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The amount of light entering the human eye is controlled by
Ciliary muscles
Cornea
Pupil
Iris
None of the above
Iris
The amount of light entering the human eye is primarily controlled by the iris, a pigmented, muscular ring. It acts as an adjustable diaphragm that regulates the diameter of the pupil, the central opening of the eye.
The amount of light entering the human eye is primarily controlled by the iris, a pigmented, muscular ring. It acts as an adjustable diaphragm that regulates the diameter of the pupil, the central opening of the eye.
The iris functions exactly like the aperture or diaphragm of a camera lens, which opens or closes to control how much light hits the sensor.
I-P-L: Iris controls Pupil size to manage Light.
IntensityтИЭArea┬аof┬аPupil=╧Аr2 тАФ where r is the radius of the pupil.
The iris contains two layers of smooth muscles: the sphincter pupillae (circular muscles) and the dilator pupillae (radial muscles). In bright light, the sphincter muscles contract, causing the pupil to constrict (miosis) to limit light exposure. In dim light, the radial muscles contract, causing the pupil to dilate (mydriasis) to allow more light to reach the retina.
The iris provides the eye's color.
Pupil constriction/dilation is an autonomic reflex controlled by the nervous system.
The process ensures the retina is not damaged by high-intensity light and receives enough photons in low-light conditions.
Protects delicate retinal photoreceptors from intense glare.
Maintains optimal vision across a wide range of ambient light intensities.
The iris adjustment is not instantaneous, leading to temporary blindness when moving between extreme light conditions (e.g., entering a dark theater).
Autonomic nervous system function assessment.
Ophthalmological examination using dilating drops.
The pupil is not a physical structure, but simply a hole in the center of the iris.
Option A (Ciliary muscles) control the shape of the lens for focusing, not the amount of light.
Option B (Cornea) acts as the outer protective covering and provides most of the eye's optical power.
Option C (Pupil) is the aperture itself, but the 'control' is performed by the surrounding iris tissue.
D is correct тАФ The iris is the muscular structure that regulates light entry by adjusting the diameter of the pupil.
Always distinguish between 'refraction' (done by Cornea and Lens) and 'light regulation' (done by Iris/Pupil) to avoid confusion in exams.
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