Transcript Contact lenses-2

Contact lenses-2
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Advanced Applications of Contact Lenses-2
Complications of contact lens wear
Instructor: Areej Okashah
7/1/2010
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Orthokeratology:
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i.e. contact lens corneal reshaping: is the planned
application of specially designed RGP contact
lenses to reshape the cornea; this temporarily
reduces myopic refractive error & improves
unaided visual acuity.
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This procedure allows patients to see well enough
in order to perform daily activities without the
need for spectacle or CLs correction for at least
part of the day…
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Orthokeratology has been practiced for more
than 40 years; however its efficacy & safety still
controversial
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…
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Overnight wear of ortho-K is relatively a recent
development
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Remember that conventional rigid lenses have secondary &
peripheral curves that are progressively flatter than the
central (base) curve
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Modern ortho-K lenses employs a reverse-geometry lenses
to produce the desired corneal changes; these lenses have
secondary peripheral radii of curvature that are steeper
than the back optic zone radius (BCR). This alteration in
design allows the lens to re-approach the cornea beyond
the base curve which results in improved lens centration. &
this steeper secondary curve causes the corneal tissue to
redistribute radially from the centre of the cornea causing
the central corneal epithelium to thin & the peripheral
epithelium to thicken leading to refractive error changes
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….
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Recently used ortho-k lenses have high oxygen
permeability; which makes it possible to apply the lens on
extended wear bases or overnight wear schedule
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Overnight wear of ortho-K lenses advantages include:
convenience for patient as no optical devices are required
during the course of the day; better ocular health as the
wearing time decreased; little adaptation to lens is
required; increased effectiveness because there is an
increased eyelid pressure from closed eyes & rapid eye
movement during sleep. & could retard myopia progression
in children.
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Ortho-K has been found in some clinical trials to
correct 1.00-5.00 or 6.00 diopters of myopia & little
or no astigmatism
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….
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Some patient discontinue ortho-k use because of:
residual astigmatism; poor comfort; treatment
failure; poor motivation; unideal lens fit
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Overnight ortho-k could have some complications
e.g. corneal staining; corneal ulcer; CL
adherence these are relatively similar to
complications of using conventional CLs..
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Good candidates: patients with one to six
diopters of myopia; & who have less than two
diopters of with-rule-astigmatism; & who have
pupil with small-or-average-diameter
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Ocular complications
related to contact lens
wear…………………..
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Complications of CL wear:::
Corneal vascularization
 Immunologic complications
 Infectious keratitis
 Mechanical complications
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Corneal vascularization CV
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Vascularization i.e. neovascularization is the
appearance of new vessels within a tissue
In general its not uncommon
CL wear is the major risk factor for CV
The risk of CV is not the same for all CL types;
e.g. RGP lens < soft
When firstly detected; new vessels is a warning
sign for further damage,
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CV could scatter incident light & reduce corneal
transparency; there could be a potential for
visual interference
CV is an indicative sign for immune privilege
within anterior the chamber this could increase
the risk of infection or inflammation
Hypoxia, epithelial injury (could affect the
integrity of tear film)& wearing time (longer
wearing time is associated with higher risk for
CV), significance of limbal hyperaemia are risk
factors that can be associated with CV
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Treatment outcomes are better when CV is
detected early….
firstly should remove the causative factor in
this case CL
Evaluate lens fitting characteristics ;
material properties; cleanliness
(deposits); lens parameters
Advice: reduce wearing time; switch to
another lens material; water content; DK
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Infectious keratitis
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Causes of non-infectious keratitis: tear film abnormalities;
immune reaction; chemical injuries etc.
Causes of infectious include: bacteria; protozoa; fungi;
viruses
Risk factors in infectious keratitis: alteration of ocular
normal flora (e.g. staphylococcus epidermidis; S aureus,
propionibacterium acnes); noncompliance with standard CL
disinfection and storage (mostly pseudomonas); virulent
organisms (e.g. Serratia & Bacillus in CL solutions);
contaminated CL (mostly pseudomonas); diabetes mellitus
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Bacterial keratitis non-related to contact lens
wear mainly caused by gram-positive bacteria
e.g. Staphylococcus, Streptococcus
Bacterial keratitis related to CL wear mainly
caused by Gram-negative bacteria e.g.
Pseudomonas; Serratia.
Protozoal keratitis related to CL wear: e.g.
Acanthamoeba ; usually from contaminated lens
solution
Viral infections related to CL wear are rare but
could enhance other microbial infections of the
cornea
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Common symptoms for infective keratitis:
pain; photophobia; tearing;
blepharospasm; reduced vision, discharge
(watery, or purulent)
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Treatment could include :antimicrobial
agents (e.g. neomycin; chloramphenicol);
steroids; penetrating keratoplasty
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Final exam: all the course material’s
except the 1st material
Good Luck with your finals
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