PelliRobson

Pelli-Robson is a clinical chart used to measure contrast sensitivity, the ability to detect differences in luminance that separate an object from its background. It was developed by Pelli and Robson and is widely used in ophthalmology and optometry to assess visual function beyond standard acuity.

The chart presents letters in triplets of equal size, arranged across a series of contrasts. Each triplet shares the same contrast, with the contrast level decreasing along the line. The patient reads the letters aloud, and the test proceeds until the observer makes an error on a triplet. The result is reported as a log contrast sensitivity (logCS) score, reflecting the lowest contrast at which letters can be reliably recognized. Higher scores indicate better contrast sensitivity.

Pelli-Robson testing is commonly used to evaluate visual function in a range of conditions, including cataracts, glaucoma, macular disease, diabetic retinopathy, and amblyopia. It is valued for being quick to administer, relatively easy to standardize, and less dependent on letter size or overall visual acuity than some other tests. The score can help monitor disease progression, assess impact of treatment, and relate to real-world tasks such as reading in low-contrast environments.

Limitations include sensitivity to lighting and glare, the need for proper chart luminance and distance, and variability with age and cognitive factors. Results should be interpreted in the context of the patient’s overall visual function and other ophthalmic measurements, rather than in isolation.