Chapter 40, Problem 1Q

Summary Introduction

To review:

The part of the iris that is affected by the epinephrine injection, on the basis of experimental results obtained from the surgeries performed with or without epinephrine.

Given:

A cataract refers to the clouding of lens that can occur either due to exposure to ultraviolet light or due to aging. The eye lens in this condition becomes cloudy and nontransparent. For the proper sight, the cataract that is the cloudy lens needs to be removed by the surgeon. In doing so, the surgeon has to make sure that pupil is dilated properly and for a longer time. The dilation of the pupil is controlled by adrenal medulla that releases epinephrine and norepinephrine.

Researchers conducted an experiment to deduce if epinephrine can help in keeping the pupil dilated for a longer time during cataract surgeries. They injected epinephrine into the eye of 27 patients for cataract surgery and did not inject in the eyes of 43 other patients that were also taken into consideration.

The table data shows the patients percentage whose eyes had the pupil diameter size less than 5 mm during the different stages of cataract surgery:

Introduction:

The eye is an important vision organ and its improper functioning causes loss of sight. To cure cataract, which is a disease where the lens of the turns a bit cloudy and nontransparent, people go to surgeons for different surgeries. For the surgery to take place properly, the pupil which is a opening in iris of eye should be properly dilated. The pupil dilation is controlled by various hormones.

Explanation of Solution

Iris forms the major part of the eye, is a thin and circular aperture and is responsible for the contraction and dilation of the pupil of eye. Along with the two types of muscles that constitute the iris, pupil is present. The pupil is responsible for the amount of light that reaches the retina of eye. The size of the pupil is variable and can increase or decrease according to the amount of light to be perceived. It is controlled by the hormone epinephrine that helps in its dilation, which in turn, helps in the better perception of light.

During the experiment, epinephrine (which was injected into the patient’s eye for cataract surgery) dilated pupil and helped in the surgery. Thus, the injected epinephrine affects the pupil of the eye causing it to dilate and increasing in size. The increase in size makes it easier for the surgeons to carry out the surgery. It is clearly evident by the results of the two cases that epinephrine injected patients have less percentage of those having pupil diameter <5 mm while the patients that were not injected by epinephrine have a larger percentage at all the stages of surgery. Epinephrine controlled the diameter of pupil and injected patients pupil remain dilated during the surgery.

Conclusion

Hence, it can be concluded that pupil is the smallest opening in the iris of the eye, which is affected when epinephrine is injected into the patients. The presence of epinephrine in the eye causes the pupil to dilate and increase in size while the absence of epinephrine keeps the size of the pupil small as interpreted from the experiment’s data.