Aims To assess chloroquine (CQ) toxicity by visual field testing, multifocal electroretinography (mfERG) and measurement of retinal nerve fibre layer (RNFL) thickness in patients with rheumatoid arthritis (RA) under treatment with CQ but with normal ocular fundus manifestation.

Methods 60 RA patients taking CQ, 30 RA patients not receiving CQ treatment and 100 normal subjects were enrolled in this study. Examinations included visual field testing (Humphrey 10-2 testing strategy), mfERG and scanning laser polarimetry (GDxVCC) to measure RNFL. Data from one eye of a patient were used for analysis.

Results The mfERG ring 2 data among the three groups differed, and a correlation between cumulative dose of CQ and mfERG N1 response of ring 2 was detected. Two patients in the CQ group had central or paracentral scotoma, but all others were normal. No difference in mean deviation and pattern standard deviation values of visual field were found among the three groups, and there was no correlation between the cumulative dose of CQ and these values. There was a significant negative correlation between the cumulative dose of CQ and RNFL loss and a positive correlation between the cumulative dose of CQ and the nerve fibre indicator.

Conclusion Visual field, scanning laser polarimetry and mfERG are useful tools for early detection of CQ retinopathy. Thinning RNFL and reduced ring 2 response of mfERG may be useful signs for early CQ retinopathy.