A M O D E L F O R T H E P U P I L L A R Y L I G H T R E F L E XS I M E O N W O N G , C I N D Y B U I

O U T L I N E

• Background

• Light Reflex

• Pathologies and Drug Influences

• Pre-existing Models

• Project Objectives

B A C K G R O U N D

• Main purpose of pupillary light reflex to moderate intensity of lighting entering the eye

• Important to protect retina function

• Retina is extremely sensitive to light to maximize visible dynamic range

B A C K G R O U N D

• Effected through antagonistic muscle pairs on iris:

• Constriction - Circular Sphincter

• Dilation - Radial Dilator

196 Chapter 6

Aqueous humor is produced at a rate of about 5 ml/day by a capillary network within the ciliary body, a specialized ante-rior derivative of the choroid layer. Th is fl uid drains into a canal (the canal of Schlemm) at the edge of the cornea and eventually enters the blood (● Figure 6-12).

If aqueous humor is not drained as rapidly as it forms (for example, because of a blockage in the drainage ca-nal), the excess accumulates in the anterior cavity, caus-

ing the pressure to rise within the eye. Th is condition is known as glaucoma. Th e excess aqueous humor pushes the lens back-ward into the vitreous humor, which in turn pushes against the inner neural layer of the retina. Th is compression causes retinal and optic nerve damage that can lead to blindness if the condi-tion is not treated.

The amount of light entering the eye is controlled by the iris.Not all the light passing through the cornea reaches the light-sensitive photoreceptors, because of the presence of the iris, a thin, pigmented smooth muscle that forms a visible ringlike structure within the aqueous humor (see ● Figure 6-11a and b). Th e pigment in the iris is responsible for eye color. Th e varied fl ecks, lines, and other nuances of the iris are unique for each individual, making the iris the basis of the latest identifi cation technology. Recognition of iris patterns by a video camera that captures iris images and translates the landmarks into a com-puterized code is more foolproof than fi ngerprinting or even DNA testing.

Ciliary body

Suspensoryligament

Posterior cavitycontainingvitreous humor

Canal of Schlemm

Posteriorchamber

Anteriorchamber

Aqueoushumor

Iris

Ciliary musclein ciliary body

Anteriorcavity

● FIGURE 6-12 Formation and drainage of aqueous humor. Aqueous humor is formed by a capillary network in the cil-iary body, then drains into the canal of Schlemm, and eventually enters the blood.

Parasympathetic stimulation Sympathetic stimulation

In dimlight

In brightlight

In normallight

Circular(constrictor)muscle runs

circularly

Pupil IrisRadialmuscleof iris

Circular muscle of iris

Radial(dilator)

muscle runs radially

Pupillary constriction Pupillary dilation

● FIGURE 6-13 Control of pupillary size.

91845_06_Ch06_182-235.indd 196 11/18/08 11:45:01 AM

“Control of Pupillary Size” Sherwood, L. (2001). Human physiology: from cells to systems (4th ed.). Pacific Grove, Calif.: Brooks/Cole.

PAT H O L O G I E S

• Pupil area pathologies are usually caused by defects in the sympathetic or parasympathetic innervation pathways

• Sympathetic defect: Miosis

• Uncontrollable over-constriction of pupils

• Parasympathetic defect: Mydriasis

• Uncontrollable dilation of pupilsMydriasis. (2013, October 26). Wikipedia. Retrieved October 28, 2013, from http://

en.wikipedia.org/wiki/Mydriasis

Miosis. (2013, October 24). Wikipedia. Retrieved October 28, 2013, from http://

en.wikipedia.org/wiki/Miosis

D R U G S

• Mydriatic drugs antagonize sympathetic nicotinic receptors in the eye and prevent contraction, causing dilation

• Eg. Tropicamide, Scopolamine, LSD

• Miotic drugs overstimulate sympathetic pathway in the eye and cause excessive contraction

• Eg. Organophosphates, Trazodone, Heroin (Opiods)

T R E AT M E N T S

• Oriented towards restoring pupil function to protect the retina

• Dependent on root cause

• Symptoms may be treatable by using drugs with opposite effect

• If side effect of medication, doctor may prescribe alternative to resolve adverse effects

O T H E R S T I M U L I

• Ongoing studies on effects of:

• Hormones

• Attractive People

• Anxiety

• Mental Activity

• Serotonin

P R E - E X I S T I N G M O D E L S

N E U R O M U S C U L A R R E F L E X

C O N C E P T U A L D I A G R A M O F P U P I L D I L AT I O NKhoo, M. C. (2000). Physiological control systems. IEEE press. Chicago

L I G H T R E S P O N S E E Q U AT I O NPamplona, V. F., Oliveira, M. M., & Baranoski, G. V. (2009). Photorealistic models for pupil light reflex and iridal pattern deformation. ACM Transactions on Graphics (TOG), 28(4), 106.

Khoo, M. C. (2000). Physiological control systems. IEEE press. Chicago

P R O J E C T O B J E C T I V E S

• Combine current models together into one cohesive Simulink model for pupil diameter in response to varying stimuli

• Use neuromuscular reflex blocks as CNS block in conceptual diagram

• Combine with differential equation expressed in s-space

• Add blocks for drug influence and pathology

• Mydriatic and miotic drugs

• Pinched oculomotor nerve from trauma

R E F E R E N C E S

Sources

Sherwood, L. (2001). Human physiology: from cells to systems (4th ed.). Pacific Grove, Calif.: Brooks/Cole.

Khoo, M. C. (2000). Physiological control systems. IEEE press. Chicago

Pamplona, V. F., Oliveira, M. M., & Baranoski, G. V. (2009). Photorealistic models for pupil light reflex and iridal pattern deformation. ACM Transactions on Graphics (TOG), 28(4), 106.

Images

Sherwood, L. (2001). Human physiology: from cells to systems (4th ed.). Pacific Grove, Calif.: Brooks/Cole.

Miosis. (2013, October 24). Wikipedia. Retrieved October 28, 2013, from http://en.wikipedia.org/wiki/Miosis

Mydriasis. (2013, October 26). Wikipedia. Retrieved October 28, 2013, from http://en.wikipedia.org/wiki/Mydriasis

Q U E S T I O N S ?