Table 1

Table of experimental studies included in the review

Ref	year	Design	Participants	Intervention	Factors that might lead to or prevent bias	Size of effect	OCEBM level of evidence9
11	1980	Controlled trial	131 with intellectual disability and refractive errors ≥+2.0D, ≤0.5D, ≥1D anisometropia	Distance spectacles vs none	Observers not masked	81% compliance at 8 weeks. Variable effects on multiple behaviours	3
12	1987	Before/after	105 with intellectual disability and refractive errors ≥+2.5D, ≤−3.0D, ≥1.5D anisometropia or astigmatism	Distance spectacles	Observers not masked but also used VEPs as objective outcome measure	Qualitative results given—VEPs larger after spectacles given in 58 of the 105. Some anecdotes of marked improvements in awareness	3
23	1991	Controlled trial	17 (of 58) with severe visual impairment diagnosed <13 months of age and with severe learning difficulties	Individualised vision training programme vs general development programme	A third of participants allocated by non-random procedure. Masked observer for final outcome Groups not matched for diagnoses	Separate data for children with VND not given but qualitatively VND group did better in vision training arm as compared with general development arm	3
24	1999	Before/after	10 children with vision of only PL or worse and additional impairments	Training/practice in looking at striped visual stimuli	Observers may not have been masked	Teller acuity card vision improved but number of blinks or fixations unchanged	3
34	2005	Controlled trial	34 children with Down syndrome and accommodative lag	Bifocal spectacles	Allocation not random Examiners not masked but no examiner bias seen on video review	Improvement in lag was 2.9 D in bifocals group vs 0.5`D in controls	2
³⁵	2009	Before/after	40 children with Down syndrome and accommodative lag	Bifocal spectacles	Examiners not masked	38/40 showed accurate accommodation through bifocal near segment	2
36	2010	Before/after	11 children with Down syndrome and accommodative lag	Bifocal spectacles	Examiners not masked No baseline for visuoperceptual outcomes but accommodation was stable 5 months prior to intervention	Near acuity improved from 0.58 LogMAR to 0.42 LogMAR. Variable improvements in visuoperceptual test results	3
37	2007	Before/after	5 children with CP using hyoscine patches; acuity at 1 m 6/30 or worse	Spectacles giving clear focus at 1 m	Examiners not masked	Qualitative improvement in near vision	3
46	1983	Before/after	10 children with CP and nystagmus and/or poor oculomotor control	Training/practice in tracking moving target with eyes and/or other parts body	Examiners not masked but objective outcome using eyetracker	Accuracy of smooth pursuit increased, sometimes markedly. Errors and latencies in saccadic movements decreased	2
48	2008	Before/after	3 children with CP and nystagmus	Selective dorsal rhizotomy	Examiners not masked but objective outcome using eyetracker	2 of the 3 showed improved accuracy of smooth pursuit	3
52	1980	Controlled cross-over trial	4 children with CP and visual impairment	White light vs UV light for training in looking at a target object	Examiners not masked	Overall (p<0.001) more fixations on target in UV light condition	2
53	1983	Controlled trial	13 children with IQ <20 and legally blind with some residual vision	White light vs UV light for training in shape matching task	Random allocation; examiner not masked	Overall (p<0.01) better score in post-test shape matching task if had been trained with UV light condition	2
54	1998	Before/after	6 children with visual impairment and intellectual or multiple other impairments	Exposure to a MSE	Examiners not masked Prespecified list of behaviours used as outcome; inter-rate reliability of videotaped observations of behaviour 93%	Mean scores for prespecified skills observed on video greater after 5 weeks’ exposure to MSE, greater for visual impaired (88 vs 93) group than for autism group (95 vs 96)	3

CP, cerebral palsy; MSE, multisensory environment; OCEBM, Oxford Centre for Evidence Based Medicine; PL, perception of light; UV, ultraviolet; VEP, visual evoked potential; VND, vision and neurodevelopmental.