Competency 7.1.1

Question 1

Relationship Between Prescription and Vision

Answer 1

• For low myopic refractive errors a change of -0.25DS corresponds to around 1 line of blurring
• This means that a -1.00DS myope with optimal VA of 6/3 will be able to see the 6/9 line unaided.
• WTR and ATR astigmatic refractive errors have a similar effect in that -1.00DC has a similar effect as a -0.50DS spherical refractive error i.e a 2 line drop in vision.
• Oblique astigmatism gives a slightly higher degradation of vision.

Question 2

What is Normal Vision?

Answer 2

• VA of 6/6 is often considered normal, however it has been found that this is only normal VA for those over 70 years
• hose younger than this should often be able to be corrected to levels of 6/4.5 or better.
• If we are not using lines below the 6/6 line then it is possible that we could miss early pathology or uncorrected refractive error.

Question 3

Visual Symptoms of Myopia

Answer 3

• Blurred distance vision however clear close vision (at a distance depending upon degree of refractive error)
• Headaches
• Squinting of eyes
• Eye strain especially whilst undertaking distance tasks

Question 4

Visual Symptoms of Hypermetropia

Answer 4

• Blurred Vision
  o Blurred vision at near but clear as distance in lower degrees of hypermetropia
  o Blurred vision at all distances if higher degrees of hypermetropia
  o No blurred vision at all especially in young patients
• Eyestrain
• HA
• Asthenopia associated with near tasks or VDU use

Question 5

Visual Symptoms of Astigmatism

Answer 5

• Blurred Vision
  o Blurred vision at all distances
  o Vision unaffected
• HA
• Asthenopia
• Monocular diplopia
• Glare/difficulty with vision at night

Question 6

Visual Symptoms of Presbyopia

Answer 6

• Blurred vision up close even with refractive correction
• Having to hold things further away
• Asthenopia

Question 7

When to use Duochrome

Answer 7

The duochrome test can be used to check the best vision sphere at two points of the refraction:
- After BVS determination, prior to the use of JCC
- After JCC and refining of BVS

The first use of duochrome prior to JCC is to check that the circle of least confusion is on the retina. The circle of least confusion being on the retina is a prerequisite for the JCC technique.

The second use of duochrome occurs after JCC and the BVS has been re-refined to ensure that the refraction is accurate.

Question 8

Advantages of Duochrome

Answer 8

• Quick and easy
• Works in majority of patients
• Can be used with colour defective patients

Question 9

Disadvantages of Duochrome

Answer 9

• Some patients prefer one colour (often red) regardless of prescription
• Increased absorption of low-wavelength light by a nuclear opacity can result in a preference for the Red side
• Red side will appear duller to protans

Question 10

Tips for Duochrome Procedure

Answer 10

• Turning off room lights dilates pupils and increases chromatic aberrations
• If more than ±0.50DS is required to change a result then the results are inaccurate and should be ignored
• Can leave a young patient on green prior to JCC as a patient will be able to accommodate to bring circle of leave confusion onto the retina, leave them on red at the second check