Unit 2 Flashcards
GP options for astigmatism
- Spherical GP lenses
- Front surface toric
- back surface toric
- Bitoric
Spherical GP for astig
These lenses are called for when there is no astigmatism and when the degree of astigmatism is corneal
-The lacrimal lens neutralizes the astigmatism
Rule of thumb when considering spherical GP
The astigmatism if the pxs spectacle rx should be less than 2.50
-If the spectacle cyl is greater than 2.50 we might need a toric lens
Mathematically, how do we know if the astigmatism is corneal?
Recall total astigmatism = corneal astig + lenticular astig
-calculate the RA
Design of front surface toric
-Spherical posterior curve
-Toric anterior
ex. BC 7.50mm
Anterior curves 8.00mm/7.40mm
When is front surface toric used?
When there is over 1.25D of rx cylinder correction w/ a spherical or near spherical cornea
-1.5BD prism is used to help stabilize the lens
Design of a back surface toric
-Toric posterior curvature
-Spherical anterior curvature
When is back surface toric used?
Used when corneal astigmatism is approx 2/3 of the refractive astigmatism
Mathematically- Corneal astig power / spectacle rx power
design of a bitoric
Toric curvatures on both the anterior and posterior surfaces.
When is bitoric used>
When there is high corneal astigmasim
-High means more than 2,50
-Can improve lens positioning in high corneal astigmatism
SPE bitoric design (spherical power effect)
Has both front and back surface toric surfaces but the optics of a sphere when combined with a tear lens
-Can rotate on the eye without impacting vision
what does SPE correct ?
ONLY for the induced cylinder
how does SPE bitoric lens work
plus cylinder ground on the front surface which cancels out the induced cylinder power created by the lacrimal lens and posterior curve
example of a SPE bitoric lens
43.00/46.00
-2.00/-5.00
-SPE have the same difference in base curve meridians as power curve meridians
Design of CPE bitoric lens
Used when a SPE bitoric results in significant cylindrical over rerefraction
-Front surface corrects both the induced astig and the residual astig
-CPE lenses must be rotationally stable to avoid inducing further astig
how does CPE bitoric lenses work
perform a sphero-cylindrical OR and add the OR to the diagnostic lens power per meridian
Bitoric fitting philiosphy - SADDLE FIT
-fit on k in each meridian
-allows for better alignment with the overall toric corneal shape
-tighter fit, more centered
-not used often
bitoric fitting philosophy - LOW TORIC SIMULATION
-fit flat meridian on k and steep meridian 0.75D flatter than steep k
-More common fitting philosophy
-provides stability
benefits of GP multifocals over soft cl multifocals?
-better optical correction
-corrects corneal astigmatism
-resist deposits better than soft
-more stable w. blink
-often more comfortable for dry eye pxs
Who is a good candidate for GP multifocals
-someone w astigmatism or higher rx
-someone who has worn GP lenses in the past
-someone who wants the best possible vision
who is NOT a good candidate for GP multifocals
-someone who is looking for occasional use
-someone who has only worse soft CLs and is not interested in GP lenses due to perceived comfort issues
Modalitites of GP multifocals
- Corneal GP lenses
- Hybrid lenses
- Scleral lenses
types of multifocal RGP lenses
- Simultaneous
-aspheric
-concentric - Translating / alternating
Simultaneous designs ; features
-blend the rx for distance and near
-place 2 images on the retina at the same time
~ relies on the visual system ot select clearer image when needed
-same design used in multifocal soft CLs
aspheric lens
-gradual change in power from distance to near
-allows distance , intermediate and near correction
-pupil dependent
-more balanced all around
concentric lens
-discrete rings of distance and near power
-central portion of the lens is typically distance
-less pupil dependent
-can cause ghosting and flare
customization options for aspheric lenses
-you can adjust distance zone on many of the lenses
-you can customize the add powers with add zone sizes
features of translating and alternating design
-AKA segmented multifocal design (upper and lower segment)
-Similar to bifocal or trifocal eyeglass lenses
-relies on the physical movement of a lens on the eye for gaze-specific positioning
-lower lid holds the lens in palce so when the px looks down the pupil looks down into the segment
types of translating/alternating deisgn
-crescent design
-inverted cerescent
-straight top
fitting translating/alternating design GPs
-obtain proper lens movement
-move segment height up or down dependent on px needs
-add prism if needed to help move the lens down more quickly and improve rotation
which CL is better with some degree of lid control? Concentrics and aspheric or translating design?
Concentrics and aspherics
which CL is better when it is resting on or above the lower lid? Concentric and asphric or translating desig?
Translating designs
which one often has a longer adaptation period ? Simultaneous or translating ?
Translating design but it has exceptional VA
considerations on what to chose between simultaneous vs translating
-practitioner preference
-px eyelid anatomy (lid position, lid laxity)
-other px considerations (adaptation)
what is corneal warpage
altered or distorted shape of the cornea
causes of corneal warpage
Poor fitting GP lens
-exessive movement
-eccentric location
-localized heavy bearing
Long term PMMA wearer
Signs of corneal warpage
-distorted mires on keratometry
-irregular astigmatism on topography
Symptoms of corneal warpage
Blurry vision - even with glasses
-once the CL are removed the px experiences significant blurred vision
treatment for corneal warpage
-refit
-discontinue lens wear until cornea returns to normal shape
what is GP lens warpage
-GP lens gets twisted or bent out of shape
-creates permanently induced toricity within the lens
aquired over time and permanent
causes of GP lens warpage
-heat generated from routine lens handling
-storing a lens in a hot enviroment
-agressive rubbing while cleaning lens
GP lens warpage
-GP lens warpage can be hard to see with the “naked eye”
-verify the presence of warpage using a radiuscope (a spherical GP lens will have 2 different radii of curvature in the radiuscope)
Alternative - perform over keratometry (will measure toricity over the spherical GP lens)
other sides of GP lens warpage incudle..
-no precise end point on over refraction
-unusual fluroscein pattern
-altered lens fit
symptoms of GP lens warpage
blurry vision
treatment for GP lens warpage
-lens replacement if warpage is >0.50D
what is lens flexure
bending of a GP lens while the lens is on the eye
physiology of lens flexure
-all GP lenses show some flexibility
-a combination of lid pressure, blinking, and capillary attraction combine to bring the GP lens in closer contact with the cornea
causes of lens flexure
-corneal astigmatism (>1.50D)
-steep lens
-centre of lens is to thin
signs of lens flexure
-cylinder OR
-over-keratometry : will measure toricity (assuming a spherical GP lens)
Symptoms of lens flexure
-blurry vision
-fluctuating vision
-CL discomfort
treatment for lens flexure
-flatten the lens
-increase thickness
-fit a back surface toric or bitoric
the cylindrical over-refraction changes by the amount of warpage or flexure ..
-if the cornea is WTR and the OR is WTR, the amount of WTR cylinder in the OR increases by the amount of warp/flexure
-if the cornea is WTR and the OR is ATR, the amount of cylinder in the OR decreases by the amount of warpage/flexure
GP complications defined
-Negatively impact the health of the eyes (discomfort)
-reduce the CL corrected VA (blurred vision)
-result in undesirable lens fit and lens conditions (CL dropout)
Px causes of GP complications
-Not following proper cleaning and sterilization instructions
-purchasing CLs from unautharized CL sources
-sharing their CLs with others
-sleeping in their CLs if they are not approved for extended wear
GP lens complications: role of the optician
-identify abnormal situations that represents a GP lens complication
-take action to over-come the complication, if possible
-educate the px to prevent complications from happening in the future
Common GP complications well cover
-corneal staining (3 and 9 oclock)
-dellen
-foreign body tracking
-lens adherence
-crazing
-dimple veiling
-poor surface wetability
what is 3 and 9 oclock staining
horizontal dying of the cornea and/or adjacent conjunctiva
causes of 3 and 9 staining
GP related: thick edge, decentered lens
eye related: poor tear film, incomplete blink
symptoms of 3 and 9 staining
irritation, tearing
treatment for 3 and 9 staining
-refit GP; thinner lens edge, improve centration
-ocular lubricants
Dellen
-localized areas of peripheral corneal thinning
-often appear as oval shaped excavations running parallel to the limbus
-fluroscein pools in the DELLEN
symptoms of dellen
-ranges from none to mild irritation
-no impact on VA b/c only the peripheral cornea is involved
treatment for dellen
-stop wearing CL temporarily so the cornea can return to its normal thickness
-improve GP fit
Foreign body tracking
when a FB is trapped underneath the lens, it causes epithelial damage and corneal staining
-often a track like appearance in a random pattern
-often unilateral
symptoms of foreign body tracking
-range from none to severe discomfort
treatment for foreign body trackign
-clean the lens
-preservative free AT
-may require anti-biotic drop
lens adherence
-results when a GP lens “Sticks” to the eye (no movement with blinking)
-GP lens can adhere in any position (MOSTLY NASSALLY)
-most common with extended/overnight wear but also in daily
symtpoms of lens adhernce
-difficulty removing lenses
-intermittent cloudy vision (from trapped mucous underneath)
signs of lens adherence
-corneal indentation
-patch of corneal staining
causes of lens adherence
-dryness or deposits on back surface
-lens decentration
-peripheral sealoff
treatment for lens adherence
px education
-use lubricants
-NO overnight wear
Refit lens
