Retinoscopy

1
Retinoscopy

• OP1201 Basic Clinical Techniques
• Part 2 - Astigmatism
• Dr Kirsten Hamilton-Maxwell

2
Todays goals

• By the end of todays lecture, you should be able
  to
• Describe the major types of regular astigmatism
• Explain key issues in retinoscopy
• Describe how to perform retinoscopy in a patient
  with astigmatism
• Be aware of procedural adaptations for difficult
  cases
• By the end of the related practical, you should
  be able to
• Assess distance refractive error in both
  meridians using retinoscopy, within 10min for
  both eyes

3
Astigmatism

• Astigmatism means not spherical
• You will find yourself describing it to patients
  as your eye is shaped like a rugby ball instead
  of a football
• The difference in curvature (usually of the
  cornea or crystalline lens) results in the eye
  having two different powers along two different
  meridians
• In regular astigmatism, the two meridians are
  exactly 90deg apart

4
Describing astigmatism

• Two powers and an axis
• Power 1 most positive (or least negative)
  meridian
• Power 2 least positive (or most negative)
  meridian
• Axis the orientation of the flattest side of
  the rugby ball. More specifically, orientation
  of the least positive (most negative) meridian.
• Lying on its side Axis 180 and sitting on its
  point Axis 90

Hint Look at a trial frame
5
Note orientation of line foci will change with
cyl. axis, separation will change with cyl. power.
cyl. 2.00 DC, axis vertical (900)
cyl. 1.00 DC, axis horizontal (1800)

Note vertical power gives horizontal line
focus, horizontal power gives vertical line focus
6
Simple myopic astigmatism
7
Simple hypermetropic astigmatism
8
Compound myopic astigmatism
9
Compound hypermetropic astigmatism
10
Mixed astigmatism
11
What does it look like?
12
Distribution of astigmatism

• Power

• Axis

• 1/3 of all prescriptions are spherical
• 1/3 contain an astigmatic correction of 0.25 to
  0.50DC
• 1/6 contain an astigmatic correction of 0.75 to
  1.00DC
• remaining 1/6 contain an astigmatic correction of
  over 1.00DC
• 1 contain an astigmatic correction of gt 4.00DC

• With the rule axis within 15? either side of
  horizontal (38)
• Against the rule Axis within 15? either side of
  vertical (30) respectively
• All other axes considered as oblique (32)
• Prevalence of oblique astigmatism is unaffected
  by power, but with the rule becomes more
  prevalent (and therefore against the rule less
  prevalent) as astigmatic power increases.

13
More on astigmatism

• As a rule, astigmatism is equal and symmetrical
  across the two eyes.
• Degree of astigmatism is unrelated to spherical
  errors between and -8.00DS. Beyond these
  values, higher spherical refractive error is
  associated with higher astigmatic errors.
• Can consider /-8.00DS range as normal eyes
  with normal refractive errors.
• Errors beyond /-8.00DS can be considered
  abnormal.
• Higher errors of both spherical and astigmatic
  type are increasingly associated with ocular
  pathology.

14
Homework

• See what you can find out about how astigmatism
  changes with age. In particular
• Many babies are born with astigmatism. How much
  would be considered normal and how does it
  change in the first 2 years of life?
• Why does against the rule astigmatism become
  more common in older patients?
• Please revise your Dispensing notes on sphero-cyl
  format
• Spectacle prescriptions by optometrists are
  always written in sphero minus cyl format

15
Ret for astigmatism

• What does the reflex look like
• Finding the axis
• Finding the power
• Recording your results

16
Astigmatism

• As we have just discussed, the eye can be a
  different power along different meridians (in
  different directions)
• Astigmatism
• The primary meridians are always 90deg apart, but
  can be in any orientation
• The axis
• Retinoscopy can measure the powers of both
  meridians and determine the axis

17
Correction of astigmatism

• To correct astigmatism, we need a lens that has a
  different power in different meridians
• Cylindrical lens, abbreviation DC
• When doing ret, we will scan and then correct
  each of the meridians separately
• The (eventual) idea is
• Find and then correct the most positive (least
  negative) meridian first with a sphere
• At exactly 90deg to that (always 90deg), add a
  minus-cyl until corrected

18
In 3D
This example is against the rule astigmatism
Always use cyl, i.e. not the option in brackets
move posterior focal line onto retina with
sphere, collapse anterior backwards with ve cyl.
19
Identifying astigmatism
Oblique movement
20
Set up

• Measure your patients pupillary distance (PD)
• Dial your patients PD into the trial frame and
  fit it to your patients face
• Place a working distance (WD) lens in the back
  cell for the trial frame (if using)
• Illuminate a non-accommodative target
• Usually the duochrome
• Turn room lights off

21
Procedure

• Turn retinoscope to brightest setting, with
  collar at the bottom
• Scan along 90 and 180deg to quickly check
  adequate fogging in both eyes
• There should be against movement in both eyes
  (accommodation control)
• WD lens provides some fog but it will not be
  enough in many hypermetropes
• Quick guesstimate of refractive error
• Reflex brightness? With or against movement?
  Astigmatism?

22
Finding the axis

• Return the light to vertical and focus light to
  thinnest beam on the face using collar
• Is the beam in the pupil aligned with the beam on
  the face?
• Rotate until they are
• This will occur in two positions
• These are the primary meridians
• Scan along the primary meridians
• Does the reflex move along the same axis?
• If there is oblique movement, further rotation is
  required

23
Finding the sphere power

• Return the collar to the bottom
• Find the most hypermetropic meridian
• Slowest with or fastest against
• This assumes you are using minus cyls (some
  textbooks talk about plus cyl refraction)
• Neutralise the most hypermetropic meridian first
• Use the bracketing technique from last week
• As you have found the most hypermetropic
  meridian, youll be adding plus (or reducing
  minus)
• Check for reversal
• Refine in smaller steps until neutrality

24
Finding the cyl power

• Rotate the beam 90deg to the other primary
  meridian
• You should see against movement
• Fast low astigmatism
• Slow high astigmatism
• Confirm no oblique movement
• Neutralise this meridian using minus spheres
• This is an intermediate step!
• You can, and should, use cyls
• Replace the sphere with a minus cyl of the same
  power, with the axis lined up with your beam
• All meridians should now be neutralised

25
The final steps

• Repeat all steps for the LE
• Return to the RE to recheck that you do not need
  to add more positive power
• Remove WD lens from both eyes
• Check vision monocularly and record
• Should be within 0.50D in both meridians and
  within 15deg of the axis
• Complete both eyes within 10min

26
Recording results

• You will now have used two different sphere
  powers at two primary meridians (not including
  the WD lens)
• For example 2.00DS axis 20deg and an additional
  -1.50DS axis 110deg
• The highest positive power becomes the sphere
  power (2.00DS)
• The amount of astigmatism is recorded as
  cylinder, and is the difference between the power
  of the two primary meridians (-1.50DC)
• The axis is the position of the beam in the most
  negative/least positive meridian (110deg)
• Result 2.00DS/-1.50DCx110

27
Another example

• You have found
• RE -1.00DS axis 90 and an additional -2.00DS axis
  180
• Sphere power -1.00DS
• Cyl power -2.00DS
• Axis 180deg
• -1.00DS/-2.00DCx180
• This is called with the rule astigmatism
• Axis within 15deg of horizontal
• Most of your classmates will have this

28
Another example

• You have found
• RE 1.00DS axis 180 and an additional -4.00DS
  axis 90
• Sphere power 1.00DS
• Cyl power -4.00DS
• Axis 90deg
• 1.00DS/-4.00DCx90
• This is called against the rule astigmatism
• Axis within 15deg of vertical
• Some of your classmates will have this

29
Overcoming problems

• Reflex is very dim in high prescriptions
• Use high powered lenses to see if reflex becomes
  brighter and movement more obvious
• Also look out for differences in brightness in
  different meridians because this means high
  astigmatism
• Small pupil makes retinoscopy and ophthalmoscopy
  more difficult
• Move closer, try dimmer lighting, or consider use
  of tropicamide to dilate pupil
• Asphericity of cornea/lens can result in change
  in power with increased distortion in the
  peripheral pupil
• Concentrate on centre of ret reflex

30
Overcoming problems

• Lenticular or corneal opacities will make reflex
  dimmer
• Slide collar up (but watch how far) and/or move
  closer (change WD lens to compensate for change
  in working distance)
• Reflex may become distorted with lenticular or
  corneal opacities or distortions
• e.g. keratoconus and cataract, which may produce
  scissors movement

31
Scissors movement
32
Issues in retinoscopy

• Controlling accommodation
• Optical effects of being off axis
• Effect of pupil size

33
Controlling accommodation

• Intraocular lens can change in shape and thus
  change the power of the eye
• Accommodation system is particularly
  strong/unstable in young people so needs to be
  controlled
• The WD lens is part of the solution
• Vision becomes worse if accommodates, so patients
  tend to avoid doing this
• Longest working distance possible
• Use non-accommodative target
• Green(? by convention) light on duochrome

34
Being on axis

• Oblique astigmatism is induced if retinoscopy is
  performed more than 5deg from the visual axis
• -0.50DCx90 induced if 10deg from visual axis
  along the horizontal
• Check that you are almost blocking the fixation
  target with your head, both horizontally and
  vertically
• Completely blocking the target will induce
  accommodation

35
Effect of pupil size

• Small pupils limit the visibility of the reflex
• Use dimmest beam possible (to decrease
  constriction due to light)
• Use shorter working distance
• Dont forget to use a different working lens
• Short WD also helps if your patient has a dim
  reflex. Eg. Cataracts
• This will commonly be an issue for your older
  patients
• Large pupils suffer from peripheral aberration
• Look only at the centre
• This will commonly be an issue for your younger
  patients

36
Sources of error

• Not being in the right position
• Incorrect working distance (getting too close is
  most common)
• Head blocking the patients view
• Off axis
• Observation errors
• Failure to obtain reversal
• Failure to locate principal meridian
• Paying too much attention to peripheral movement
  with a large pupil

37
Sources of error

• Not fogging appropriately
• Forgetting to account for the WD lens, or not
  removing it when you are finished
• Patient not looking at an appropriate target

38
Further reading

• Read Elliott sections 4.5-4.7
• Real examples of ret can be found in Elliott
  Online