Chapter 1 Flashcards
Define the following terms:
1. Myopia
2. Hyperopia
3. Astigmatism
4. Anisometropia
5.Presbyopia
6. Supression
7. Amblyopia Exanopsia
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Differentiate Optical Image of the Eye and Retinal Image
Optical Image of the eye are formed by the optical system (Cornea, Iris, & Crystalline Lens)
Retinal Image are formed on the retina by the optical system. Its either sharply focused or blurred
Give the English Equivalent of each of the following Metric Visual Acuities:
1. 6/30
2. 6/120
3. 6/12
4. 6/60
5. 6/45
- 6/30 = 1/5 X 20/20 = 20/100
- 6/120 = 1/20 X 20/20 = 20/400
- 6/12 = 1/2 X 20/20 = 20/40
- 6/60 = 1/10 X 20/20 = 20/200
- 6/45 = 1/7.5 X 20/20 = 20/150
Transpose the following spectacle prescription:
1. PLANO = -1.00 D Cyl x 180
2. +1.50 D Sph = -2.50 D Cyl x 170
3.+2.50 D Sph = +1.00 D Cyl x75
4. PLANO = +1.00 D Cyl x 100
- -1.00 D Sph = +1.00 D Cyl x 90
- -1.00 D Sph = +2.50 D Cyl x 80
3.+3.50 D Sph = -1.00 D Cyl x65 - +1.00 D Sph = -1.00 D Cyl x 10
What effect does the shape of the lens capsule as describe by Fincham have on the form of the lens during Accommodation?
Lens capsule thickness is greater at the anterior and thickest at the equator.
Give the following values for Gullstrand Schematic eye:
1. Corneal Radii
2. Lens Thickness
3. Axial Length
4. Index of refraction of
A. Crystalline lens (Cortex & Nucleus)
B. Aqueous Humor
C. Vitreous Humor
- 7.7 mm
- 24 mm
- A. Cortex - 1.386 ; Nucleus - 1.406
B. Aqueous Humor - 1.33
C. Vitreous Humor - 1.33
If a patient has to walk toward the chart until px is 4 Ft from it to see the 20/400 E line, What is the patient visual acuity in
A. English
B. Meter
C. Decimal
A. 4/400
B.
C. 4/400 = 0.01
If a patient retinoscope finding (in which it is assumed that the accommodation is completely relaxed) is +4.00 D Sph & VT#7 is +2.50 D Sph. Wha is the patient
A. Manifest Hyperopia
B. Latent Hyperopia
A. Manifest Hyperopia = +2.50 D Sph
B. Latent Hyperopia = +1.50 D Sph
A given patient has a 5 mm pupils in dimly illuminated examination room but has 2 mm pupils in a brightly illuminated examination room.
How would be the patient visual acuity compare in bright illumination as opposed to dim illumination if
A. The patient were a -5.00 D uncorrected myope
B. The patient were a -5.00 D myope wearing an adequate spectacle correction
A. The 2 mm pupil resulting in brightly illuminated room would increase the depth perception of the focus of the eye and therefore would be expected to improve the patient visual acuity as compared with dim illumination with a 5 mm pupil.
B. For a corrected -5.00 D Myope there would probably be little, if any difference in acuity in the 2 situations
If a patient is a +2.00 D Hyperope and has +3.00 D of accommodation,
A. How much Facultative hyperopia doe the pateint have?
B. How much Absolute Hyperopia does the patient have?
A. +2.00 D
B. None
Using Javal’s rule, what would be the expected refractive astigmatism for each of the following amounts of corneal astigmatism:
A. Zero
B. -1.00 x 180
C. -1.00 X 90
D -2.00 x 180
E. -2.00 x 90
FORMULA:
WTR = 1.25 (AC) + (+0.50 D Cyl x 180)
ATR = 1.25. (AC) + (-0.50 D Cyl x 90)
ANSWERS:
A. -0.50 D Cyl x 90
B. WTR = 1.25 (-1.00 D Cyl x 180) + (+0.50 D Cyl x 180)
= -0.75 D Cyl x 180
C. ATR = 1.25. (-1.00 X 90) + (-0.50 D Cyl x 90)
= -1.75 D Cyl x 90
D. WTR = 1.25 (-2.00 x 180) + (+0.50 D Cyl x 180)
= -2.00 D Cyl x 180
E. ATR = 1.25 (-2.00 x 90) + (-0.50 D Cyl x 90)
= -3.00 D Cyl x 90
If a patient requires a -6.00 Spectacles lens when refracted at a vertex distance of 12 mm, what would be the required power of a contact lens for the same patient?
Formula:
Lens Power = SR/1-VD(SR)
Lens Power = -6.00 D Sph/1-0.012(-6.00 D Sph)
= -5.597 OR -5.50 D Sph
For a patient who has a pupil 5 mm or more in diameter, are the rays of light entering the peripheral portion of the pupil refracted more or less than the axial rays
A.In the unaccommodated eye?
B. In the partially accommodated eye?
A. More refracted than the axial rays
B. Less refracted than the axial rays
On the basis of the Purkinje images reflected from the front & back surfaces of the lens, what lens changes are known to occur during accommodation? On the basis of this and other information, what mechanism did Helmholtz propose to account for accommodation
Front surface of the lens moves forward and increases in curvature while its posterior surface maintains its position & slightly increases in curvature. Helmholtz proposed that during accommodation, Ciliary muscle contracts and zonular fibers relaxes therefore the crystalline lens becomes more biconvex
Briefly discuss the effects on visual acuity of
A. Retinal Location
B. Luminance
C. Contrast
A. Visual acuity falls off rapidly for off foveal fixation, reaching 20/100 at about 10 degrees from the fovea and 20/200 at about 20 degrees from the fovea
B.Reducing luminance very much below the “standard” luminance of 10 foot lamberts (say to 5 foot lamberts or below) causes a considerable loss in visual acuity, but increasing luminance to 100 or even 1,000 foot lamberts causes little improvement in visual acuity.
C. Visual Acuity decreases with a decrease in contrast below approximately 90%
Define Contrast
What are the 4 changes that takes place during accommodation according to Helmholtz.
What are the 2 additional changes that takes place during accommodation not described by Helmholtz
Differentiate Depth of Focus & Depth of Field
Define the different aberration of the eye
What is the far point & near point of myopia
What is the near point & far point of hyperopia
Give & explain the different clinical types of astigmatism
Differentiate Latent, Manifest, Absolute & Facultative Hyperopia
Differentiate Corneal, Internal & Refractive Astigmatism
Define Visual Acuity
