Mechanism of Vision MCQ - Practice Questions with Answers

MECHANISM OF VISION

1. LENS ACCOMMODATION

2. IMAGE FORMATION

1. LENS ACCOMMODATION

• Accommodation is adjustment of eye lens for various distances
• Ciliary body and Suspensory body bring about this accommodation
• The accommodation for close(near) and far away objects is as follows :

       CLOSE OBJECT                                                       FAR AWAY OBJECT

• CLOSE                                                             CILIARY BODY RELAXES
• CILIARY BODY                                                SUSPENSORY LIGAMENT CONTRACTS
• CONTRACTS                                                   LENS BECOMES FLAT
• SUSPENSORY LIGAMENT RELAXES      
• LENS THINS OUT

2. IMAGE FORMATION

•  LIGHT RAYS ENTER CORNEA AND REACHES RETINA
• TRAVELS FROM GANGLION TO BIPOLAR TO PHOTORECEPTORS
• THE OUTER SEGMENT OF PHOTORECEPTORS HAVE PHOTOPIGMENTS
• PHOTOPIGMENTS = LIGHT ABSORBING PART (RETINAL)+ OPSIN
• INITIALLY, OPSIN IS ATTACHED TO cis RETINAL
• AS LIGHT FALLS, cis BECOMES trans 
• trans IS SEPARATED FROM RETINAL
• THIS CREATES IMPULSES WHICH VIA OPTIC NERVE REACHES THE BRAIN
• AS IMPULSES ARE FORMED , trans BECOMES cis AGAIN AND ATTACHES WITH RETINAL AND THUS NOW WAITS FOR NEW IMPULSE 

DISORDERS RELATED TO ACCOMMODATION