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.