Janet Approved Flashcards
Simple Hyperopic Astigmatism
After minus or plus transposition: Plano +
Parallel rays of light
come to two line foci,
one falling on the retina
and the other falling
behind the retina
Simple Myopic Astigmatism
After minus or plus transposition: Plano -
Parallel rays of light
come to two line foci,
one falling on the
retina and the other
falling in front of the
retina
Compound Hyperopic Astigmatism
After minus or plus transposition: + +
Both parallel light rays fall
behind the retina
* Both major meridian powers
indicate hyperopia
Compound Myopic Astigmatism
After minus or plus transposition: - -
Both parallel light rays come
to two line foci in front of
retina
* Both major meridian powers
indicate the refraction is
myopic
Mixed astigmatism
After minus or plus transposition: + -
Parallel light rays come to two-line foci,
one falling in front of the retina and the
other falling behind the retina
* One major meridian indicates the
refraction is hyperopic and the other
meridian indicates the refraction is
myopic
Dk/L
refers to the amount of oxygen which pass
through a lens material of specified thickness
Myoflange design
an increase in edge thickness to aid in better centering lenses that position low on the cornea.
Extra edge thickness creates greater lid interaction.
Hyperflange design
a decrease in edge thickness is indicated in many high minus power lens designs to limit
lid interaction, allowing the lens to position more centrally
on the cornea.
Vertex Distance
the distance between the back vertex of
the correcting lens, and the front surface of the eye
Wetting angle
the spreadability of water over a lens
surface. The lower the angle, the more wettable the
surface.
Lescometer
An attachment that holds
the calibration balls for
the keratometer
Also contains a lens
holder which enables the
keratometer to be used
to measure the base
curve of a rigid contact
lens
when you can’t locate the kertometric mires
The instrument and/or patients is not aligned properly
Keratometer has transient mire clarity
ask the patient to blink and measure quickly
Transient mire focus in keratometer
ensure patient’s forehead is against the headrest
Unstable patient gaze in keratometer
close the other eye
H and v mires cannot be measured concurrently in keratometer
irregular astigmatism
Only 1 minus sign is visible in the keratometer
patient’s eyelid is drooping
Only 1 plus sign is visible in the keratometer
occluder is in the way
The modulus of a lens material is the measurement of the
material’s resistance to deformation under tension. In
practical terms, the ____ the lens material, the _____ the
lens modulus
stiffer
higher
Visibility tint
blue or light green
Spin casting
this process, the liquid polymer mix is introduced into a spinning, open top, concave mold that will determine the
front surface configuration of the lens.
The back surface of the lens is formed in air.
Lathe Cutting
- have exhibited the greatest consistency from lens to lens,
based on the ability to very closely control surface
curvatures. - In this process the polymerized plastic, in a dehydrated,
rigid state, is formed into lens blanks, mounted in a base
curve lathe, and the posterior curves
Cast Molding
- In overcoming the previous inconsistency and quality
disadvantages. The result has been the increasing
availability of improved quality products at lower costs. - Hydrogel lenses produced in a molding process may be
formed in the rigid, dehydrated state, resulting in a finished
product that will subsequently be immersed in saline and
hydrated to the specified degree
3-point touch
for soft lenses
