Lecture 4 presbyopic contact lens fitting and aftercare Flashcards
What physiological changes can you get to eyelids with age?
How does this affect the lens fitting?
-reduced elasticity due to orbital fat atrophy
causes changes in eyelid position (ectropion, entropion, ptosis)
effects eyelid and lens interaction
What physiological changes can you get to the anterior eye?
How do these effect the lens fitting?
*Decreased corneal sensitivity-symptoms for px will be less so wont report discomfort of lens
*Age related corneal degeneration e.g., Guttata, metal appearance on the endothelium which can be suggestive of loss of function of endothelial pumps.
Amount of oxygen getting through to the eyes can be less. Eye may be more prone to oxidative metabolic stress
*Pupil size changes-as we get older, pupil gets smaller
*Lens changes- can cause disruption to light scatter, can effect quality of vision
What tear film changes can you get with age?
*Decreased in tear production
*Decrease in tear stability. Tears more prone to drying out.
*Decrease in goblet cell density
*Change in meibomian gland secretions
*Lid changes-affect tear film e.g., blinking
*Changes to lacrimal ducts. Can get blockage of gland so more fluid in the eye, disruptions to tear surface causing fluctuation in vision
*Changes in tear osmolarity
What conjunctival pathology is a contra indication for CL wear?
pterygium
How can a pinguecula effect CL wear?
Can have problems with soft contact lens due to lens edge.
-Area can become redder due to friction from lens edge.
-Can change dynamic fit of lens.
-no impact with RGP lens.
How can you assess dominance using your hands?
-ask the px to make a triangle at arm’s length
*Px fixates on a distant target and gradually brings triangle closer to their eyes, maintaining the target in the centre of the triangle
*Practitioner watches which eye the triangle is moved towards. Px. will keep dominant eye central.
*Can hold triangle at arm’s length and shut one eye then the other and see which eye has the target more in the centre.
How can you assess dominance using lenses?
Why is this the preferred method?
*With distance correction, ask px to view the chart
*Present a plus powered lens before each eye
*Follow fitting guide of lens (+1.00 to +2.00)
*Ask the px when the letters on the chart appear worse
*The letters will appear most blurred when the lens is Infront of the dominant eye
*Preferred method for assessing dominance as closest method to what a multifocal will be like. Can determine dominance accurately.
What are the contact lens options for presbyopes?
-over spectacles
-Monovision (enhanced, partial, modified)
-Multifocals (simultaneous, alternating)
What is the over spectacle option?
*Full distance correction contact lenses
*Easy to adapt to but still need to wear specs
*Need to wear near ADD specs on top
*More used when px is a new presbyopic for certain hobbies
What are the advantages of over spectacles?
*No difference to cost, px may continue to use existing brand of CL
*Allows stable distance vision
*Simple
*Inexpensive
*Easy to use
What are the disadvantages of over spectacles?
*Still need specs to see, inconvenient
*Use of specs negates some of the cosmetic benefits by CL wear
What is monovision?
What ADD can you use this method for?
What is a good indicator for this method?
*Patient wears single vision contact lenses
*One eye (the DOMINANT eye) is fully corrected for distance
*Other (NON-DOMINANT eye) has reading prescription added to distance rx
*Monovision may work well for low adds
*+2.50D is the limit to the amount of difference between the 2 eyes that can be tolerated
*As we increase difference in eyes, the blur effect becomes more noticeable.
Dominance
What are the advantages for Monovision?
-no increase in cost
-no changes in lens type
-wider range of lens material
-useful for existing wearers
-easy to fit
What are the disadvantages for Monovision?
-loss of stereopsis and contrast
-adaptation is required
-cant be used in monocular px
-px must have strong ocular dominance
-not suitable for strong near visual task demands
What type of multifocal can you get?
alternating design
simultaneous design: aspheric, multizone, zonal aspheric
What does the alternating design look like?
like a bifocal
can get a curved bifocal- wider FoV for reading
What are the fitting parameters for fitting an alternating design?
*Lower eyelid shouldn’t be lower than the inferior limbus. This helps support lens.
*If lens moves a lot during blinking, lens will move up and you will get line in-between the pupil which causes blur
*RULE OF THUMB: for px to ignore this line and for successful wear, approx. ¾ of the pupil region must be covered by the correct section of lens
*On downward gaze lens should be lifted by at least 2mm
*In normal lighting, top of segment should be level with or slightly below the inferior pupil margin
*Lenses need to be stabilised e.g., prism or truncation
What are the advantages of alternating design?
What are the disadvantages?
binocularity
good visual quality
stereopsis unaffected
relies on lens-eyelid interaction
not suitable for those reading at eye level
adaptation required
How does the simultaneous design work?
What is a contra-indication of fitting these?
*2 images from correction of distance and near are placed simultaneously on the retina
*Relying on brain to ignore the image it doesn’t need
*Analogy of chicken wire: when you want to look in distance you can look past the blur. When you want to look at near you ignore the distance.
ambylopes-require both eyes to have equal vision and no supression
How does the aspheric design work (sub-type of simultaneous design)?
Who should you not fit these in?
How does the centre near design work?
*you have a portion in the centre dedicated to distance or near surrounded by the opposite
*Referred to as centre distance or centre near lenses
PEOPLE WITH VERY SMALL PUPILS:
*If you have small pupils, you will get pinhole effect in centre part of lens.
*In low illumination= pupil will be larger= distance VA favoured
*In high illumination= pupil will be smaller=near VA favoured
What are the advantages of aspheric design?
What are the disadvantages?
-doesn’t rely on lens movement
-stereopsis
-good for lots of VDU
dependant on pupil size
adaptation required
lens centration is critical or you can get ghosting
loss of contrast sensitivity
need to be mindful of cataracts
How does the multizone design work?
- Reduced reliance on pupil size- will be some rings of corrections px can look through rather than 1 zone like in aspheric design
- Concentric zones alternate between distance and near
- enables good function in different lightening conditions
- Increase the number of concentric zones powered for D and N alternatively
- Centre-distance multifocal design
How do zonal aspherics work?
- Uses principles of aspheric and multi zone lenses
- Zone distribution for each ADD power (high, medium, low) is optimised across the lens to account for the normal physiological change in pupil size that occurs with age
How does enhanced monovision work?
How does partial monovison work?
Enhanced monovision
*Correct distance vision in dominant eye
*Use multifocal lens in the non-dominate eye
*Some binocularity
Partial monovision
*Full near correction isn’t incorporated into the non-dominate eye, only partial correction is used for better tolerance
How does modified monovision work?
- Used by cooper vision
- Multifocal has centre near or centre distance design
- Will get stereopsis
- Dominant eye= Centre distance design
- Non-dominant eye= Centre near design
What should you consider when fitting multifocals?
*History and symptoms with particular attention to occupation and hobbies. E.g., if they place golf don’t do monovision as it removes stereopsis. Office workers benefit more from centre near multifocal.
*Consider the patient’s expectations- not high-end detailed vision. Will get to N8. ideally. Can correct vision for day to day but not fine detailed hobbies.
*Refractive error – distance and near. Suppression? Amblyopic? Big difference in rx?
*Check sight test records for the presence of other ocular conditions e.g. cataracts
*Pupil size -think about lighting and how that might affect pupil size
How do presbyopic aftercares work?
*Vision Assessment
-Binocular, not monocular
-consider Real world tasks – consider the size of print (normal print is N8)
*Over Refraction
-Follow the fitting guide first
-When changing prescription for distance consider the impact on near and vice versa
No +1.00 blur, duochrome limited, no PH
*Discussion
Always involve your patient in decisions. If they are hesitant then you may wish to demonstrate it
