Question

As people age, their ability to see at night decreases. What changes in the retina might explain this?  

A clinician shines a light into a patient’s left eye, and neither pupil constricts. Shining the light into the right eye elicits a normal consensual reflex. What problem in the reflex pathway and explain these observations?  

Answer 1

As people age, their ability to see at night decreases. What changes in the retina might explain this?  

Ans: Retina is innermost tunic of the eyeball. It delicate, thin membrane. It consists of rod and cone which contain photosensitive substance called rhodopsin and iodopsin.

As age progress changes in retina, pupil and lens occur which cause loss or diminished night view. In normal eyes; light enter into the eye and hit the photoreceptor present in the retina which triggers the biochemical changes to those cells. These cells send signals to optic nerve. Those signal reaches to brain and image is interpreted. Rods provide only black and white color but critically important for night vision.

Hence, age increasing brings changes in the retina, specially the number of light sensitive rods in the retina decreases.

A clinician shines a light into a patient’s left eye, and neither pupil constricts. Shining the light into the right eye elicits a normal consensual reflex. What problem in the reflex pathway and explain these observations?  

Ans: pupil light reflex- it helps in adjustment pupil size with changes in level.

Pupilar light reflex control allow the eye to adjust amount of light reaching the retina and protect photoreceptor from bright light. Iris contain 2 smooth muscle

1. Sphincter muscle cells/fiber- it forms rings and sphincter causes the pupil contract.

2. Dilator muscle fiber/cells- it dilates the constricted pupil.

Light enter into the eye through the pupillary light reflex and signal directed to iris sphincter muscle, so that amount gets adjusted.

Muscle fiber are control by parasympathetic and sympathetic nervous system

Problem is light relax pathways occur, mainly disruption in parasympathetic nerve (cause pupil constrict) or hyperactivity of sympathetic nerve cause pupil relax.

Observation include-

1. left eye is don’t react to light or consensually.

2. Right eye responds to light consensually

3. Left eye loss motor response but not sensory response (as right eye responded to light)

4. Pathway affected- the parasympathetic disturbance of eye.

Parasympathetic Preganglionic(oculomotor) or postganglionic (short ciliary nerve) innervation of left eye result in loss of motor response towards the direct or consensual pupillary light response.

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