Transcript Contact lenses-2

Contact lenses-2
Advanced Applications of Contact
Lenses-1
31/12/2009
Instructor: Areej Okashah
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Presbyopia & Contact lenses
• Presbyopia is a gradual decrement of visual functions @ near
among elderly (40 years or older)
• Bifocal & multifocal contact lenses (either GP or soft designs) are
designed to substitute bifocal or multifocal glasses; respectively.
• Bifocal contact lenses: provide two corrections (distance & near)
• Multifocal contact lenses: provide correction for more than two
distances; usually in a progressive design..
• Either bifocal or multifocal contact lenses use simultaneous or
alternating vision technique.
• Monovision: means that one lens corrects distance vision in one
eye; & another lens corrects near vision in the fellow eye
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•
a.
b.
c.
&
a.
b.
Which is more effective for our patients ?
Monovision
Multifocal
Or bifocal designs
GP or
Soft material
Answer: you should evaluate your individual
patient: consider tear, tear film, lids, …..etc.
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• A good candidate for bifocal or multifocal contact lenses is
the good candidate for contact lens wear in general….
Case history: surgical history; medications (e.g.
antihistamines); visual requirements; occupational
requirements….. Discuss with patients
External (anatomical) measurements: pupil size; lid position;
palpebral fissure size; blink rate & quality
Tear quality & volume
Corneal integrity
Refraction
K/ corneal topography
Are very important preliminary evaluations
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• Patient satisfaction with presbyopic lenses starts
after 6weeks of the initial application
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Single-vision CL & reading glasses
• i.e. a CL (GP or soft; sphere or toric)
for distance correction; & a spectacle
for near add.
• Provides good bilateral vision at D &
N
• Low cost
• Simplicity of fitting
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Monovision
• i.e. anisometropic contact lens correction; one eye is
corrected for distance ; the other eye is corrected for near..
So, patients will be able to see D & N as they keep both
eyes open
• Using conventional lens designs
• Decrease professional effort
• < expense for patients
• This design is thinner than bi-or-multifocal CL
Howevere
It impairs stereoscopic depth perception & one eye produces a
dominant response (ocular dominancy) usually the one for
distance; reduce the contrast sensitivity
If the patient has strong dominancy in one eye; it then be
difficult to ignore the out of focus monovision image
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• Check for VA for both D & near
• Patient comfort & adaptation are important to consider
Consideration in fitting monovision
Fit patients who don’t require long time of critical D vision
Examine binocular function i.e. stereopsis
Select the proper eye for N correction; i.e. the better eye is usually for D
correction
Prescribe the full amount of correction & underplus the N eye & overplus the
D eye  to reduce the anisometropia
Discuss adaptation time with the patient
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Bifocal CLs
• 70% of presbyopes who wear CLs are
fitted with monovision; 30% are fitted
with bifocal designs ????
• Bifocals are either simultaneous vision, or
alternating vision designs
•
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Simultaneous vision i.e. bivision
• Simultaneous vision is achieved
when the D & N power are
positioned within the pupil at the
same time; the patient will
selectively suppress the most
blurred image at the selected
distance
• Three designs are available with
simultaneous vision………cont
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cont
…..1) aspheric : has a gradual change of curvature
along one surface 2) concentric/annular : has
small central zone (the central zone either for D
or N; but D is more often) 3) diffractive :
available in soft design only & is independent on
the pupil size; central diffractive zone that
focuses image at distance by refraction of light &
at near through diffraction principle)
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Alternating/translating vision
• i.e. vertical movement results in one power zone to position
in front of the pupil at any one time (the distance zone is in
front of the of the pupil when viewing @ D; & the near zone
when viewing at N)
• Intentional shifting of lens position in which separate
discrete images formed by the two power segments in the
lens focus on the retina with a change of gaze from
distance (up) to near (down) or vice versa..
• Prism ballast or truncation are usually involved in this
design to maintain lens stability
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Therapeutic Cls
• Trauma
• Disease
• Surgery
• Bandages
• Corneal reshaping
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Ocular trauma
• Contact lenses can cause trauma which causes visual
impairment and participate in rehabilitation
• Trauma can be caused mostly by metallic injury & motor
vehicle accidents
• Always check the corneal topography
• Corneal staining; abrasion; scarring
• Cls may give a protective benefit against ocular trauma
• Cls is a useful tool to heal corneal & conjunctival wounds by
allowing the regeneration of affected cells; & by the
prevention of direct contact with lids while blinking
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• Cls also help in vision rehabilitation after trauma
or injury
• It also help manages aphakia; irregular
astigmatism; iris/pupil abnormalities; amblyopia
management (e.g. instead of patch); gross
disfigurement (e.g. lids)= post-trauma
• Bandage Cls: (soft, GP, or piggyback designs):
after penetrating-keratoplasty; post-refractive
surgery : to improve healing or to prevent
infection or contamination; corneal abrasion
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Paediatric contact lenses
• Usually CL wear in children is elective
• Either to improve vision or to improve appearance
• Correction of refractive errors among children depends on
the refractive error type; age; requirements; & parents
motivation
• Myopia: is rare among children; & if low-to-moderate
occasionally causes amblyopia
• Spectacle correction of high myopia results in image
minification; peripheral distortion; reduced field of view; 
CLs reduce these effects
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Rigid CLs slow the progression of myopia in children ….
“controversial”
• Hyperopia: the most common refractive error among
children; however refractive error correction doesn’t alter
emmetropization; many practitioners recommend
correction of hyperopia to improve vision & to prevent the
onset of accommodative esotropia
• With spectacle correction of hyperopia: plus lenses are
heavy; magnify the patients eyes & the viewed object &
they distort the peripheral vision… Cls avoid these
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• Cls in paediatric can be used to correct
astigmatism as in adults; anisometropia (to
reduce the retinal image disparity & to prevent
amblyopia) as well as aphakia
• Children can be fitted with smaller diameter e.g.
RGP OAD/ OZD = 9.2/7.88 mm because they
have smaller palpebral fissure…
• Children can be fitted with larger diameter lenses
because they may fall while on their eyes
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BCR selection:
Corneal Cyl
BCR
0.00
0.50 D flatter than flat k
=<0.75D
0.25D flatter than flat k
>0.75-<1.50D
Fit on flat k
>=1.50D
1/3 times the toricity steeper than flat k
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Keratoconus
• Is a progressive disorder in which the cornea has
irregular shape
• Onset: around puberty
• Autosomal dominant
• Usually bilateral; but assymetrical
• Systemic association: e.g. Down syndrome;
Turner syndrome; Marfan syndrome
• Ocular association: e.g. retinitis pigmentosa;
vernal keratoconjunctivitis;
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• According to
morphology can be
classified into
• Nipple cones: small
size 5mm; steep
curvature; the
apex of the cone is
central or inferonasally
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• Oval cones: 56mm size; ellipsoid
(oval) & displaced
inferotemporally
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• Globus cones: the
largest >6mm
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• Presentation: visual impairment due to progressive myopia
& astigmatism (usually reported for one eye); changes in
spectacle Rx; decrease tolerance to contact lens wear;
• Signs: central or paracentral stromal thinning; apical
protrusion; irregular astigmatism; steepening of the cornea
graded according to keratometry readings (mild <48D,
moderate 48-54D, severe >54D)
Early in the disease: oil droplet reflex on ophthalmoscopy;
irregular scissor reflex on retinoscopy; Vogt lines (i.e. deep
vertical stromal striae) on slit-lamp exam; irregular
astigmatism on keratometry; abnormal corneal topography
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Vogt striae (i.e. line) in keratoconus
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Late in the disease:
Munson sign (i.e.
bulging of the
lower lid on
downgaze); visual
acuity worsens;
watering; oedema;
stromal scarring
after beaks
healing;
Munson sign in keratoconus
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• Treatment: spectacles to correct
regular & mild irregular astigmatism;
contact lenses (e.g. rigid; toric);
Keratoplasty
• http://www.youtube.com/watch?v=8jDBvjbKMR4
• http://www.youtube.com/watch?v=Kwv9juznA7c
• http://www.youtube.com/watch?v=QRNzDC5xlc8
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