Retinoscopy Flashcards
What is Retinoscopy?
Method used to obtain objective refraction.
What is another term for Retinoscopy?
Sciascopy
What is Objective Refraction?
Process of determining the refractive status of the eye, independent of patients response or input.
How does Retinoscopy work?
It works on the principle of manipulation of the Far Point Plane so it is coincident with the practitioners retinoscope - this place the far point at infinity.
How do practitioners use Retinoscopy?
Means of objectively assessing the distance refractive error of the eye.
Light is shone into the eye and the motion of the returned light is analysed.
Why use Retinoscopy?
- It is a good, initial estimate of refraction.
- It is the only estimate of refractive error for young children or patients with limited communication due to mental or language difficulties.
- Can assess clarity of the media i.e.
- Lens irregularities in early cataracts
- Corneal irregularities in early keratoconus and ocular aberrations. - Portable
- Cheap
- Can give a measure of a person’s accommodation.
- Domicilary work
- Autorefractors have limitations.
Describe how Retinoscopy physically works?
- Retinoscopy involves imaging a patch of light onto the patient’s retina.
- The retinal image then becomes an object that diffusely reflects light back through the optics of the eye to form an external image.
- If accommodation is relaxed, external image is formed at the ‘far point’ of the eye.
- Position of image used to determine patient’s refractive error and lenses can be placed in front of the eye to correct the error.
Define Far Point -
The Far point of an eye is the position in space of an object that is conjugate with the fovea when the accommodation is relaxed.
So this is the furthest distance from the eye at which the observer can focus a stimulus clearly.
If an image is past a person’s far point, it will be out of focus.
Define Near Point -
The Near point is the distance closest to the eye at which a person is able to focus an object’s image clearly.
If an image is closer than the near point, the stimulus will be blurred.
Static Retinoscopy:
Determines refractive state of the patient with their accommodation at rest, by getting the patient to fixate in the distance.
Dynamic retinoscopy:
Determines refractive state of the patient with their accommodation active, by getting the patient to fixate at near.
Actively encourages an accommodative response.
Incident light is..
Co-axial
What is the external image called?
Retinoscopic Reflex
The Retinoscopic reflex…
Appears to be located in patients pupil but in relaity, the image is anywhere in front of or behind the ret.
Define a With Movement -
Light patch and the reflex move in the same direction.
Define an Against Movement -
Light patch and the reflex move in the opposite direction.
Define a Neutral Movement -
No apparent movement
or
Moving infinitely fast
How to correct a With Movement -
Neutralise with a Plus lens
How to correct an Against Movement -
Neutralise with a Minus lens
Why does the Ret collar need to be down?
To maximise beam divergence as the retinoscope mirror is now in plano position.
Orthogonal
90’/180’
Oblique
45’/135’
If there is an Oblique motion, you need to..
Move on axis with the streak parallel to the motion.
What is Reversal?
Once the Far Point Plane has been established, corrective trial lenses can be introduced in front of the eye to mimic an Emmetropic eye.
Far point is at infinity.
This is called Neutralising or Reversal of the reflex seen.
What is one key point that needs to be remembered in Retinoscopy?
The practitoner is sat at a finite distance, so the working distance of the practitioner must be taken into account.
So the lenses that achieve reversal can be considered the sum of the 2 components:
- A lens that represents the spectacle correction to the Retinoscope.
- A lens that accounts for the working distance.
What is the equation for Retinoscopy?
F = Fsphere - (+Fworking distance)
What is the procedure for Retinoscopy?
Working distance lenses - Keep the lens in the trial frame.
- Dim room illumination to provide a high contrast and brighter view of the pupillary reflex.
- Px observes target at 6m
- Examiner sits at a WD of 2/3m or arms length
- For RE assessment, use your RE with Ret in right hand when examining.
- Switch on duochrome (biochromatic) spotlight.
- Explain to patient:
“I’m going to shine a light across your eye to get an indication of what your prescription may be.
Please look at the green target and let me know if my head blocks your view. Don’t worry if the target appears blurry.”
Working distance is ALWAYS…
Negative
How to set up a Trial frame correctly?
- The Optom should put the trial frame on the Px and adjust it.
- The apertures should be set to the PD already measured.
- The nose pad should rest on the bridge of the nose.
- The eyes should be central within the apertures.
- Once the trial frame is fitting adequately, you measure Back Vertex Distance in mm from the back cell of the trial frame to the apex of the px’s cornea.
Why should the room lights be dim and not off with Retinoscopy?
A totally dark room may induce a dark focus response.
Observation of the Ret Reflex should include?
- Direction of the Reflex
- Assess the brightness of the reflex i.e. dull or bright.
- Assess the speed of reflex i.e. slow, fast.
- Assess the size of the reflex i.e. small or big.
What do you do if you see no movement?
What does that mean?
Its either:
- At neutral already = Bright Reflex
- Very far from Neutral =
Dull Reflex
May be super fast
What is the Bracketing Technique?
A method for checking neutrality has been reached.
How to perform the Bracketing Technique?
- Lean forwards - A with movement should be seen.
- Lean backwards - An against movement should be seen.
Retinoscopy rarely shows a spherical refractive error in the Human eye.
The majority of patients will have a small amounts of Astigmatism.
Compare Neutralisation and Retinoscopy?
Neutralisation –
- Stationary test object
- Lens under test is moved
- Lens power is indicated by direction and speed of image movements.
- Trial lenses of known power added to neutralise movement.
- End point = no movement
Retinoscopy –
- Test object moves across retina.
- Eye examined is stationary.
- Refractive error indicated by the direction and speed of reflex movement due to fundal glow in pupil.
- Trial lenses added to obtain ‘reversal’.
- End point = extremely rapid movement and disappearance of reflex.
Allowance for Working Distance -
The alteration made to the lens power at reversal.
Where is the Far Point Plane in Myopia?
In front of patient between Ret
Where is the Far Point Plane in Hypermetropia?
Hypothetically behind patients.
What are the 3 elements that determine the eyes refractive ability?
- Shape of the cornea, +40D
- Power of the lens, +20D
- Axial length, 23-24mm
Proximal Accommodation
Is induced by the awareness of the nearness of a target, this can be triggered by an Auto refractor.
Astigmatism
Compound refractive error where light will come to a focus in different points i.e. there are multiple focal points. This is due to irregular curvature of the cornea or lens.
Positive
Convex
Negative
Concave
Minus cyl form for Retinoscopy and Subjective Refraction.
Universally Understood
Eye has two principle meridians that are perpendicular to each other.
Each principle meridian has its own far point.
Correcting the meridians on Retinoscopy?
Neutralise most positive meridian with sphere which leaves residual against movement.
And you use minus cyl to correct residual against.
Correcting the meridians Acronym.
SWFA
Correct:
- Slowest With or
- Fastest Against first
Or if you are faced with BOTH then:
- Correct the With movement first with spheres.
Linder’s method to refine cyl axis:
- Neutralise the more positive meridian.
- Move ret approx. 45’ to cyl axis, to both sides of cyl axis and the movement at each side should be equal.
What are 3 causes for a Dim Reflex -
- Media Opacities
- Small Pupils
- High Ametropia
How to cope for a Dim Reflex -
- Ensure room is as dark as possible
- If you suspect the patient has high ametropia, add a high powered positive or negative lens and see what happens to the reflex.
If a patient has high Myopia on Ret
Try moving closer to the patient because the far point plane is between the practitioner and the patient so by moving closer to that far point plane it means you are closer to neutral when looking at reflex; hence why reflex will be brighter and faster.
Working distance correction must be correct for the new working distance.
If you reduce working distance, the margin for error narrows so ensure you maintain the new working distance.
Scissor or Split Reflex -
The reflex may occassionally appear to split and moves in opposite directions from the centre of the pupil.
Scissor/Split Reflex is often seen in…
Large pupils
Corneal Abnormalites like Keratoconus
Corneal Scarring
Scissor/Split Reflex is also called…
Oil-Drop Reflex
Scissor/Split Reflex can be due to..
Optical Aberrations
How to cope with Scissor/Split Reflex -
- Use steps larger than 0.25DS and bracket to see if neutral.
- Increase room light as it reduces patient’s pupil size and cuts down the peripheral aberrations.
- Concentrate on centre reflex
What is an issue with Large Pupils?
Spherical Aberrations
Spherical Aberrations:
Increased refraction of light rays when they strike the periphery in a sphere, in comparison with those that strike nearer to centre.
Results in a loss of definition in the image.
Adaptation of Retinoscopy for Older Patients:
1) Perform retinoscopy at a closer distance like 25cm as this can provide a brighter reflex– radical retinoscopy.
You will have to subtract a larger value from your retinoscopy result to compensate for the reduced working distance.
2) Use the least number of lenses in the trial frame.
You will lose 8% of the reflex for each lens used due to reflections.
3) Use larger aperture sight hole
Radical Retinoscopy?
This Retinoscopy is performed in case of media opacities like corneal opacity, cataract etc.
Observers have to move closer to the patient and perform the Retinoscopy. Distance should be 20 cm or less.
Why should you use less lenses in the trial frame when conducting Retinoscopy?
You will lose 8% of the reflex for each lens used due to reflections.
What type of error can Incorrect Working distance or Collar Position induce?
Spherical Errors
What type of error can Working off Axis induce?
Astigmatic Error
What type of error can Blocking the patients view of chart induce?
Spherical Error
Stimulate Accommodation
Mohindra Near Monocular Retinoscopy
- Estimates the refraction
- Uses a dimmed light in a dark room as a fixation target
- Ret is used at 50cm
- Good with children without the use of cycloplegics
Why is Dynamic Retinoscopy Used?
This is performed to find out about a patient’s Accommodation:
- Overaccomodation (lead)
- Underaccommodation (lag)
It can be also be used to determine the reading prescription addition
MEM - Monocular Estimate Method Retinoscopy
This is a form of Dynamic Retinoscopy to find information about a patient’s accommodation.
The aim is to determine the Accommodative Lag by estimating the reflex motion without disturbing the accommodative state. This technique is particularly useful for observing a patient’s spontaneous accommodative response to a detailed target at their normal working distance.
How does MEM Work?
- The head of retinoscope is fitted with a target (letters).
- Ret is carried out at 50cm with the patient’s refractive error in place.
- The trial lens that brings neutrality will give an indication of how the patient’s accommodation is functioning.
Wet Retinoscopy
This is retinoscopy carried out after the installation of a drug, cyclopentolate.
Cylopentolate causes a condition called
Cycloplegia.
What does Cycloplegia cause?
- Paralysis of the Ciliary Muscle
- Causes a loss of Accommodation
- Pupil Dilation
Fogging
You need to fog the eye to ensure that accommodation is relaxed.
However, if you overdo it, you can induce accommodation, so the fogging should be less than 2.00D.
How to calculate the Working Distance Allowance lens in D?
1 / WD in cm x 100
Foucault Principle
The examiner should stimulate infinity at the working distance to obtain refractive error.
What is the aim of Retinoscopy?
To neutralise the movement observed on Retinoscopy to achieve Reversal i.e. no movement, which occurs when the Far Point of the eye being examined conoincides with the Nodal point of the Practitioner’s eye.
Before commencing Retinoscopy on the RE, use the retinoscope to…
Quickly eliminate any ‘with’ movement seen in the LE by adding Positive spheres.
A fogging lens is not required if..
An against movement is seen first.
Subjective Refraction
A method of ascertaining a patient’s refractive error by using their responses to a series of lens presentations thru trial and error.
What are the 4 principles regarding Subjective Refraction?
- Accommodation relaxed like Static Retinoscopy
- Maximum plus/Minimum minus
- Trial before prescribing
- Take into account BVD
What are the steps in Subjective Refraction?
- Objective Refraction
- Best Vision Sphere using Presentation Technique
- Jacksons Cross Cylinder or Fan & Block
- Best Vision Sphere
- Check Tests
Flippers
Also known as Twirls or
Presentation/Confrontation lenses
Back Vertex Distance (mm)
The distance between the back surface of a corrective lens to the apex of the cornea.
When does BVD become significant?
+/-4.00D Rx and more
Best Vision Sphere
Highest plus sphere that gives the best VA.
Procedure for Best Vision Sphere -
Explain: “During the test, I will place various lenses in front of your eyes to find those that give you the best vision. Don’t worry about giving the wrong answer as everything is double-checked.”
- Occlude LE and work on RE first
- Switch on the letter chart and Ask: “Please look at the smallest line you can see.”
- Establish the VAs and consider Pinhole
- Present the +0.25DS twirl and Ask:
“Are the letters clearer, more blurred or the same?”
If clearer or the same, keep adding +0.25DS until Acuity first blurs = Sphere for best VA.
If blurred do not add +0.25DS and proceed to the next step.
- Add -0.25DS and Ask:
“Are the letters clearer now or just smaller and blacker?”
If clearer, keep adding -0.25DS lenses until no further improvement in Acuity occurs.
If smaller and blacker, don’t add -0.25DS = Sphere for best VA.
Circle of Least Confusion
Best Vision Sphere moves the Circle of Least Confusion on the retina.
It is the point between the First and Second Focal line.
Vision is better with Best Vision Sphere but not absolutely clear, Why?
The Interval of Sturm is not shortened hence why vision is still blurred, so manipulation is required.
Astigmatism Correction -
- Find Axis
- Find Cyl Power
- Refinement
- Rejection of Cyl
What is Jackson Cross Cylinder?
A combination of 2 cylinder’s of equal strength but opposite signs placed 90’ to each other.
How does JCC work?
By presenting 2 lenses to the patient sequentially, the patient should be able to decide which lens is clearer.
- One lens decreases the Interval of Sturm and improves vision slightly.
- One lens increases the Interval of Sturm and blurs vision slightly.
JCC is a tool…
to help ascertain the cyl axis and power by manipulating the Interval of Sturm.
Which JCC should you initially select and Why?
±0.25DC for VA 6/12 or better
±0.50DC for VA 6/18 or worse
Why do you correct the Axis first before Cyl power?
The correct axis can be found in the presence of an incorrect cyl power.
What target is used for JCC Assessment?
Verhoeff’s Circle - 2 black concentric circles.
What does the Verhoeff circles represent?
The thickness and overall diameter of the inner ring is equivalent to 6/6
The outer ring equivalent to 6/15
Procedure for JCC?
1) Turn room lights on
2) Explain: “During this test, I will place various lenses in front of your eye to find those that give you the best vision. Don’t worry about giving the wrong answer as everything is double-checked.”
3) Test RE first (occlude LE)
4) Switch on the concentric ring target and ask: “I want you to compare the clarity of the rings while I hold this lens in two positions. The rings may look slightly blurred in both positions but tell me which position is clearer or whether they both look the same”
Find Cyl Axis -
- Add -0.25DS to sphere in young px (less than age 40)
- Select JCC:
±0.25DC for VA 6/12 or better,
±0.50DC for VA 6/18 or worse - Set the JCC so that it is minus cyl axis and the plus cyl axis assume the 90’ and 180’ positions.
- Flip the JCC while asking: “Is it clearer in position 1 or 2?”
- Note the orientation of the minus cyl axis in the position that patient-reported that vision was best.
- Rotate the JCC so that the axes are in the 45’ and 135’ positions.
- Repeat – Flip the JCC whilst asking “Is it clearer in position 1 or 2?”
- Note the orientation of the minus cyl axis in the position the patient reported that vision was best,
- Put a -0.25DC in the trial frame with the axis set at the approximate midpoint between the two – e.g. if the patient preferred the 180’ and the 45’ axis, place the cyl at 25’.
- Flip the JCC with its handle along the trial cyl axis and ask: “Is it clearer in position 1 or 2?”.
- Adjust trial cyl axis towards minus cyl axis of preferred JCC position.
- Continue until no difference detected.
- Can initially rotate trial cyl axis 5-10° away from the value so that definite preference occurs and test better understood.
- Hold JCC with one of its axes parallel to the trial cyl axis and ask whilst flipping: “Is it clearer in position 1 or 2?”
- Increase cyl power if minus JCC axis preferred
- Reduce cyl power if plus JCC axis preferred - Continue until no difference detected
What is the Rule of Thumb for Sphere/Cyl Ratio?
Add +0.25DS for every -0.50DC increase
What do some practitioners do when it comes to Subjective Refraction?
Some practitioners leave younger patients slightly Over-minused/Under-plussed i.e. on the green with the duochrome and assume that they will accommodate to bring the Circle of Least confusion onto the retina.
If you add -0.50DC in older presbyopes, you should add +0.25D to the spherical lens to keep the circle of least confusion on the retina.
Methods to identify Ametropia:
VA will give a rough estimate of the amount of Ametropia an individual might have.
Objective:
- Retinoscopy
- Autorefraction (Optometers)
Subjective:
- Subjective refraction with Jackson Crossed Cylinder
- Subjective refraction with Fan and block
