Lecture 3- contact lens for presbyopia. Flashcards
what is presbyopia?
Loss of accommodation resulting in impaired near vision, primarily associated with the loss of elasticity of the crystalline lens with increasing age. Onset is usually around the age of 45 years but depends on the individual’s depth of focus (pupil size), health and near working distance. A positive lens is required to focus rays from a near object, leading to a different ‘prescription’ for distance and near vision.
What are the age related changes to the eye have potential implications for contact lens wear?
•Reduced contrast sensitivity due to increased light scatter and neurological degeneration – can they tolerate a further reduction in CS associated with lenses?
•Pupil miosis – many multifocal lenses require a pupil >3mm diameter to allow light rays to pass through both distance and near portions of the lens
•Increased prevalence of systemic and ocular disease which may require medication that is incompatible with lens use.
•Tear film changes leading to greater prevalence of dry eye (15% of the population by age 65), less antimicrobial protection, potential for more CL deposits and more variable vision
o Tear stability and quantity reduce
o Atrophy and fibrosis of tear secreting glands
o Aqueous portion particularly reduced in quantity during and after the menopause
• Increased irregularity of ocular surface, e.g. pingueculae, conjunctival folds
o Lid margin irregularity
o Reduction in number of goblet cells
• Lid changes leading to a less effective blink, poorer tear spread and potential for dry patches
o Reduced elasticity of skin
o Reduced muscle tone, leading to entropion, ectropion, senile ptosis
o Increased prevalence of blepharitis
• Corneal changes
o Reduced sensitivity, increased fragility and slower wound healing lead to greater risk of infection and greater prevalence of staining
o Endothelial pump becomes less effective due to loss of endothelial cells – greater risk of oedema
Why is difficult to handle lenses with older presbyopes?
older presbyopes often loose dexterity making it difficult to handle lenses
What are the issues with myopia and hyperopia?
A myope wearing contact lenses needs to accommodate and converge more than when wearing spectacles, and a hyperope needs to accommodate and converge less.
Why is the presbyopic market significant?
The presbyopic market is now significant (>40% of patients) because of the size of the post-war baby boomer generation. Being able to successfully fit presbyopes can be a significant practice builder but practitioner’s still shy away from fitting such patients as they wrongly feel it is too complicated.
What are the lens modalities and materials for older eyes?
The slightly increased risk of infection means that extended wear should not be encouraged in presbyopes. Having said that, for elderly presbyopes with particularly poor dexterity who are very reliant on contact lens correction (e.g. an aphake), extended wear may be the best option.
If tear film changes mean that deposition is an issue, daily disposable or at least 2 weekly replacement lenses are preferable to monthly replacement lenses.
The need for a material that can withstand a borderline dry eye, is easy to handle and provides a large amount of oxygen points to a silicone hydrogel lens or high Dk RGP lens as the best option.
What must an ideal CL for a mature px have?
Correct presbyopia Provide good quality vision Provide plenty of oxygen Be comfortable Cope with a potentially poor tear film Be easy to handle
What must you do to overcome challenges faced by fitting older pxs?
Detailed prefitting examination Identifying potential contraindications Significant dry eye Eyelid problems Discuss visual needs Set expectations happy with supplementary glasses for some activities? Follow manufacturers’ fitting guides
Describe Soft lenses for prebyopia
Ideal for current soft lens wearers and the majority of new pxs to CL
2nd or 3rd generation silicone hydrogels
-High oxygen permeability
-Modulus 1-2x higher than conventional hydrogel
-Low water content, limiting dehydration
Internal wetting agents giving good wettability
Or conventional hydrogel with superior wettability for short periods of wear
Describe RGPs for presbyopia
Ideal for current RGP wearers and those with significant astigmatism or requirement for very sharp vision
Alternating designs work well with small pupils
No visual compromise
High oxygen permeability and low wetting angle
E.g. Boston XO2 (Dk 106 ISO units)
what is Monovision CLs?
Dominant eye corrected optimally for distance, non-dominant eye for near
Wearer must suppress the blurred image
No longer the most popular form of presbyopic contact lens correction but:
Cheapest and simplest option
Single vision lenses
Only one lens needs changing (NV)
Good solution for those with astigmatism
What are the variations of Monovision?
Partial monovision
Low add, additional reading spectacles for prolonged reading
Enhanced monovision
Single vision lens for dominant eye, multifocal for non-dominant
Modified monovision
Different multifocal lens designs in each eye, biasing the dominant eye for distance (e.g. Proclear or Biofinity: CD and CN)
What is the tolerance for Monovision?
Dissimliar images tolerated by ~70% of presbyopes (Jain et al. 1996)
Some cannot suppress the blurred image
Takes around 2 weeks to adapt
Works better for early presbyopes where the add is <2.00D
Increased add = increased blur
Avoid in those with binocular vision problems
What is the visual performance with monovision?
Greatest reduction in contrast sensitivity of all presbyopic contact lens options (Rajagopalan et al. 2006; Collins et al. 1989)
Reduced stereopsis (Jain et al. 1996)
80% report halos and ghosting under low illumination
Driving with monovision
Controversial, particularly night driving
Driving over-spectacles recommended
What is the Monovision fitting routine?
Determine refraction for distance and near
Check for good binocular vision
Use trial frame not photopter
Better fusion
Determine dominant eye
Pointing test
Hole in the card
Blur tolerance
Select CL powers to blur non-dominant eye by distance MSE + partial near add
Under binocular conditions
Check DV and NV with both eyes open
Offer +0.25/-0.25D to each eye in turn to achieve best outcome (balance)
Trial lenses in the ‘real’ world for 2-3 days min.
Ask them not to compare vision between eyes
They wouldn’t do this normally
Do not drive with lenses until adapted
Supply with over-specs for night driving when lenses finalised
