Retinoscopy Flashcards
What are the refractive states of the eye?
1) Emmetropia - a distant object is in sharp focus on the retina with the lens of the eye in a relaxed state, with no correction required
2) Myopia - Distant object focused in front of the retina
3) Hypermetropia - Distant object focused behind the retina
4) Astigmatism - diff degrees of myopia/hypermetropia. If the eye is shaped more like a rugby ball than a football, this results in 2 points of focus. Only one part of the object is in focus at one time
How do we know whether light is focused in the right place?
Asking the px what they can see
If light isnt focused in the right place, how do we get it to focus?
Refraction
- objective - retinoscopy
- subjective eg letter chart
What is Retinoscopy?
An objective technique to determine the refractive error of the eye, eg myopia, hypermetropia and astigmatism
-can use an autorefractor but not ideal with kids as they move around more, over-accommodate their eyes, so reading isnt as accurate
Advantages of using retinoscopy?
Quick, easy, reliably accurate and requires minimal cooperation from the px
How does retinoscopy work?
- Light is shone into they eye through the pupil
- Light is reflected from the anterior eye (the beam) -falls on face
- Light reflected from the fundus (back of the eye) -called the reflex
- optom sweeps/oscillates the ret from side to side and observes movement of the reflex compared to the beam
Spot vs Streak Retinoscope
Spot
-allows you to see both principal meridians at the same time
- easier for children and uncooperative px
Streak
-better at detecting and correcting small amounts of astigmatism
-axis easier to determine more accurately, esp in high cyls
Set up of a Retinoscope
1) Vergence slide
2) Streak Ret
3) Working Distance
How should you set up the vergence slide on a ret?
- keep collar down
- vergence control should be in down position
- by moving the vergence control up, a with movement can be changed into against - confusing
Streak Ret?
- when ret beam is horizontal, sweep the ret vertically
- when ret beam is vertical, sweep the ret horizontally
- ie beam is always perpendicular to the meridian being assessed
What is the working distance?
- distance from ret to px eye
- set ret at same visual axis - eye level on axis
- usually held at 2/3m from the eye (arms length)
What are the implications of working distance?
- ret light isnt at a short distant from the eye, and light from a source close to the eye is divergent and will be focused further back than light from a source further away
- so eye will seem to be more long sighted than it truly is
- ret result corrects this divergence and is more positive ie more plus, convex power lens is needed than it would be for a distant target
- at about 2/3m, light has divergence of 1.5D, and to neutralise this divergence we need a positive lens of 1.50D meaning final estimate is too positive by the above amount
- for this reason we need to reduce our estimate by set amount = WORKING DISTANCE ALLOWANCE
Interpreting the reflexes
With movement, against movement and reversal
What does a ‘with’ movement indicate?
- ret reflex may be ‘with’ the movement of the beam
- a with movement indicates eye is wither hyperopic or has low myopia (less than divergence due to WD)
- to correct a with movement we need a positive lens
- a positive lens will cause convergence of the light as it passes through the eye
What does an ‘against’ movement indicate?
- ret reflex against the beam
- against movement indicates myopia
- to correct an against movement we need a negative lens
