The D Chart is a new clinical test that has been developed by researchers in Glasgow to assess the degree and location of metamorphopsia (distortion) and field loss in the central visual field.
Currently the most common method of detecting and monitoring changes in central visual field function is the Amsler chart, however, this method is not quantitative and largely relies of subjective responses and the interpretation skills of a practitioner.
Other clinical tests that measure metamorphopsia can be expensive, have limitations in terms of patient level of visual acuity and do not always provide reliable and accurate mapping of visual distortions within the central visual field. The lack of information regarding the central visual field leads to difficulties for clinicians in deciding if macular disease is progressive, and whether or not surgical or medical intervention is required. Quantifying the amount and location of distortion within the macular region will allow clinicians to determine which patients would benefit from treatment and allow changes in central vision to be monitored following surgical or pharmaceutical intervention.
The D-Chart offers a simple and effective alternative method of measuring metamorphopsia. Details of the development of the card based test and some clinical outcomes are provided in a recent publication (McGowan et al. 2015). In addition to metamorphopsia, the chart also offers a straightforward method of mapping areas of scotoma in the central visual field.
The D Chart was initially developed as a series of cards similar to LogMAR acuity cards. The examiner turned over each card in the series to measure the level of distortion in all the sampled areas of the central visual field. This provided useful information but swapping between cards in the series and data recording made the process quite time intensive. To overcome this problem a new PC based version of the D Chart has been developed. This has resulted in the measurement time being significantly reduced and additional features and functionality have also been added.