Abstract
Purpose :
To investigate the associations between monocular fixation stability and luminance contrast sensitivity function (CSF) measured under monocular and dichoptic viewing conditions in amblyopia.
Methods :
Participants were 16 (mean age = 33.6 ± 9.5 years, six females) amblyopic patients. Monocular BCVA was measured with ETDRS chart. Monocular and dichoptic CSFs were obtained from both eyes as previously described (Barboni et al. IOVS 2020, 61:23). Area under the log CSF (AULCSF) was calculated for the full (0.5 to 8cpd), low (0.5 to 2cpd) and high (2 to 8cpd) spatial frequency ranges. Amblyopic sensitivity decrement (ASD) was the AULCSF of the amblyopic eye normalized to the dominant eye. Fixational eye movements were recorded using the MAIA microperimeter and stability was assessed as the bivariate contour ellipse area (BCEA) encompassing 68% of the fixation points.
Results :
Amblyopia was associated with larger BCEAs and reduced BCVAs, monocular and dichoptic AULCSFs as expected. The amblyopic BCEA correlated positively with BCVA (Spearman rho=0.65, p=0.009) and with ASDMono for the full frequency range obtained under monocular (Spearman rho=0.64, p=0.007) but not under dichoptic condition (ASDDichoptic), showing that worse amblyopic fixation corresponds to larger monocular amblyopic CS decrement. This was due to the high spatial frequency CS strongly correlating with amblyopic BCEA (rho=0.73, p=0.001), while no correlation was observed at the low spatial frequency range for ASDMono. Conversely, ASDDichoptic showed pronounced positive correlation with amblyopic BCEA in the low (rho=0.71, p=0.001) but not in the high spatial frequency range. Importantly, this differential effect was supported by a significant interaction between fixation stability, viewing condition and frequency range.
Conclusions :
The results confirmed that the absence of finely tuned fixational eye movements prevented high spatial resolution to take place affecting CSF in addition to BCVA in amblyopia. Interestingly, dichoptic viewing condition was differentially affected by the unstable fixation of the amblyopic eye, which might indicate that fixation stability is related to binocular balance. The data emphasize the importance of stable fixation in acuity and contrast tasks. Thus, it should be targeted during amblyopic treatment to improve binocular balance, as we have recently suggested (Bankó et al. Sci. Rep. 2022, 12:10311).
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.