Prebyopia 1/2 - Week 5 Flashcards
What are 3 possible causes of Presbyopia?
- loss of lens elasticity
- changes in lens curvature
- loss of power of the ciliary muscles
What diopter of accommodation corresponds to the moment when the ability of the eye first becomes insufficient for satisfactory near vision without corrective plus glasses?
4 diopters of accommodation
At what age does presbyopia (the symptoms) usually start? Does this vary based on region?
In Europe, North America, Aust: Around 42-48yrs old
For people living closer to equator: 30s to early 40s yr olds
Describe the Lenticular and Extralenticular theories of Presbyopia
Lenticular - changes to the lens and capsule
Extralenticular - changes to ciliary muscle. And changes to elastic components of zonule/ciliary body
Where is the lens capsule thickest?
At the equator
How does the lens capsule thickness change as you age?
Goes from being the thickest at the equator and gradually shifts to the anterior pole, such that it is then thicker at the anterior pole
What is the typical near-point for people of the following ages:
- 20
- 50
- 70
20: Near point at 10cm
50: Near point at reading distance
70: Near point at 4 metres
What near requirements of the patient should you take into consideration when correcting near vision?
- Near tasks undertaken
- Range of working distances needed
- Environment in which near tasks undertaken (e.g. looking down, looking up, etc for near)
- Duration of near tasks
*NERD - Near, Environment, Range, Duration
Describe the procedure for determining near addition
Place distance correction in trial frame
Adjust trial frame to patient’s near PD
Use initial add formula to estimate and insert a ‘near add’
Use a habitually illuminated near reading chart and check for N5 at habitual
Move reading chart closer until first sustained blur, then move it away until N5 can no longer beread
If range too far away, add +0.25DS. If range to close, add -0.25DS.
Why do you typically NOT use a phoropter for the near addition procedure?
Because the phoropter is much more intrusive and the eyes won’t be in a natural position for reading. Doesn’t properly simulate a real environment
Why do you want a good illumination reading chart for near addition?
Because we don’t want to cause glare or have too bright as this will reduce pupil size and increase depth of focus, which is likely to differ from habitual environment
What is the lowest diopter of near addition that we generally prescribe?
+0.75DS
What is the range of near addition prescriptions that we typically prescribe?
+0.75DS - +2.50DS
Name 2 scenarios where we would prescribe a near addition of more than +2.50DS
- if patient has a very close working distance
- if patient has poorer V.A (basically if 6/9.5 or worse)
What are the recommended near additions for the following ages:
- 45
- 50
- 55
- 60
45: 0-+1.00DS
50: +1.00-+1.75DS
55: +1.50-+2.25DS
60: +1.75-+2.50DS
Which of the following patients is likely to experience the effects of presbyopia first? Myopes or Hyperopes?
Hyperopes
What is the general guide for estimating near add with respect to age?
50 years old = +1.00DS +/- 0.25 for +/- every 2 years
What are the formulas we use for determining near addition based on working distance and amplitude? Do we use these formulas for prescription?
Initial add = 1/working distance -1/2NPA
Initial add = 1/working distance - 2/3NPA
- using binocular NPA. WD is in metres.
We only use these formulas to get an INITIAL ESTIMATE
What happens with a higher near addition?
The higher the near addition, the smaller the working range of clear vision
Therefore we should NOT overplus the patient’s near addition
When deciding between 2 near additions, which one should we prefer?
The one with the least +ve.
Where would the ideal best near addition place the near working distance of the patient?
Slightly closer than the middle of range of clear normal vision
How should you record the final near add?
Write the value of the near add, the level of near vision it provides (e.g. N5), the habitual working distance and range of clear near vision provided
What are some other techniques to determine near addition? (3)
- Binocular Cross Cyl
- Duochrome
- Polarized techniques (rarely used)
How does Binocular Cross Cylinder work?
Patient observes horizontal and vertical lines at near with a 0.50D cross cyl added in both eyes [minus axis vertical]
Patient asked which set of lines are blacker and clearer:
- if under-plused: horizontal lines clearer
- if over-plused: vertical lines clearer
What technique do we often use to determine near addition for a first time presbyopic patient?
Binocular Cross-Cyl. Usually, we don’t need many diopters of near add so it’s just faster
What are the disadvantages of the Binocular Cross Cyl?
- It is behind a phoropter
- more complex technique and less natural viewing target
Describe the duochrome test at near
Red focuses behind green wavelengths. Aim is to centre them onto the retina. If undercorrected at near, green is clearer. If overcorrected, red is clearer
If a patient reports green is clearer for duochrome at near, what would you do?
Just leave on green as eye naturally has lag of accommodation
Name 4 presbyopia correction apparatuses
- Readers
- Multifocals
- Bifocals
- Extended focus lenses: near-intermediate
What are the disadvantages of duochrome/bichromatic tests for near addition?
- chromatic aberration of eye at near is different to distance
- in elderly patients, the yellowing of the lens affects results, causing a bias for red
What type of contact lens options are there for correcting presbyopes? (other than simple near add)
Bifocals
Monovision CLs
What are alternating vision bifocal contact lenses?
are so named because your pupil alternates between the 2 powers, as your gaze shifts upwards or downwards
Describe simultaneous vision bifocal contact lenses
require your eye to be looking through both distance and near powers at the same time. Your visual system learns to select the correct power choice depending on how close or far you’re trying to see
Name the 2 types of simultaneous vision bifocal contact lenses
- Concentric ring designs
2. Aspheric designs
What are Monovision contact lenses?
You wear a contact lens on one eye to correct distance (typically dominant eye), and other eye to correct near.
Typically results in clear vision with both eyes open for all distances
What combination of colours would theoretically be better for ducochrome at near? But why doesn’t this work in practice?
Blue and Yellow. Doesn’t work in practice due to the low energy of blue
“sounds good, doesn’t work”
Name and describe 4 surgical options for presbyopia
- Monovision Lasik: to correct one eye for distance and one for near
- Monovision and Conductive Keratoplasty: using controlled radio-frequency energy to shrink collegen fibres in periphery to steepen cornea of one eye to view near objects
- Refractive lens exchange - replace lens with an accommodating IOL
- Corneal Inlays - small disc inserted in corneal flap to either change corneal power or reduce aperture to increase depth of focus
