August 2016
Volume 57, Issue 10
Open Access
Letters to the Editor  |   August 2016
Neutral-Density Filters Are Not a Patch on Occlusion
Author Affiliations & Notes
  • Jiawei Zhou
    School of Ophthalmology and Optometry and Eye Hospital, Wenzhou Medical University, Wenzhou, Zhejiang, People's Republic of China; and the
    McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
  • Robert F. Hess
    McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada.
Investigative Ophthalmology & Visual Science August 2016, Vol.57, 4450-4451. doi:10.1167/iovs.16-20316
  • Views
  • PDF
  • Share
  • Tools
    • Alerts
      ×
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Jiawei Zhou, Robert F. Hess; Neutral-Density Filters Are Not a Patch on Occlusion. Invest. Ophthalmol. Vis. Sci. 2016;57(10):4450-4451. doi: 10.1167/iovs.16-20316.

      Download citation file:


      © ARVO (1962-2015); The Authors (2016-present)

      ×
  • Supplements
A number of studies over the past decade have shown that a neutral-density (ND) filter placed in front of an eye of a healthy adult can mimic certain aspects of amblyopic function,1,2 particularly those related to contrast sensitivity loss,3 binocular summation,4 and interocular imbalance.2,5,6 Furthermore, wearing a ND filter over the fellow eye of an amblyope can rebalance the dominance1,2,6 and, in some cases, recover stereoscopic function.7 Neutral-density filters reduce the mean luminance of scenes without perturbing the physical contrast. However, the contrast gain of visual neurons from retinal to cortex810 is dependent on the mean luminance. What this means is that the visual systems' contrast sensitivity is modulated by the mean luminance even though the physical contrast is itself unaltered.11 Because it has recently been demonstrated that a rebalancing of the contrast between the eyes of amblyopes can lead to a restoration of binocular function,12 one might reasonably conclude that the rebalancing effects reported in amblyopes as a result of changes in interocular mean luminance (i.e., use of ND filters) are simply due to indirect changes in contrast sensitivity. This leads to the expectation that occlusion with a ND filter might provide a way to treat amblyopia and recover binocular function based on the contrast rebalancing principle.1315 This could provide a simple alternative to that of lens blur if occlusion was the preferred approach over the alternative of contrast rebalancing using the dichoptic videogame training. 
This proposal has merit if, and only if, the rebalancing effect produced by a ND filter over one eye is simply dependent on the relative luminance seen by the two eyes (as is the case for contrast), a point recently made by Ding and Levi.6 However, if on the other hand, it depends on the absolute luminance seen by the occluded eye, this approach is doomed to failure because the luminance can vary by more than 100,000:1 (5 log units) between indoor and outdoor conditions across the day. The effectiveness of ND occlusion would be constantly varying and could not provide a stable level of binocular balance. 
We measured how ocular dominance varies with the absolute interocular luminance when the relative interocular luminance ratio is kept constant in five adults (age, 29.2 ± 2.9 years), who have normal or correct to normal (20/20) visual acuity in both eyes and normal stereopsis. Ocular dominance was measured using the binocular phase combination task.2 This result is seen in the Figure, where the average ocular dominance for healthy subjects is plotted against the ND filter values in front of each eye. There is an interocular ND difference of 2, meaning a constant relative interocular luminance ratio of 100. This ratio is constant while the absolute levels of luminance seen by each eye are varied, mimicking what would occur throughout the day. There was a systematic relationship between eye dominance and the absolute luminance while the relative interocular luminance ratio was kept constant (F(2,8) = 16.85, P = 0.001). 
Figure
 
The effect on ocular dominance as reflected by our balance point measure of the effect of the same interocular luminance ratio (i.e., 2ND; ×100) at different absolute viewing luminance (×100). Ocular dominance change (results for 0/2ND; 1/3ND; 2/4ND are all significantly different; F(2,8) = 16.85; P = 0.001) depends not only on the relative luminance between the two eyes but also on the absolute luminance levels. Error bars, SEM. DE, dominant eye; nonDE, nondominant eye.
Figure
 
The effect on ocular dominance as reflected by our balance point measure of the effect of the same interocular luminance ratio (i.e., 2ND; ×100) at different absolute viewing luminance (×100). Ocular dominance change (results for 0/2ND; 1/3ND; 2/4ND are all significantly different; F(2,8) = 16.85; P = 0.001) depends not only on the relative luminance between the two eyes but also on the absolute luminance levels. Error bars, SEM. DE, dominant eye; nonDE, nondominant eye.
These results suggest that ocular dominance changes induced by a ND filter over one eye not only depend on the interocular luminance ratio2,5,6 but also on the absolute luminance. Because the light levels can vary across the day by as much as 100,000:1, the effectiveness of a particular ND occluder that is set within the clinic would vary continually throughout the day in an uncontrollable fashion, which would render it impractical as a solution for amblyopic therapy based on rebalancing the inputs from the two eyes. 
Acknowledgments
Supported by the National Natural Science Foundation of China Grant NSFC 81500754 (Beijing, China) to JZ and the Canadian Institutes of Health Research Grants MOP-53346, CCI-125686, MT-10818 (Ottawa, ON, Canada) to RFH. 
References
Leonards U, Sireteanu R. Interocular suppression in normal and amblyopic subjects: the effect of unilateral attenuation with neutral density filters. Percep Psychophys. 1993; 54: 65–74.
Zhou J, Jia W, Huang C-B, Hess RF. The effect of unilateral mean luminance on binocular combination in normal and amblyopic vision. Sci Rep. 2013; 3: 2011–2017.
Baker DH, Meese TS, Hess RF. Contrast masking in strabismic amblyopia: attenuation noise, interocular suppression and binocular summation. Vision Res. 2008; 48: 1625–1640.
Baker DH, Meese TS, Mansouri B, Hess RF. Binocular summation of contrast remains intact in strabismic amblyopia. Invest Ophthalmol Vis Sci. 2007; 48: 5332–5338.
Zhang P, Bobier W, Thompson B, Hess RF. Binocular balance in normal vision and its modulation by mean luminance. Optom Vis Sci. 2011; 88: 1072–1079.
Ding J, Levi DM. Rebalancing binocular vision in amblyopia. Ophthalmic Physiol Opt. 2014; 34: 199–213.
Hess RF, Mansouri B, Thompson B. Latent stereopsis for motion-in-depth in strabismic amblyopia. Invest Ophthalmol Vis Sci. 2009; 50: 5006–5016.
Purpura K, Kaplan E, Shapley RM. Background light and the contrast gain of primate P and M retinal ganglion cells. Proc Natl Acad Sci U S A. 1988; 85: 4534–4537.
Shapley R, Enroth-Cugell C. Visual adaptation and retinal gain controls. Prog Retin Res. 1984; 3: 263–346.
Hess RF. Vision at low light levels: role of spatial temporal and contrast filters. Ophthal Physiol Opt. 1990b; 10: 351–359.
van Nes FL, Koenderink JJ, Nas H, Bouman MA. Spatiotemporal modulation transfer in the human eye. J Opt Soc Am. 1967; 57: 1082–1088.
Mansouri B, Thompson B, Hess RF. Measurement of suprathreshold binocular interactions in amblyopia. Vision Res. 2008; 48: 2775–2784.
Birch EE, Li SL, Jost RM, et al. Binocular iPad treatment for amblyopia in preschool children. J AAPOS. 2015; 10: 6–11.
Hess RF, Mansouri B, Thompson B. A new binocular approach to the treatment of Amblyopia in adults well beyond the critical period of visual development. Restor Neurol Neurosci. 2010; 28: 1–10.
To L, Thompson B, Blum J, Maehara G, Hess RF, Cooperstock J. A game platform for treatment of amblyopia. IEEE Trans Neural Sys Rehabil Eng. 2011; 19: 280–289.
Figure
 
The effect on ocular dominance as reflected by our balance point measure of the effect of the same interocular luminance ratio (i.e., 2ND; ×100) at different absolute viewing luminance (×100). Ocular dominance change (results for 0/2ND; 1/3ND; 2/4ND are all significantly different; F(2,8) = 16.85; P = 0.001) depends not only on the relative luminance between the two eyes but also on the absolute luminance levels. Error bars, SEM. DE, dominant eye; nonDE, nondominant eye.
Figure
 
The effect on ocular dominance as reflected by our balance point measure of the effect of the same interocular luminance ratio (i.e., 2ND; ×100) at different absolute viewing luminance (×100). Ocular dominance change (results for 0/2ND; 1/3ND; 2/4ND are all significantly different; F(2,8) = 16.85; P = 0.001) depends not only on the relative luminance between the two eyes but also on the absolute luminance levels. Error bars, SEM. DE, dominant eye; nonDE, nondominant eye.
×
×

This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.

×