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Histology of the Eye Homework


She suffered from achromatopsia and moon blindness. What have happened with her eyes?


She suffers from achromatopsia because her eyes’ retina cone cells are not functioning and thus lose ‘cone vision’. Therefore, the photoreceptor cells in her eyes’ retina only have rod cells. As a result, her eyes will only have ‘rod vision’ and carry out only the function of rod cells; which means she will not be able to perceive color and is either totally colorblind or almost totally colorblind, has poor visual acuity, extreme light sensitivity and nystagmus. Achromatopsia is an inherited disease.

However, if she suffers from moon blindness, or nyctalopia or night blindness, this means that the rod cells in her eyes’ retina do not function well. As rod cells are very sensitive to light, malfunctioning of rod cells results in difficulty or inability to perceive image at night or low light circumstance. She might have suffered from a genetic eye disease called Retinitis Pigmentosa (RP). RP is a disorder in which the rod cells in the retina slowly lose their ability to respond to the light. She might also develop tunnel vision which means loss of peripheral vision with only the retention of central vision and RP might eventually lead her to blindness.



Comparison between Rod and Cone cells


Rod Cell

Cone Cell




·         Cylindrical (rod) shape.

·         Narrower than cone cell.

·         Concentrated at the outer edges of the retina (peripheral).

·         High area for visual pigment and thus substantial efficiency of light absorption.

·         Have only one type of light-sensitive pigment.



·         Cone shape

·         Shorter than rods, but wider and tapered

·         Concentrated at the center of the retina

·         Have 3 types which respond to variation in color in different ways





·         Low light photoreceptor.

·         Responsible for night vision.

·         More sensitive than cone cells.

·         Rods have little role in color vision.


·         Required light in order to be activated (high light photoreceptor).

·         Responsible for daylight vision.

·         Cones are less sensitive to light than the rod cells.

·         Allow the perception of color; to perceive finer detail and more rapid changes in images.



Related disease


·         Nyctalopia (night blindness)



·         Hemeralopia (day blindness)

·         Achromatopsia (Color Vision Disorder/Color blind)