This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Optics and Errors of Refraction, Subject name: Ophthalmology
[{'content': 'Which of the following is true regarding Helmholtz theory of accomodation \nSelect and explain. \nA. Ciliary muscles relax, B. Zonules contract, C. Posterior Movement of Ciliary Muscles, D. Decrease in equatorial diameter', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Accommodation: Mechanism by which eye changes its focal length by change in curvature of crystalline human lens According to Helmhotz theory during accommodation following changes takes place during accomodating for near vison Ciliary Muscles Contract(relaxation is all around 360o) Zonules Relax Anterior Movement of Ciliary Muscles Increase in thickness of lens Decrease in equatorial diameter Presbyopia results from the loss of lens elasticity with age. Note- sphincter pupillae are present all aorund the iris they increase / decrease the size of pupil ciliary muscles and zonules control the curvature of lens', 'role': 'assistant'}]