Question

Which of the following gives the correct path for light rays entering the human eye?

• A. Sclera, retina, choroid, lens, cornea
• B. Fovea centralis, pupil, aqueous humour, lens
• C. Cornea, pupil, lens, vitreous humour, retina
• D. Optic nerve, sclera, choroid, retina, humours

Answer 1

Answer: (C)

Cornea, pupil, lens, vitreous humour, retina

1. The first thing light encounters when it enters the eye is the cornea, a protective clear covering over the pupil and iris. The cornea bends the light and begins to form an image.
2. Light passes from the cornea to the pupil, the dark circle in the centre of the iris, which is the coloured portion of the eye. The pupil regulates the amount of light that will enter the inner eye based on environmental conditions: It dilates, growing bigger to receive more light under dim lighting conditions, and shrinks in response to bright light. This response is quicker in young individuals and tends to slow with increasing age.
3. From the pupil, light waves travel to the lens of the eye. The lens is a clear, flexible structure that focuses an upside-down image onto the retina. It is flexible so that it can focus on images that are close or far away. Eye injuries, normal variations in the eye and age can distort the lens, making it difficult to focus on nearby or faraway objects -- you see the objects, but details are hazy. Late in life, the lens can also become clouded and form cataracts that make images seem hazy and dim.
4. The lens focuses light and images on the retina, a layer of light-sensitive cells at the back of the eye. It is made up of two kinds of photoreceptor cells: cones and rods. The cones transmit colour and sharp images. The concentration of cones is low on the sides of the retina and increases as the cones approach the centre of the retina or the macula. The rods are more sensitive to light and are more numerous than cones; They let you see when lighting is dim, although what you see lacks colour and clear details.
5. Once the retina senses the image, it sends impulses to the optic nerve at the back of the eye. The optic nerve then transmits them to special areas in the brain, which automatically flips the upside-down image so that it becomes upright again. Disease or injury can damage the optic nerve, resulting in varying degrees of blindness.

So, the correct answer is 'Cornea, pupil, lens, vitreous humour retina'.