Week 9 - RGP lenses Flashcards
Is presbyopia important for Cls?
• Entering presbyopia can lead to dropout
• Px often dont know about all options with lenses
• Not being offered can demotivate
What is Monovision?
• One eye corrected for DV, other for NV
• Visual system can alternate central suppression when alternating between distance/near
• All forms of soft/rigid lenses can in theory be used
How is monovision fitted?
• Mainly trial and error
• Make sure cyls > 0.75 are corrected
• Check BVA, should be similar to glasses
• Over-refract to test add, full distance one eye near in other then check DVA/NVA binocular
Who is monovision not suitable for?
• Compromised visual acuity
• Distance VA <6/12
• Very precise vision required for distance or near
How is ocular dominance established?
• The +1.00 D sensory test
• Full correction in the trial frame.
• Px look at the smallest line they can see
• +1.00D lens in front of the right then left eye.
• Ask whether 1 (RE) or 2 (LE) is clearer
• If it is 1 then the left eye is dominant as the right eye being blurred hasn’t affected the patient as much, Vice versa
What are the advantages of monovision?
• Good for early presbyopia (problems from approximately +2.00 upwards).
• Easy to fit
- range of lens designs, materials & modalities
• Reduced chair time?
• Less costly
What are the disadvantages of monovision?
• Reduced stereopsis/contrasts
• Glare when driving at night
• Adaptation period (suppression)
• Intermediate vision (higher add) = reduced near add to improve intermediate and incorporate reading spects for intensive close work
• Unsuitable for monocular patients
How can monovision be modified?
• Reducing DV power slightly in dominant eye to help with NV or vice versa
• Reducing the add to allow most tasks and then having reading glasses for small print
• Dominant eye with single vision distance, non-dominant with a multifocal - if distance is the priority
• Dominant eye with single vision near, non-dominant with distance-bias multifocal - if near is the priority
What is Alternating design?
• Majorty are ROP
• Distance and near powered portions
• Similar to a conventional bifocal spectace lens
•Stabilised with prism, truncation or both
what are some challenges to alternating design?
• Lower lid position, must be no lower than the inferior limbus otherwise translation is less effective
• Need the lower lid to have enough muscle tone to nudge the lens up as the patient looks down
• Pupil size, ambient pupil size greater than 3mm may interfere with the near portion when looking in the distance and vice
versa
What should the ideal fitting for alternating design be?
• Aim for alignment fit or with slight central touch, lens should sit slightly low
• 2mm smaller than HVID to encourage inferior centration
• Generally aim for upper line for near segment to he in line with lower pupil margin in ambient lighting
• When px looks down, 75%> should be within near segment
What are simultaneous designs?
• Dv/Nv (and Iv) are in front of pupil same time
• Depending on target, one zone is clear and other blurred
• Relies on visual system bring able to ignore out of focus
- can reduce image quality
- this reduction can be acceptable to some
• Pupil size may mean
Why is pupil size important?
• Smaller with age
• Some multifocal designs reflect this as the higher add design tends to be focused on the middle of the lens
• Also note that research has shown smaller pupils in hyperopes than in myopes
What are the two biconcentric designs?
• Centre distance Vision
- Distance vision will improve in bright light
• Centre near Vision
- Distance VA will improve low light
(Not used so often now due to development of new designs)
What are Multizone concentric designs?
• Minimises impact of pupil size
• Favours distance VA in extreme bright and extreme low light, and provides more equal distribution in ambient setting
Note : Can also have Multizone concentric modified monovision
