Box 2.

Details of interventions used in intensive and control groups

Strabismus testing

Cover testing was carried out each time a child was seen, including at the final assessment. Failure on cover testing (any manifest strabismus, any latent convergent strabismus, or a latent divergent strabismus of 10 prism dioptres or more) led to referral to the hospital eye service for full evaluation, including cycloplegic refraction and fundoscopy. Any new cases of strabismus discovered at the final assessment were also referred.

Protocols for vision testing

Children in the intensive group only were tested at 8 months and 12 months with Cardiff cards at 1 m.¹¹,¹² At 18, 25, and 31 months children in the intensive group only were tested with Cardiff cards at 1 m and with Kays picture test at 6 m.¹³,¹⁴ At 37 months children in both groups were tested with Kays picture test at 3 m or 6 m and with single HOTV letters, with and without crowding bars,¹⁵ displayed on a computer monitor at 6 m.¹⁶

Failure on any vision test led to referral to the hospital eye service, where cycloplegic refraction was carried out and treatment instituted if needed.

At all ages non-cycloplegic autorefraction was carried out,¹⁷ but referrals to the hospital eye service were not made on the basis of this until the 37 month clinic.

At 7.5 years LogMAR (log₁₀ minimum angle of resolution, using ETDRS charts) at 4 m was measured in the child's habitual state (that is, with glasses if worn) both with and without a pinhole.¹⁸,¹⁹ If the better (smaller LogMAR score) acuity obtained either with or without pinhole for either eye was 0.2 or worse or if there was a difference between the best acuity of the two eyes of 0.2 or more, the child was seen again in a further research clinic where cycloplegic retinoscopy and fundoscopy were carried out. Glasses, referral to the hospital eye service, or both were offered if needed. If the best visual acuity of either eye was better than 0.2 but improved by 0.2 or more with the pinhole, the child's carer was advised to see an optician and given a referral note describing the study findings.