Development and Validation of a Novel Mobility Test for Rod-Cone Dystrophies: From Reality to Virtual Reality

PURPOSE

To validate a novel mobility test (MOST, MObility Standardized Test) and performance outcomes in real (RL) and virtual (VR) environments to be used for interventional clinical studies in order to characterize vision impairment in rod-cone dystrophies, also known as retinitis pigmentosa (RP).

DESIGN

Prospective, interventional, noninvasive, reliability and validity analysis.

METHODS

We designed MOST to be used in both VR and RL and conducted 3 experimental studies with 89 participants to (1) validate the difficulty of the mobility courses (15 controls), (2) determine the optimal number of light levels and training trials (14 participants with RP), and (3) validate the reproducibility (test-retest), reliability (VR/RL), sensitivity, and construct/content validity of the test (30 participants with RP and 30 controls). A comprehensive ophthalmologic examination was performed in all subjects. Outcomes of interest included MOST performance score, visual acuity, contrast sensitivity, dark adaptation thresholds, visual field parameters, and correlation between the performance score and visual function.

RESULTS

The mobility courses exhibited statistically similar difficulty, and 5 trials are sufficient to control for the learning effect. MOST is highly reproducible (test-retest correlations >0.98) and reliable (correlations VR/RL = 0.98). MOST achieved a discrimination between participants with RP and controls (accuracy >95%) and between early and late stages of the disease (82.3% accuracy). The performance score is correlated with visual function parameter (0.57-0.94).

CONCLUSION

MOST is a validated mobility test, with the controlled learning effect, excellent reproducibility, and high agreement between RL and VR conditions, as well as sensitivity and specificity to measure disease progression and therapeutic benefit in rod-cone dystrophies.

Rewarding objects appear larger but not brighter

Whether reward can accentuate the perception of visual objects, that is, makes them appear larger than they really are, is a long-standing and controversial question. Here, we revisit this issue with a novel two-alternative forced-choice paradigm combining asymmetric reward schedule and task reversal. In a first experiment, participants (n = 27) choose the larger of two unequally rewarded objects in some sessions and the smaller one in other sessions. Response biases toward the most rewarding object differ significantly between the reversed tasks, revealing an influence of reward on perceived sizes. In a second experiment, participants (n = 27) indicate either the brighter or darker object. In contrast with the first experiment, response biases are similar between those reversed tasks, indicating that the perceived luminance is immune to reward manipulation. Together, these results reveal that if two objects are associated with different amounts of reward, participants will perceive the more rewarded object to be slightly larger, but not brighter, than the less rewarded one.

Collective migration of an epithelial monolayer in response to a model wound

Using an original microfabrication-based technique, we experimentally study situations in which a virgin surface is presented to a confluent epithelium with no damage made to the cells. Although inspired by wound-healing experiments, the situation is markedly different from classical scratch wounding because it focuses on the influence of the free surface and uncouples it from the other possible contributions such as cell damage and/or permeabilization. Dealing with Madin-Darby canine kidney cells on various surfaces, we found that a sudden release of the available surface is sufficient to trigger collective motility. This migration is independent of the proliferation of the cells that mainly takes place on the fraction of the surface initially covered. We find that this motility is characterized by a duality between collective and individual behaviors. On the one hand, the velocity fields within the monolayer are very long range and involve many cells in a coordinated way. On the other hand, we have identified very active "leader cells" that precede a small cohort and destabilize the border by a fingering instability. The sides of the fingers reveal a pluricellular actin "belt" that may be at the origin of a mechanical signaling between the leader and the followers. Experiments performed with autocrine cells constitutively expressing hepatocyte growth factor (HGF) or in the presence of exogenous HGF show a higher average velocity of the border and no leader.