Resources - Safety Info
Contact Lens Safety In The Science Classroom
From September 1994 issue of ‘Crucible’
A relatively large fraction of the Canadian population
requires corrective lenses to obtain optimal vision. While many of these
individuals choose to wear eyeglasses, an increasing number are being
fitted with contact lenses. The recent technological advances in the contact
lens industry have greatly increased the options available to the contact
lens wearer. Futhermore, certain eye conditions make it difficult for
some contact lens wearers to switch freely between their contact lenses
and spectacles. This raises the question of whether it is permissible,
or prudent, to allow students (and teachers!) to wear contact lenses in
the science classroom or laboratory.
The intent of this article is to provide the information
needed to make an informed decision on whether teachers and their students
should be allowed to wear contact lenses in the science laboratory/classroom.
About Contact Lenses
Until the late 1970s, contact lenses were made from two
basic materials. The hard contact lens was made of polymethymethacrylate
(PMMA), while the soft contact lens was made of a hydrated polymer, hydroxyethylmethacrylate
(HEMA), which contained 37.8% water by weight. Although biologically inert
and capable of providing excellent optics, both PMMA and HEMA lenses reduced
the supply of oxygen to the cornea. This led to adverse changes in corneal
physiology and anatomy in some contact lens wearers. Today, PMMA has all
but vanished, to be replaced by a variety of rigid plastics which are
mostly hydrophobic materials with high oxygen permeability. Lenses made
of these polymers are termed Rigid Gas Permeable (RGP). In the soft lens
market, HEMA is giving way to polymers which contain as much as 80% water.
These soft lens materials (called hydrogels) have a high level of oxygen
transmission, and show remarkable structural strength for their degree
of hydration. The combination of thinner lenses (as thin as 0.04 mm) and
high oxygen transmission has greatly reduced the corneal problems due
to hypoxia, but there is still the potential for many other complications.
Disposable contact lenses, extended wear schedules (lenses worn continuously
for days to months), allergies to preservatives in care solutions, incompatibility
between contact lens materials and care solutions, contamination of lenses
and solutions, and other factors present many challenges to the contact
A contact lens must not only provide the wearer with a
clearly focused retinal image, but also conform to the shape of the cornea
and remain in position in front of the pupil. This mechanical requirement
is referred to as the fit of the contact lens. By measuring the curvature
of the front surface of the cornea, assessing the tears, and determining
the refractive error, a contact lens fitter can select the appropriate
material and optical and physical parameters for a contact lens. An improper
fit may result in physical and physiological changes in the cornea. If
a bad fit is not corrected, the corneal changes may become permanent.
The fit of a contact lens and the health of the eye must therefore be
assessed at regular intervals; such eye examinations are referred to as
A contact lens does not actually touch the surface of
the eye. Instead, it is bathed in the tears which lubricate the eyeball,
and floats in front of the cornea on a thin tear film. A rigid lens is
smaller than the corneal diameter, and is held in position by capillary
action of the tears. The front surface of the contact lens is also covered
by a tear layer. In contrast, a soft lens covers the entire cornea and
rests on a thin ring of the conjunctiva (the clear membrane covering the
white of the eye). The tear film covers the entire lens, and fills in
the space between the lens and the eye. For either rigid or soft lenses
to fit properly and provide good vision, a good tear film on the eye is
essential. The difference between rigid and soft contact lenses are summarized
in Table 1.
Tear fluid is essentially a 0.9% NaCl solution (saline)
with additional constituents such as albumin, lysozyme, and glucose. It
is secreted by the lacrimal glands. Glands at the edges of the eyelids
secrete an oily component of the tear film, which helps to retard its
evaporation. Specialized cells within the conjunctiva secrete mucin which
spreads across the surfaces of the eye and eyelids to increase their wettability.
The mucous base of the tear film ensures that the entire eye is evenly
coated by the tear film. In an eye examination, the integrity of the tear
layer and its components can be assessed by a variety of techniques involving
dyes and observations at moderate to high magnification with a biomicroscope.
Every contact lens wearer should also have eyeglasses
made to the current prescription as a back-up in case the contact lenses
cannot be worn. Ideally, either eyeglasses or contact lenses should give
the wearer the same level of vision, but in some ocular conditions (see
Table 2 ) only contact lenses can provide optimal visual acuity.1
Contact lenses and hazards in the science laboratory
Surveys of accident reports from industry and emergency
facilities show that up to 80% of all eye injuries are caused by small
flying particles, dust, and larger objects striking the eye.2,3 About
10% of reported injuries are due to exposure to sources of ultraviolet
radiation, mostly electric welding arcs. Other classes of injury tend
to be specific to certain occupations or workplace activities. A 1981
survey of accidents in British school science laboratories reported that
22% involved chemicals in the eyes.4
Science experiments do involve some risk of eye injury,
particularly in the biology and chemistry classroom. However, hazards
may be present in the physics lab as well. In assessing our laboratories
for eye safety, and developing safety rules and procedures regarding contact
lens wear, we must ask ourselves a number of questions.
- Is there an actual ocular hazard?
- Does wearing a contact lens place the eye at greater
risk than wearing glasses?
- Does wearing a contact lens increase the risk to the
eye, or increase its susceptibility to injury?
- Is the risk different for various contact lens designs
- Are there associated risks for a contact lens wearer
who removes lenses?
- Do contact lenses negate other safety procedures?
One of the most common minor eye injuries is the superficial
corneal foreign body. The symptoms of pain, excessive tearing, and foreign
body sensation are relieved quickly by simple removal of the particle,
often by flushing the eye with a stream of physiological saline or water.
Such injuries may be caused by high concentrations of airborne dust, or
by small particles (under 1 mm size) moving at slow speeds. A missile
of suitable size, shape and speed may become embedded in the cornea, conjunctiva
or sclera, or in extreme cases, may perforate the eyeball (intraocular
foreign body). Contact lenses may provide better eye protection than eyeglasses
in some circumstances.
Foreign bodies may become trapped under a rigid contact
lens, but this does not occur with soft lenses unless the particle was
inserted with the lens. A Swedish study showed that workers wearing soft
contact lenses in an industrial setting with high concentrations of airborne
metal particles and oil droplets for up to 2 years had no subjective complaints
and no evidence of eye damage. This study showed that hydrogel lenses
can be worn safely in environments where hard lenses cannot.5
The protection of eyes by contact lenses from flying particles
depends on the thickness and rigidity of the lens. There are many documented
cases in which a hard or soft contact lens protected the eye from impact
of an object which would have caused severe or sight-threatening injuries
to an eye not wearing a contact lens. Controlled laboratory studies have
confirmed this clinical observation.
Sharp-edged or pointed missiles such as glass fragments
are more likely to cause perforating injuries. Rigid contact lenses can
protect the eye from these objects better than hydrogel lenses. A case
involving a traffic accident has been described in which rigid lenses
protected the eyes when the broken windshield glass cut the patient's
face across the eyebrow and cheek. It was speculated that spectacles would
have increased the risk of eye injury.7
It can be concluded that an individual wearing contact
lenses is at no greater risk of mechanical injury due to flying debris
in a laboratory accident than a spectacle wearer. Indeed the clinical
and experimental evidence suggest that the contact lenses may help to
protect the eye from more severe injury. However, contact lenses do not
provide adequate protection from mechanical injury. Appropriate protective
eyewear (goggles or safety spectacles with solid sideshields) must be
There are many sources of information on the direct toxic
effects on the eye of thousands of chemical substances, as well as the
secondary effects on the eye and visual system following inhalation, ingestion,
or absorption through the skin and mucous membranes. It is often alleged
that chemicals are trapped behind hard contact lenses, or absorbed, concentrated
and released by hydrogel lenses to further injure an already compromised
cornea. Some safety bulletins have claimed that contact lenses cause worse
than normal corneal injuries by holding chemicals against the eye, and
that the presence of a contact lens on an eye prevents adequate irrigation
following a chemical injury. These claims are unsupported by documented
evidence, and the descriptions of the accident and resulting injuries
to the eye often cannot be reconciled with what is known about the toxicity
of the chemical agent.
Noxious gases, vapours, fumes, aerosols and smoke can
seep behind inappropriate eye protectors and affect the surface tissues
of the eye. The ocular response depends on concentration and physical
and chemical properties of the substance. Highly toxic materials which
are likely to cause tearing and lid closure upon reaching the eye, will
also stimulate the respiratory tract. Systemic absorption of airborne
toxins is more likely to occur through the mucosa of the respiratory tract
than that of the eye.
Wearers of soft lenses often report that they can peel
onions without the usual ocular irritation. A number of studies have shown
that hydrogel lenses protect the eye from tear gases. Thus, hydrogel lenses
appear to protect the eye from airborne ocular irritants which have low
solubility in water.
It is often assumed that water-soluble gases and fumes,
and substances that may bind to, or be absorbed into hydrogel materials
would cause more severe ocular responses or a chronic effect because of
prolonged exposure to the eye. However, this has not been borne out in
laboratory studies. For example, Nilsson and Andersson8 found that the
uptake of trichloroethylene by hydrogel lenses suspended in a concentration
of 640 ppm was up to 90 times the uptake of physiological saline. However,
the release into simulated tears was far less than the release into air.
They concluded that the 'vacuum cleaner' effect of the soft lens resulted
in a lower concentration at the cornea than if the eye were exposed directly
to the fumes. This and other studies suggest that when proper eye protection
is used, stringent restrictions on contact lens wear are not as important.
The accidental splashing of toxic substances into the
eye is one of the most frequent causes of serious eye injury. More serious
injuries occur when a large volume of liquid is involved. Most commonly
used organic solvents affect only the external eye, causing loss of the
corneal and conjunctival epithelium and extreme discomfort. However, the
effects disappear with regrowth of the epithelium. Similar responses are
found with detergents and surfactants. Wesley9 showed that when solutions
of creosote, H2SO4 or NaOH were sprayed onto anesthetized rabbit eyes,
those not wearing a PMMA contact lens were 1.8 times more likely to develop
total corneal opacity than eyes with the lens, and that an eye was more
likely to be damaged if the contact lens were dislodged during the splash
or subsequent irrigation. Instead of trapping material behind it, the
lens acts as a barrier.
The pH of acid and alkali solutions is an important determinant
of the level of damage resulting from a chemical splash. Solutions with
extreme pH values cause rapid destruction of the eyelids, anterior eye
and surrounding tissues. Weak acid solutions are self-limiting, affecting
the superficial cells of the cornea and mucous membranes of the lids and
eyeball. Alkali solutions saponify the lipid membrane structure of cells;
they readily soften, disrupt and penetrate the anterior eye to reach the
internal structures. Thus, alkali splashes have much more severe consequences,
even at low concentration.
Nilsson and Andersson8 demonstrated that contact lenses
can reduce the eye damage due to concentrated HCl by about 75%, while
the presence of a contact lens on the eye in a splash of NaOH neither
reduces nor worsens the resulting eye injury. Leaving the lens on the
eye for a minute or two after the splash made no significant difference.
These studies indicate that contact lenses may help to
protect the eyes from certain chemical agents, but that they should not
be regarded as a substitute for protective eyewear. It is important to
recognize that a contact lens wearer with appropriate protective equipment
is at no greater risk than an individual who does not wear contact lenses.
However, even an apparently trivial eye injury involving chemical splash
can have disastrous consequences on vision, and emergency procedures including
immediate irrigation of the affected eye must be followed. The loss of
a contact lens during flushing would be acceptable in these circumstances.
Optical Radiation Hazards
Optical radiation includes electromagnetic radiation with
associated wavelengths between approximately 200 nm and 3000 nm. These
wavelengths are considered optical because conventional lens material
(glass, plastic, and fused silica) can be used to alter the focus and
direction of propagation of the radiant energy. Wavelengths between 200
and 400 nm comprise the ultraviolet spectrum, while visible light includes
the band from 400 to 780 nm, and the infrared waveband ranges from 780
to 3000 nm. The UV spectrum is divided into 3 wavebands according to their
effects on living cells. These are UVC between 200 and 280 nm, the UVB
from 280 to 315 nm, and the UVA from 315 to 400 nm.
There are many sources of optical radiation that both
students and teachers may encounter in the school science laboratory.
These include a wide variety of spectral lamps, black light (UV) sources,
lasers, infrared (IR) lamps, and various sources of visible light. The
exposure factors which must be considered include wavelength(s) and intensity
of exposure, the duration and frequency of exposure, and whether contact
(or spectacle) lenses can protect the eye from the radiant energy. The
transmission of optical radiation by the tissues of the eye determines
whether a given tissue may be damaged by the radiation; to have an effect,
the photon must reach the target tissue and be absorbed by it.
The effects of optical radiation on the tissues of the
eye are well known (see Table 3 ). They are characterised by exposure
thresholds which are expressed as the total energy per unit area of irradiated
tissue needed to produce a just detectable level of damage. Exposure thresholds
for the UV are on the order of mJ.cm-2, while IR thresholds are at the
kJ.cm-2 level; these relate to the photochemical and physical mechanisms
leading to tissue damage.
Short wavelength optical radiation triggers a complex
series of oxidative chemical reactions at membranes structures within
cells involving the generation of highly oxidative species such as H2O2,
OH-, and other free radicals. Damage occurs when the intracellular defence
mechanisms which neutralize free radicals in the cytoplasm are overwhelmed.
The severity of the photic injury depends upon the location of the damaged
membrane. UVC exposure produces lethal damage to nuclear membranes in
cells; it is therefore used to sterilize items which are readily damaged
by other sterilization techniques. UVB exposure affects the membranes
of cytoplasmic organelles and may disrupt metabolic processes in the exposed
cell. Whether this results in temporary or permanent impairment of the
cell, or cell death, depends upon the total dose of absorbed energy. Similar
oxidative photochemical injuries can result from high levels of exposure
to blue and green light (400 to approximately 550 nm). A characteristic
of photo-oxidative injuries is the latent period of 6 to 12 hours between
exposure of the tissue and the onset of clinical signs and symptoms. During
this time, the damaged tissue continues to function normally.
Unlike the skin, the tissues of the eye do not develop
a tolerance to UV radiation with repeated exposure. Tanning of the superficial
layers of the skin is a defence mechanism which increases the threshold
exposure for sunburn. No such defence exists in the eye.
Damage resulting from exposure to long wavelength visible
light (> 600 nm) and IR radiation is due to conversion of optical radiation
energy into heat by passive absorption. Thermal injury occurs when the
intracellular temperature rises more than 20o C above ambient. Cell impairment
or death occurs as cytoplasmic proteins are coagulated. Unlike photochemical
injuries, thermal injuries have no latent period before the onset of clinical
signs and symptoms.
Exposures to optical radiation may be described as acute
or chronic. In an acute exposure, the radiant energy is delivered to the
target tissue within a period of seconds to hours. Chronic exposure occurs
over periods ranging from days to decades. The frequency of repeated exposures
is also a factor. For example, repeated subthreshold exposures of the
cornea to UVB during a day can accumulate to a suprathreshold total exposure,
resulting in photokeratitis.
The principal concern in contact lens wear is the exposure
of the cornea and conjunctiva to UVB radiation. Light sources which are
rich in UVB include mercury lamps, xenon flashlamps, and special sources.
Suprathreshold exposure (greater than 0.025 J.cm-2 ) to UVB results in
inflammation of the cornea and conjunctiva (photokeratoconjunctivitis),
commonly known as welder's flash or snow blindness. The symptoms of extreme
pain, sensitivity to light, profuse tearing and greatly reduced visual
acuity begin several hours after exposure. In contrast, the physical signs
are much less dramatic, involving sloughing of the superficial layers
of the corneal epithelium, and swelling and clouding of the cornea. In
extreme exposures, the entire thickness of the epithelium may be lost.
If the corneal endothelium is damaged, the swelling and loss of transparency
of the cornea is even greater.11 The cornea returns to normal within days.
Welders experience many episodes of photokeratitis throughout their working
lives, apparently without permanent effects on the cornea. However, it
has been shown that there are changes to the corneal endothelium with
long-term repeated exposure to UVB from welding arcs.12 Exposures of more
than 0.75 J.cm-2 of UVB can produce anterior subcapsular cataracts.13
Chronic exposure to environmental UV may be a factor in
the development of droplet keratopathy and earlier development of some
age-related changes in the cornea. The prevalence of degenerative changes
to the conjunctiva (pterygium and pinguecula) appears to correspond to
exposure to solar UV and certain occupations. Chronic exposure to UVB
and possibly UVA in the environment has also been implicated in the development
of age-related cataract.14
The need for ocular protection from environmental and
occupational exposures to UV radiation is generally accepted. Many spectacle
and contact lens materials provide little protection from UV. Recently,
several RGP and hydrogel contact lens materials have been introduced that
offer various levels of protection from UV.15 Several studies have shown
that areas of cornea that are covered by UV-blocking contact lenses are
protected from photokeratitis.16-19 It has also been demonstrated that
an eye wearing a UV transmitting contact lens is at no greater risk of
UV-induced injury than an eye without a contact lens.18
Visible light levels which are high enough to produce
retinal damage, are uncomfortable and trigger aversion responses and the
blink reflex to protect the eyes. When individuals look at light sources
such as the sun (especially during eclipses) and lasers, a temporary or
permanent loss of function of the exposed retina may result. Visible light
damage may be either photochemical (due to UVA or short wavelength visible
light), thermal (due to long wavelength visible light and/or IR), or a
combination of both. The blue light threshold for retinal damage is several
orders of magnitude below that for red light or IR. The primary site of
injury is the photoreceptors; it is more usual for the damaged cells to
recover, and there is normally only a temporary loss of function of the
affected area of retina. Thermal injuries occur at the retinal pigmented
epithelium and normally result in a permanent loss of function in the
Contact lens wearers often complain of photophobia (severe
discomfort from light) when wearing their lenses. Although 8% more light
reaches the cornea through a contact lens compared to a spectacle lens,
it is difficult to understand how a relatively modest increase in retinal
irradiance can result in visual discomfort. It has been suggested that
fluorescence of the crystalline lens of the eye in the presence of high
levels of UVA in the environment may be a factor.20
Should contact lenses be worn in the school science
The question of whether contact lenses cause a greater
risk of ocular injury in an accident has been raised ever since they were
first introduced. Much misinformation and many misconceptions appear and
reappear in the popular press as well as in industrial safety articles.
There are many anecdotal reports as well as documented cases and laboratory
studies which show that contact lenses provided protection or at least
reduced the severity of injury. In many instances, contact lenses are
far safer than spectacles. There is no evidence that contact lenses increase
the risk of accidental injury to the eyes.
Contact lenses are popular among adolescents. When students
wearing contact lenses enter the school science laboratory, they should
be informed of the hazards that my be encountered as they participate
in classroom activities and instructed in the proper use of protective
eyewear. It is important that the teacher has conducted an appropriate
hazard analysis, and ascertained whether contact lens wear during a particular
experiment is unduly hazardous. An individual who must wear contact lenses
during that session (see Table 2 ) may be adequately protected by wearing
closed eyecup goggles or unvented cover goggles. In the event that a contact
lens wearing individual is exposed to volatile materials, smoke, fumes
or airborne irritants, it may be advisable to clean and disinfect the
contact lenses after the class.
Stones and Spencer21 have concluded that a universal ban
on contact lenses in the workplace cannot be justified. When proper eye
safety practices are followed and contact lens wearers are adequately
trained in the proper use of their lenses, there should be no greater
risk of eye injury in the industrial workplace. Each case must be decided
on its own merits. The same can probably be said of the school science
First Aid Procedures
Regardless of how carefully experiments are preformed
or whether adequate safety precautions are taken, accidents do happen.
Contact lens wearer should carry a card or Medic Alert bracelet identifying
the type of lenses worn. They should also have contact lens solutions
and spectacles on hand in case the lenses have to be removed.
In the event of a chemical splash in the eye:
- Remove the contact lenses immediately, if possible.
- Irrigate the eye immediately with copious amounts of
fresh water for at least 30 minutes.
- If the lenses cannot be removed, irrigate the eyes
with lenses in place and let the stream of water dislodge the lenses.
- Transport the victim to emergency care facilities as
soon as possible, continuing to irrigate the eyes.
In the event of mechanical trauma or foreign body injury:
- Cover the injured eye with a hard protective shell.
DO NOT APPLY PRESSURE DIRECTLY TO THE EYE.
- Cover both eyes lightly with gauze bandage to prevent
eye movements which may cause further injury.
- Transport immediately to emergency care facility.
Differences between Rigid and Soft Contact
||< 1% by weight
||35.5% to 79% by weight
||8 to 10
||13 to 14.5
||0.10 to 0.18
||0.04 to 0.7
|Rx for Astigmatism
||up to -8.00 D cylinder, but spherical lens may mask
up to 2.00 D astigmatism
||up to -8.00 D cylinder, spherical lenses may reveal
||up to 4 weeks
Reasons Why a Contact Lens May Not Be
Removed in the Science Laboratory (Adopted from Cullen1 )
- No alternate spectacle correction
- Blur from long-term wear of PMMA lenses is not
relieved by spectacles
- Oblique astigmatism
- irregular astigmatism
- Change in depth or space perception
- Eye disease that precludes use of spectacles
- Artificial eye
- Disfigured eye
- No access to clean facilities
- No case
- No solutions
- Rigid adherence to wearing schedule
- Lens used to aid colour discrimination
- Unable to remove lens due to poor instruction
- Ignorance of hazard
Optical Radiation Effects on the Eye
||Corneal epithelial damage
||Corneal epithelial damage (welder's
Anterior subcapsular cataract
|Droplet keratopathy Endothelial
degeneration of Corneal endothelial
cornea Pterygium/pinguecula Nuclear cataract
||Tanning of eyelid skin Photochemical
retinopathy in aphakia
||Macular degeneration Age related
||Photochemical retinopathy (damage
||Age-related macular degeneration
||Thermal retinopathy (damage to
retinal pigmented epithelium)
|Near IR (780 to 1400 nm)
|Far IR (>1400 nm)
||Corneal and skin burns
- Cullen AP. The Environment in Bennett ES, Weissman
BA (eds). Clinical Contact Lens Practice. Philadelphia, J.B. Lippincott,
- Chartrand PE. Analysis of 1989 accident causal statistics
for eye injuries in the Ontario construction industry. Toronto, Construction
Safety Association of Ontario, 1990.
- Duke-Elder S, MacFaul PA. System of Ophthalmology,
Vol. 14, Injuries, Part I. Mechanical Injuries. St. Louis, C.V. Mosby
Company, 1972. pp 34-48.
- Everett K, Jenkins EW. A Safety Handbook for Science
Teachers, 4th Ed. London, John Murray (Publishers) Ltd., 1991.
- Nillson SEG, Lindh SHS, Andersson L. Contact lens
wear in an environment contaminated with metal particles. Acta Ophthalmol
(Copenh) 1983; 61: 882-888.
- Ritzmann KE, Chou BR, Cullen AP. Contact lenses as
eye protectors against mechanical trauma.Internat Contact Lens Clinic
1992; 19: 162-166.
- Dickinson F. Contact lenses: The safety factor. Optician
1969; 157(4070): 355.
- Nilsson SEG, Andersson L. The use of contact lenses
in environments with organic solvents, acids or
alkalis. Acta Ophthalmol 1982; 60(4): 599-608.
- Wesley NK. Chemical injury and contact lenses. Contacto
1966; 10(3): 15-20.
- Cullen AP, Chou BR, Egan DJ. Industrial non-ionizing
radiation and contact lenses. Can J Pub Health 1982;73:251-254.
- Cullen AP, Chou BR, Hall MG, Jany SE. Ultraviolet-B
damages corneal endothelium. Am J Optom Physiol
Optics 1984; 61: 473-478.
- Karai I, Matsumara S, Takise S, Horiguchi S. Morphological
changes in the corneal endothelium due to ultraviolet radiation in welders.
Br J Ophthalmol 1984; 544-548.
- Pitts DG, Cullen AP, Hacker PD. Ocular effects of
ultraviolet radiation from 295 to 365 nm. Invest
Ophthalmol 1977; 16(10): 932-939.
- Taylor HR, West SK, Rosenthal FS et al. Effect of
ultraviolet radiation on cataract formation. N
Engl J Med 1988; 319(22): 1429-1433.
- Chou BR, Cullen AP, Dumbleton KA. Protection factors
of ultraviolet-blocking contact lenses. Internat Contact Lens Clin 1988;
- Pitts DG, Lattimore MR. Protection against UVR using
the Vistakon UV-Block soft contact lens. Internat Contact Lens Clin
1987; 14: 22-29.
- Bergmanson LPG, Pitts DG, Chu LWF. The efficacy of
a UV-blocking soft contact lens in protecting cornea against UV radiation.
Acta Ophthalmol (Copenh) 1987; 65: 279-286.
- Cullen AP, Dumbleton KA, Chou BR. Contact lenses and
acute exposure to ultraviolet radiation. Optom
Vis Sci 1989; 30(6): 407-411.
- Ahmedbhai N, Cullen AP. The influence of contact lens
wear on the corneal response to ultraviolet radiation. Ophthal Physiol
Opt 1988; 8: 183-189.
- Dumbleton KA. The effect of UV-A induced lenticular
fluorescence on visual finction. M.Sc. Thesis, University of Waterloo,
- Stones I, Spencer G. Contact lenses in the workplace
- the pros and cons. Publication P85-1E. Hamilton, Canadian Centre for
Occupational Health and Safety, 1985.