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Of all the users of contact lenses in the U.S. about 6% experience
contact lens related complications yearly. Wearing of contact
lenses causes alterations in corneal physiology, which in turn
leads to epithelial, stromal and endothelial damages, disorders
of the ocular surface and can aggravate already present complications.
Complications range from practically harmless allergic conjunctivitis
to the adverse microbial keratitis. Other associated disorders
are giant papillary conjunctivitis, corneal edema or hypoxia,
neovuscularization, limbal keratoconjunctivitis, sterile infiltrates,
red eye and tight lens syndrome.
Causes
All kinds of contact lenses affect the health of the eyes to
some extent leading sometimes to complications. However, RPG lenses
have less adverse complications compared to soft lenses used for
daily wear or extended hydrogel lenses. Contact lenses are found
to be the most significant cause in the development of the extremely
serious and damaging microbial keratitis.
These disorders are caused by the failure of contact lens maintenance
systems, and patient related reasons like non-adherence to wearing
schedules. Pre existing complications aggravate the problems but
are not a cause of these.
Microbial Keratitis
This is the ultimate corneal damaging complication associated
with contact lens usage and is distinguished from other forms
of harmless sterile infiltrates. Microbial keratitis is serious
to the extent that it can lead to permanent loss of vision due
to scars and perforations in the cornea. Though the occurrence
of this disorder is low, its high morbidity makes it a serious
cause for concern. In a study it was found that for every 10,000
persons using 1.1 suffer from it annually. The figures in the
case of daily wear contacts and extended wear contacts are 3.5
and 20 respectively pointing to the fact that extended wear contact
lenses leads to the highest incidence of microbial keratitis compared
to any other modality.
The organisms responsible for the development of microbial keratitis
are the gram-negative Pseudonomas aeruginosa as well as the gram
positive Staphylococcus. Corneal hypoxia and the adherence of
organisms on the corneal epithelium particularly in the case of
extended wear lenses are risk factors. Also improper care and
use of lenses play a significant role. Thus, epithelial damage
and exposure to pathogenic bacteria are major factors in the aggravation
of microbial keratitis.
The infiltrates are larger than 1.5mm, stromal and have a whitish
overlying epithelial defect. Patients experience moderate to severe
pain, foreign body sensation, photophobia, and tearing. The anterior
chamber of the cornea shows moderate to severe activity.
Therapy includes broad-spectrum topical fortified antibiotics
that should be started without delay. For milder cases, monotherapy
with fluoroquinolone is advised. Therapy is initiated after the
responsible organism is identified and return of sensitivity.
The results of microbial keratitis are corneal scarring, sometimes
irregular astigmatism and low visual acuity and some patients
require corneal transplantation to improve visual acuity. Contact
lenses can be used again after healing but in accordance to the
instructions given y the doctor. Daily wear RGP lenses caned vision
be used by patients experiencing irregular astigmatism can improve
vision.
Hypoxia or corneal edema
Hypoxia occurs when sufficient oxygen does not reach the cornea
due to contact lens imermeability. Decrease in the levels of oxygen
in the cornea mainly to the endothelium and the stroma results
in change of metabolic activity and stromal swelling. Tight lenses,
Dk lenses, PMMA’s or extended wear of regular hydrogel lens
are sources of hypoxia, which in turn leads edema either chronic
or acute.
In acute edema, microcystic epithelial changes occur and with
further advancement can lead to cell death and imbalance of traumatized
epithelial cells. Symptoms include extreme pain, tearing, reduced
vision, photophobia and intolerance of contact lens wear.
Chronic edema occurs with extended contact lens use and the symptoms
and findings are subtler. Presence of epithelial microcysts, thickening
of stroma, endothelial blebs with hypoxia and neovascularizaton
develop. There is no extreme pain and vision is affected minimally.
The treatment for hypoxia mainly involves the termination of contact
lens wear until edema is resolved. Lubrication and topical steroids
can be used. After healing, patients can use a flat high oxygen
permeable lens.
Tight lens syndrome
Hydrogel lenses with high water content results in the steeping
of the base curve and leads to contact lens tightening and drying.
This occurs when the lens has been on the eye surface for some
time. The symptoms include irritation, pain, photophobia and blurred
vision. There is conjunctival injection and corneal staining,
epithelial damage, infiltrates, anterior chamber reaction. There
is negligible movement of the lens on blinking. There is the dragging
of conjunctival vessels on the edge of the contact lens wear,
use of topical antibiotics and cyclopegic agents, topical steroids
to decrease inflammation. Once healed, patients can be fitted
with a flat high oxygen permeable lens.
Red Eye
This manifests itself as acute red eyes due to corneal infiltrates.
When the eye is closed toxins from bacteria are activated resulting
in inflammatory response. Symptoms include ocular discomfort,
foreign body sensation and redness of the eye on awakening.
There is presence of conjunctival injections, mild chemises,
anterior chamber reaction. The treatment involves termination
of contact lens wear till complete healing, which usually occurs
within two weeks of therapy and no medicines are prescribed.
However, this condition can recur if extended wear lenses are
used again.
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