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Lecture slides on retinoscopy and very basic physics of light. Retinoscopy for clinicians and students. Recognising astigmatism and normal reflexes via retinoscopy.
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01/08/2014
1
Biological Optics & Retinoscopy
Introduction & Principles
Introduction
• Retinoscopy - an objective measure to determine refractive error
• Retinoscope illuminates the eye and we observe the light reflected from retina
• Refractive components of the eye influences the way the light is reflected i.e. reflex
Introduction
• Refraction and final Rx are usually from the combination of objective measurement (retinoscopy) and refinement with subjective refraction Principles of Retinoscopy
• When light enters the patient’s eye, cornea and crystalline lens focus (converge) the light and an image is formed on the retina (fovea)
• Important term: Conjugates*
– The position of the image can be determined if the position of the object is known, and vice versa and both of them are conjugates
Ametropia
• The far point is not at infinity
• Further divided into:
– Spherical ametropia (myopia & hyperopia)
– Aspherical ametropia (astigmatism)
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Reflex Analysis: Spherical Refractive Error
Principles
• Illuminate patient’s retina with light from retinoscope, and observe the reflected light
• With regards to the location of the far point, if the patient is
– Emmetropic: reflected light is parallel
– Hyperopic: reflected light is divergent
– Myopic: reflected light is convergent
What does it all mean?
• If the patient’s far point is behind the retinoscope (the peephole)
– WITH movement is observed
• If the far point is in front of the retinoscope
– AGAINST movement is observed
In real life,
• We can only observe the movements of the reflex (with/against)
– We cannot really observe if the far point is behind or in front of the peephole
• Based on the reflex’s movement, we can deduce that if
– AGAINST – far point is in front of the retinoscope
– WITH – far point is behind the retinoscope
• If a positive lens is placed in front of an emmetropic patient’s eye,
– The retina will conjugate with the dioptric distance of the positive lens, and no movement is observed (neutral)
– The lens is known as working distance lens
– E.g. If a +1.50DS is used, the retinoscopist should perform the examination at 67cm away (why?)
Working distance lens
• Movement of reflex (with working distance lens)
– Emmetrope • No movement, NEUTRAL
• Retinoscope is at the far point, ie, infinity
– Hyperope
• WITH movement
• Far point is behind the retinoscope
– Myope
• AGAINST movement
• Far point is in front of the retinoscope
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Video
Working distance & Working distance lens
• Any working distance can be used when performing retinoscopy
• Need to consider:
– Brightness of the reflected light from the retina
– Access to patient
– Distance error when choosing a working distance
The Power of the WD Lens?
• If the working distance is too small, eg. 25cm
– Brighter retinal reflex, but larger distance error
• If the working distance is too large eg. 100cm
– Dimmer retinal reflex but smaller distance error
• Usually working distance of 67cm or 50cm is used
Neutral zone
Reflex characteristics
• Speed – Fast when approaching neutral
– Slow when far from neutral
• Brightness – Bright when approaching neutral
– Dim when far from neutral
• Width – Wide when approaching neutral
– Narrow when far from neutral
Neutral zone
• There is a zone (not a point) where neutral reflex can be observed
• Inside the neutral zone: there is a confusion whether the movement is WITH or AGAINST
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Handling the Retinoscope
• Right hand/Right eye – examines patient’s right eye
• Left hand/Left eye – examines patient’s left eye
• Look through peephole with one eye
Handling the Retinoscope
• Hold with one hand
– Change the streak orientation only
• Ambidexterity (skill) & the ability to suppress the unused eye is very important
• Align the retinal reflex with pupil
– Retinoscope’s head rests on brow or spectacles
Model eye
• Simulation is achieved by changing the length of the model eye
– Increase length: simulate myopia
– Decrease length: simulate hyperopia
• To simulate high spherical Rx (using trial lenses), use:
– positive lens: __________
– Negative lens: _________
Retinoscopy:
Neutralising Astigmatism
Astigmatism
• Meridian: 1 to 180 deg • Two meridians are usually 90 deg from each
other – Regular astigmatism (meridians 90 and 180 deg) – Oblique astigmatism e.g. 45 and 135 deg – Irregular astigmatism – principal meridians are not 90
deg from each other
• With the Rule (WTR) – Axis of the –ve cyl lens is at 180 deg
• Against the Rule (ATR) – Axis of the –ve cyl lens is at 90 deg
Type of Astigmatism
• Simple hyperopic
• Compound hyperopic
• Simple myopic
• Compound myopic
• Mixed
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Reflex of an Astigmatic Eye Neutralising Astigmatism
Techniques
• Minus-cyl technique
– Neutralise least minus or most plus meridian first
• Plus-cyl technique
– Neutralise most minus or least plus meridian first
• Minus-cyl technique is most commonly used
– However you can opt to do any one of them – but must be aware of the advantages and disadvantages
Two ways of neutralising
• Using spherical lenses only
– Neutralise both meridians using spherical lenses of different power
– Transpose the findings into sph-cyl
• Using spherical and cylindrical lenses
– MOST PLUS or LEAST MINUS meridian is neutralised first using spherical lens
– The other meridian is neutralised using MINUS cylindrical lens
Neutralising with sph-cyl lens for Hyperopic eye
Neutralising with sph-cyl lens for Myopic eye
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Summary: Minus-cyl Technique
Minus cyl Technique
• To obtain the spherical power of the first meridian:
– Neutral meridian with most plus or least minus first
• Reflex at second meridian
– Must be against movement
– Neutralise second meridian with –ve cyl lens, with axis parallel to streak orientation
Determining Position of Cylinder Axis
• Four ways to determine position of a cyl’s axis:
– Break phenomena
– Streak width
– Reflex intensity
– Reflex skewness
• Use enhanced light to observe (sleeve is in midway position)
• All four phenomena are observed simultaneously
• Break and width
– Easiest to observe when the cylindrical refractive error is high
• Skew and intensity
– Easiest to observe when the cylindrical refractive error is low
Retinoscopy on Human Eye
Dr. Mohd Izzuddin Hairol
UKM 2013
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Refraction
• Fixation target – Must not cause the eye to accommodate, i.e. non-
accommodative target
– E.g. spot light at 6 metres away
• Fogging lens – the eye must relax – so must use positive lenses
– Usually the power of the working distance lens (+1.50DS or +2.00DS) is enough to fog the eye – place WDLs before both eyes
– DO NOT occlude the non-tested eye
Refraction
• The position and alignment of the eyes are important to get accurate results – WDL power must match the examiner’s working
distance • If not will cause errors in the final spherical power
– Alignment with patient’s visual axis • If not will cause errors in the final cylindrical power
• Patient’s fixation of the target must not be blocked
Refraction
• Use your right eye (and right hand) to examine patient’s right eye, vice versa
• Start examination with the RE followed by the LE (do NOT take out lenses from the RE when examining LE)
Minus Cyl Technique
• Neutralise MOST PLUS or LEAST MINUS first
– This is the spherical power for the first meridian
• Reflex observed at the second meridian
– Must be against
– Neutralise the second meridian with minus cyl lens
– Axis of lens is aligned with the orientation of the retinoscope’s streak
Retinoscopy (without WDL)
• Retinoscopy can be done without WDL
– E.g. when using lens rack
– Or to reduce the light reflex from trial lenses
• Final power = spherical lens power to achieve neutrality – WDL power
Retinoscopy: Sources of Errors
• If there is a marked difference in the final Rx between objective and subjective refractions, it could be due to
– Neutral point misinterpretation
– Retinoscopist’s technique
– Confusing and irregular reflex
• Spherical aberrations
• Scissor movement
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Retinoscopist’s Techniques
• Errors could be due to incorrect working distance or misalignment of visual axis
• Incorrect working distance causes an error in final spherical correction
– Make sure that your working distance and WDL match
• Misalignment of visual axis (off-axis) causes an error in final cylindrical correction
– Make sure retinoscope is in line with patient’s corresponding visual axis
Irregular reflexes
• Sometimes reflexes can be irregular and confusing
• Different movements seen at the pupil’s centre and periphery – E.g. WITH movement at the centre and AGAINST
movement at the periphery when approaching neutrality
• Spherical aberrations especially with larger pupils – Occurs when pupils are naturally large or when using
cycloplegic agents
• To overcome: neutralise reflex movement seen at the centre of the pupil only
Common problems
• Reflex is hard to see when patient has smaller pupils – E.g. elderly patients
• To overcome: change to a shorter working distance – Make sure that the new working distance matches
the WDL used
– When reflex is observed with correcting lenses, change working distance back to 50 cm or 67 cm to minimise distance error
Common problems
• Dull reflex
– could be due to
• Cloudy media e.g. cataract
• High refractive error
– To overcome
• Cloudy media: change to a shorter working distance
• High refractive error: try using high +ve or –ve lenses until a clear reflex is observed, or use the convergent beam
Convergent beam (verifying AGAINST)
• If a patient is a high myope, an AGAINST movement is sometimes hard to observe
• Use convergent beam to verify – With a convergent beam (sleeve in UP position), a
reversal of movement is observed i.e. WITH if a patient is a myope
– If WITH movement is observed with a convergent beam • Patient is definitely a myope
• Change sleeve back to divergent and neutralise as usual
High refractive errors
• Difficult to judge reflex when refractive error is high
• Dull reflex is observed – Place high plus or high minus trial lens before
patient’s eye e.g. +5.00DS or -5.00DS, and observe the reflex
– If with +5.00DS, WITH movement is observed – continue adding plus lenses until neutral
– If with -5.00DS, AGAINST movement is observed – continue adding minus lenses until neutral
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High refractive errors
• If dull reflex is still observed with +5.00 DS or -5.00DS – Try using lenses with higher power, e.g. +8.00DS or -
8.00DS
• Reflex in uncorrected eyes with high refractive errors sometimes looks neutral (as if there is a full reflex and no movement is observed) – To differentiate:
• Reflex must be bright with fast movement
• Move forward, and reflex must be WITH. If not/does not change – the reflex observed earlier was not neutral.
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