NROS 418 Exam 1 questions with correct answers

Why does the organization of the eye guarantee that we have a blind spot? Why can't we normally detect the blind spot? - Answer Lack of photoreceptors in this area because it is where the optic nerve and blood vessels exit the eye. We cannot detect the blind spot because we use our surroundings to fill in the information with the ipsilateral and contralateral visual inputs Ideal Answer: The natural blind spot in the eye is due to the lack of photoreceptors where the optic nerve and blood vessels exit the eye. Our brain interpolates the blind spot by using information that surrounds the area where the blink spot occurs using both ipsilateral and contralateral visual input. The blind spot is located about 12-15° temporally and 1.5° below the horizontal and is roughly 7.5° high and 5.5° wide in each eye What is different about the fovea and the rest of the retina? Why is visual acuity best when images fall on the fovea? - Answer The fovea has the most cones and basically no rods due to it being the centermost part of our eye and where light is focused. Since it is only made up of cones any small change is noticeable making the visual acuity strong. Rods are favored the farther you move away from the fovea. Ideal Answer: The fovea is an area of the eye that is densely populated by cone receptors and where light is focused on the retina. The center of the fovea is the foveola - about 0.35 mm in diameter - or central pit where only cone photoreceptors are present and there are virtually no rods. Every cone sends input to 1-3 retinal ganglion cell(s). Thus, the cone mosaic that comprises the fovea is the only limiting factor that determines visual acuity. The rest of the retina comprises of rods and cones with the ratio favoring rods the further away you move from the fovea.