REFRACTIVE MANAGEMENT Flashcards
(36 cards)
Purpose of an optometer
Measures refractive state of the eye. Determines the degree of ametropia and assists identifying focal point.
Difference between subjective and objective optometer
-Subjective;
Requires px feedback
Indicate when target is clear
-Objective;
No input required
Uses retinoscopy
Observes stimulus
Description of design of simple optometer
-Consists of high plus lens
-Mounted in frame
-Attached target
-Positioned along a graduated scale
-Target is moved until clear
-Distance between lens to target is measured to calculate refractive error
How the simple optometer is used
-Px looks through lens at the target
-Target is moved forward or backward until clear
-This point corresponds to the far point
-Distance from lens to target is used to calculate refractive error
-F=1/f
Formula for calculating distance from lens to target
F = 1/f
Why would results from the simple optometer not be accurate?
-Accommodation; inaccurate measurements if inadertently accommodating
-Misalignment; target not aligned results may be distorted
Depth perception
The visual ability to perceive the world in 3D ad judge distance of an object
Stereopsis
Binocular component of depth perception. Brain combines different images to allow precise depth judgement.
Overlapping
When one object partially covers the other.
The covered object appears further away
Geometric perspective
Parallel lines appear to converge as they recede into the distance
Relative size
Objects known size appear smaller as they get further away
Light and shade
Shading provides information about surface contours and depth
Ariel perspective
Distant objects appear hazier and less detailed due to atmospheric scattering
Parallax
As the observer moves, nearby objects appear to move faster across the field of vision than distant objects
Explain the limit of Stereopsis
The smallest detectable depth difference a person can perceive
Perimetry
The assessment of the visual field to detect any loss of peripheral vision.
Identify/ monitor conditions such as glaucoma
Static perimetry
A stationary stimulus presented at different locations of the visual field. The patient presses a button when seen. Assesses threshold sensitivity
Kinetic perimetry
Moving stimulus from periphery towards central visual field. Patient signals when first seen and maps the extent of the field
3 benefits of using Bailey-Lovie chart instead of Snellen
1.Equal letter spacing;
Logarithmic progression, equal spacing and number of letters
2. LogMAR notation;
More sensitive and reliable, allows better tracking
3. Reduced guessing bias;
Letter spacing and consistent crowding reduces chance of px guessing improving test accuracy
Near point
Nearest point at which the eye can focus on an object clearly while fully accommodating
Amplitude of accommodation
The dioptric difference between the far point and near ointment of the eye.
Indicates eyes accommodative capacity
Incomitancy when used to classify heteropia
Refers to the type of heterotropia in which angle of deviation between the visual axes varies with the direction of gaze
Test to investigate iincomitancy heterotropia
Hess chart to map ocular mobility
Ishihara colour vision test
-Screening methods for red-green colour deficiencies
-Pseudoisochromatic plates printed with dots of various sizes and colours
-A pattern or number embedded in colours that differ only by hue
