Formulas/General Rules Flashcards
Total Frame PD/Box distance measurement
A+DBL
Individual Frame PD/Box distance measurement
(A+DBL)/2
Horizontal Decentration
Frame PD-Patient PD/2
Vertical Decentration/ Seg Drop or Height
OC Height - B/2
Minimum Blank Size
MBS= ED + (total decentration) + 2
MBS = ED +2(decentration per lens) + 2
Nominal Lens Formula
Power = Front Surface Power + Back Surface Power or Dn = D1 + D2
Focal Length
Diopter
F.L=1/Diopter
Diopter= 1/F.L (meters)
Prentices Rule
Prism=cF
c=distance in cm
F=Dioptre
Effective Power (Vertex distance Adjustment)
Peff= P/1-dP
P eff= Effective power
P = Original lens power
d = Change in vertex distance (in meters, positive if moved closer to the eye)
How to find Base Curve
BC = 337.5/K
CL RX Over Refraction
CLRx=SpectacleRx−VertexAdjustment+Over-refraction
Seg Inset
Distance PD-Near PD
Given Prismatic effect and Prescription. Find decentration needed to create prismatic effect
C = Prism
F=Dioptre
c=distance in cm
C/F=c
mm to cm?
cm to mm
5mm - 0.5cm
?/10 = cm
?x10 = mm
How to find percent of a number
PercentageofaNumber=
Percentage/100×Number
example 2/100 x -9.25 = -0.185
FAP = ?
SAM = ?
Flatter add plus
Steeper add minus
Steps to RGP solving.
1) Identify Corneal astigmatism, Direction and within or outside of nomogram
2) Compensated CL RX?
3)Residual Astig?
4)Use the nomogram to determine BC and DIA.
5)determine sph power and design of lens using SAM/FAP
What is the relationship between K measurments and BC?
The steeper the K(the higher the number) the smaller the BC.
The flatter the K (the lower the number) the bigger the BC.
How do you loosen (too steep) the fit of a soft lens? 2
flatten the BC (larger number BC)
Decrease the DIA
How do you steepen (too flat) the fit of a soft lens? 2
Steepen the BC (small number BC)
Increase the DIA
How do you find the DIA on a soft cl lens? 2
HVID + 2mm
based of nomogram given
What is WTR astigmatism?
More power in the vertical meridian so it has a steeper curvature.
42.00/45.00@090
What is ATR astigmatism?
More power in the horitonzal meridian so it has a steeper curvature
45.00/42.00@090
Where do you see touch in a WTR astig RGP picture?
horizontal like a figure of 8 on its side
Where do you see touch in a ATR astig RGP picture?
vertical, like a hour glass figure
If the Astigmatism is between 30 degrees of 90 and 180 it is considered WTR and ATR.
If it is out of these parameter what is the astig called?
Oblique
If the mires are Clear Clear Clear the fit is ………..
Good fit
If the mires are Clear Blurry Clear the fit is …………
Flat fit
If the mires are Blurry Clear Blurry the fit is ……………….
Steep fit
How do we find Corneal astigmstism ?
Difference between the K readings
How do we find Residual Astig?
Difference between Corneal Astig and Astigmatism of Prescription after vertexing
What are the steps for Standard Alignment? 1-6
1)Horizontal Alignment
2)Vertical Alignment
3)Open temple Alignment
4)Temple Parallelism
5)Alignment of the Bent Down Portion of the Temple
6)Temple Fold Angle
What is the formula to calculate Total Seg Inset using Binocular PD?
DBC - Near PD /2
What are the two things you check for in horizontal alignment?
Rotated lens
Skewed bridge
What is checked for in vertical alignment? 3
x-ing
face form
Variant/vertical planes
What needs to be adjusted first when addressing glasses out of alignment?
The bridge
The x-ing
What is the Open Temple Spread?
The angle that each open temples forms in relationship with the front of the frame (90-95 degrees)
How do you check for Temple Parallelism?
Do a flat surface touch test - place the glasses upside down on a flat surface
What are the 4 steps if the temple parallelism is not equal?
1)check for a bent endpiece
2)check for loose or broken rivets or loose hidden hinge
3)check for bend in the temple shaft
4) if none of the above is wrong, hinge needs to be bent
When looking at the alignment of the bent down portion of the temples what are we checking? 2
1) Check for equality in the downward bend.
2) Check for equality of the inward bend.
When checking the temple fold angle what do we do/look at?
Fold temples to closed position and observe angle formed at the temples cross.
What 3 angles are part of adjusting nosepads?
1-Frontal angle
2-Splay angle
3-Vertical angle
Does the frontal angle change height of the frame?
No - it is used for flat or tall noses.
Does the Splay angle change height of the frame?
No- The twist on the nosepads adjusts to the specifics of a pxs nose
Does the vertical angle change the height of the frame?
It can do slightly but no it mainly moves frames further away or closer.
Do changing the angles of the 3 nosepads angles (splay,frontal,vertical) change the height of the frame?
No they dont, increasing + decreasing the distance between them changes the height of the frames
What is the solution to inequality in vertex distance? Left + Right 4
If left lens is IN = bring left temple IN
If right lens is OUT = bring right temple OUT
If right lens is IN = bring right temple IN
If left lens is OUT = bring left temple OUT
What is the solution when the lenses are different heights? Right + left 4
If left lens is UP = bend left temple UP
If left lens is DOWN = bend left temple DOWN
If right lens is UP = bend right lens UP
If right lens is DOWN = bend right temple DOWN
What is the relationship between the nosepads and the height of the lenses?
Widen the nosepads = lowers glasses
Narrow the nosepads = heightens glasses
What kind of tilt is needed in these conditions:
Eyes at OC =
Eyes above OC =
Eyes below OC =
= No Pantoscopic tilt
= Pantoscopic tilt required
= Retroscopic tilt needed (not done in practice/new frame choice)
If the bifocal segment is too high what should you do to the tilt?
Increase the pantoscopic tilt
If the oc height is too low how do you adjust the panto tilt to help ?
decrease the pantoscopic tilt (not practical)
What is the Compounding table for Prism?
Right Eye Left Eye
Base out - Base out
Base In - Base in
Base Up - Base Down
Base Down - Base Up
What is the Cancelling table for Prism?
Right Eye Left Eye
Base out - Base in
Base In - Base Out
Base Up - Base Up
Base Down - Base Down
What is the rules for decentering the lens of a Minus Prescription?
Up - Base Down
Down - Base Up
In - Base Out
Out - Base In
What is the rules for decentering the lens of a Plus Prescription?
Up - Base Up
Down - Base Down
In - Base In
Out - Base Out
When finding if the cyl is out of ANSI standards what must we do?
Find the difference between the two powers (Transpose) use that difference for the tolerance chart. Should be the same as the cyl measurement
When looking if the add power is out of ANSI what do we look at?
Total add power
What are the 1/8th increments from 0.00 to 1.00?
0.00, 0.125, 0.25, 0.375, 0.50, 0.625, 0.75, 0.875, 1.00
The causes of SPK include viral conjunctivitis, blepharitis, Keratoconjunctivitis sicca and …………..
solution sensitivity
Corneal Abrasion can be caused by ……………….
improper insertion or removal of contact lens
Sleeping in contact lenses can lead to a lack of oxygen in the cornea causing …………….
corneal edema
Blunt force trauma or abnormal vessel growth can both cause ………………
hyphema
Blepharitis can be caused by allergy, poor hygiene and ……………….
disruption of the tear film from dry eye
Blanching is caused when the ……………..
edge of the lens fits too closely to the eye
……………… can be caused by over-wearing contact lenses or by sleeping in them which leads to annoxia or hypoxia.
corneal vascularization
Aging, contact lens wear, ocular surgery, trauma and damage can lead to a variation in the size of corneal endothelial cells known as …………………..
Polymegathism
Dellen can be caused by corneal dryness and the ………….
GP rubbing on the limbus
UV damage, dust, and wind can cause ……………
Ptergyium
………….. can form because of infection, or pathological condition
chalazion
Dendritic Ulcer is caused by the ……………..
Herpes simplex virus
The leading cause of a corneal ulcer is ……………… although there are many causes for the open sore on the cornea.
infection
Age, hypoxia, and genetics can lead to …………..
corneal guttata
GPC can be caused by………………… 4
overwearing or sleeping with contact lenses,
poor hygeine,
tight fitting lenses
allergy to protein buildup on the lens
……………. and ……………… can be caused by atrophy of the lid muscles from aging, scarring, or trauma.
Ectropian
Entropian
When do we refer the patient on the efron grading scale?
2.5 or more
What are 2 ways to increase DK (oxygen permeability) in a HYDROGEL lens?
- Decrease lens thickness.
- Increase water content.
More Water Content = more breathable lenses as more oxygen transmission T/F
TRUE
Does a low water content lens have a longer lifespan and less breakage?
YES
What is the disadvantage to a low water content lens?
less breathable lens - more chance of vascularization
The high water content materials have faster adaption with comfort and wearing time. T/F
true
What are advantages of Silicone Hydrogel lenses? 2
-high Dks with rapid adaptation
-good for patient with vascularization and mild dry eyes.
What are disadvantages of Silicone Hydrogel lenses? 2
-greater incidence of GPC and arcuate
staining in certain materials
-more likely to have mucin balls
The lower the Dk value the less breathability. The more the DK value the more breathability. T/F
TRUE
How do we now if a lens is well fitting? 3
- Good centration with full corneal coverage in all direction of gaze
- Sufficient movement to allow tear exchange under the lens during the blink (0.2 to 0.5 mm is generally
considered optimal) - Satisfactory Push-Up Test
What are 6 signs and symptoms of a tight/steep fitting lens? (centration/comfort/vision3/physical sign)
- Good centration
- Good comfort
- Fluctuating vision between blinks
- Poor visual acuity
- Temporary improvement on blinking
- Blanching/ lens indentation
What are 6 signs and symptoms of a loose/flat fitting lens? (comfort/ centration2/ vision2/ physical sign)
- Vision may be blurred after the blink
- Comfort of fit is poor
- Poor centration
- Post blink movement is >0.4mm
- Peripheral edge standoff
- Vision is variable
What could a loose/flat fitting lens be mistaken for?
Inverted lens - check to see if the lens is inverted if signs and symptoms of a loose lens occur.
What can happen to the edges of a loose/flat lens?
edge stand off
What can happen to the edges of a tight/steep lens?
conjunctival indentation/blanching
When over refracting what prescription do we start with?
Plano - +0.25D
then
Plano- -0.25D
If the lens rotates clockwise (to the left) what do we do to the axis?
If the lens rotates anti-clockwise (to the right) what do we do the axis?
add the axis rotation (100, rotates 30 clockwise, order 130)
subtract the axis rotation (100, rotates 30 anti-clockwise, order 60)
What are the 4 checks when checking for CLs movement?
the push up test
upward gaze
lateral gaze
blinking
Wearing Extended Wear (EW) contact lenses for 7 nights in a row is being compliant with this type of modality. T/F
FALSE - 6 nights would be within compliance
Name the modality for lenses that are worn only during the daytime, not worn at night and have a strict cleaning regime.
Daily Wear (DW)
What is the ‘umbrella’ term used to describe a condition that affects the choroid, ciliary body and the iris? You also observe white blood cells in the anterior chamber.
Uveitis
If there is too much water in the stroma what might happen to the patients vision? 2
Haze
Potential blindess
What can cause an inferior arcuate staining?
Incomplete blink
A patient presents to care with Superficial Punctate Staining what could of caused it?5
improper use of hydrogen peroxide
cls overwear
viral conjunctivitis
blepharitis
chemical burns/Uv exposure
If a patient is suffering from fleicher’s ring what disease is also present?
keratoconus
A patient presents to care and reports a severe allergy to pollen and a swollen conjunctival tissue. What is the condition and do we need to refer?
Chemosis
No need to refer for allergy
What is the condition called where structural thinning observed? What are the 4 causes?
Dellen
Corneal dryness
GP rubbing on edge of limbus
Injury
Disease
A patient comes in complaining of not being able to wear their lens due to comfort and blurred vision while wearing the lenses. What is the probable cause?1 What is it NOT and why?2
Scratches and/or dirty lens
(not corneal edema as blurry only with CL on)
(not fit as they ‘come back’ complaining and we would have fit well)
If you are making an Bi Toric or Back Toric lens once you have found DIA/BC what do you do? next 3 steps
-Find ∆k 2.75D
-Find induced cyl = ∆K X 0.4 1.1D
-Find Calculated over correction (Coc)= induced cyl - Residual cyl
a. If Coc <0.75 use back toric
b. If Coc > 0.75 use bi-toric
Stye/Chalazion - What would you do? 3
-Hot compression 4 times per day
-No cl wear
- If severe refer to Dr
Cataract - What would you do? 1
-Refer to Dr
Imbedded Foreign Object - What would you do?
-Refer to Dr/hospital - emergency
Entropian - What would you do? 2
- bandage lens only
- no to normal cls
Pterigium - What would you do? 2
- no to normal cls - depending on the location (near limbal area or not)
-Refer to Dr
Pingecula - What would you do? 1
- yes -depends on the location (not near limbal area)
basal cell carcinoma - What would you do? 1
-no cls due to touching there lid, risk of infection.
Hordeleum - What would you do? 3
-Refer to Dr
-no cls depending on severity
-hot compression if small
Ectropian - What would you do? 2
- no cls due to exposed eye
-Refer to Dr
GPC - What would you do? 2
- throw lens out - discontinue wear until clear
- if severe refer to DR
Corneal Abrasion - What would you do? 2
- refer to dr/emergency
- no cls
Subconjunctival Hemorrhage - What would you do? 1
- no cls
Steep fitting lens - What would you do? and how? 2
- order a flatter lens
-decrease the diameter
-increase the BC
Flat fitting lens- What would you do? and how? 2
- order a steeper lens
- increase the diameter
-decrease the BC
What are jelly bumps?
jelly like bumps on a contact lens normally due to unhygienic conditions
What condition can also be present if a patient has jelly bumps on their cls ?
GPC as the jelly bumps can rub the undernath of the eyelid
How does GPC affect a soft contact lens? and what should we do?
makes a good fitting lens ride high
issue with the pxs hygiene, refit to higher DK or/and daily disposables
How do you identify iritis in a picture?
redness around the iris mainly but the sclera will be mostly white
What is the difference between jelly bumps and mucin balls?
jelly bumps are on the outsude of the contact lens
mucin balls found between the back side of the contact lens and the front of the cornea
H/V @ axis
H/V @ axis
Lens is too tight/steep on the eye
Need to loosen the lens by decreasing sag 2
- Flatten base curve (larger number)
- Reduce overall diameter
Lens is too loose/flat on the eye
Need to tighten the lens by increasing sag 2
- Steepen base curve (smaller number)
- Increase overall diameter
When checking the fit of the frame in the service section of NACOR what do we need to check for? 5
Fitting triangle
Panto
Vertex Distance
LTB
Nosepads
What checks do we need to perform on the patient when checking the fit of the frame during service? 5
Look to the side - panto
Look down - vertex
TUG TEST
Look to the side + pull ear forward to check LTB
Px to look at my nose - nosepads
How do we find out Vertical Imbalance at the reading level? 4
Find power at 090
Prentices rule (reading level x power)
Cancel between the two eyes
Final vertical imbalance on the lens which has the most prism
What are we looking for during Diffuse illumination? 3
Overall view of the eye
Lids/eyelashes
Caruncle/scleral vessels
What are we looking for during Specular Reflection illumination? 4
Polymegathism
Endothelial blebs
Endothelial guttata
Pleomorphism
What are we looking for during Parrellpiped illumination? 4
anterior surface irregularities
where a foreign body is
tear layer assessment
evaluation of the cl fit
What are we looking for during Conical Beam illumination? 2
Debris floating in the anterior chamber
Aqueous flare
What are we looking for during Retro illumination? 5
Scars
Pigments
Neovascularization
How big a foreign body is
Microcysts
What are we looking for during Sclerotic Scatter illumination? 3
Corneal Edema
observe if disturbance in cornea opacity is present
Nebula
What are the steps to finding the Soft Cls prescription?
1) Draw a cl cross
2) Vertex
3) Determine new sph + difference between them (cyl)
4) New axis using LARS
5) Do not overminus - check if it asks for empirical fitting or diagnostic
When should we question if the K’s have changed too much in a case study or follow up exam?
0.50D
During the eyeglass exam section in NACOR when do we wash hands? 2
When dont we need to wash hands in eyeglass exam section in NACOR? 2
Before touching px to adjust frame in service
Before touching px to take any measurements
Verification section
Neutralisation section
During the contact lens exam sections in Nacor when do we wash hands? 3
When dont we need to wash hands in contact lens exam section in NACOR? 1
In Keratometry before measuring the ball (as your px)
In Insertion and Removal 5 times before each task.
In follow up before proceding with anything. Then clean equipment EVERYTHING including pen/table etc. Also before ‘lid eversion and TBUT tests’.
Verification of CLS
What are two ways prism can be incorporated into the lens?
Ground in - Can NOT centre
Decentred - Can centre
If the prism is ground in how do you find the amount of prism in the glasses?
Using prism compensator, will get a strange pd as cannot centre.
If the prism is in the lens due to vertical decentration how do you find the amount of prism in the glasses? 4 steps
1)find the strongest powered lens in the 090
2)centre and dot the stronger lens
3)move glasses over dont move stage
4)read prism of the lowest power lens.
In theory we should be told the Px pd if horizontal prism has been induced through decentration. If it has not been told what should be assume the PX PD is.
Frame PD - 2 = Monocular
What are typical measurements forseg sizes for:
Bifocals? 5
Trifocals? 2
25,28,35,40,45
7x28, 8x35
How many times should you check your measurments in the eyeglass section?
THREE TIMES for each thing
Check soft cls three times. You have time. Remember if the power is above 5.00 the steps are in 0.50D T/F
True
RGP power notation should be written like ……. can be in 8th Dioptre measurements
-7.00/-6.00 x 090
-7.00(sph lines) x 180 / -6.00(cyl lines) x 090
When considering LARS/CAAS, if you are looking at the px and the toric marker is to my left what do we do to the axis? to my right? +
left - add to the axis (also clockwise movement)
right - subtract from the axis (also anticlockwise movement)
What are some important things to remember across each section of NACOR? 5
-say hello + introduce yourself
-breath
-make sure familar with equipment before starting, focus the equipment
-wash hands constantly
-sanitise verything
If there is prism in the glasses where do you measure the CT, BC + PDs? CHECK WITH LILLIAN
At the optical centre (where the glasses are centered) which is different than the PRP
When measuring the distance PDS versus the near PDS with the ruler and penlight what different instructions do you give/what do you do differently?
Distance PD - arms length away, one eye open then swap to the other eye
Near PD - get closer to the px and instruct them to look at my nose
