The 4th IEEE International Conference on E-Health and Bioengineering - EHB 2013 Grigore T Popa University of Medicine and Pharmacy, ia:ji, Romania, November 21-23, 2013

Study of pupil reflex under chromatic light radiation

incidence Mihaela Ioana Baritz

University Transilvania Brasov; Product Design, Mechatronic and Environment Department

Brasov, Romania e-mail: mbaritz({j)unitbv.ro

Cristina Singer UMF Craiova

Craiova, Romania e-mail: singercristina@gmail.com

Abstract- Some theoretical and experimental considerations

upon the pupil behavior at iris level of human subjects with no

previous detected pathologies are presented. Thus, in the first

part of the paper we presented and analyzed the aspects related

to the iris dynamics and bio-optics for different subjects'

samples, out of which the examples for applying the proposed

methodology will be selected. In the second part of the paper the

required analysis structures for recording and assessing the iris'

biomechanics are developed and presented, also the behavior for

various radiation levels. In the third part of the paper we

presented and processed the results and conclusions concerning

the iris' behavior subjected to different light radiations.

Keywords- pupil reflex, light radiation, iris.

I. INTRODUCTION

According to the authors of some ophthalmology treaties,

the iris is defined as the upper part of the uveal tract,

differentiated as a slim diaphragm located in the frontal plane

and crossed by a central orifice called the pupil. It has an

optical role by accomplishing a diaphragm with variable

opening, which controls the light intensity entering the

eyeball. [1]

Iris has a double function: on one hand it takes part in

creating the blood aqueous barrier and on the other hand

plays the optic role of a diaphragm.

Vascular endothelium at iris' level determines by an

endocytosis phenomenon an active transport of aqueous

humor in the anterior chamber on uveal-scleral path.

The iris has the role of an opaque screen, which doses the

light quantity reaching the retina according to the light

intensity.

Actinic and myosin filaments contraction determines the

shortening of muscular fiber, while the desmin filaments help

transmitting this motion to the neighboring cells.

The pupil orifice prevents light from passing through the

crystalline periphery, diminishing thus the spherical and

chromatic aberration.

Diana Laura Cotoros University Transilvania Brasov; Product Design, Mechatronic

and Environment Department Brasov, Romania

e-mail: dcotoros@unitbv.ro

Fig. 1. Structure of the iris [2]

When the pupil contracts, the focus deepens by reducing

the focusing circles at retina's level and the image located on

the retina becomes clearer. [I]

Nonnally the iris is identically colored at both eyes. In the

heterochromatic iris, the iris of one eye presents a different

color to the iris of the other eye. Heterochromatic irises may be congenital or acquired, being

determined by inflammatory diseases, where the iris' color is darker due to congestion or presents a grey chromatic due to the exudates on its surface.

There are several manifestations at iris' level modifying both its structure and its functioning. Thus, the circulation changes highlight the iris' blood vessels, which normally are not visible. In inflammatory processes, in the cilliar part, the vessels appear rectilinear or slightly undulated, radial oriented. At coreleta's level, the small arterial circle often appears very obvious. In the pupil's part the vessels form an irregular network; these are iris' vessels which become visible. [2]

In some of the analysis presented in ophthalmology treaties, it shows that the iris' atrophy occurs as a torpid uveitis sequel or in advanced glaucoma stages. The atrophy of the pupil margin is frequently noticed as a manifestation of a senile involution or as a sequel of an inflammatory stage. The so

978-1-4799-2373-1/13/$31.00 ©2013 IEEE

called pigment collar disappears and appears as a vitreous, translucent membrane with well defined edges. This pigment sheet is much retracted at pupil's edge in the form of a thin pigment layer, with an apart aspect. These atrophies lead to changing the iris' thickness or dimensions, respectively of the pupil. [8]

The iris' dimensions are various between different individual categories, but in average it is 12 mm in diameter and presents a 30011 thickness, its axial shape being slightly conical.

The pupil is represented by the circular central opening of the iris' diaphragm and works as a mobile opening. It doses the light quantity and protects retina against bright light; participates in obtaining a light clarity, by controlling the field depth and diminishing the spherical and chromatic aberration. Normally both pupils of the eyeballs are equal. Normal diameter of the pupil varies between 2 and 4 mm, in average being of 3 mm. When the diameter is smaller the pupil is in miosis and over 4mm it is in mydriasis.

Fig. 2. Axis of the iris and pupil [3]

Normally pupil is smaller in newborn children and elderly people; its diameter is larger for females. According to the ocular refraction, pupil is larger for short-sighted than hyperopic and according to the vegetative nervous system the pupils are more dilated in simpaticotomy subjects and smaller in parasimpaticotomy subjects. [9]

A difference in size between the two pupils of the eyeballs represents the anizocoria state, which may occur also in physiological conditions by newborns with a 2% frequency in case of a sphincter lack of development. The physiological anizocoria state is considered only when the pupil reflexes are normal.

Normally the pupil is roundly shaped, regular being located a little eccentric on the nasal side and respectively the pupil appears black colored at direct examination or red at ophthalmoscope examination.

The color changes with age, getting a yellow-grey reflex for elderly people (at direct examination) due to the senile densification of the crystalline.

Pupil reflex in light (photo-motor reflex) occurs after a 0,2 seconds latency and becomes maximum after I second.

Consensual photo-motor reflex is emphasized by covering one eye while the other one is free, then the hand is removed

from the covered eye and we notice the change of pupil diameter for the other eye. [6]

Accommodation-convergence reaction consists of the pupil contraction in near sight.

Human subject looks at a large distance and then looks at the finger placed 15 cm before his eyes on the median line.

Convergence and miosis state should be symmetrical and of the same intensity for both eyeballs.

After ceasing gaze fixation, the pupils dilate again equally symmetrical. Conscious and forced closing of eyelids is accompanied by pronounced bilateral miosis in orbital-pupil reflex. When opening the eyelids the pupil dilates and the examination is performed by maintaining an open palpebral slit while the subject tries to close his eyes. [7]

According to the eye specialists' opinion, photophobia may be a physiological manifestation when the eye is stimulated by a bright beam that goes into the eyeball and is received by the retina. In most of the situations photophobia represents a symptom associated to multiple ocular diseases. Photophobia manifestation is a form of discomfort that may occur both for adults and for children. [10]

Thus the correlative analysis of the pupil operating mode, respectively of the pupil reflex, together with the analysis of iris' structures may determine a thorough knowledge and understanding of the mechanisms working at eyeball level subjected to light radiation with different wavelengths, continuous or intermittent emission.

II. MODELS OF PUPIL DYNAMICS

In professional literature there are several models for the

analysis of pupil dynamics, especially the ones related to the

use of different radiations but also for determining balance

cases and/or malfunctions. [4]

Authors like Link and Stark (1988), Ellis (1981) or Smith

(1995) analyzed and defined a category of empirical models

based upon a series of experiments which showed the

connection between the pupil size and the type of light

radiation entering the eyeball. Of all the study models of the

pupil reflex, the most cited and used is the one defined by

Moon and Spencer (1944), according to the formula (1).

D = 4.9 - 3tanh [O.4(1g(Lb) - 0.5)] (I) where the pupil diameter D varies from 2 to 8mm, and Lb is

the background luminance level expressed in Blondels,

varying from 105 Blondels in sunny days to 10-5 Blondels in

dark nights, tanh is the hyperbolic tangent.

Another model, equally important is the one created by

Groot and Gebhard (1952) and defines the pupil diameter

according to (2).

D = lO{o.x55s-o.ooo4o[lg(h,)+x.IY} (2) where the background luminance level La is measured in

millilamberts (mL).

The Pokorny and Smith model (1995) expressed by the

formula (3) is simplified and easier to use.

D = 5 - 3tanh(0.4(1g(Lcd))) (3)

where the luminance Lcd is measured in candelas per square

meter (cd/m2).

These models represented the basis of many studies and determined the development of other models (statistic or computerized) that allowed the highlight of some manifestations specific to pupil dynamics. [5].

III. EXPERIMENTAL SETUP

The system used for the analysis of pupil reflex and of

dynamic and static behavior of the pupil most be considered

in the first stage, the use of models presented before but also

the selection of a subjects' sample that will be investigated

upon the iris structure. Also the iris' pigmentation of the

Fig. 3. Subjects' sample

entire sample was chosen to be different; they presented no

malfunction or pathology. Thus, following anamnesis, four

subjects were selected (fig.3), with different iris color, in a

good health state, with no refraction issues or functional

abnormalities of the ocular structures.

Fig.4.Positioning of light source on the analyzed eye

In the environment where the examination and recordings

took place, the temperature was kept the same (1S°C) and

also the same type of general illumination (natural and

artificial) with values varying between 190-230 Ix on the

entire duration of tests.

The structure of recording methodology of pupil static and

dynamic behavior was the same for the entire sample

allowing thus a correlation between the measurements and

observations performed at the same type of analysis.

The analysis system includes firstly a continuous light

radiation source with the possibility of altering the

wavelength in the visible spectrum from blue to red and

respectively compound white, also with the possibility of

varying emission frequency and getting thus a stroboscopic

effect. In order to obtain the recording of pupil motions

behavior we used an image acquisition and processing system

that allowed also the measuring of motion duration of the

pupil for each eye under the influence of light radiation. In

order to analyze the pupil behavior, the selected subject gazed

to infinite in accommodation, with one of the eyes in

occlusion, and the other subjected to the light radiation (with

continuous emission) for 5 seconds. On each eye, a

continuous emission beam was projected with different

wavelengths (compound white, yellow, red, green and blue)

(fig.5).

Following this set of light sequels, for each selected subject

we recorded the corresponding values of the pupil response

duration until the moment of pupil opening stabilization, by

acquisition and image processing procedures. [3] After each

Fig.5. Applying the light radiation filters

application of a light beam, the subjects were allowed to

adapt again to the environmental light intensity, so that the

dynamic responses were only due to the chromatic radiation

level applied for 5 sec. Also the subjects' position and posture

with respect to the illumination source was the same, fixed,

the other eye totally covered and without blinking during the

light beam application.

IV. RESULTS AND CONCLUSIONS

Following the recordings of the pupil reflex behavior for

each eye we were able to measure the pupils diameters at the

moment of adjusting process stabilization and also follow the

dynamics of this process in order to evaluate the adjustment

degree. In the same analysis methodology we used in the

second stage a discontinuous light beam (frequency of 2

impulses/sec) in order to follow the adjustment degree and

dynamics of pupil response in stroboscopic light. These

manifestations were recorded the same way, by acquisition

and image processing and highlighted a much more dynamic

behavior of the pupil reflex in the first 3 seconds when the

eye was under the influence of pulsing light radiation. After

this period of time the pupil motion stabilized and its

diameter was measured. For the red color filter this pulse was

lower, the pupil diameter oscillating around the initial value

measured before each test.

In table no.1 the data obtained from the selected subjects'

sample tested with continuous emission light radiation beam

are presented, while in fig.6 and fig.7 the variations of RE, respectively LE diameters are presented for vanous

wavelengths.

TABLE 1.

beam subjl subjl subj2 subj2 subj3 subj3 subj4 subj4 light I RE LE RE LE RE LE RE LE diam. [mm] [mm] [mm] [mm] [mm] [mm] [mm] [mm]

white 201 2.02 2.52 2.51 2.53 2.5 2.02 2.05

yellow 1.75 1.77 2.03 2.02 2.08 2.02 2.01 2.01

red 4.04 4.02 3.05 3.03 3.08 3.02 3.04 3.54

green 3.13 3.04 3.06 2.54 2.75 3.03 2.57 3.04

blue 3.53 3.51 2.05 2.54 3.11 3.05 3.08 3.08

average 2.89 2.87 2.54 2.52 2.71 2.72 2.54 2.74

4.5 -

4

/. �� 3.5 -3 2.5 �ject3 � D subject '""! ODSU� 2 --..

1.S

1

0.5

0 white yellow 'ed Breen blue

Fig.6. Evolution of pupil diameters RE (00) for different radiations

4.5

1.5

0.5

o

2.9

2.8

wl)ite yellow ,ed green blue

Fig.7. Evolution of pupil diameters LE (OS) for different radiations

Y"" *O.Q031x3+ O.0586x2·O,3356x+ 3.208 S::J = O�525-1-

2.7 +------=�lc-T;;==:---�ft>===""=__==.._..:.r--2.6

2.5 Average values of pupilar diameter for OD and OS

2.4

2.3 6 8

Fig.S. Average variation of pupil diameter for right eye 00 and left eye OS

From the figures above we may notice that the variation

tendency was constant both for right eye and for left eye,

emphasizing the fact that for the red color radiation, in

continuous illumination, the pupil diameter changed very

little about the initial value. Also the influence of the director

eye in this type of test can be observed in diagram shown in

fig.8, the director eye being the one that participated less,

maintaining a higher value of the pupil diameter in case of

continuous illumination (close to the initial one). In this

respect we may conclude that the eye movements of the four

subjects were constant in displacement along the two axes,

vertical and horizontal. Fixation existed along the entire

duration of the exercise for all four subjects.

For all four subjects the pupil reflex analyzed at the

moment when one eye was in occlusion, the pupil opening

oscillated between the minimum-high/average-average value,

while at the binocular examination, both eyes reacted the

same way. Also the pupils remained in the same position for

3-4 seconds from iIIumination.The analysis of nistagmus

movements was accomplished for near vision but also for

distance vision.

For the analysis of the pupil reflex for different

wavelengths we noticed how the pupil changed its diameter.

In case of the subjects with light color iris (blue) this reaction

was easier to notice. Mostly for the red color filter and less

for the green and blue ones, the pupil changed its diameter in

average with only 30% by comparison to the reaction to the

yellow filter, when the reaction was 70-80% of the initial

diameter

ACKNOWLEDGMENT

These researches are part of the current researches in

optometric laboratory and we've developed the investigations

with equipments from Advanced Mechatronic Researches

center in University Transilvania Brasov.

REFERENCES

[1] Paul Cernea,. Tratat de oflalmologie, 2nd ed., Editura Medicala 2002. 973-39-0313-2;

[2] Michael O. Hughes, Anatomy of the Anterior Eye for Ocularists. Journal of Ophthalmic Prosthetics, fall 2004;

[3] WWW.lflscamera.com. [4] V. F. Pamplona, "Photorealistic Models for Pupil Light Reflex and

Iridal Pattern Deformation," Master thesis, Porto Alegre, April 200S, Universidade Federal do Rio Grande do SuI.

[5] YF. Pamplona, M.M. Oliveira, G.Y.n Baranoski "Photorealistic Models for Pupil Light Reflex and Iridal Pattern Deformation," ACM Transactions on Graphics, Vol., No., 20, Pages 1-20, 2009.

[6] C../. Ellis, "The pupillary light reflex in normal subjects," British Journal of Ophthalmology, 1981, 65, 754-759

[7] A. Longtin and J. G. Milton, Modelling Autonomous Oscillations in the Human Pupil Light Reflex Using Non-Linear Delay-Differential Equations. Bulletin of Mathematical Biology Vol. 51, No. 5, pp. 605-624, 19S9.

[S] M. O. Hughes, "Anatomy of the Anterior Eye for Ocularists", Journal of Ophthalmic Prosthetics,

[9] H Kenneth Walker, W Dallas Hall, J Willis Hurst. "Clinical Methods " 3rd edition. Boston 1990. 10: 0-409-90077-X,

[10] A. de Castro, P. Rosales, S. Marcos, "Tilt and decentration of intraocular lenses in vivo from Purkinje and Scheimpflug imaging Validation study" Journal of Cataract & Refractive Surgery Volume 33, Issue 3, March 2007, Pages 41S-429