The retina – the light detector of the eye, Physics

The retina – the light detector of the eye:


The physical aspects of the retina:
1.The absorption of a light photons in a photoreceptor triggers an electrical signal to the brain-an action potential fig(4).
2. The energy of the photon is about 3 eV: the action potential has an energy millions of times greater.
3. The light photons apparently causes a photo chemical reaction in the photoreceptor which in some way initiates the action potential.
4.the photon must be above the minimum energy to cause the reaction.

 

1583_The retina – the light detector of the eye.png



The image on the retina is very small .A convenient equation for determining the size of the image on the retina comes from the ratios of the lengths of the sides of similar triangle fig (4).


O/P=I/Q


Where O is the object size ,I the image size ,P the object distant and Q the image distance usually about 2 cm. Fig(5)

 

1132_The retina – the light detector of the eye 2.png


There are two photoreceptor in the retina:

The cones and the rods .Though out most of the retina cones and rods are not on the surface of the retina but lie behind several layers of nerve tissue through which the light must pass fig(6) The rods and cones distributed symmetrically in all directions from the visual axis except in one region- the blind spot.

 

269_The retina – the light detector of the eye 3.png


-The rods are used for night or scayopic vision and for peripheral vision, they are much more abundant than the cones(~120 million in each eye).
- The rods are most sensitive to blue- green light(~510 nm).

The blind spot: It is a region from about 13o to 18o  that has neither cones nor rods ,this is the point at which the optic nerve.


-The cones (~ 6.5 million in each eye),they are primarily used in day light or photopic vision.
- With cones we can see fine details  and recognize deferent colors.
- The cones are not uniformly sensitive to all colors but have maximum sensitivity at about 550 nm in the yellow- green region .

Posted Date: 10/1/2012 8:42:20 AM | Location : United States







Related Discussions:- The retina – the light detector of the eye, Assignment Help, Ask Question on The retina – the light detector of the eye, Get Answer, Expert's Help, The retina – the light detector of the eye Discussions

Write discussion on The retina – the light detector of the eye
Your posts are moderated
Related Questions
The weight of a body is the force with which it is attracted in the direction of the centre of earth. When an object is stationary with respect to the planet, its weight equivalent

The Law of Reflection While a ray of light strikes a plane mirror and the light ray reflects off the mirror. Reflection includes a change within direction of the light ray. The

Derive the relation Relationship  between  α and  β: Beta  factor  (β)  is  the  current  gain  factor  of  a common emitter circuit is defined as ratio of change in coll

Angle of Minimum Deviation: The angle of deviation has least value when incident ray and emergent ray make equivalent angle with the normal. The value of angle of deviation is

Consider air (ideal gas) as working substance inside a piston-cylinder device (closed system). This air undergoes a power cycle as shown in figure. Determine work output per unit m

A rectangular coil of sides 8cm by 6cm is rotating in a magnetic field such that the longer sides cut the magnetic field. Calculate the maximum generated e.m.f. if there are 6

Causes of Low power factor The major causes of low power factor in the electric supply system are as follows. Due to reactive load Most of the AC motors used in i


Fungal Prophylaxis in HSCT  A prospective randomized double- blind trial in 882 adults and children compared prophylaxis with mica fungin 50 mg IV once daily (1 mg/kg for patie