Chapter 16: Practical clinical refraction

Question 1

What should you do when testing visual acuity in a patient with nystagmus?

Answer 1

fog the fellow eye with a high plus lens, as complete occlusion makes nystagmus worse and lowers uniocular acuity

Question 2

Why should detailed scrutiny of the fundi be left until after refraction?

Answer 2

to avoid photostress-induced reduction of acuity

Question 3

When is it not possile to test the muscle balance using the Maddox rod?

Answer 3

it patient has manifest squint without diplopia i.e. binocular vision is lacking (Maddox rod + wing tests depend on binocular vision)

Question 4

What should the patient be focusing on for objective refraction (i.e. retinoscopy)?

Answer 4

gazing at distant object e.g. top letter of test type

Question 5

Which eye should the examiner use for patient’s L eye and vice versa?

Answer 5

L eye for L eye, R eye for R eye

Question 6

Should the fellow eye be occluded in retinoscopy and why?

Answer 6

no, best to fog it rather than occlude to discourage involuntary accommodation

Question 7

When might you have to occlude the fellow eye in retinoscopy?

Answer 7

manifest squint, to achieve steady fixation with the non-dominant eye

Question 8

When might you have to occlude the fellow eye in retinoscopy?

Answer 8

manifest squint, to achieve steady fixation with the non-dominant eye

Question 9

Who should be given a cycloplegic drug for retinoscopy and why?

Answer 9

young children or children with latant or manifest squint, to paralyse ciliary muscle

Question 10

What type of lens should you add if the retinoscopy reflex is ‘against’ the movement of the retinoscope?

Answer 10

minus (concave) lens

Question 11

How can the axis of astigmatism be foundwith retinoscopy?

Answer 11

rotate axis of cylindrical small amounts rechecking retinoscopy each time; if the axis of the cylindrical lens lies outside the axis of astigmatism, the reflex will move obliquely; reflex will only align with the axis of the cylindrical lens if they all lie in the axis of the astigmatism

Question 12

Why can it be beneficial to try to correct astigmatism with plus cylinders with plus spheres, and minus cylinders with minus spheres?

Answer 12

most patients don’t accept the full value of the cylinder found on retinoscopy; if plus cylinder is reduced e.g. by +0.5 D, the higher value meridian would now be undercorrected which is better tolerated than overcorrection

Question 13

What is an example of when refraction varies between the central and peripheral parts of the pupillary aperture?

Answer 13

nucleosclerosis - central zone relatively myopic compared with periphery

Question 13

What is an example of when refraction varies between the central and peripheral parts of the pupillary aperture?

Answer 13

nucleosclerosis - central zone relatively myopic compared with periphery

Question 14

What can cause ‘scissor shadows’ with retinoscopy, giving the apearance of two reflexes in the pupil?

Answer 14

difference in refraction between different zones of the pupillary aperture

Question 15

What should be used as the end point in the case of scissor shadows on retinoscopy?

Answer 15

one blade of scissors usually brighter than the other - end point taken when brighter reflex reverses

Question 16

What can cause the oil drop sign on retinoscopy?

Answer 16

keratoconus - swirling reflex, reflex from apex of cone darker than periphery

Question 17

How is subjective refraction performed?

Answer 17

• occlude fellow eye, using distance test type, verify sphere achieved with objective refraction by offering small plus and minus additions until no further improvement can be made
• then verify axis of cylinder before adjusting its power
• if patient myopic, duochrome test should be done monocularly and binocularly

Question 18

How should the result from the duochrome test be interpreted?

Answer 18

• If the images on the green are clearer, add plus +0.25 DS until you obtain balance.
• If the rings on the red look clearer, add minus -0.25 DS until you obtain balance

Question 19

If clarity is better from green to red or red to green with one 0.25 change in lens power, how should you leave the patient (i.e. slightly clearer red or slightly clearer green)?

Answer 19

leave on the red

Question 20

At what degree of refractive error must you emausre and record back vertex distance?

Answer 20

power of cylindrical lens exceeding 5 dioptres

Question 21

What is the most frequent reason that a patient seeks a refraction retest?

Answer 21

too strong a near additino ha been prescribed

Question 22

What is the maximum reading add that should be given in normal circumstances?

Answer 22

no more than +2.50 DS

except pseudophakic patients - often prefer +3.00 DS

Question 23

What is the maximum reading add that should be given in normal circumstances?

Answer 23

no more than +2.50 DS

except pseudophakic patients - often prefer +3.00 DS

Question 24

What is the Maddox wing used for?

Answer 24

used to check near muscle balance

Question 25

What does orthophoria (perfect alignment of the 2 eyes) for distance but a large exophoria for near indicate?

Answer 25

convergence insufficiency

Question 26

What should be the initial management of convergence insufficiency that is symptomatic and why?

Answer 26

• convergence should be strengthened by means of convergence exercises
• if base-in prisms are prescribed, convergence may become weaker still and progressively stronger prisms will be required

Question 27

What is a common cause of intolerance of aphakic spectacles?

Answer 27

poor central of spectacle lenses causing prismatic effect - can be due to incorrect interpupillary distance

Question 28

How is the anatomical interpupillary distance measured?

Answer 28

patient looks at examiner L eye and zero of rule set to pt R eye nasal limbus, then asked to look at R eye and measurement taken to L eye temopral limbus (alternatively look at fixation light in front of eaminer’s eyes and corneal light reflexes measured on patient’s eyes)

Question 29

What measurement is used when making spectacles for IPD?

Answer 29

distance between visual axes for distance vision; approx 1mm less than anatomical IPD

Question 30

How should you leave refraction of hypermetropes and why?

Answer 30

don’t overcorrect - best to leave 0.25 DS undercorrected so can read bus numbers in far distance

Question 31

How should you leave refraction of myopes and why?

Answer 31

do not fully correct - best to leave 0.25 DS undercorrected so don’t need accommodation for distance

Question 32

When does hypermetropia, which is very common in infants and children, require full correction?

Answer 32

in presence of esophoria or esotropia

Question 33

What degree of hypermetropic anisometropia must be corrected and why?

Answer 33

> 1 dioptre, to prevent refractive amblyopia

Question 34

Why might it take a few days for a hyeprmetropic child to adapt to new spectacles?

Answer 34

uncorrected hypermetropic child overcomes some or all hypermetropia by exercising extra accommodation; when glasses worn for first time, accommodation may not relax and vision will be blurred initially

Question 35

Why might it take a few days for a hyeprmetropic child to adapt to new spectacles?

Answer 35

uncorrected hypermetropic child overcomes some or all hypermetropia by exercising extra accommodation; when glasses worn for first time, accommodation may not relax and vision will be blurred initially

Question 36

What are 2 reasons why myopia should be corrected in a child?

Answer 36

1. if sufficient to prevent child fom seeing what is written on the blackboard
2. in presence of exophoria or exotropia, to stimulate accommodation and convergence

Question 37

Why do myopic children need to have stronger glasses as they grow?

Answer 37

eye also grows increasing axial myopia

Question 38

How do young children tolerate spectacles for uniocular high myopia?

Answer 38

young brain copes with greater degrees of aniseikonia than adult is able to

Question 39

When does astigmatism require correction?

Answer 39

if visual acuity reduced in affected eye

Question 40

How common is astigmatism in babies and infants?

Answer 40

present in many to high degrees, but usually reduces or disappears by age of 2.5 -3 years

Question 41

How often should refraction be reviewed in children once glasses are established?

Answer 41

annually