temperature changes in contact lenses in

8/16/2019 Temperature Changes in Contact Lenses In

1/6

Scand

j.

work environ

health 5 1979

280-285

emper ture

ch nges

in cont ct

lenses

connection

with

r di tion from infr red

he ters

by

PER LOVSUND,

M.SC.E.E.,l SVEN ERIK

G.

NILSSON, M.D.,

Ph.D.,2

and

P. AKE OBERG, Ph.D.I

LOVSUND,

P. ,

NILSSON, S. E. G. and OBERG, P.

A. Temperature

changes

in

contact

lenses

in

connection

with radiation from infrared heaters. Scand j. work

environ health 5 1979) 280-285.

number

of

reports have appeared over the

past

few years with

warnings about

th e

wearing

of contac t l ense s

i n cert ain t rades

involving

exposure

to

arc

flash.

In view

of

these reports and i n light

of knowledge

on th e

marked

absorption by contact lenses, within the infrared R) region, tem

perature changes

were

measured

in

soft contact lenses under radiation from IR

heaters

used, for example,

i n t he motor indust ry

for

drying

paint.

The

lenses

were

tested while free-hanging and when applied to rabbit

eyes.

Great increases

in

tem

perature

were

noted with one of th e

heaters

at a dis tance corresponding to safe.

During 10

min

of

exposure the tempera ture

of a

free-hanging

lens rose from

21

to

59°C,

whereas the temperature in th e surrounding air increased

only

from 26 to

30°C.

The

final temperature

of

the lens was

thus

29°C

higher

t han tha t

of

the

air.

In lenses applied

to rabbit

eyes

th e temperature

rose

within

only 0.5, 1.0, and 1.5

min from approximately

33°C

to about

44, 49,

and

51°C,

respectively;

the air tem

perature rose f rom 25 to only 28°C. In other

words,

the u lt imate

lens

temperature

was

23°C

higher than

the

ambient ai r temperature.

In t he rabbi t experiments most

of the

lenses

dried out

completely.

There

would

thus

seem

to be

considerable

risk

of

contact

lenses

dry ing and

becoming

adherent

to and damaging th e corneal sur

face among

workers

exposed to power fu l

radiation

from

IR rad ia tors

IR heaters ,

unless

they use

e ff ic ien t eye protector s.

IR heaters appear to be

associated

with

greater

hazards

than

arc flashes,

since

there is

no

warning from powerful

visible light and because

they

are capable

of

causing a very rap id increase

in

tem

perature.

Key

words

corneal damage,

infrared

heaters,

radiation

hazards, sof t contact lenses,

temperature

changes,

worker

safety.

has been a ss er te d

on

several occasions

in

t he l it er at ur e that welding

arcs and

other h igh-energy a rc s may constitute a

serious

hazard

for

wearers of

contact

Department

of Biomedical Engineering, Uni

versity of

Linkoping, Sweden.

2

Department

of Ophthalmology,

University

of

Link6ping,

Sweden.

Reprint requests

to: Prof. S. E. G. Nilsson,

Department

of Ophthalmology,

University

Hos

pital, Un iver sity of Link6ping,

S-581

85 Lin

k6ping,

Sweden.

0355-3140/79/030280-6

lenses

1,

4, 7, 9,

10, 13).

The case that set

off

th e

discussion

was that of

a

shipyard

wo rker w it h

con tact l ense s who developed

corneal

lesions after exposure

to a

power

ful

f lash occurr ing

when

a circuit

breaker

arced durin g th e connect ion o f a welding

cable. He

was

wear ing s af et y glasses

at

the time.

has since

been

alleged that

the

injury

was due

to

17-18

h

of con

tinuous

wearing

of

the lenses

8,

10,

11,

12)

and

that

the original

report

was noth

ing

but

an indus tr ia l a troc ity s to ry

12).

No

e xp erime nta l in ves tig ation s o n

the


2/6

problem have been carried out

to

our

knowledge however,

and

existing

reports

offer

too flimsy a bas is for recommenda

tions

to contact lens

wearers exposed daily

to

electric

arcs

or o ther

radiation.

there

fore seems a matter of interest to elucidate

the question.

This investigation

is

a

direct continua

tion of studies on the t ransmit tance and

absorption properties of certain contact

lens

materials

3

and on temperature

changes

in

contact lenses during

radiation

from certain welding processes 2

that

we

have car ried out.

We

have

shown that

marked

absorption occurs

in the infrared

IR) region 3 .

The

present

work

was

therefore undertaken

to

investigate th e

temperature

changes that take

place in

contact

lenses on exposure

to

radiation

f rom two dif feren t

IR

heaters.

IR heaters are used,

fo r

example,

in

th e

motor

industry and

at workshops

for d ry

ing paint on cars.

is

suspected

that

IR

radiation

may cause

damage

to

th e eyes

radiation cataract). The Swedish

National

Board

of Occupational Safety and Health

has therefore analyzed work

conditions

in

connection

with IR

heaters

and has

also

investigated th e emission from 10 common

heaters

6).

The

heaters

were examined

with

regard to

spectral

distribution, ra

diance

at

different

distances,

source area,

luminance, and other factors.

MATERIAL AND METHODS

Temperature re or ings

Copper-constantan

T) thermocouples

High

Temperature

Instruments

Corpora

t ion, U.S.A.)

were

used. The tips were

flattened

to

approximately 80 / The

tem

perature

was

read from

a five-channel

digital indicator oric, U.S.A.)

with

a

res

olution

of 0.1°C and with built-in lineari

zation and compensation for the cold junc

tion.

The following control exper iment was

done to establish

whether a false

rise

temperature may

occur as a result of

IR

radiation absorption

by the naked

thermo

couple.

Two

identical

thermocouples

were

mounted

at

th e same level and 0.2 m

apart

at

a

dis tance of

0.5

m

from one

of

th e IR

heaters dcoat). A powerful air

current

was

fanned

over them from one side. The

same

air

temperature was recorded

by

both thermocouples. When one of them

was screened from th e

IR

radiation

no

change

in temperature

was noted

in either

thermocouple. Thus, no false

temperature

increase

from

the absorption of IR radia

tion

by the naked

thermocouple

was found.

nfrared heaters

IR

radiation

was

generated by two diffe r

ent

heaters,

Elektrofem

IF-03, 6 kW)

and

Adcoat

AB

IR 2200, 2.2 kW).

Their main

specifications

are summarized in

table

1

and

fig.

1.

The

safe

distances calculated

for the

hea te rs a re taken

from the

recom

mendations of the Swedish National Board

of

Occupational

Safety and

Health 6),

and

they

are based

on

th e estimated

risk

of

cataract caused by absorption of near IR

radiation by

the lens

of

the eye

5).

easurement of temperature in

free-

hanging

contact tenses

Soft lenses of th e HEMA hydroxyethy

methacrylate) type

were

used.

The

ther

mocouple was placed

at

th e center of

the

lens with the probe tip

inside

th e lens. The

lens was

thoroughly wet with

physiological

saline

at

the s ta rt of

each

recording. Two

makes of lens were used, Weicon 15.50

D

or

Soflens

17.00 D,

both

of which

have a water content of 39 and a lens

thickness

in the wet state) of approxi

mately

0.5

mm

at

th e point where

the

temperature

was recorded. A second ther

mocouple placed in

front

of th e

lens

was

used

to

record

ai r

t empera ture . The

radia

tion f rom

the IR heater

was direc ted

to

wards th e front of the lens.

easurement of temperature in contact

tenses

applied

to

rabbit

eyes

The exper iments with rabbits were done

so

that

th e

true

conditions

at

a place of

work could

be reproduced as

closely

as

possible. Soft, HEMA-type lenses were

used,

applied

to

the

eyes of adult,

pig-

281


3/6

Table 1.

Specifications

of

t he inf ra red hea te rs

[from

Ruth et al . 6 ].

Infrared

Spectral

Approx.

Power

Luminance

Safe

heater

region radiation max.

kW

cd/m

2

distance

nm

nm

m

Elektrofem

1,000 -

>

3,200 2,500

6.0 0

0.5

IF-03

Adcoat AB,

750 -

>

3,200

3,300

2.2

40 1.0

IR

2200

500 1000 1500 2000 2500 3000

Wavelength

nm

ElEKTROFEM

kW

100

500 1000 1500 2000 2500 3000

Wavelength nm

O O T kW

ig

1 Spectral dis tr ibut ion curves for

the

two

infrared

heaters [from

Ruth et al . 6 ].

mented

rabbits. The animals

were

awake

and

unanesthetized.

In these experiments

it

proved impos

s ib le to retain the thermocouple in a

single

lens,

as it became

dislocated by the least

eye

movement. A double lens one Hydron

- 1.75 D and

one

Soflens + 3.50 D was

therefore

constructed in which

th e radii

of

curvature of the

inner

lens

matched ex

actly

those

of

the cornea

and th e

posterior

surface of the

outer

lens. The lenses

were

glued together

at

the

extreme periphery,

and

the

thermocouple,

flexed to fit,

was

introduced between the wet lenses, care

being

taken

to exc lude

air bubbles. The

wet

combination

was 0.6 mm thick at the

measuring point. In

these

experiments

only the Elektrofem

heater

was used.

Changes

in air temperature were

record

ed

with a thermocouple in front of the

lens. The animal was

arranged

so that the

optical axis

of the

eye

under

investigation

was directed towards the IR heater. The

lenses

were rewet

between each

experi

ment.

282

RESULTS

emper ture

ch nges in free h nging con-

t c t lenses

Temperature

changes

in the lenses and the

surrounding air during 10 min of con

tinuous radiation from each of the two

IR

heaters at a

distance

of 0 5 m are shown

in table

2

No significant difference was

found between the two

types

of lens, and

the results

are

therefore given

as

the

means of the two. In absolute figures

the

lens

temperature

increased

in 1 3 and 10

min

from 21°C to 42, 50, and 59°C, re

spectively, with the Elektrofem heater.

With the

Adcoat

the lens temperature

rose

from

20

to 45°C in 10 min.

The air tem

perature

rose

from

26

to

30°C and

from

25 to 28°C for the two heaters, respective

ly ;

in

other

words

the

final

temperatures

in the lenses were 29

and

17°C higher

than

in

the surrounding air. With Elektro

fern

the

distance tal l ied with

the

safe

dis

tance.

For Adcoat

the

safe distance is


4/6

1 m,

however, and with radiation

at

this

distance th e lens temperature

did not

in

crease

more

than that of th e surrounding

air.

emper ture ch nges in ont t lenses

pplied

to

r bbit

eyes

was found that

in the

conscious

animal

th e unanesthetized

eye,

equipped with

a

double lens,

was often shut o r almost shut

when

exposed to

th e IR heater.

When

th e

eye was completely shut ,

th e

increase

in

temperature

was

halted o r

reversed. The

results are therefore

divided

into

record

ings made with

th e

eye open and with

an

approximately 3-mm palpeb ral fissure.

The dis tance was

0.5 m,

which corresponds

to

the

safe

distance for

th e

Elektrofem

heater.

The

results

are

given in

table

3

and

fig.

2 Exposures of

0.5, 1.0

and

1.5

min with the eye fully

open

caused th e

lens temperature

to increase from about

33°C

to

approximately 44, 49, and 51°C,

respectively. Because

th e

air

temperature

rose only f rom 25

to 28°C,

the increases

in the lenses

were 16, 21, and 23°C

greater

than in the surrounding air. With

an

ap

proximate ly 3-mm palpebral fissure and

an exposure t ime of

1.5

min th e lens tem

perature

increased

to only

44°C average .

In al l th e experiments in which

th e

eye

was kept

open,

and

also

in several in

which th e

palpebral fissure was slight ly

smaller, th e lenses dried completely and,

as

a

rule,

also

became deformed and fell

out of the

eye.

In

a

few

cases

th e

lenses

became

adherent

to

th e

corneal surface.

In one exper iment the tempera tu re of

th e naked

corneal

su rface was measured

during radiation from the Elektrofem

heater

at

a d istance of 0.5 m.

The

tem

perature of th e corneal surface

a lso rose,

and the

increase was pract ical ly ident ical

to

that recorded

in

th e contact

lenses.

DISCUSSION

The two

IR

heaters tested

emit

radiation

within

roughly th e same

region of the

spectrum. The power is

near ly three times

greater

in Elektrofem 6

kW

than in

Adcoat

2.2 kW ,

however.

Of

the heaters

tes ted by the

Swedish National Board of

Occupational Safety and Health, Elektro

fem had the greatest power, whereas Ad

coat was among

those with

the

lowest

power. Because both generate

very l it tl e

visible

light,

there

is

only

a

limited warn

ing of

th e

radiation,

and prolonged expo

sure

may occur. A

worker with contact

lenses therefore

runs

th e risk that the

l enses become overhea ted, dry out, and

become

adherent

to

the

corneal

surface.

The cornea

itself

and

it s

tear

film

also

show

marked

absorption in the IR region

and consequently also

an increase

in

tem

perature.

Without contact lenses, however,

the th in

tear film

is

probably

maintained

by blinking. On

th e other

hand, it

seems

ble

2.

Increase in temperature

0C)

in wet, free-hanging contact lenses

after

10

min of radiation: A comparison of two infrared heaters.

Infrared heater

Elektrofem N =

2

Adcoat

N

=

3

Lens temperature

Initial

21 20

Final

59 45

Increase

38

25

Air temperature

Initial

26

25

Final

30 28

Increase

4 3

Difference between

in l

lens and

air

temperatures

29

17

283


5/6

Table 3. Increase

in

temperature

0C

in contact lenses applied to rabbit eyes.

Eye fully open throughout experiment

Experimental

time 1 min

=

3

Experimental

time 1 5 min

= 1

Palpebral fissure

about 3 mm wide,

experimental time

1 5 min

N

= 5

Lens temperature

Initial

33

32

33

Final

49

51

44

Increase

16 19

Air temperature

Initial

25

25

26

Final 28 28 28

Increase

3 3

2

Difference between final

+

21

+

23

+ 16

lens and air temperatures

30

55

T M

sec >

that water-containing

contact lenses

carry

a considerable risk

of

drying out,

and

therefore they may become adherent to

th e corneal surface and cause

epithelial

lesions.

Thus

t he hazard is not primarily

due

to th e rise in temperature but to the

adherence

of

the contact

lens.

No

epithelial

lesions

caused

by adherent

lenses were found in th e rabbit

experi

ments. The rabbit

cornea

is

much more

resistant to mechanica l

trauma than

th e

human counterpart , however. Also, con

tact

lenses

ar e

fitted

with much greater

precision

in

practice in man than they

were

in these

animal experiments.

Fur

thermore the weight of th e thermocouple

constituted a force tending to lift the lens

from

the eye. I t may

therefore

be assumed

that

the

better fi t of

and the

lack of

ther

mocouple force

on

th e

human

lens

will

contribute

to a

more

complete adhesion

of

th e lens.

Workers

should therefore

be

ad

vised

against

wearing

contact

lenses while

operating

long-wave

IR radiators unless

they also wear

safety

glasses that

absorb

the IR radiation.

Some other

IR

heaters in

use produce

radiation

of considerably

longer

wave

lengths than the

two tes ted

in

this

study.

The hazards with these are undoubtedly

even greater ,

as

th e emission

lies

within a

region

that

is

absorbed

to

almost

100

0/ 0

by contact lenses 3 .

=5

In:t

0

0

.,.------+------

O::t

o

ig 2. Increase in temperature in contact

lenses applied to rabbit eyes. 0 0 and

=

open eyes,

--

=

palpebralfissure about

3

mm wide,

=

surround

ing air temperature

284


6/6

ACKNOWLEDGMENTS

This

investigation

was supported by

the

Swedish Work

Environment

Fund

project

no. 76/174.

We wish to thank

Mr.

H. Lindh for fit

ting

the

contact lenses and

Ms. M. Old

back who

assisted in the animal exper i

ments.

REFERENCES

1. FOX S. L. Industrial and occupational

ophthalmology Charles C

Thomas

Spring

field,

IL

1973. 203 p.

2

LOVSUND, P., NILSSON S. E. G.,

LINDH

H.

and OBERG

P.

A Temperature chang

es in contact lenses in connection with ra

dia tion f rom welding

arcs.

Scand

j

work

environ

health

5 1979) 271-279.

3

NILSSON S. E. G., LOVSUND, P., OBERG,

P. A.

and

FLORDAHL L.-E.

The trans

mittance

and absorption properties of con-

Received

for publication: 6 November 1979

tact lenses. Scand j

work

environ

health

5 1979) 262-270.

4 NOVAK J.

F.

and

SAUL

R W. Contact

lenses in industry.

J.

occup

med

13 1971)

175-178.

5. RUTH W. A

method to eva luat e

occupa

tional hazards from infrared radiation.

Project report submitted

in part

fulfillment

of th e

requirements

for the

postgraduate

course

in ergonomics at th e

Loughborough

University

of Technology l i75. 156

p.

6 RUTH, W

LEVIN,

M and KNAVE, B.

rbetshygienisk

bedomning av infrarod-

stralare fOr

torkning

av biUack Under

sokningsrapport

AMMF

104/76). Arbetar

skyddsstyrelsen Stockholm 1976. 69

p.

7. Contact lens hazard.

Qual

eng 38

1974) 95.

8. Contact lens hazard. Qual

eng

38

1974) 150.

9

Contact

lenses

and arc

welders.

r

med

j

4 1974) 586.

10. Contact

lenses

and electrical

arcs.

Weld ins

res bul

15 1974)

43-44.

11. Flash and contact

lenses.

Occup

saf

health

5 1975) 11.

12. An

industrial

atrocity story.

Occup

saf

health

7 1977) 85.

13. Position statement -

Contact

lenses

in industry.

Ind

med

41

1972)

38-39.

285

temperature changes in contact lenses in

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