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Effect Of Cafeine On Pupillary Size Among Students Of Imo State University




The aim was to determine the effect of caffeine on pupil size among students of Imo State University. A total number of 311 subjects within the age range of 18 to 53 years with mean age of 31.5 years and standard deviation of 1.72. They were made up of 160 males and 151 females. The pupil size of each subject was measured before the consumption of one heaped teaspoon of coffee dissolved in 250ml warm sterile water. The pupil size was again measured 30mins, 60mins and 90mins after ingestion of coffee. The findings showed coffee has statistically significant effect on pupil size at 30mins and 60mins after consumption, but no effect was noticed at 90mins. It is recommended that those consumed coffee but with history of family glaucoma should always go for IOP check.



1.1     Background to the study.

Pupillary response and accommodation are important physiological processes of the eye that affect vision. Ocular accommodation is a blur driven reflex and results in focusing of images onto the retina.The pupil regulates retinal illumination to optimize visual perception. Other visual functions such as contrast sensitivity, color perception, and visual acuity are influenced by pupil size and accommodation (Alfonso et al. 2007). The iris and ciliary muscles, which are directly responsible for the manifest structural changes in pupillary response and accommodation respectively, receive autonomic innervations from both the mesencephalic

Edinger–Westphal nucleus and hypothalamic center in the diencephalon (Loewenfied et al. 1993). Parasympathetic innervation of the iris sphincter muscle results in reduction of pupillary diameter, whereas sympathetic innervation of the iris dilator muscle increases pupil diameter. However, the accommodative state is largely controlled by parasympathetic innervations of the ciliary muscle, although sympathetic innervations play a complementary role in relaxing accommodation

Caffeine, a psychoactive drug, is commonly consumed in various forms and in variable amounts by people worldwide. The absorption of caffeine into the bloodstream after oral intake is very efficient, and widely distributed to all organs of the body including the nervous system because of its hydrophobic properties (Nehlig et al. 1992). Interestingly, caffeine has wide variations in its nature of action on biological tissues, an attribute that makes it worth of study. Because of the increased awareness of the wide spread effects of caffeine on the nervous

system, scientists have sought to investigate forocular and visual changes associated with caffeine intake. This is because ocular tissues including the iris muscles, ciliary muscle.

1.1.1 Caffeine

Caffeine is a naturally occurring, central nervous system (CNS) stimulant of the methylxanthine class and is the most widely taken psychoactive stimulant globally. This drug is most commonly sourced from the coffee bean but can also be found naturally occurring in certain types of tea and cacao beans. It is also an additive to soda and energy drinks. The primary goal of caffeine consumption is to combat fatigue and drowsiness, but there are many additional uses. This activity reviews the mechanism of action, adverse event profile, toxicity, dosing, pharmacodynamics, and monitoring of caffeine, pertinent for clinicians and other interprofessional team members where caffeine is already in use or might be necessary.

1.1.2 Mechanism of Action

Caffeine’s primary mechanism of action is on the adenosine receptors in the brain. As it is both fat and water-soluble, it readily crosses the blood-brain barrier, resulting in antagonism to all four adenosine receptor subtypes (A1, A2a, A2b, A3). Specifically, the antagonism of the A2a receptor is responsible for the wakefulness effects of caffeine Ferre  et al. 2004).

Adenosine receptors are not limited to the CNS but are present throughout the body. In cardiac muscle, direct antagonism of receptor A1 results in positive inotropic effects. Likewise, adenosine receptor antagonism stimulates the release of catecholamines, contributing to the systemic stimulatory effects of caffeine and further stimulating cardiac inotropy and chronotropy. At the vascular level, caffeine undergoes a complex interaction to control vascular tone, which includes direct antagonism of vascular adenosine receptors to promote vasodilation, as well as stimulation of endothelial cells to release nitric oxide. This action promotes further relaxation of vascular smooth muscle cells. This vasodilation becomes counteracted by the increase in sympathetic tone via catecholamine release and positive cardiac inotropic and chronotropic effects, promoting vasoconstriction. As there are multiple constriction and dilatation mechanisms at work, the overall result is individualized and dependent upon caffeine dose, the frequency of use, and comorbidities such as diabetes or hypertension. Overall, caffeine seems to increase systolic blood pressure by approximately 5 to 10 mmHg in individuals with infrequent use. However, there is little to no acute effect on habitual consumers (Echeverri et al. 2010).

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Furthermore, adenosine receptor blockage stimulates respiratory drive by increasing medullary ventilator response to carbon dioxide, stimulating central respiratory drive, and improving diaphragm contractility. Caffeine increases renal blood flow, glomerular filtration, and sodium excretion resulting in diuresis. It is also a potent stimulator of gastric acid secretion and gastrointestinal (GI) motility (Boekema et al. 1999).

Metabolism of caffeine primarily occurs in the liver via the cytochrome P450 oxidase system, specifically enzyme CYP1A2, Metabolism results in 1 of 3 dimethylxanthine, including paraxanthine, theobromine, and theophylline, each with unique effects on the body. These metabolites are then further metabolized and excreted in the urine (Zandvliet et al. 2005).

The half-life of caffeine is approximately 5 hours in the average adult. However, multiple factors can influence metabolism. Half-life is reduced by up to 50% in smokers compared to nonsmokers. Conversely, pregnant patients, especially those in the final trimester, will demonstrate a prolonged half-life upwards of 15 hours. Newborns will also have a significantly prolonged half-life, up to 8 hours for full-term and 100 hours for premature infants, due to reduced activity of cytochrome P450 enzymes and immature demethylation pathways. Children older than 9 months will have similar half-life eliminations to that of adults. Additionally, patients with liver disease or those taking cytochrome inhibitors will also experience prolonged half-lives due to reduced enzyme activity (Verbeek RK 2008).

1.1.3 Administration

Caffeine has nearly 100% oral bioavailability and is the primary route of administration. Caffeine can be sourced from coffee beans, cacao beans, kola nuts, tea leaves, yerba mate, the guarana berry, as an additive to sodas and energy drinks, or consumed as powder or tablets (Nehlig et al. 1992). When taken orally, onset typically occurs in 45 to 60 minutes and lasts approximately 3 to 5 hours. Absorption is somewhat delayed when taken with food and its administrable via is the parenteral route, which is a common method when treating apnea of prematurity in newborns or post-dural puncture headaches.

Alternatively, caffeine can be absorbed rectally, insufflated, or inhaled. Consumption via insufflation or inhalation is generally a form of misuse with the intention of getting high. These routes lead to significantly faster absorption, usually within minutes, and bypass the first-pass metabolism. Although this route can lead to a faster onset of action, multiple studies have shown lower bioavailability from inhalation of caffeine; approximately 60% to 70%. When taken via this route, the duration of action is shorter (Laizure et al.2017).

1.1.4 Adverse Effects

As with most drugs or medications, there comes a long list of adverse effects associated with its use, and caffeine is no different. The adverse effects of caffeine range from mild to severe to even fatal and are generally related to the dose consumed and an individual’s sensitivity to the drug. The most common side effects are listed below. Mortality is usually associated with cardiac arrhythmia, hypotension, myocardial infarction, electrolyte disturbances, and aspiration (Kerrigan et al. 2005).

  1. Mild

Anxiety, restlessness, fidgeting, insomnia, facial flushing, increased urination, muscle twitches or tremors, irritability, agitation, elevated or irregular heart rate, GI upset

  1. Severe

Disorientation, hallucinations, psychosis, seizure, arrhythmias, ischemia, rhabdomyolysis are the results of severe effect of caffeine; caffeine can also cause withdrawal symptoms if habitual users abruptly stop.  These symptoms usually begin 12 to 24 hours from last consumption, peak in 1 to 2 days, and may persist for up to 1 week. Withdrawal is preventable if caffeine is tapered off instead of abruptly discontinued. If symptoms do arise, they are promptly reversible by re-administration of caffeine (Juliano et al. 2004).

1.1.5 Contraindications

Although there are no absolute contraindications to caffeine, there are some medical conditions in which caution is necessary, which includes (Fabrizio et al. 2016).

  • Severe anxiety
  • Cardiovascular disease or symptomatic cardiac arrhythmias
  • Peptic ulcer disease or gastro esophageal reflux disease
  • Hepatic impairment
  • Renal impairment
  • Seizures (as may lower seizure threshold)
  • Pregnancy

1.1.6 Pupil

The pupil is the central opening of the iris on the inside of the eye, which normally appears black. The grey/blue or brown area surrounding the pupil is the iris. The white outer area of the eye is the sclera. The central outermost transparent colorless part of the eye (through which we can see the iris and pupil) is the

The pupil is a black hole located in the center of the iris of the eye that allows light to strike the retina (Cassin et al. 1990). It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil. The term “pupil” was created by Gerard of Cremona (Arraez-Aybar et al. 2015).

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In humans, the pupil is round, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats have horizontally oriented pupils, and some catfish have annular types. In optical terms, the anatomical pupil is the eye’s aperture and the iris is the aperture stop. The image of the pupil as seen from outside the eye is the entrance pupil, which does not exactly correspond to the location and size of the physical pupil because it is magnified by the cornea. On the inner edge lies a prominent structure, the collarette, marking the junction of the embryonic pupillary membrane covering the embryonic pupil.

1.1.7  Structure

The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.

  • Iris

The iris is a contractile structure, consisting mainly of smooth muscle, surrounding the pupil. Light enters the eye through the pupil, and the iris regulates the amount of light by controlling the size of the pupil. This is known as the pupillary light reflex.

The iris contains two groups of smooth muscles; a circular group called the sphincter pupillae, and a radial group called the dilator pupillae. When the sphincter pupillae contract, the iris decreases or constricts the size of the pupil. The dilator pupillae, innervated by sympathetic nerves from the superior cervical ganglion, cause the pupil to dilate when they contract. These muscles are sometimes referred to as intrinsic eye muscles (Larson et al. 2008).

The sensory pathway (rod or cone, bipolar, ganglion) is linked with its counterpart in the other eye by a partial crossover of each eye’s fibers. This causes the effect in one eye to carry over to the other.

1.1.8  Effect of light

The pupil gets wider in the dark and narrower in light. When narrow, the diameter is 2 to 4 millimeters. In the dark it will be the same at first, but will approach the maximum distance for a wide pupil 3 to 8 mm. However, in any human age group there is considerable variation in maximal pupil size. For example, at the peak age of 15, the dark-adapted pupil can vary from 4 mm to 9 mm with different individuals. After 25 years of age, the average pupil size decreases, though not at a steady rate (Amateurastronomy, 2013). At this stage the pupils do not remain completely still, therefore may lead to oscillation, which may intensify and become known as hippus. The constriction of the pupil and near vision is closely tied. In bright light, the pupils constrict to prevent aberrations of light rays and thus attain their expected acuity; in the dark, this is not necessary, so it is chiefly concerned with admitting sufficient light into the eye.

When bright light is shone on the eye, light-sensitive cells in the retina, including rod and cone photoreceptors and melanopsin ganglion cells, will send signals to the oculomotor nerve, specifically the parasympathetic part coming from the Edinger-Westphal nucleus, which terminates on the circular iris sphincter muscle, when this muscle contracts, it reduces the size of the pupil. This is the pupillary light reflex, which is an important test of brainstem function. Furthermore, the pupil will dilate if a person sees an object of interest

1.19   Effect of drugs

  1. Pupil dilated for retina examination

If the drug pilocarpine is administered, the pupils will constrict and accommodation is increased due to the parasympathetic action on the circular muscle fibers, conversely, atropine will cause paralysis of accommodation (cycloplegia) and dilation of the pupil. Certain drugs cause constriction of the pupils, such as opioids (Larson et al. 2008). Other drugs, such as atropine, LSD, MDMA, mescaline, psilocybin mushrooms, cocaine and amphetamines may cause pupil dilation (Johnson et al. 2008).

The sphincter muscle has a parasympathetic innervation, and the dilator has a sympathetic innervation. In pupillary constriction induced by pilocarpine, not only is the sphincter nerve supply activated but that of the dilator is inhibited. The reverse is true, so control of pupil size is controlled by differences in contraction intensity of each muscle.

Another term for the constriction of the pupil is miosis. Substances that cause miosis are described as miotic. Dilation of the pupil is mydriasis. Dilation can be caused by mydriatic substances such as an eye drop solution containing tropicamide.

  1. Diseases

A condition called bene dilitatism occurs when the optic nerves are partially damaged. This condition is typified by chronically widened pupils due to the decreased ability of the optic nerves to respond to light. In normal lighting, people afflicted with this condition normally have dilated pupils, and bright lighting can cause pain. At the other end of the spectrum, people with this condition have trouble seeing in darkness. It is necessary for these people to be especially careful when driving at night due to their inability to see objects in their full perspective. This condition is not otherwise dangerous.

  1. Size
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The size of the pupil (often measured as diameter) can be a symptom of an underlying disease. Dilation of the pupil is known as mydriasis and contraction as miosis.

Not all variations in size are indicative of disease however. In addition to dilation and contraction caused by light and darkness, it has been shown that solving simple multiplication problems affects the size of the pupil. The simple act of recollection can dilate the size of the pupil, however when the brain is required to process at a rate above its maximum capacity, the pupils contract. There is also evidence that pupil size is related to the extent of positive or negative emotional arousal experienced by a person (Partala et al. 2003).

 1.2     Statement of the problem.

Pupillary response and accommodation are important physiological processes of the eye that affect vision. Ocular accommodation is a blur driven reflex and results in focusing of images onto the retina.1 The pupil regulates retinal illumination to optimize visual perception. Other visual functions such as contrast sensitivity, color perception, and visual acuity are influenced by pupil size and accommodation. Caffeine being a weak stimulant called xanthenes has been supposedly known to account for the changes in some visual functions or vision-related task associated with caffeine intake, but the effect of its consumption on the papillary size among Nigerian blacks has not been widely documented.

 1.3     Study Objectives.

1.3.1       Aim.

The aim of this study was to determine the effect of caffeine consumption on pupil size.


1.3.2       Specific Objective.

  1. To determine the effect of caffeine on pupil size based on age.
  1. To determine the effect of caffeine on pupil based on gender

1.4     Research questions.

  1. What effect does intake of caffeine have on pupil size of different age group?
  1. What effect does intake of caffeine have on pupil size of different gender (male/female)?

1.5     Research hypotheses.

  1. H0: Caffeine has no statistically significant effect on pupil size.
  1. 2. H0: Age has no statistically significant relationship with the effect of caffeine on pupil size.
  2. 3. H0: gender has no statistically significant relationship with the effect of caffeine on pupil size.

1.6     Significance of the study.

The result of the study will be of immense benefit to the following groups.

  1. Optometrists: Variations in pupil size has influence on the rate of out flow of aqueous humour which is the determinant factor in maintaining the intraocular pressure of the eye. Therefore, this study will serve as a platform for Optometrists and other eyecare practitioners on how to handle their patients with glaucoma or ocular hypertension.
  2. Patients: Patients who have been diagnosed of glaucoma or ocular hypertension will have the knowledge of how taking caffeine can influence their ocular health.
  3. Researchers: It will make room for further research studies in areas of visual function and components.

1.7     Scope of the study.

This was carried out using students of Imo State University community who were within the age range of 18 to 53 years. In this study, most of the subjects were habitual caffeine users. Subjects that regularly ingest caffeine might have yielded insignificant results because of the tendency for them to develop a tolerance level towards the effect of caffeine. There was non-equal gender distribution and an underrepresentation of the geriatric population. Few subjects included had some degree of presbyopia might have caused a bias in the data.

1.8     Justification of the study.

Some glaucoma patients on medication often times experience changes in their intraocular pressure despite they are on medication. Some of them present with dilated pupils, some with normal sized pupils and with some slightly constricted pupils, it becomes obvious that pupil size could be a contributory factor in such variation. Therefore, this study was aimed to examine the effect of caffeine on pupil size and appropriate suggestions to be recommended.

Pages:  46

Category: Project

Format:  Word & PDF         

Chapters: 1-5                                 

Material contains Table of Content, Abstract and References.


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