optics 2 Flashcards
what is the wAVELEGNTH OF VISIBLE LIGHT
400 NM - 700 NM
laser stands for
light amplification by stimularted emission of radiation
what is snells law
sin(angle1) / sin (angle2) = n1/n2
Formula for focal length?
f = 1/F
focal legnth = 1 / lens power
f inmeters and F in dioptres
Power in convex and concave lens?
Concave lens has negative power (diverges light)
Convex lens converges light and has positive power
Lens power in thin lenses?
F = (n-1) x (1/R1) - (1/R2)
R1 and R2 and radius of curvature of front of lens and back of lens respectively
Lens power in thick lenses?
F = (n-1) x (1/R1) - (1/R2) + (n-1)(d) / n(r1)(r2)
d= thickness of lens
Dioptre = 1/metre
DS = ?
DC?
spherical dioptres
DC = Cylindrical dioptres
refractive error caused by?
corneal curve (steeper = more myopia) Axial legnth (longer = myopic) Refractve index of the lens
Far point = point of clear focius in myopia. What is the formula?
1/ spherical dioptres = Far point ( in meters)
at birth what is mean refractive error
-2 to +6 = normal refractive error
70% have astigmatism at birth
What are the types of regular astigmatism
Regular- 90 degrees apart
with the rule : steepest part is vertical ( -ve cyl axis 180)
against the rule : steepest part is horizontal 9 -ve cyl axis 90)
What are the types of regular astigmatism
Regular- 90 degrees apart
with the rule : steepest part is vertical ( -ve cyl axis 180)
against the rule : steepest part is horizontal 9 (-ve cyl axis 90)
Magnitude of astigmatis is the difference between meridia
compund myopia/hyper etc
correction astigmatism is
toric lens
steepest/stongest part of eye needs flattest/weakest part of lens when refracting
circle of least confusion
where best vision is achieved with only a spherical lens
used to work out spherical equivalant power
Best spehere = circle of least confusion = best vision
best sphere = sphere power + (cylinder power /2)
Formula for transposition of lens?
Prescription is: A/ +B x C
Formula: (A+B) / -(B) x C+/- 180
regarding prisms
where is the image
where is light deviated
imageis towards apex of prism
light deviates towards the base
To correct strabismus with prisms, how do you point the prims
BASE IN for divergent squint
BASE OUT for convergent squint
how to test vision in babies
20 dioptre base out in front of one eye- check both eyes and movement should be seen
lenses and prisms
+ve lens (same as base up prism)
-ve lens (same as base down prism
Prentice’s rule = prismatic power through decentred lens
formula?
P = cF
c = decentration (in cm) F = lens power (in dioptres)
What prism difference will start to cause proiblems?
more than 1.5 prism dioptres
causes double vision
