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EYE DISORDERS
CONTACT LENSES
CONTENTS
Contact lenses have provided an excellent alternative to glasses for
correction of refractive errors, and the technology of lenses continues
to improve. However, contact lens use is not without risk, and the potential
for vision threatening problems is present, especially in those who
abuse the use of contacts. On this page can be found discussion about
contact lenses in general, contact lens related problems. A listing
of topics discussed include:
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There are many reasons why a contact lens may be uncomfortable to
wear, including underlying eye disease and other contact lens complications
discussed on this page. In cases where the eyes are healthy and the
contact lenses are new, there is always the possibility that a lens
is defective. Generally, if a lens of a given brand and curvature
has been worn successfully in the past without problem, a new and
uncomfortable lens makes one strongly suspicious of an abnormally
curved lens, or a lens with a scratch or other defect. Since most
manufacturers offer a warrantee for defective lenses, it may be reasonable
to return the lens for replacement or refund. Usually the lens must
be returned in the bottle in which it was sent in order to get credit.
In cases of new gas permeable or hard lenses, sometimes the lens can
be smoothed or polished to improve the comfort.
If a new lens of a different brand than has been worn before is uncomfortable,
the problem may be with the fit (tightness) of the lens, the thickness
of the lens, and the edge design of the lens. Some soft contact lenses
have a very high oxygen permeability (extended wear type lenses),
and these may be more comfortable for some people. If a lens is too
tight, the cornea may become starved for oxygen, leading to discomfort
(see Tight Lens Syndrome below). On the other
hand, a lens that is too loose may irritate the eye due to excessive
movement with blinking. Finally, certain characteristics of lenses
(thickness and edge design) may be simply uncomfortable for some people.
It may take a follow-up examination by the lens prescriber to distinguish
between these problems.
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An old lens that becomes uncomfortable may be developing deposits
on the lens, scratches or nicks in the lens, or problems with the
tears lubricating the surface of the lens. People are different
with how long a given lens will remain comfortable, and good care
of lenses will usually extend the life of a lens. Having to replace
lenses frequently due to rapid protein deposit formation or other
problems is a good reason to consider disposable lenses.
As mentioned above, the development of an underlying eye disorder
not related to the contact lenses can make their use uncomfortable.
Some conditions include eye allergy, dry eye, blepharitis, conjunctivitis,
eyelid problems, iritis, phlyctenulosis, and pterygium. These conditions
are discussed in the
Ocular
Symptoms and Diagnosis section. Pregnancy or hormonal changes
are known to cause difficulty in contact lens use in women. Finally,
other contact lens complications discussed below can cause discomfort
with lens use.
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- People can develop problems with being unable to wear a lens as
long as they would like. Sometimes this problem is simply related
to external problems such as a high pollen count or being in an environment
with poor air quality or low humidity. In cases where it becomes increasingly
difficult to wear an older lens as long as previously, the lens may
be developing protein deposits or other defects. Hard or gas-permeable
lenses can often be polished, and will be comfortable to wear again,
while soft lenses usually have to be replaced.
Some people are unable to wear any type of lens for the entire
day, but can only wear the lens for a limited period of time. In
cases where the eyes are somewhat dry, the use of rewetting drops
(preferably preservative-free) can extend the time that the lenses
can be used. Some people need to remove the lenses at some point
during the day, such as lunchtime, and can then subsequently wear
them longer during the afternoon. If one is having a problem with
the wearing time of lenses, it is usually a good idea to have an
eye examination to rule out any other potential problem such as
infection or allergy. A lens case with solution should be carried
if the lenses need to be removed during the day, since wearing a
lens longer than it is comfortable can lead to disaster. One should
never put a contact lens in tap water, or in solutions not designed
for lens storage or disinfection.
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- Contact lenses are better at correcting certain types of vision
problems than others. Simple nearsightedness or farsightedness is
usually easily corrected using contact lenses, but astigmatism can
be more challenging to correct, especially with soft lenses. Contact
lenses have varying success in correcting the need for reading glasses,
with bifocal contact lenses being successful in only about 50% of
people.
Toric soft lenses have an astigmatism correction built into the
lens, but rotation of the lens can lead to a shifting of the astigmatism
correction, and temporarily blurred vision. For people with severe
or irregular astigmatism, gas-permeable lenses or hard lenses may
offer better visual results. Irregular astigmatism is a situation
where the cornea is distorted due to a scar or underlying disorder.
Sometimes rigid contact lenses are the ONLY way to correct the vision
in these cases, as even glasses will not help (as in keratoconus).
Many people who use contact lenses may experience halos around
lights at night, and sometimes ghost images. This probably is a
normal phenomenon in most people, and occurs when the pupil is larger
(or more dilated) than the optical area of a soft lens, or of the
lens itself in cases of rigid lenses. However, seeing a rainbow
around lights indicates swelling of the cornea (corneal edema),
and indicates that the lenses have been in too long and should be
removed.
Blurred vision in one eye or the other with a contact lens that
was previously clear could indicate a more serious eye problem,
and should be checked by the lens prescriber. Of course, it is possible
that lenses can become switched between the eyes, but usually this
is fairly obvious. An older lens can develop deposits and other
surface problems which can make the vision not only blurry, but
also can make the lens uncomfortable to wear.
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- The fact that a contact lens is constantly touching the eye leads
to the possibility of an allergy developing to the lens material,
deposits on the lens, or to solutions used with the lens. The conjunctiva
is a thin membrane which lines the white surface of the eye and the
inside of the eyelids. Soft lenses usually extend somewhat onto the
conjunctiva outside of the cornea. The inside of the eyelids are also
in contact with lenses especially during blinking. The conjunctiva
contains cells which can rapidly respond to allergens, leading to
redness, itching, tearing or discharge, and a general inability to
wear a contact lens.
A common source of allergy is a preservative found in the contact
lens solutions. Thimerasol was used frequently as a presevative
in the past, but severe allergic problems developed. Now, benzalkonium
choride and EDTA are common preservatives found in contact lens
solutions. If one develops an allergy or sensitivity to these preservatives,
symptoms of allergy (redness, itching, discharge) frequently develop
especially when the lens is first inserted, or when rewetting drops
containing these preservatives are used. Solutions marked as being
for "sensitive eyes" usually contain no less preservatives
than other solutions. If a lens solution allergy is suspected, switching
to a preservative free lens disinfection system may help.
Developing an allergy to protein deposits on lenses is common,
and this may lead to a condition called "giant papillary conjunctivitis".
(see below) Regular enzyme cleaning may help prevent this complication,
but often lenses with deposits need to be replaced. Rarely, one
can develop an allergy to lens material itself, and trying a different
brand, or switching to a rigid type of lens may help.
A more unusual but common allergy problem is the development of
an allergy to bacteria present on the edge of the eyelid. These
bacteria produce toxins which become trapped in the tears, especially
beneath a contact lens. For more information on this condition,
see
Phlyctenulosis
.
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Protein deposits can frequently form on both soft and rigid
types of lenses. With soft lenses, the regular use of enzyme
cleaners as well as proper disinfection and daily cleaning
of lenses can help prevent the protein deposition. Rigid lenses
may develop deposits especially during seasons with high pollen
counts, and polishing the lenses usually will buff off any
deposits.
When a lens develops deposits, the eye can become irritated,
itchy, and red. Wearing time may be decreased, and the vision
may be somewhat blurred. Complications such as "giant
papillary conjunctivitis (GPC)" may occur, which can
limit the use of contact lenses for an extended period of
time. Once deposits form on a soft lens, the lens usually
has to be replaced. Rapid development of deposits on lenses
is a valid reason to consider disposable lenses. Some contact
lenses (Aquaflex and CSI) are resistant to deposit formation.
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Normally a contact lens should move slightly on
the surface of the eye with blinking or eye movement. Soft lenses
usually move a few millimeters with a blink, while rigid
lenses (gas-permeable or hard lenses) move more. This movement
allows tears to circulate across the surface of the eye, helping
to provide oxygen to the cornea. Of course, some oxygen can
diffuse directly through a contact lens also (more so in soft
lenses and disposable extended wear lenses). For different
reasons, a contact lens during the course of the day may begin
to fit more tightly onto the surface of the eye. This may be
because the lens was too tight fitting to begin with, or it may
be related to increasing drying of the lens and eye as the day
proceeds. If the lens reaches a point where it stops moving on
the eye, several things may happen. |
The oxygen transmission to the cornea will begin to drop, and the
cornea may begin to swell (corneal edema). This leads to further tightening of the lens on the
eye, with a further worsening of swelling. Symptoms during this
period may include redness, eye irritation or burning, and a
dry sensation. The vision may begin to blur, and halos or rainbows
may be seen around sources of light.
The use of rewetting drops may help prevent this cycle of lens tightening
onto the eye, and may help to prevent complications. The fit of the
lens may need to be checked as well, and sometimes a new lens is needed.
Once the lens has tightened onto the eye enough to cause symptoms,
the lens should be carefully removed. Lubricating drops should
be placed several times to help loosen the lens before removal.
Sometimes removal of a tight lens can lead to a painful corneal abrasion,
which would require further treatment by an ophthalmologist. Another
risk of the tight contact lens syndrome is of infection (corneal ulcer).˜
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- The development of a corneal ulcer (an infection of the cornea)
unfortunately can be a complication of contact lens use. Soft contact
lenses have a higher risk of corneal ulcer than rigid lenses, but
all lenses have some risk. Disposable contact lenses worn extended
wear were found to have a much higher risk of corneal ulcer than any
other type of lens, for reasons that are not fully understood. A corneal
ulcer starts when a bacteria (or rarely a fungus or parasite) infects
an area of breakdown in the corneal surface. The surface may break
down, forming a small corneal abrasion, due to routine lens use. Overwear
of lenses, improper cleaning of lenses, extended wear use of lenses,
and overly tight lenses may increase the risk of developing this surface
breakdown. Normally, a corneal abrasion, even if tiny, is uncomfortable.
However, a contact lens can act as a bandage on the eye masking symptoms,
and some contact users develop a lack of sensitivity of the cornea.
Once an infection begins, most people experience severe symptoms.
The eye typically becomes red and painful. There may be tearing
or discharge and sensitivity to light. The vision may be variably
blurred. There are other disorders which can cause these symptoms,
but the risk of corneal ulcer in contact lens users is such that
the most important thing to do initially is to remove the contact
lens. An appointment should be arranged immediately with an ophthalmologist
to determine if an infection is present. A corneal ulcer needs to
be treated intensively with antibiotic eyedrops, and often a culture
of the infected cornea, or of the lens or lens case is performed.
Frequent follow-up appointments will help the ophthalmologist determine
if the infection is being adequately treated with the antibiotics.
Usually a week or two of antibiotic eyedrops is needed, and contact
lenses cannot be worn during this time.
A successfully treated corneal ulcer may still leave a scar which
could affect the vision. It is important to avoid situations which
can lead to corneal ulcer, such as overwear of lenses, poor disinfection
techniques, and ignoring symptoms of pain or redness.
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"Warpage" of the cornea refers to a distortion in the shape
of the cornea, usually due to the use of rigid contact lenses, and
especially poorly fitting rigid lenses. The type of lens most notorious
for this is the "hard" type of lens, which is a non-gas-permeable
lens made of a plastic called PMMA. This type of lens is still used
today successfully by many people. However, the lens is known to flatten
out the cornea, often reducing or eliminating astigmatism. When lens
use is discontinued, the cornea will try to spring back to its original
shape. Thus, it may be impossible to find a glasses prescription that
will consistently give clear vision for times when the contact lens
is not in. Often only the contact lens itself can give clear vision.
A condition known as "irregular astigmatism" refers to an
irregular curvature of the cornea, usually caused by poorly fitting
rigid lenses.
It may take several weeks of not using a contact lens for the cornea
to return to its normal curvature. At this time, the proper fitting
measurements can be made to determine the shape of a contact lens
needed which will not distort the shape of the cornea.
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Corneal edema, or swelling, occurs when there is an inadequate
supply of oxygen reaching the cornea due to contact lens wear.
Essentially, the cornea becomes smothered by the lens. Sleeping
in contact lenses, as with extended wear lenses, greatly increases
the risk of corneal edema. In this situation, even less oxygen
reaches the cornea because the eyelid is closed over it. Also,
the normal blinking of the eye is not present, which helps
tears and oxygen to circulate under the lens.
Symptoms of corneal edema included blurred or foggy vision,
seeing rainbows around lights, redness, and possibly irritation
or pain. Complications of corneal edema include corneal abrasion,
a tight lens syndrome (see above), and corneal ulcer or infection.
Generally, a lens should not be worn if symptoms of corneal
edema are occuring.
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- Giant Papillary Conjunctivitis (GPC) is a type of allergic reaction,
usually to protein deposits on contact lenses. Since these deposits
are more common with soft contact lens use, GPC is more common with
soft lenses also. Sometimes GPC can occur as a reaction to the presence
of a lens itself, or in reaction to lens solutions used. GPC is visible
as large lumps beneath the upper eyelid (usually). These lumps can
interfere with lens use, as they may "grab" the lens when
the upper eyelid blinks over the lens. Other symptoms include itching,
discharge, and redness.
Regular enzyme treatments and proper contact lens cleaning techniques
may reduce the chance of GPC. The use of preservative-free solutions
can help as well. However, once GPC develops, the use of contact
lenses often must be temporarily discontinued while the condition
resolves. Anti-inflammatory and anti-allergy eye medications may
help to speed resolution and to ease symptoms. Frequent cases of
GPC due to protein deposits on lenses may be prevented by using
disposable lenses, since these do not have a chance to build up
the deposits.
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- The development of eye redness with contact lens use is always a
warning sign. At the least, it may mean that the lenses have been
in too long, and should be removed. Many conditions can cause eye
redness (see the
Red
Eye section), but contact lens use makes certain problems more
likely. Often, a red eye with contact lens use is treated like a case
of conjunctivitis (pink eye), when actually the redness may be due
to a contact lens related allergy or infection. Some common causes
of a red eye with contact lens use include:
- Lens allergy, lens solution allergy, or allergy to protein build-up
on lenses.
- Lens overwear with corneal edema, with corneal drying or a tight
contact lens syndrome.
- Interaction of bacterial toxins (from the eyelids) trapped beneath
the contact lens leading to corneal irritation (phlyctenulosis).
- Corneal ulcer.
- Giant papillary conjunctivitis.
- Poorly fitting or defective contact lenses.
Eye redness associated with contact lens use should not be ignored,
and the eye should be examined by an ophthalmologist to determine
the cause.
Contact lenses are generally designed to correct the distance vision,
leaving the eye itself to focus additionally for near vision. However,
as people age, the focusing ability of the eye gradually declines. Usually
in the early forties, this becomes noticeable, and reading material
has to be held further away to be able to focus on it. Eyestrain symptoms
and headache can occur. In people who do not use contact lenses, a bifocal
prescribed in glasses can eliminate any problems with reading. However,
what options are available for contact lens users?
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Reading Glasses -
This is the simplest option for reading with contact lenses in:
using reading glasses over top of the lenses. However, most contact
lens users prefer to avoid glasses use, and it may be difficult
to keep up with a pair of reading glasses when the distance vision
is clear with contact lenses.
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Monovision -
This refers to using one eye for distance vision, and one eye for
near vision. Usually the non-dominant eye is set for reading (usually
the left eye). Advantages of this system include the ability to
read and see at distance without glasses using relatively inexpensive
contact lenses. Disadvantages include a loss of depth perception
and the possibility of eyestrain symptoms. Some people are simply
not comfortable with this arrangement.
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Bifocal Contact Lenses -
A bifocal contact lens can be used in one or both eyes to maximize
both near and distance vision. Unfortunately, sometimes clear reading
vision comes with some sacrifice of clear distance vision. Probably
on 50% of people successfully use bifocal contact lenses, and they
are among the most expensive of contact lenses.
Disposable contact lenses can be a useful option for some contact lens
users, and there seems to be a trend toward increased use of this type
of lens. Even disposable lenses that are discarded on a daily basis
are available, although most people use the type of lens that is discarded
after 2 weeks. Some reasons and situations for which disposable lenses
may be useful include:
- Rapid deposit formation on lenses, with or without the development
of giant papillary conjunctivitis.
- Having to replace contact lenses frequently, whether it be because
of lens deterioration, damage, or the losing of lenses.
- Sensitivity to solutions used to clean or disinfect lenses.
- Difficulty in finding another type of lens that is equally comfortable
for an individual.
Some problems associated with disposable lenses include:
- A higher cost than most lenses.
- A tendency to abuse the use of the lenses, such as wearing a lens
for more than two weeks, an absence of lens disinfection, and wearing
the lenses in situations not usually recommended, such as swimming.
(These factors may lead to the increased risk of infection).
- A lak complete range of parameters
There are definate situations where disposable lenses are appropriate,
and some situations where they should be avoided. Exercising caution
with the use of any contact lens helps to prevent complications.
Many people are able to wear lenses continuously for many days with
no apparent problem or complication. However, sleeping in contact lenses,
while convenient, substantially increases the risk for infection and
other complications. The oxygen supply to the cornea drops overnight
while wearing a contact lens. This can lead to swelling of the cornea
(giving blurred vision or the visualization of rainbows around lights),
breakdown of the corneal surface, and ultimately infection of the cornea
(ulcer). This risk is high enough that many eyecare providers discourage
against the use of contact lenses on an extended wear basis. If the
lenses are used this way, extreme caution should be taken, and the lenses
should be removed with any sign of trouble (eye redness, pain, blurred
vision, sensitivity to light, etc.) In fact, it may be reasonable to
consider refractive surgery as an alternative to extended wear contact
lens use.
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