16. Clinical Refraction

Question 1

fitting trial frame

Answer 1

o Lens aperture’s must be centred on the pupils and level across the frame
o High power trial lenses are placed in the BACK cell

Question 2

set up for retinoscopy

Answer 2

o Patient should focus on a distant target
o Need to perform close to the patients visual axis but must not obstruct their view (shouldn’t start accommodating)
o Fog the other eye so that they don’t involuntarily accommodate
o In children should be performed yntil cyclopentolate (paralyse ciliary muscles)

Question 3

retinoscopy

Answer 3

o Start with WITH motion – ask the lights goes across the eye, the red reflex follows
o ADD power to neutralize the reflex (add +)
o SUBTRACT the working distance at the end (usually -1.5D)
o Cylindrical lenses may then be used to neutralise the other meridian and find the axis of the astigmatism present

Question 4

movement in retinoscopy

Answer 4

Question 5

Answer 5

Reflex stage in hypermetropia
- AF = illuminated retina
- B = retina
- C = principal plane
- H = nodal point

Question 6

Answer 6

Reflex stage in myopia
- HE = illuminated retina
- A = retina
- B = principal plane
- G = nodal point

Question 7

measurement of IPD importance

Answer 7

decentration will cause unwanted prismatic effect

Question 7

Answer 7

Reflex stage in emmetropia
- FC = illuminated retina
- A = retina
- B = principal plane
- H = nodal point

Question 7

two ways of measuring of IPD

Answer 7

• Mm rule is rested on nose, patient asked to look at examiner’s left eye, zero of rule is aligned with the nasal limbus of the patient’s right eye, then asked to look at right ear, measurement taken to temporal limbus given the anatomical IPD
• Distance between the corneal light reflexes

Question 8

Retinoscopy

Answer 8

Negative cyl with positive axis

Question 9

Focimeter

Answer 9

negative cyl with negative axis