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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.