Assessment


Precise tests of acuity, spatial and temporal contrast, colour and stereo vision

Metropsis is a complete test suite suitable for clinical, pre-clinical research, applied vision research, drug trials, screening, sports science and human factors research. The tests have been developed to investigate diseases of the eye and the brain, as well as changes in visual functions as a secondary effect of systemic disorders, such as cardiovascular diseases or neurological dysfunctions.

Guide Price: £13250

SKU: M0400

Visual Acuity

  • Visual Acuity - ETDRS Chart
  • Visual Acuity - Landolt C or Optotypes (with optional crowding bars)

Accurate, automatic measurements of near and far visual acuity are obtained with optotypes, using either ETDRS, the single Landolt ring or individual letters.  

Metropsis presents randomized optotypes faster than traditional visual acuity charts, and offers a wider range of optotype sizes. It eliminates any operator’s biases or mistakes made during the scoring procedure.

Default test protocols are preset and locked for quick and easy testing; however, the psychophysical and stimulus parameters are highly configurable, and can be unlocked for advanced users.

For advice on setting up your own protocols, please Contact our Staff Scientist. 


Visual Acuity ETDRS Chart

The benefits of the ETDRS chart are well known, and it's useful for quick and easy screening before performing more precise meaurements with other Metropsis protocols.

Metropsis implements ETDRS charts using the recommendations reported in Ferris et al. (AJO, vol. 94, 91-96, 1982).

It's extremely convenient to use - the experimenter notes the observer's responses directly onto a matching chart on the iPad.



  • Charts are automatically randomised and quickly presented.
  • The observer reads the letters out loud, just like the familiar chart test.
  • The experimenter records the observer's responses directly to the iPad, as they're read.
  • The test ends automatically when termination criteria are reached.
  • All the charts, responses and and acuity scores are securely saved to the iMac, and can be printed or emailed.

Visual Acuity with Landolt C (VAC)

The Landolt C test provides a more accurate test than the ETDRS chart. It's suitable for monitoring disease progression or the results of treatment, where the step size between lines in the ETDRS chart is too coarse to measure small changes.

The Landolt C is also a better option when testing illiterate observers or pre-readers, and to avoid possible criticism that some letters are harder to distinguish than others.

The VAC protocol measures visual acuity using the Landolt C as a Sloane optotype. The protocol uses a staircase procedure to change the size of the optotype according to the observer's responses.

The optotype appears in the centre of the screen in one of four orientations. The observer is instructed to indicate the perceived position of the optotype’s gap and press the corresponding button on the response box. For example, the correct response for the stimulus shown below is the TOP button. 

The stimulus stays on the screen for two seconds; the observer can answer from the moment the stimulus appears on the screen until two seconds after it has disappeared. Two tones are played during the test: one indicates that the stimulus has been presented and the other that the observer has provided their response.

When the experiment is complete, the full results are plotted, and visual acuity threshold is reported in arc min.


Visual Acuity with Optotypes

This test is similar to the VAC protocol, but the stimulus consists of a single letter instead of the Landolt C.  This alternative allows a more consistent comparison if the the experimenter wishes to relate visual acuity measured with Metropsis to thresholds obtained with standard acuity charts.


Visual Acuity with crowding bars (VACC)

The VACC protocol is similar to the VAC protocol described above, but measures visual acuity using the Landolt C or optotypes surrounded by crowding bars, as shown below.

The flankers act as distractors and create an inhibitory effect on the detection of the optotype’s gap, which provides a more sensitive test for amblyopia.



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