OBJECTIVE: To confirm if using a neutral density filter (NDF) affects eyes with 
strabismic amblyopia differently compared to fellow non-amblyopic eyes, and to 
determine if a similar effect could be observed when using a NDF during 
peripheral visual field testing.
DESIGN: Prospective controlled case series.
PARTICIPANTS: 19 subjects with strabismic amblyopia with visual acuities between 
20/400 and 20/40 in their affected eyes were recruited to the study. Fellow 
non-amblyopic eyes served as the control group.
METHODS: Visual acuity in both eyes was assessed using a projected Snellen eye 
chart with two NDFs (0.4 and 3.0 densities). Visual fields were assessed using a 
Humphrey perimeter using one NDF (0.4 density). Best corrected visual acuity and 
visual fields were also recorded.
RESULTS: When using a 3.0 NDF, visual acuity was reduced in all eyes (p < 
0.0001). When using a 0.4 NDF, visual acuity was significantly improved in eyes 
with strabismic amblyopia compared to unfiltered conditions (p = 0.0011). There 
was no significant effect by NDFs on visual field testing in eyes with 
strabismic amblyopia or fellow non-amblyopic eyes.
CONCLUSIONS: Neutral density filters affect eyes with strabismic amblyopia 
differently than they do non-amblyopic eyes. A significant improvement in visual 
acuity of eyes with strabismic amblyopia was observed when using a 0.4 NDF 
compared to non-amblyopic eyes. Visual acuity was reduced in amblyopic as well 
as non-amblyopic eyes when viewing through a 3.0 NDF. No significant change in 
visual fields was observed when using a 0.4 NDF in amblyopic or non-amblyopic 
eyes.