Optics: Subjective Snd Objective Refraction Flashcards
What are devices that control the focus of the retinal image for the purpose of measuring the power of the eye?
Optometers
A simple optometer consists of a _________ target and a fixed ___________ lens.
Movable target
Fixed positive power lens
What is an advantage of a simple optometer?
Allows both positive and negative vergence
What is a disadvantage of a simple optometer?
Image size will vary as target moves
How did the Badal optometer overcome the challenges of the simple optometer?
Movable Auxiliary Lens
In the Badal Optometer, an Auxiliary lens is placed in between the _________ and the ________ lens.
Target and the badal lens
Badal Optometer: Auxiliary lens is a ________ lens.
Minus
Badal Optometer: Badal lens is a __________ lens.
Plus
What remains independent of the target distance with a Badal Optometer?
Target vergence and angular size
With Badal Optometer, power is ________ related to the actual target distance.
Linearly
With Badal Optometer, the angular size of the target remains __________.
Unchanged
With Badal Optometer, the irradiance of the source at the eyes is ___________ for any distance of the Target.
Constant
With Badal Optometer, the apparent position of the eye will be at the ___________ for all position of the target.
Optical infinity
What is a badal optical system?
A system in which an object can be moved toward or away from the eye without changing the retinal image’s angular subtense
With a badal optical system, the size of the image is __________ regardless of its optical distance.
Constant
Consider a Badal Optometer with a +5D Badal Lens and a -6D auxiliary lens. What are the ocular Vergence and angular magnification at the eye for d= 0 m?
Q= -0.83D, M = 0.833x
Consider a Badal Optometer with a +5D Badal Lens and a -6D auxiliary lens. What are the ocular Vergence and angular magnification at the eye for d= 0.2m?
Q= 4.17D, M = 0.833x
What is the Badal Optometer Ocular vergence formula?
Ocular Vergence, Q = [-F - F2(1- d*F a)/ Fa]
What is the Badal Optometer Magnification formula?
Magnification, M = (-F/ Fa)
What optometer uses a laser light reflected from a surface or transmitted through a diffuser?
Laser speckle Optometer
The apparent velocity of the speckles in the pattern is determined by the distance between the _________ and the ______________.
Plane of stationarity and the plane of focus
In a myopic eye, the speckle pattern appears to move in what direction?
Same direction as the moving screen
In a Hyperopic eye, the speckle pattern appears to move in what direction?
Opposite direction of motion is observed
If the point source is adjusted Axially until it is conjugate with the retinal plane, how will the speckle appear?
That it is not moving and appears to boil
What is the resting place of accommodation?
The distance at which the eyes focus when there is nothing to focus on
What is the eyes default accommodation distance?
Resting place of accommodation
When using a chromatic optometer, an emmetrope sees a ________ disc.
Purple disc
Because the red and blue images are approximately equal in size
When using a chromatic optometer, a myope sees a ________ disc.
Red central spot surrounded by a blue annulus
When using a chromatic optometer, a hyperope sees a ________ disc.
Blue central spot surrounded by a red annulus
What gives the refractive correction when using a chromatic optometer?
Strongest positive or weakest negative lens that reduces fringes to a single purple disc
What does the Duochrome test use in the determination of the near end of the refraction?
Chromatic aberration
In the Duochrome test, refraction is adjusted until what occurs?
The letters on the two colored backgrounds appear equally clear
Nagel optometer uses a _______ lens whose posterior focal point is coincident with ______________.
Plus lens
The nodal point of the eye
What does stigmatoscopy optometer measure?
Accommodative response to the VA stimulus
