PC - Presbyopia - Week 5

Question 1

Give three possible causes for presbyopia, and which is most strongly supported.

Answer 1

• Loss of lens elasticity - most strongly supported
• Changes in lens curvature from continual growth
• Loss of power of the ciliary muscles

Question 2

To what dioptre do presbyoptic lenses eventually reach?

Answer 2

4D

Question 3

At what age does presbyopia begin? Is there a difference between populations?

Answer 3

42-48 for NA, EU and AU.

People living closer to the equator become presbyopic in their thirties or early forties.

Question 4

Describe the lenticular and extralenticular theories of presbyopia.

Answer 4

Lenticular - changes to the lens and capsule

Extralenticular - changes to the ciliary muscle and elastic components of the zonules/ciliary bodies

Question 5

Where is the lens capsule thickest?

Answer 5

At the equators, and slightly anterior and posterior.

The anterior pole is slightly thinner, and the posterior pole is the thinnest.

Question 6

As an individual ages, how does the lens capsule thickness shift?

Answer 6

It shifts from being thickest at the equator gradually towards the anterior pole.

Question 7

Describe what information is needed prior to determining near addition (4).

Answer 7

Take a detailed history of near vision requirements:

• Near tasks undertaken
• Range of their working distance
• Environment in which its undertaken
• Duration of tasks

Question 8

Describe the procedure to determine near addition (9).

Answer 8

• Place prescription into a trial frame, and adjust PD and good illumination.
• Start from measurement of binocular amplitude of accommodation.
• Use the initial add formula to estimate near addition
• Place the initial add into the trial frame, or slightly less.
• Check N5 is readable habitually.
• Move the chart closer until sustained blur, and note distance.
• Move chart away until N5 no longer visible, note distance.
• If the range is too remote, add 0.25D, if too close, remove 0.25D.
• If it matches their needs, prescribe.

Question 9

What happens with a higher near addition?

Answer 9

The smaller the working range, so we want as little addition as possible to maximise clear near vision.

Question 10

At what distance is the best near add considered to be?

Answer 10

It will place the patient’s preferred working distance just slightly closer than the middle range of clear near vision.

Question 11

Describe the formula to get an estimate of near addition. Can this method be used as a quick way to prescribe near add?

Answer 11

Initial add = (1/working distance in cm) - (1/2 x accommodation amplitude)
and
Initial add = (1/working distance in cm) - (1/3 x accommodation amplitude)

Question 12

Once the final near add is determined, what should be recorded (3)?

Answer 12

Value of the near add
Level of near vision
Habitual near workng distance and range of clear vision with the near add.
i.e. WD:__cm, range:__20 - 65cm

Question 13

What is the optical basis behind binocular cross cylinder?

Answer 13

The horizontal meridian is in focus closer to the eye than the vertical meridian.
The aim is to centre focus midway between the two meridia.

Question 14

Describe how binocular cross cylinder is carried out.

Answer 14

The patient is shown horizontal and vertical lines through 0.50D cross cyl lenses - minus axis vertical.
They are asked whether the vertical or horizontal lines are clearer.
If undercorrected at near, the horizontal lines are clearer, plus is added.
If the vertical lines are clearer, they are overcorrected at near.
Check for reversal.
Correct near add is reached when both lines are equally clear.

Question 15

Define accommodative lag and lead, and describe them in terms of binocular cross cyl.

Answer 15

Lag - stimulus exceeds the response, focus is behind the target.
Lead - response exceeds the stimulus, focus is in front of the target.
Binocular cross cyl:
Lag - Horizontal lines will appear clearer.
Lead - Vertical lines will appear clearer.

Question 16

Name 2 disadvantages of binocular cross cyl.

Answer 16

Usually done with the phoropter head, which is not habitual.
-Can be done with a trial frame however.
More complex technique for the patient, and less natural viewing targets for reading.

Question 17

Describe the duochrome test at near.

Answer 17

Red focusses behind green wavelengths.
Aim is to centre them onto the retina.
If undercorrected, green is clearer, if overcorrected, red is clearer.

Question 18

Consider a patient who reports green is clearer for duochrome at near. What is typically done?

Answer 18

Usually left on green as eyes naturally have a lag.

Question 19

Name 2 disadvantages of the duochrome test.

Answer 19

Chromatic aberration of the eye is different for distance vs near.
In elderly patients, the yellowing of the lens affects results, giving a bias towards red, and not ideal for >60yoa.

Question 20

List two colours are theoretically better than red/green for duochrome at near, and explain why they aren’t used.

Answer 20

Blue and yellow

Not used in practice due to the low energy of blue.

Question 21

Name 5 alternative corrections for presbyopia.

Answer 21

• Bifocal CL
• Monovision CL
• Lasik for presbyopia
• Corneal inlays
• Lens extraction and replacement with an accommodating intraocular lens

Question 22

Consider bifocal CLs. Describe the alternating vision and simultaneous vision designs, and how they work.

Answer 22

Alternating - also called translating lenses, pupils alternate between the two powers as gaze shifts upward or downward. One half of the CL is for distance, the lower half for near.
Simultaneous - two types, concentric and aspheric.
-These lenses require looking through both distance and near powers. The visual system adapts to select the correct power depending on how close or far youre trying to see.
Concentric - has a concentric ring design in alternating distance and near power.
Aspheric - central near power and peripheral distance power.

Question 23

Describe how monovision contact lenses are worn.

Answer 23

Two contact lenses are worn, one for distance, one for near.

The distance correction is worn on the dominant eye.

Question 24

Describe how lasik is performed to treat presbyopia.

Answer 24

Monovision lasik is carried out, where one is is corrected for distance, and the other for near.

Question 25

Describe conductive keratoplasty.

Answer 25

Like monovision lasik, but controlled radiofrequency is used to shrink peripheral collagen fibres in one eye to steepen its cornea.

Question 26

Describe refrective lens exchange.

Answer 26

Surgical removal of the biological lens with an accommodating IOL replacement.

Question 27

Describe corneal inlays.

Answer 27

A small disc is inserted into a corneal flap to change the power of the cornea or reduce aperture to increase depth of focus.