Ocular refraction Flashcards
(26 cards)
What is the aim of the Ocular Refraction course?
To introduce refractive error, build an optical model of the human eye, define emmetropia and spherical ametropias, and calculate ocular refraction of reduced model eyes.
Define emmetropia.
The refractive state of the eye in which, with accommodation relaxed, the conjugate focus of the retina is at infinity.
What are the two types of ametropia discussed?
- Myopia
- Hyperopia
What is myopia?
The refractive condition of the eye in which the images of distant objects are focused in front of the retina when accommodation is relaxed.
What is hyperopia?
The refractive condition of the eye in which the images of distant objects are focused behind the retina when accommodation is relaxed.
What is the total optical power of the human eye approximately?
+60.0D
What is the assumed uniform refractive index of the reduced model eye?
1.333
What is the distance from the anterior corneal surface to the retina known as?
Axial length, symbolized as k’.
What symbol represents the radius of curvature of the single surface of a reduced model eye?
rEYE
What does K’ represent in dioptric terms?
The axial length in dioptres, representing the required vergence for light to image on the retina.
What is the ocular refraction symbolized as?
K
What is the relationship between K’, K, and F EYE?
K’ = K + F EYE
What does K = 0D signify?
The eye is perfectly focused for distance.
Fill in the blank: Ametropia means _______.
not emmetropia
What is the formula for K’ in terms of nEYE and k’?
K’ = nEYE / k’
When is the eye perfectly focused for distance?
When k’ = f’EYE.
What happens if F EYE is not equal to +60.0D?
The length of the eye necessary for emmetropia must also have some other value.
What is the focal power of the single refracting surface represented by?
F EYE
What does K represent in ocular refraction?
The error between the optical power and the size of the eye.
What is the required radius of curvature for a reduced model eye with +60.0D of optical power?
Calculated based on the model parameters.
What does the term ‘retinal conjugate’ refer to?
The position where light converges after passing through the eye.
True or False: The human eye has a single refracting surface.
False
What is the symbol for the distance to the retinal conjugate?
k
What does the axial length k’ equal when the eye is perfectly focused for distance?
F EYE
