Rigid lens verification and evaluation

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Rigid lens verification and evaluation

• Week 14

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Rigid lens verification

• After taking all the measurements, fitting a
  trial lens, and ordering the lens, we must
  verify the lens once it is received.
• We do this to make sure the parameters we ordered
  are correct.
• We do this BEFORE we dispense the lens.
• The parameters we verify are
• Power
• Base curve
• Diameter
• Center thickness

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Rigid lens verification

• Power verification

• lensometer

• The power of the lens must be checked for
  accuracy the same way we verify a pair of
  spectacles before dispensing to the patient.
• We do this by using the lensometer.
• The lens is placed convex side up on the lens
  stop of the lensometer.
• You measure the lens the same way as a pair of
  glasses, the lens will be spherical.

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Lens verification

• Base curve verification

• radiuscope

• Base curve is just as important as power and
  diameter and must be verified.
• To verify the base curve is what we ordered, we
  use the radiuscope.

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Lens verification

• Using the radiuscope

• radiuscope

• The lens holder is removed and ONE drop of water
  is placed in the depression. The lens floats on
  top of the drop of water, convex side up.

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Lens verification

• Using the radiuscope

• The lens holder is put on the table with the
  water and lens in it.
• This must be placed so the green light from the
  radiuscope is directly on the center of the lens.
• The table can be rotated and shifted to center
  the green light.

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Lens verification

• Using the radiuscope

• Look through the eyepiece and focus the star
  shaped mire by turning the knob on the right.
• Use the knob on the left to move the number scale
  to zero.
• There is a small knob under the eyepiece to focus
  the number scale.

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Lens verification

• Using the radiuscope

• Once the star is in focus and the number scale is
  at zero.
• Measure the base curve by turning the star
  focusing knob away from you. The star will
  disappear and then will come back into focus, the
  scale reading will also move away from zero.
• Once the star comes back into focus, use the
  fine focus knob.

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Lens verification

• Using the radiuscope

• When the star mire comes into focus the 2nd time,
  it may not be centered.
• You can center the star by rotating the table to
  bring the star into center again.

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Lens verification

• Using the radiuscope

• The base curve is read by the position of the
  number scale line.
• This is in radius of curvature and is in mms.
• There is a conversion chart to convert to
  diopters, which is how we order BC.
• This reading is about 8.41

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Lens verification

• Diameter verification

• V gauge pd ruler

• The diameter of the lens must be verified before
  fitting it on the patient.
• To do this, you can use a pd ruler and measure
  the diameter or a V gauge. There is a channel
  in the shape of a V in the ruler.
• The lens is dropped in the channel and when it
  stops, the diameter is read on the side of the
  ruler in mms.

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Lens verification

• Center thickness verification

• Radiuscope thickness gauge

• Center thickness of the lens is important,
  especially if you specified a thinner or thicker
  lens than the norm.
• Lenses are generally fit as thin as possible for
  better O2 permeability. Keep in mind a high
  powered convex lens will be thick to begin with,
  so you may want to see what the lab can do to
  make the lens thinner.
• To verify the thickness, we use a radiuscope,if
  it has a thickness gauge on it or a thickness
  gauge.

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Lens evaluation

• After the lens is verified, we inspect for
  scratches, chips and warping and then put it on
  the patients eye for evaluation.
• We evaluate by checking
• Positioning and movement
• Condition
• Visual acuity
• Flexure
• Residual astigmatism
• Comfort
• Fluorescein pattern
• Corneal and eyelid integrety

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Lens evaluation

• flexure

• VA and residual astigmatism

• Flexure occurs when the lens bends over the
  cornea (astigmatic ridge) when the patient
  blinks.
• We can check for this with keratometry. With the
  lens on the eye, after the patient blinks, the
  mires will change. This happens because the lens
  bends in a different shape over the cornea.
• We can also check for this with retinoscopy. With
  the lens on the eye, flexure is evident when the
  reflex suddenly changes after blinking.

• Check the VA and make sure it is what you
  expected it to be, if not, over refract and make
  modifications.
• If there is astigmatism not corrected for by the
  tear lens, this may be residual astigmatism.
  This is not corneal or refractive astigmatism but
  lenticular astigmatism and is caused by the
  crystalline lens.
• This should have been dealt with before fitting
  with a trial lens. Residual astigmatism is
  usually tolerated if it is less than the amount
  of the spherical power.

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Lens evaluation

• Positioning and movement

• The lens should always move 1mm upon blinking. If
  there is no movement, the lens is too tight. If
  the lens is moving all over or too much, it is
  too flat.
• The lens should be positioned over the pupil,
  centered. The lid attachment fit should be under
  the upper lid but centered over the pupil and
  move at least 1 mm after blinking.

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Lens evaluation

• comfort

• Fluorescein patterns

• New gas perm lens wearers may take up to 6 weeks
  to build up tolerance for the lens but if an
  established wearer that complains of discomfort
  or pain, you have to find out why.
• What are some reasons a patient will complain of
  pain?

• Fluorescein can stain the tears so you can
  evaluate the tear film under the lens.
• If you encounter a dumb bell shape pattern, this
  signifies a large amount of astigmatism and you
  may need to modify with a change to the BC, D or
  making the lens a bi toric.
• A bi toric has 2 base curves, one horizontally
  and one vertically. This is typically used with
  large amounts of astigmatism, -3.00D or more.

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Lens evaluation

• Fluorescein patterns

• Flourescein patterns

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Fluorescein patterns
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Fluorescein patterns
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Fluorescein patterns

• It is important to remember that even though the
  lens has a steep or flat fit does not mean that
  it is a bad fit.
• lens is steep or flatbecause that is the way you
  chose to fit the lens. The tear lens is making up
  for the cylinder that was not ground into the
  lens. There is supposed to be a fluorescein
  pattern.
• When evaluating the fluorescein pattern, you
  should know what to expect before looking under
  the slit lamp. If you fit an apical fit, the lens
  should fit tight, just not too tight !

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Lens evaluation

• Corneal integrity

• Corneal abrasion

• This is regarding the patient that has already
  worn CLs.
• Always inspect the cornea before fitting with new
  lenses.
• Check with fluorescein under the slit lamp for
  any staining, scratches, ulcers, erosion, and or
  edema that may prevent the patient form wearing
  lenses.
• Tear film integrity should always be tested as
  well.
• These types of problems need be heal before
  wearing lenses.
• All of the above should be evaluated in the exam,
  well before the fitting starts.

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Thats it !

• See you next time for lens modifications!