AS REPORTEDno primary record reached; this is what the reporting says
The available sources present conflicting information on whether human eyes can be voluntarily half-closed, with one source questioning the ability and another discussing normal lid function.
Normal and abnormal lid function - PubMed
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## Abstract
This chapter on lid function is comprised of two primary sections, the first on normal eyelid anatomy, neurological innervation, and physiology, and the second on abnormal eyelid function in disease states. The eyelids serve several important ocular functions, the primary objectives of which are protection of the anterior globe from injury and maintenance of the ocular tear film. Typical eyelid behaviors to perform these functions include blinking (voluntary, spontaneous, or reflexive), voluntary eye closure (gentle or forced), partial lid lowering during squinting, normal lid retraction during emotional states such as surprise or fear (startle reflex), and coordination of lid movements with vertical eye movements for maximal eye protection. Detailed description of the neurological innervation patterns and neurophysiology of each of these lid behaviors is provided. Abnormal lid function is divided by conditions resulting in excessive lid closure (cerebral ptosis, apraxia of lid opening, blepharospasm, oculomotor palsy, Horner's syndrome, myasthenia gr
# Why can't we half-close our eyes?
Tags: physiology, eyes, human-eye
- Score: 7
- Views: 520
- Answers: 2
- Answered: yes
- Asked by: Harsh Kumar (183 rep)
- Asked: 2017-01-16
- Edited: 2017-01-21
- Site: biology
## Question
Can we half-close our eyes such that they don't vibrate?
If not, then why we are unable to half-close our eyes properly?
Alternatively, why isn't it possible to keep the upper eyelid close to the lower eyelid without it vibrating?
## Answers
### Answer by Luboš Motl (score: 9 [ACCEPTED])
The motion of the eyelid is driven by the levator palpebrae superioris, i.e. elevating muscle of upper eyelid, and it can be positioned to the intermediate, half-closed positions. At least I can do it.
Yes, this muscle tends to shake or oscillate simply because it's a very weak muscle. It's similar with the muscles controlling the motion of the little finger (or ring finger). Vibration and "noise" is present in all muscles but the stronger muscle you have, the more accurately the random motion is averaged out.
If you connected $N$ eyelid muscles so that they move in unison, the noisy vibrations would be reduced by the factor of $\frac{1}{\sqrt{N}}$. This is the well