Comparative reliability of Pelli-Robson and Lea number chart for contrast sensitivity measurement

Alina Firdous, Ayesha Sarfraz


Objective: The objective of the study was to find reliability of Lea contrast sensitivity chart and its comparison with Pelli-Robson chart taking the latter as gold standard.

Method: Contrast sensitivity was measured with Pelli-Robson and Lea number contrast sensitivity chart. Study was conducted on 50 subjects having 6/6 visual acuity and no ocular disease which affect contrast sensitivity. To check reliability, tests were performed twice with six week interval on same individuals under same conditions.

Results: Contrast sensitivity tested with Pelli-Robson chart showed that right eyes of 92% subjects and left eyes of 94% individuals had same contrast sensitivity between both visits. Reliability of Lea contrast chart had been found low for both eyes of all fifty individuals using standard testing protocol. With Lea contrast chart, 40% subjects presented different results between both visits. Right eyes of 60 % individuals had same contrast level between both visits. Left eyes of 58% had same values between 1st and 2nd visit with Lea chart.

Conclusion: Pelli-Robson chart is more reliable to use in clinical practice. Lea contrast chart has relatively less test-retest repeatability than PR chart hence less reliable. Normal values are 1.65log and 1.25% with PR and Lea chart respectively. 

Key words: Contrast sensitivity, Pelli-Robson (PR) chart, Lea contrast chart, Repeatability.

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