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228 Cards in this Set
- Front
- Back
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3 layers of the eye in order are
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fibrous tunic, vascular tunic, nervous tunic
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fibrous tunic (outer layer) consists of
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sclera, cornea
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vascular tunic (nourishment) consists of
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iris, choroid, ciliary body
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nervous tunic (photoreceptors & neurons) consists of
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retina
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3 fluid filled chambers of the eye are
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anterior, posterior, & vitreous chambers
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volume between the cornea & iris is known as
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anterior chamber
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volume between iris & lens is known as
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posterior chamber
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anterior & posterior chambers are filled with what watery fluid
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aqueous humor
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the ciliary body produces
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aqueous humor
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what does aqueous humor do
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maintains IOP and provides nutrients to the lens & cornea
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aqueous humor is continually drained from the eye thru
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Canal of Schlemm
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the greatest volume found between the retina and lens is
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vitreous chamber
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a thicker gel like substance which maintains the shape of the eye is
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vitreous humor
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light enters the eye thru the
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transparent, dome shaped cornea
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5 layers of the cornea are
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epithelium, Bowman's membrane, endothelium, Descemet's membrane, & stroma
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epithelium and bowman's membrane do what
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protect the cornea from injury
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epithelium has the ability to
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regenerate quickly
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bowman's membrane provides
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a tough, difficult to penetrate barrier
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removes water from the cornea, keeping it clear
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endothelium
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endothelium rests on
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Descemet's Membrane
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makes up 90% of the middle layer of cornea, between bowman's & descemet's membranes
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stroma
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from the cornea, light passes thru the
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pupil
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the amount of light thru the pupil is controlled by the
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iris, colored part of the eye
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the dilator & sphincter muscles are
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the 2 muscles of the iris
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opens the pupil allowing
more light into the eye |
dilator muscle
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closes the pupil, restricting light into the eye
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sphincter muscle
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has the ability to change the pupil size from 2 millimeters to 8 millimeters
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iris
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purpose is to focus light on the retina, lying just behind the pupil
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crystalline lens
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process of focusing on objects based on their distance is called
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accommodation
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the closer an object is to the eye, the more power is required of the _________
to focus the image on the _____ |
crystalline lens, retina
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The crystalline lens achieves accommodation with
the help of |
the ciliary body which surrounds the lens
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The ciliary body is attached to the lens via
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fibrous strands called zonules
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when the ciliary body contracts, the zonules relax allowing
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the lens to thicken, adding power, allowing the eye to focus up close
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when the ciliary body relaxes, the zonules contract drawing
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the lens outward, making the lens thinner, and allowing the eye to focus at distance
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light reaches its final destination at
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the retina
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retina consists of
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photoreceptor cells called rods and cones
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sensitive to light and are suited for nite & peripheral vision
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rods, 120 million in retina
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have the primary function of detail and color detection
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cones, 6 million in retina
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center of the retina containing 6 million cones
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fovea
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corresponding colors to 3 types of cones are
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red, green, or blue
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signals received by the cones are sent via the ______ to the brain where they are interpreted as _____
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optic nerve, color
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people who are either missing or deficient in any one type of cone are
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color blind
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refractive errors occur when
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abnormalities of the eye prevent the proper focus of light on
the retina |
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refers to an eye free of refractive errors
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emmetropia (normal vision)
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2 common types of refractive errors are
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myopia and hyperopia
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occurs if the eye is longer than normal or the curve of the cornea is too steep, causing light rays focus in front of the retina
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myopia, (near-sighted)
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are able to see objects at near, but distant objects appear blurred
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myopia
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can be corrected with minus power lenses
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myopia
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occurs if the eye is too short or the curve of the cornea is too flat, causing light rays to focus behind the retina
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hyperopia, (far-sighted)
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are able to see objects at distance, but near objects appear blurred
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hyperopia
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mildly hyperopic patients may be able to see clearly at near without correction by
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using accommodation to compensate
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can be corrected with plus power lenses
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hyperopia
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more common type of refractive error is
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astigmatism
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occurs when the cornea has an oblong, football-like shape in one or more directions (or axis) causing light rays to focus on more than one point on the retina
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astigmatism
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can be compensated for with cylinder power lenses
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astigmatism
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moves the eye upward and slightly outward
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superior rectus
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moves the eye downward and slightly inward
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inferior rectus
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moves the eye outward and downward
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superior oblique
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moves the eye outward and upward
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inferior oblique
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stabilization of eye movement is accomplished by
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6 extraocular muscles
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addition to movement and tracking, extraocular muscles maintain
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alignment between
the eyes |
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when the eyes are properly aligned, the brain is able to
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fuse the disparate images received by each eye into a single image
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if any of the extraocular muscles are stronger or weaker than they should be, eye alignment can be affected by
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making fusion difficult or impossible
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difficulty with fusion can cause double vision, also known as
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diplopia
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when the brain "turns off" one image in an effort to eliminate diplopia is called
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suppression
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when the eye has a tendency to turn from its normal position it's called a
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phoria
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when the eye has a definite or obvious turning from its
normal position, it's called a |
tropia
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meaning outward or in a temporal direction
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exo (exotropia)
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meaning inward or in a nasal direction
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eso (esotropia)
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means up
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hyper (hyperphoria)
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means down
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hypo (hypophoria)
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electromagnetic energy travels at the speed of light =
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186,000 miles/sec, in the form of a wave
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we classify electromagnetic energy according to its
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wavelength
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the distance between two corresponding points on two consecutive waves
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wavelength
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electromagnetic wavelengths range in scale from that of an
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atomic nucleus (gamma rays) to that of a small planet (radio waves)
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one billionth of a meter
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nanometers (nm)
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the wavelengths of the visible spectrum lie between
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400 and 700nm, with red light at the longer end of the spectrum and violet light at the shorter end
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visible spectrum is
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ROY G BIV
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just below the visible spectrum
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1 to 400nm lies ultraviolet (UV)
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just above the visible spectrum
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750nm to 1mm lies infrared
(IR) |
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as light moves from
one transparent medium to another, at any angle other than perpendicular to the material surface, the change in speed will also result in a change in direction = |
refraction
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principle that allows the creation of optical lenses that alter the path or focus of light
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refraction
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index of refraction (n) can be
calculated using the following equation: |
n = speed of light in air / speed of light in selected material
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CR-39 Plastic:
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1.49
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Crown Glass:
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1.52
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polycarbonate:
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1.58
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high index plastics:
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1.60 - 1.74
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high index glass
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1.60 - 1.80
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in a plus power lens, light rays
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converge
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point at which light rays converge
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focal point
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focal point in plus lens is
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behind the lens surface
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focal point in minus lens is
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in front of the lens surface
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lens power is expressed in
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diopters (D)
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power =
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1/Focal Distance
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Light rays pass through a lens and converge 0.50 m from the lens. What is the power of the lens?
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Power = 1 / 0.50 m
Power = 2.00 D |
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can be used to correct strabismus
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prism
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occurs when eyes aren't aligned
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double vision
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occurs when brain "shuts off" one eye
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monocular vision & loss of depth perception
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cross - eyed
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strabismus
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occurs when images are seen by both eyes, or eyes see the same image
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fusion
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prism is measured in
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diopters (Δ), but measured differently than lenses
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2 ways direction of prism is specified
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prescriber's method, 360* method
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base up, base down, base in, base out
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prescriber's method
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base in =
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nasal
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base out =
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temple
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labs use this method to describe base direction of prism
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360*, 180*
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360* resultant prism equation =
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R = Sqrt( V^2 + H^2 )
v = vertical prism h = horizontal prism |
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360* resultant angle equation =
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Tan(Δ) = V/H
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prism by decentration =
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induced prism
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prism in diopters (Δ) is = to decentration distance (c) in
centimeters x the lens power (D) |
prentice's rule (Δ = cD)
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the corrective power of a lens is determined by adding the front curve to the back curve, equation:
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+6.00 D + -2.00 D = +4.00 D
+4.00 D + 0.00 D (pl) = +4.00 D +2.00 D + +2.00 D = +4.00 D |
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occurs as the eye moves away from the optical center of the lens, the lab will choose curves to minimize this
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aberrations
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lenses with curves chosen to minimize aberrations are called
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"corrected curve" or "best form" lenses
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is curved along a single axis and flat along the perpendicular axis
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cylinder curve
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the focus of a spherical curve is
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a single point
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the focus of a cylinder curve is
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a line
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the meridian along which there is no cylinder power in the lens and consequently the meridian of the cylindrical focus is
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the cylinder axis
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expressed in degrees between 0 and 180
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cylinder axis
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lens that combines spherical and cylinder curves is called
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a compound lens or toric
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measures lens curve surface
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lens clock or lens measure
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total power equation =
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(F1 + F2 = FTotal)
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defined as lenses that are non-spherical
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aspheric
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transpose a prescription written in plus cylinder form to minus cylinder form by
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1. Add the sphere and cylinder powers to determine the new sphere power.
2. Change the sign of the cylinder. 3. Change the axis by 90 degrees. |
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transpose -3.00 +2.00 x 30
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-1.00 -2.00 x 120
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reflectance =
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R = (n - 1)2/(n + 1)2 * 100%
Thus a material of refractive index 1.5, has a reflectance of (0.5/2.5)2*100 = 4% per surface |
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describes the amount of light (usually specified for a given waveband) that will pass through that material
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transmittance
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glass pros
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Superior optics
Stable material Scratch resistant |
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glass cons
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Does not accept tint
Not impact resistant Heavy |
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CR-39 pros
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Lighter than glass
Readily tintable Less likely to fog |
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CR-39 cons
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Susceptible to scratching (correctable by coating)
Lower index of refraction makes it less suitable for higher powered prescriptions |
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polycarbonate pros
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Thinner and lighter than glass and plastic
Highly impact resistant (used for safety glasses) Inherent UV protection |
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polycarbonate cons
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Poor optical quality
Susceptible to scratching (correctable by coating) Susceptible to stress fractures in drill mounts Does not readily accept tint |
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hi-index pros
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Thinner and lighter than glass and plastic
Better optical quality than polycarbonate |
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polycarbonate cons
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Susceptible to scratching (correctable by coating)
Susceptible to backside and inner-surface reflections (correctable with AR) |
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trivex pros
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Impact resistance of polycarbonate
Better optical quality than polycarbonate Tintable Lightest material on the market Inherent UV protection High tensile strength (ideal for drill mounts) |
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trivex cons
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Susceptible to scratching (correctable by coating)
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is not only perceived by
others as glare, but also represents a loss of light transmitted through to the eye |
reflected light
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minimizes lens surface reflections, reducing eye strain, while allowing more light to reach the eye, improving contrast and clarity
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AR coating
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light waves undergo destructive
interference and effectively cancel each other |
AR coating
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states that energy can neither be created nor destroyed
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The Law of Conservation of Energy
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what happens to the energy from the cancelled light waves?
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it's transferred through the lens medium to the patient’s eyes
improving contrast and clarity! |
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defines a lens with a characteristic of changing state
from clear to sunglass dark when exposed to light |
photochromic
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4 types of photochromic lenses
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transitions, PGX/PBX, Sunsensors, Life RX
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removes glare and improves visual quality, creating detail, color, & contrast
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polarized
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light waves coming directly from the sun vibrate in all directions and are considered
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non-polarized
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when vibration is restricted to a single direction or plane, the light is considered
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polarized
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when non-polarized sunlight is reflected by surfaces, it can become
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polarized (all but a single angle is either absorbed or scattered)
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Bright, flat
surfaces such as water, wet roads, sand, snow, car hoods, and windshields are major sources of |
reflected polarized light
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blocks the transmission of light from certain angles while allowing it from other angles
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polarized len (venetian blind)
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cross hatch pattern is
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induced visible stress
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protects the lens from
abrasions and scratches |
scratch resistant coating
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4 main types of coatings
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dip, spin, in mold, vacuum
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added to CR-39 lenses to increase the absorption of harmful UV rays
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UV coating
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Have a minimum center thickness of 3.0mm regardless of lens material; or
• Have a minimum edge thickness of 2.5 mm if it is a+3.00D lens or higher • Pass a drop ball test of a 1 inch diameter steel ball dropped 50 inches • Sandblasted with the manufacturer’s identification • be delivered to the wearer bearing a Warning Label indicating that the protector only meets the Basic Impact Standard |
Basic impact lenses
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Have a minimum center thickness of 2.5 mm regardless of lens material
• Pass a high velocity test in which a ¼ inch steel ball is shot at a lens at 150 ft/second • Sandblasted with the manufacturer’s identification and a plus (+) sign • Be manufactured from either polycarbonate, Trivex, or SR-91 |
High impact lenses
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These frames are able to retain a lens during high impact testing
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Z87+
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a condition in which the eyes have unequal refractive power
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Anisometropia
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bicentric grinding, is a method of correcting vertical imbalance for patients with anisometropia
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Slab-off
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In some cases, one eye will be myopic while the fellow eye
is hyperopic, a condition known as |
antimetropia
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unequal
refractive powers result in differing amounts of induced prism as the eyes move away from the optical center of the lenses, often causing |
diplopia or double vision
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may
be corrected by adding Base Up prism (slab-off) or Base Down prism (reverse slab-off) to one or both spectacle lenses |
diplopia or double vision
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an opacity in the crystalline lens of the eye; a cloudiness that occurs in some of us as we age
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cataract
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to restore clarity, this is removed from the eye
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crystalline lens
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eye loses its natural ability to focus and is referred to as
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aphakic
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Most cataract surgeries today are followed by the insertion of this
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IOL (intra-ocular lens)
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helps restore the eye’s ability to
focus |
IOL implant (pseudo-phakic)
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if an aphakic patient wants to see both far and near out of one pair of glasses, they will need
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a multi-focal lens of some type
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based upon the idea of drawing an imaginary box around a lens shape with the box's sides tangent to the outer most edges of the shape
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boxing system
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horizontal distance between the furthest temporal and nasal
edges of the lens shape or the distance between the vertical sides of the box |
"A" measurement
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"A" measurement is also commonly known as
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eyesize
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vertical distance between the furthest top and bottom edges of the lens shape or the distance between the horizontal sides of the box
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"B" Measurement
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horizontal line that runs through the vertical center of the frame
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datum
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intersection of the Datum Line and horizontal centers of each lens shape
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geometric center (GC)
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shortest distance between the nasal edges of each lens or the distance between boxes
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distance between lenses (DBL)
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DBL is also commonly referred to as
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bridge size
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horizontal distance between the geometric centers of the lenses
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distance between centers (DBC)
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DBC is also know as the
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geometric center distance (GCD) or frame PD
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Twice the distance from the geometric center of the lens
furthest edge of the lens shape |
effective diameter (ED)
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is
used in combination with decentration distance to select the minimum lens blank size required to fit a given frame |
effective diameter (ED)
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vertical distance between the bottom edge of the box and the top of the bifocal or trifocal segment
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seg height
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vertical distance between the Datum line and the top of the bifocal or trifocal segment Overall
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seg drop
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he running distance between the middle of the center barrel screw hole and the end of the temple
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temple length (OTL)
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distance between the center of the barrel and the middle of the temple bend
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length to bend (LTB)
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distance between the plane of the front of the frame and the
temple bend. Used if there is a significant distance between the frame front and the beginning of the temple |
front to bend (FTB)
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the combination of eyewires, bridge and the end pieces, also known as frame front
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chassis
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pieces that hold the chassis to the head and ears, also known as temple arms
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temple
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usually removable plastic sleeves that slip over the ends of
metal temples |
temple tips
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the area between the two eyewires
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bridge
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small pads designed to contact the nose and hold the frame
up off the nose and away from the face |
nose pads
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he small wire arms that actually hold the nose pad in place
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guard arms
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the area of the frame that actually surrounds the lens and holds the lens in place
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eyewire
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the area of the chassis that meets the temple or the point
where the temple attaches to the chassis, where half hinge is found |
end piece
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the point where the temple is connected to the chassis, allowing temple to fold
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hinge
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2 basic kinds of frame materials
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metal & plastic
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4 general types of metal frames
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monel (nickel), stainless steel, titanium, memory metals (titanium mix)
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makes up bulk of plastic frames on the market
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zyl or zylonite
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also known as library temple,
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cable temple
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things to consider for frame fit, rule of 3
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width, nose, temple,
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secondary frame fit considerations
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pd, rx
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standard or bench alignment
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4 point touch
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X-ing of eyewires =
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twisting of bridge
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should overlap and be near parallel with the top of the frame
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proper temple fold alignment
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the junction of each ear ,the skull, and the bridge of the patient’s nose
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fitting triangle
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for good cosmetics and optics, there should be 8-10* of this
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pantoscopic tilt
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particularly if the patient’s PD is narrower than the frame PD, this adjustment is helpful
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positive face form
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4 nose pad adjustments
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width, frontal angle, splay angle, vertical angle
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nose pad adjustment that should only be used to raise or lower multifocal segments, or OC height
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cal height
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a microscope used to measure the back focal length of a lens
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lensometer, (vertometer, lensmeter)
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instrument used to measure pupillary distance
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pupilometer
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instrument used to measure vertex distance
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distometer
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instrument used for visualizing & measuring lens stress
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polariscope
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ASTM
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American Society for Testing Materials
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ANSI
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American National Standards Institute
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OSHA
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Occupational Safety and Health Administration
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FDA
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Food and Drug Administration
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highly reflective and used to reduce light transmission through lenses
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mirror coatings (vacuum)
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larger lens is referred to as the carrier, while the smaller lens is typically called the segment
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multifocal
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the first multifocal (double spectacles) lens was created by
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benjamin franklin (1750’s)
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gives the ratio of the base curve to the addition created
|
(n – 1) / (ns – n)
n = index of the main lens ns = index of the segment |
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an example of this is made by grinding various curves onto the back of a single vision lens blank
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myoter bifocal
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a 22mm round bifocal with a 2-3mm transition zone which blends the two curves together
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seamless bifocal
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types of multifocals
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Flat Top – 25mm, 28mm, 35mm, 45mm, 7x28mm, 8x35mm, Double D 28mm,
Double D 35mm, Quadrifocal 28mm Curved Top – 28mm Round – Achromat, Kryptok, Ultex, 22mm, 25mm, Double Round Panoptik Ribbon Executive – Bifocal, Trifocal, ED Trifocal |
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good procedures to follow for the fitting of multifocal lenses:
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1. Adjust the frame and nosepads, 10mm - 14mm vertex distance.
2. keep your eyes on the same plane as the patient and parallel to the floor. 3. For FT, Executive, or Round bifocals, mark the lower lid margin on the demo lens. For FT, Executive, or Round Trifocals mark the position of the lower pupil margin, For Seamless bifocals place your mark at the lower lid margin then add a mm to the segment height |
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abrupt change in the position of an image due to the change in power and corresponding prism
|
image jump
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To determine the amount of jump created by a segment the following formula applies:
|
find the optical center of the segment
FT Designs (below top of segment) SegOC = (width – height) / 2 For Round Designs (below top of segment) SegOC = width / 2 = height / 2 Jump = amount or prism or image jump Add = multifocal add power SegOC = from above the measure in mm of the optical center from the top of the segment Jump = Add x SegOC /10 |
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used to treat presbyopia
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Progressive addition lenses (PALs), commonly referred to as no-line bifocals or varifocals, avoiding image jump but causing some distortion
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first commercially available PAL was designed by
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Duke Elder in 1922 named the “Ultrifo”
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PAL fitting method for good technique to follow is:
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1. Make sure the frame is 10mm -14mm of vertex distance.
2. Adjust the nose pads, Apply 5°-10° of face form, and 10° – 15° of pantoscopic tilt 3. Keep your eyes on the same plane as patient, parallel to the floor, mark the centers of pupils on demo lenses 4. Measure the distance from the pupil center on the lens to the inside bevel of eyewire. This is the segment height 5. Use the manufacturers cut out chart to verify that the DRP, NRP, PRP are properly placed and within the confines of the frame. Take monocular IPD with a corneal reflex pupilometer, double checking measurement |
