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Contact lens theory 1 Course 2 Review of contact lens
instrumentation
1. Keratometer ( Ophthalmometer )
2. Slit-lamp Bio-microscope
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Contact lens theory 1 Course 2Review of the keratometer and
slit-lamp 1. Keratometer ( Ophthalmometer )
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Contact lens theory 1 Course 2Keratometric mires*
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Contact lens theory 1 Course 2Keratometric mires *
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Contact lens theory 1 Course 2Cornea acts as a convex mirror. By
altering the focal length of the eyepiece of the keratometer a very
accurate reading of the apex of the cornea can be taken.
Keratometer is calibrated in dioptres and the inside curve of a
contact lens is measured in mm.
Range of the keratometer 36.00 D to 52.00 D Keratometer standard
refractive index n = 1.3375
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Contact lens theory 1 Course 2Functions
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Contact lens theory 1 Course 2*
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Contact lens theory 1 Course 2Parts:
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Contact lens theory 1 Course 2
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Contact lens theory 1 Course 2
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Contact lens theory 1 Course 2Steps in taking K readings:
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Contact lens theory 1 Course 2
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Contact lens theory 1 Course 2By convention the flatter (lower
meridian) is recorded first.
Normal corneal curvature readings are between 41.00 . 46.oo D
Average corneal curvature is 44.00 D *
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Contact lens theory 1 Course 24.Keratometer attachments a. Lens
Co Meter
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Contact lens theory 1 Course 2Lensco - Meter*
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Contact lens theory 1 Course 2.
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Contact lens theory 1 Course 2c. Inns Disc *
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Contact lens theory 1 Course 2d. Topogometer*
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Contact lens theory 1 Course 2 Topogometer*
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Contact lens theory 1 Course 2
5. Slit- lamp Bio-microscope
The slit lamp is a device that focuses a high intensity light
beam at the structures of the eye which can be examined by the
practitioner by looking through a microscope.
Uses the Tyndalls effect light is transmitted into a transparent
structure (anterior chamber) and is scattered through the
transparency, illuminating the smallest details (tears, showing
opacities and debris)
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Contact lens theory 1 Course 2Slit-lamp bio-microscope*
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Contact lens theory 1 Course 2Slit-lamp bio-microscope*
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Contact lens theory 1 Course 2Functions:
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Contact lens theory 1 Course 2
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Contact lens theory 1 Course 2Ocular conditions assessed with
the instrument
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Contact lens theory 1 Course 2Parts
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Contact lens theory 1 Course 2Slit lamp illuminations
Diffuse illumination or wide beam illuminationSettings: - wide
slit beam of light not focused, directed at the cornea from an
angle of approx. 45 degrees - magnification on low 6X-16X -
microscope positioned directly in front of the patients eye and
focused on the anterior surface of the cornea - light intensity is
low
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Contact lens theory 1 Course 2Diffuse illumination
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Contact lens theory 1 Course 2Uses: General eye survey
a. Under normal light: - with the patients eye open look for
irregularities of the eyelids, eyelashes, conjunctiva and
cornea
Eyelids 1. Normal situation - upper lid (covers the top
millimeter of the cornea) - lower lid- lower border of the cornea
is covered 2. Abnormal situations - ptosis (droopy upper lid) more
cornea is covered - ectropion (eye lid margin projects outward) -
entropion (eye lid margin projects inward)
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Contact lens theory 1 Course 2EYELIDS - ReviewThe eyelids are
the most anterior structures affecting contact lens fit. The
eyelids contain many of the structures for producing the tear
film.- the meibomian glands opening at the lid margin produce the
sebaceous top layer - the lacrimal glands located superior and
temporal on the underside of the lid produce the aqueous
componentFunctions: -Protection of the globe -Distribution of the
tear film -Production of tears
As the lid blinks the tear spreads film over the surface of the
eye toward the lacrimal ducts positioned on the upper and lower lid
margins. Some of the tears are lost to evaporation but the majority
drain out of the eye through the puncta, into the nasolacrimal
duct. *
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Contact lens theory 1 Course 2During the pre-fit evaluation and
follow-up examination it is important to examine the lids and lid
margins. - should be free of debris and inflammation - the
under-surface of the lid should be smooth and uniform in color and
texture. Patients with chronic allergies or blepharo-conjunctivitis
are unlikely to be successful contact lens wearers. One common
complication observed with contact lenses is giant papillary
conjunctivitis or GPC (the underside of the lid becomes red and
irritated developing a cobblestone-like texture). GPC is a
hypersensitivity reaction most commonly diagnosed in soft contact
lens wearers. *
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Contact lens theory 1 Course 2 When performing diffuse
illumination on the lids and eyelashes look for:
If the eyelids and lashes are normal are recorded as clean and
clear*
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Contact lens theory 1 Course 2Examining Lids and LashesFirst
while eye is closed, then open*
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Contact lens theory 1 Course 2*
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Contact lens theory 1 Course 2Abnormal eyelids cause:
corneal exposureexcessive
drynessTearingIrritationPigmentationtear debrisincreased number and
dilated blood vesselsblepharitis lagophthalmos
After examining the eyelids, the conjunctiva is examined*
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Contact lens theory 1 Course 2Conjunctiva Normal situation - is
thin, transparent, white, lustrous, smooth, non pigmented and
should appear uniformAbnormal conjunctiva - is inflamed, swelling,
has discharge and is hyperemic Palpebral conjunctivaPapillae
(caused by allergic diseases) appear as round bumpsFollicles
(caused by viral infections) appear as long bumps
Bulbar conjunctiva- should see blood vessels, but not grossly
engorged
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Contact lens theory 1 Course 2Conjunctiva*
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Contact lens theory 1 Course 2CorneaOverall view of cornea ( but
not fine details)1. Normal cornea - appearance smooth, uniform
thickness, avascular
2. Abnormal cornea - appearance granular, hazy, gray, thinning
zones - corneal scars and infiltrations- irregularities of the
Descements membrane- pigmentation on the epithelial layer- invading
blood vessels - severe edema of the epithelium
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Contact lens theory 1 Course 2 b) Using Rose Bengal stain and no
filters can detectdamaged cells tissues in Keratoconjunctivitis
Siccaherpatic lesions of the lids and the cornea
c) Using fluorescein sodium or Fluoresoft stain under cobalt
blue filter Assess contact lens fit - bearing - contact lens
movement - contact lens positioningAssess the tear break time -
TBUT testAssess dark drying areas of the epithelium, staining of
the cornea and conjunctivaDetect Fleischers ring in keratokonus
patients
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Contact lens theory 1 Course 2b) Direct illumination Types: b1-
optic section Settings: narrow slit 0.25 - 1.00 mm wide and 7 - 9
mm highmicroscope directed in front of the patients eye and focused
on patients closed lid, patient opens the eye and is directed to
look at the examiners opposite earillumination source is at about
45 degrees start with magnification on low to medium (6X 16 X) and
when closer to the area to observe set magnification on high (16X
-25X) layers of the cornea can be seenwhen cornea is sharp in focus
scan the cornea from temporal limbus to nasal limbus
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Contact lens theory 1 Course 2 b1- optic section
Layers of the cornea seen in optic sectionthe front surface,
bright zone, is the surface of the tearsthe next dark line is the
epithelium layerthe next brighter thin line is Bowmans membranethe
gray granular wider area is the stromalast bright inner zone is the
endothelium
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Contact lens theory 1 Course 2Used for specific investigations
to: determine the depth, elevation or location of a defect of the
cornea and conjunctiva - depths of foreign bodies - scars -
opacities see the tear film detect changes in the corneal and
conjunctival thickness identify the location of cataracts in the
crystalline lens (any lens opacity will appear white against a grey
background) see a wide section of stroma asses the degree of
openness of the anterior chamber
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Contact lens theory 1 Course 2 The Crystalline Lens This
optic-section reveals : cornea - first white line anterior chamber
- black space crystalline lens posteriorly*
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Contact lens theory 1 Course 2b2- parallelepipedSetting: - slit
beam slightly open 2 mm, height may vary providing a more three
dimensional view of the cornea and the crystalline lens -
illumination source at about 45 degrees angle may be varied to
expose more corneal epithelium, stroma and endothelium - microscope
directed on the patients eye - low magnification
Whole cornea will be scanned *
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Contact lens theory 1 Course 2Parallelepiped*
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Contact lens theory 1 Course 2Used to see:tear debris (in
allergies, sinus conditions, bacterial infections)corneal nerves -
appear white in color and bi or trifurcateblood vessels or ghost
vessels that extend from the limbus into corneacorneal scars -
appear whiter in color than the surroundingcorneal striae - appear
white in color and vertically placed (caused by a poor contact lens
fit)
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Contact lens theory 1 Course 2shows irregularities on the
cornea, opacities, abrasions, broad view of anterior and posterior
corneal surfacesassess the fit of contact lenses with fluorescein
dyeiris patterndepth of foreign body
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Contact lens theory 1 Course 2b3)- conical beamSettings:- slit
shut down to a point (circular pattern)bright, high illumination,
magnification (16 X 25 X)light 45 -60 degrees temporally directed
into the pupilmicroscope directed in front of the eyeconical beam
focused between the cornea and the anterior lens surface
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Contact lens theory 1 Course 2Conical beam
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Contact lens theory 1 Course 2Uses: to determine pathological
state of the eye to examine the anterior chamber for floating
aqueous flare and cells
Flare (protein escaping from dilated blood vessels) appearance
grey and milkyBlood cells (escaping from dilated blood vessels Red
blood cells - appear as reddish yellow dots White blood cells -
appear as grayish- white
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Contact lens theory 1 Course 2c) Indirect illuminationSettings -
slit beam parallelepiped with moderate width - slit sharply focused
on the cornea - microscope sharply focused on the area adjacent to
the light - click stop loosened (to oscillate beam)UsesUsed in
conjunction with all other illuminations to look at tissues outside
the area directly illuminated (reduced glare) to view iris
pathology (the only method by which the iris sphincter can be
seen)to view corneal epithelium irregularities (mycrocystic edema),
corneal infiltrates and tears
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Contact lens theory 1 Course 2Indirect illumination
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Contact lens theory 1 Course 2d) Retro-illuminationSettings: -
slit width 1-2 mm wide to 4-5 mm high - light source beam is
reflected off another structure like iris, lens, retina- 60 degree
angle between slit and microscopemicroscope is focused to the
anterior structures and the light is reflected back- magnification
is low to medium (6X 10X)
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Contact lens theory 1 Course 2Retro-illumination
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Contact lens theory 1 Course 2 Used to:examine size and density
of opacities, scars, pigment, blood vessels on the cornea (not
their location)see deposits on Descements membrane
Opacities appear dark against a light background Features that
scatter light appear lighter than the background (E.g.: edema of
the epithelium, precipitates)
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Contact lens theory 1 Course 2e) Specular reflectionSettings: -
parallel slit, medium width- high illumination and magnification
(20X 25 X)illuminating arm and the microscope are positioned in
such a way that the angle of incidence is equal to the angle of
reflection (approx. 60 degrees) - microsope is placed directly in
front of the patient, just off the limbus
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Contact lens theory 1 Course 2Specular reflection
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Contact lens theory 1 Course 2Used to see:details of epithelial
cells (elevations and depressions appear as dark defects on the
bright reflected light)pre corneal fluid, mucusfront and back
surfaces of the crystalline lens can be seenonly illumination to
show details of the endothelial cells of the cornea
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Contact lens theory 1 Course 2f) Sclerotic Scatter uses
principle of total reflection A halo of light will be seen around
limbus as light is internally reflected within cornea, but
scattered by the sclera. The pupil is observed with the naked eye
from an angle directly opposite from the light source.Settings: -
beam of light focused sharply at the temporal limbus, - microscope
focused on the cornea - magnification 7 -10X - angle between
bio-microscope and slit-lamp 45 degrees or greater
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Contact lens theory 1 Course 2Sclerotic Scatter
Used to see:central corneal clouding (seen with the naked eye,
without using the biomicroscope)disturbances in the opacity of the
cornea (edema, scars, pigments, deposits)
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Contact lens theory 1 Course 2 g) TangentialSettings - widest
angle (90 degrees)Uses to examine the more central portions of the
cornea (keratoconus) to examine iris, freckle and tumors
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Contact lens theory 1 Course 2Tangential
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Contact lens theory 1 Course 2Slit-lamp attachments Hruby lens -
(-55.00D lens ) - used to neutralize the power of the refractive
media and to allow the examiner to view the retina and vitreous
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Contact lens theory 1 Course 2b) 90 degree lens - used to
neutralize the refractive media and to allow to view a much wider
area than the Hruby lens
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Contact lens theory 1 Course 2c) Tonometer - used to measure the
amount of ocular pressure
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Contact lens theory 1 Course 2d) Pachometer - used to measure
corneal thickness and anterior chamber depth*
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Contact lens theory 1 Course 2Readings:Nathan Efron Contact Lens
PracticeClinical instruments page 47-67Preliminary examination page
352 - 358*
A diagnostic instrument used to measure the curvature of the two
principal meridians of the centralcornea (usually the vertical and
horizontal curvatures are measured). It is assessing the extend and
the axis of the corneal astigmatism.*
