5.1.3/5.3.1/5.3.2 Flashcards
How to select ideal BOZR and dia for RGPs according to no.7 fitting guide
BOZR - <1.5D cyl fitted on flattest K
If between 1.5D-3D of cyl then fit 0.1mm steeper than flattest K
If >3D then fit toric
All BOZR avail from 7-9mm in 0.05 steps
Dia - 9.60 is standard but also avail in 8.80,9.20,10.00mm (HVID-2mm)
What is BOZD and how does it relate to RGPs
Back optic zone diameter - central optical portion of back surface of lens and provides the main refractive power of the lens and effects vision quality and lens fitting
What are the 3 types of RGP materials
PMMA - Early RGPs which did not allow O2 permeability
Silicone acrylate - PMMA+Silicone to allow O2 to pass through
FSA - adds fluorine to improve O2/wet ability and resistance to protein deposits
What are fitting banks used for
Determine lens fit/measurements
Assess VAs
Evaluate comfort
Can customise based on trial results as come in different base curves and diameters
What are ingrediants in avizor GP Multi RGP solution
PHMB - preservative + antimicrobial to disinfect
Hypromellose - wetting agent and lubricant to keep lens moist and hydrated
Sodium chloride - maintain osmotic balance
EDTA - chelating agent to help disinfect
Citric acid - to maintain ph of solution
What does a steep fit look like with white light and nafl
Good centration/constant corneal coverage
No limbal crossing
Minimal movement on blink
Central pooling/air bubbles
Mid peripheral wider band of touch
Narrow band of nafl in periphery
What does a flat fit look like with white light and nafl
Poor centration/inf decentration
Limbal crossing
Excessive movement on blink
Edge lift in periphery
Central area of touch
No clear band of touch in mid periphery
Wide band of touch in periphery
What does an alignment fit look like with white light and nafl
Good centration/constant pupil coverage
No limbal crossing
Adequate movement on blink
Trace of nafl minimal clearance
Band of touch in mid periphery
Band of bright nafl in periphery
How are spherical RGP s designed
Uniform curvature across the lens and used for myopia/hyperopia without astigmatism
What is the design and best use for front surface toric RGP
Front surface of lens contains toric correction and back surface is spherical. Best for lenticular astigmatism and small amount of corneal astigmatism and req prism ballast for stabilisation
What is the design and best use for back surface toric RGP
Back surface of the lens is toric and creates more stable fit than spherical rgp on toric cornea. The front surface is spherical. Best for high corneal astigmatism
What is a bitoric RGP
Front and back surface of lens is toric allowing correction of high astigmatism. Suitable for high CA and px with excessive rotation with front toric designs
What is a translating(segmented) bifocal RGP
Top portion for distance and lower for reading. A flat bottom or prism ballast helps keep lens in place and lid interaction holds lens in place. Best for px who use bifocal gls
What is the design and use for concentric multifocal RGP
Concentric rings of power for nv+dv, can be centre near or centre distance depending on Px preference. Power gradually transitions between distances and best for presbyopia or good int distance req
Why does orientation matter for toric RGPs
They have diff curvatures in diff meridians and if lens rotates then the astigmatism in lens will not match astigmatism of cornea which leads to distortion
Why does orientation matter for multifocal RGPs
So that the correct power zones remain in the visual axis
How does prism ballast stabilisation work and which RGPs is it used in
A small amount of thicker lens material is added to the bottom of the lens to create weight effect to help lens settle in correct position
Used in front toric RGP
Multifocal translating bif- so near portion stays at the bottom
How does truncation stabilisation work and which RGPs is it used in
Bottom edge of the lens is flattened so it rests on lower eye lid preventing rotation, lid interaction helps keep lens in place
Translating bif lenses
Some torics if prism ballast isn’t enough
How does periballast dynamic stabilisation work and which RGPs is it used for
Thin zones at top and bottom of lens to help eyelids hold lens in position. Less thick than prism ballast which is more comfortable
Used in front toric rgps with minimal prism effect
Some concentric multis for improved stability
Differentiate corneal and lenticular asigmatism
Corneal = irregular curvature of the cornea (front toric RGP)
Lenticular = occurs from irregular shape/tilt of crystalline lens (back toric RGP)
How do u calculate lenticular astigmatism
Refractive astigmatism - CA
How does WTR astigmatism effect RGP fitting and which type of RGP is most ideal
Spherical rgp works well as it sits along horizontal(flatter) meridian while tear film compensates for vertical steepening. Lens centres well and stabilises easily
How does ATR astigmatism effect RGP fitting and which type of RGP is most ideal
Bitoric or back toric RGP may have better centration and stability. Spherical RGP may not centre well as it tends to ride nasally or temporally due to flat vertical meridian
How do u convert spec rx to rgp rx for higher rx
When rx over 4Ds use formula
F(c) = F(s) / 1 - ( d x F(s) )
F(c) = CL power
F(s) = Spec power
d = vertex distance e.g 12mm (convert to m for equation = 0.012)
How do you calculate corneal astigmatism
For every 0.05mm difference in Ks = 0.25D CA
Eg K7.80mm, K7.65mm
Difference is 7.80-7.65 =0.15
0.15 /0.05 =3
3 x 0.25D =0.75D CA
How much prism is used in a prism ballast and why
0.75-1.5D base-down. This strikes a balance between achieving proper lens orientation and and maintaining wearer comfort
How do you carry out the ocular dominance test
Place a +1.00D over 1 eye and then the other to see which one is more uncomfortable. The eye that struggles most is the dominant eye
How are aspheric CL designed
Ft a surface that flattens gradually from the centre to the periphery. It does this to correct spherical aberrations. The centre part of lens is steeper and outer edges flatten gradually. This changing curvature helps focus light rays more accurately on the retina (centre near/distance) smooth transition due to curvature
What are pros and cons of concentric multi CLs
Pros : both viewing zones are always in focus, smooth transition, customisable design (D/N or N/D)
Cons: adaptation period, reduced contrast as light is split between both zones, glare/halos due to ring design
What are pros and cons of translating multi RGP CLs
Pros : crisp vision, minimal glare as only one zone is used at a time, good for high rx
Cons : adaptation, excessive movement(sports) can displace the lens, expensive
What are pros and cons of aspheric multi CLs
Pros: smooth transition, reduced distortion,
Cons : halos due to pupil dilation in dim which expands to periphery zones of cl, vision not as sharp as monos or translating lenses
How will a spherical RGP look on a toric cornea
A dumbbell shape under NafL
How do you OR multifocal contacts
Binocularly
What are pros and cons of monovision lenses
Pros
No need for bif/varis
Less risk of distortion
Easier to manage as no complex prescription
Cons
Reduced depth perception
Adoptation period
Can cause reduced BV eyes r less balanced
How do RGP lenses improve vision in keratoconus?
They reshape the irregular corneal surface, correcting refractive errors
This includes issues like astigmatism and blurred vision.
What is the main feature of Scleral lenses?
They rest on the sclera, creating a tear reservoir
This helps create a smooth optical surface over the irregular cornea.
How do Scleral lenses help with vision?
They correct significant irregularities in the cornea
This improves comfort and vision by providing a tear cushion.
What is a key advantage of Scleral lenses for keratoconus patients?
More comfortable due to not touching the cornea directly
This is especially beneficial for individuals with advanced keratoconus.
What do Hybrid lenses combine?
Rigid gas-permeable center and soft outer skirt
This design provides sharp vision and increased comfort.
How do Hybrid lenses work?
They rest on the cornea and offer comfort from the soft outer edge
This allows them to correct irregularities while being more comfortable.
What are Piggyback lenses?
A two lens system a soft lens is worn directly on cornea to provide vision and improve comfort an rgp is placed on top to provide optical correction by nurtrlising irrreuglar corneal shape
How does Corneal Cross-Linking (CXL) work?
It involves applying riboflavin (containing vitB12) drops and exposing the cornea to UV light
The combination of riboflavin and uv light causes the formation of additional cross links between collagen fibres in the cornea making it stronger and more resistance to further deformation
What is the purpose of Bandage contact lenses?
To cover and protect the surface of the eye, particularly the cornea
They soothe and protect the cornea from irritation or damage.
Do Bandage contact lenses significantly correct vision?
No, they serve primarily as a protective barrier
They are used especially after surgery or to manage irritation.
Fill in the blank: RGP lenses help improve vision by creating a _______ surface over the cornea.
smooth, regular
True or False: Scleral lenses touch the cornea directly.
False
What are normal K reading values
7.5-7.8mm (42-44D)
What are keratoconus K readings
7.3mm or less (less than 44D)
What are Orthokeratology (Ortho-K) lenses primarily used for?
Myopia management in children and adolescents aged 6-18
Some adults may also use them, but effectiveness diminishes with age.
What is the typical prescription range for Ortho-K lenses?
-1.00D to -6.00D
Some systems may work for higher levels in younger patients.
How do Ortho-K lenses work?
They reshape the cornea overnight, creating a myopic defocus around the periphery of the retina
This reduces the rate of myopia progression by aiming to create blurred images in periphery to induce a. Process to signal the eye to stop elongating
What is the time frame for Ortho-K lenses to start working?
1-2 weeks for initial reshaping, with continued improvement over several months.
How can you know if Ortho-K lenses are working?
Reduced axial elongation and a decrease in prescription (diopters)
Regular eye exams are necessary to monitor changes.
When are Ortho-K lenses typically worn?
Overnight and removed during the day.
What age range are Ortho-K lenses best suited for?
Ages 6-18
Most effective during active myopia progression.
At what age may Ortho-K lenses be less effective?
After age 18, especially in cases of high myopia (> -6.00D).
What are Soft Multifocal Contact Lenses primarily designed for?
Children aged 8-18
Particularly effective in younger children with rapid myopia progression.
What is the prescription range for Soft Multifocal Contact Lenses?
-0.75D to -6.00D.
How do Soft Multifocal Contact Lenses work? For myopia
They have a central distance zone and a peripheral near zone to create myopic defocus on the peripheral retina.
What is the time frame for Soft Multifocal Contact Lenses to show effects?
6 months to 1 year.
How can you monitor the effectiveness of Soft Multifocal Contact Lenses?
By looking for less axial elongation and a stabilized prescription.
What is the typical wear time for Soft Multifocal Contact Lenses?
Worn during the day, typically replaced every 1-2 weeks or monthly.
What age range are Soft Multifocal Contact Lenses most effective for?
Ages 8-14.
At what age are Soft Multifocal Contact Lenses generally less effective?
In adults or individuals with severe myopia (above -6.00D).
What are Soft Single Vision Contact Lenses with Myopia Control designed for?
Children aged 6-16 years.
What is the common prescription range for Soft Single Vision Contact Lenses with Myopia Control?
-1.00D to -6.00D.
How do Soft Single Vision Contact Lenses with Myopia Control work?
They provide peripheral defocus similar to multifocal lenses to slow myopia progression.
What is the time frame for Soft Single Vision Contact Lenses with Myopia Control to show effects?
Around 6 months to 1 year.
What indicators show the effectiveness of Soft Single Vision Contact Lenses with Myopia Control?
Slowed progression of myopia and stabilization of axial length.
What is the typical wear time for Soft Single Vision Contact Lenses with Myopia Control?
Worn during the day and replaced according to the prescribed schedule.
What age range are Soft Single Vision Contact Lenses with Myopia Control best for?
Ages 6-16 years.
At what age are Soft Single Vision Contact Lenses with Myopia Control less effective?
In adults and individuals whose myopia progression has already slowed or stabilized.
How do you correct a contact lens ex if the toric marking is positioned incorrectly
Increase axis to go clockwise and decrease axis to go anticlockwise
What type of rgp fit has a negative and positive tear lens
Positive tear lens - steep fit, under the lens the tears pool up. It induces plus so when you OR you’ll get minus OR
Negative tear lens - flat fit it induces minus OR so you’ll get a positive OR
When axis is in wrong position how do u change it and give an example of an axis which is wrongly 5 degrees to the left
LARS
If left you add to axis, if right you subtract from axis
If 5 degrees to left you would add 5 degrees, CLs don’t go up in 5 degrees so u would change lens type
Only change axis if 10 degrees or more
How to check using keratometry whether a patient has WTR or ATR astigmatism
In WTR astigmatism, the vertical K reading will be steeper (lower value).
In ATR astigmatism, the horizontal K reading will be steeper.
