Normal range of eye movement and its relationship to age

Mechanisms of punctuated vision in fly flight

To guide locomotion, animals control gaze via movements of their eyes, head, and/or body, but how the nervous system controls gaze during complex motor tasks remains elusive. In many animals, shifts in gaze consist of periods of smooth movement punctuated by rapid eye saccades. Notably, eye movements are constrained by anatomical limits, which requires resetting eye position. By studying tethered, flying fruit flies (Drosophila), we show that flies perform stereotyped head saccades to reset gaze, analogous to optokinetic nystagmus in primates. Head-reset saccades interrupted head smooth movement for as little as 50 ms-representing less than 5% of the total flight time-thereby enabling punctuated gaze stabilization. By revealing the passive mechanics of the neck joint, we show that head-reset saccades leverage the neck's natural elastic recoil, enabling mechanically assisted redirection of gaze. The consistent head orientation at saccade initiation, the influence of the head's angular position on saccade rate, the decrease in wing saccade frequency in head-fixed flies, and the decrease in head-reset saccade rate in flies with their head range of motion restricted together implicate proprioception as the primary trigger of head-reset saccades. Wing-reset saccades were influenced by head orientation, establishing a causal link between neck sensory signals and the execution of body saccades. Head-reset saccades were abolished when flies switched to a landing state, demonstrating that head movements are gated by behavioral state. We propose a control architecture for active vision systems with limits in sensor range of motion. VIDEO ABSTRACT.

Ocular Weakness in Myasthenia Gravis: Changes in Affected Muscles are a Distinct Clinical Feature

Introduction:

In this study we quantitatively describe ocular weakness patterns in myasthenia gravis (MG) to help neurologists in making the clinical diagnosis and to investigate how the current outcome measures reflect ocular weakness in MG.

Methods:

We investigated ptosis and diplopia patterns in a retro- and prospective cohort of 306 MG patients. Diplopia was systematically examined by testing extra-ocular muscle (EOM) fatigability in two horizontal and four oblique directions for 60 seconds.

Results:

Of patients with initial symmetric ptosis, 40% developed asymmetric ptosis at the second visit. Changes in form of ptosis occurred less often in seronegative MG patients (50%) than in patients with acetylcholine receptor (AChR) antibodies (70%) or muscle-specific kinase (MuSK) antibodies (69%) (p = 0.038). Of patients with diplopia on the first visit, double vision contained both a vertical and horizontal component in 95%. At the second visit, 83% manifested diplopia in other gaze directions. The mean time (in seconds) to diplopia was 11.6±14.0 and the mean time to ptosis was 27.6±19.8. Diplopia or ptosis manifested within 30 seconds in 87% and 58%, respectively. Patients who manifested diplopia after 30 seconds, reported no limitations due to diplopia.

Discussion:

Changes in the gaze directions in which diplopia occurs or ptosis side occur frequently in MG. In diagnostically challenging cases, we recommend testing ptosis and diplopia in multiple gaze directions for 30–60 seconds during at least two follow-up visits to maximize the chance of observing changes in ocular weakness patterns.