Term
| What does Astigmatism mean? |
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Definition
| The inability to bring light rays to a point focus |
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Term
| What is corneal astigmatism? |
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Definition
Corneal surface having an uneven curvature
One meridian is either flatter or steeper then the majority of the corneal surface |
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Term
| What is lenticular astigmatism? |
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Definition
This condition affects the crystalline lens. It can have 3 causes
The lens is tilted in its position within the eye
The lens has uneven surface curvature, either when relaxed or through accommodation. It is sphero-cylinder in curvature
The lens has an irregular surface. This means the actual lens surface is not smooth and spherical, but rather, it has a bumpy surface |
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Term
| What are 3 causes of lenticular astigmatism? |
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Definition
lens is tilted
lens has uneven curvature
lens has an irregular surface |
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Term
| What is irregular astigmatism? |
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Definition
Usually the result of a serious corneal injury
ex. Lye burns
Light will refract differently at different locations along the SAME meridian |
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Term
| With irregular astigmatism how does the light refract due to the serious corneal injury? |
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Definition
Light will refract differently at different locations along the SAME meridian
corneal surface is scarred and bumpy due to injury |
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Term
| What is with the rule astigmatism? |
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Definition
| Describes the corneal surface when the vertical meridian has the steepest curvature |
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Term
| What is against the rule astigmatism? |
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Definition
| This describes the corneal surface when the horizontal meridian has the steepest curvature |
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Term
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Definition
| Condition in which both eyes focus the images on the retina properly |
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Term
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Definition
| The eye has a tendency to turn away from its normal position, when fusion is broken |
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Term
| What does Exophoria mean? |
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Definition
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Term
| What does Esotropia mean? |
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Definition
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Term
| What does hyperphoria-hypertropia mean? |
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Definition
| The eye turns upwards and downwards |
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Term
| Exotropia calls for what type of prism direction? |
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Definition
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Term
| Esotropia calls for what type of prism direction? |
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Definition
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Term
| Right hypertropia needs what kind of prism base? |
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Definition
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Term
| Left hypertropia need what kind of prism base? |
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Definition
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Term
| What does amblyopia mean? |
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Definition
| It is dimness of vision, and in small children it may improve by patching the good eye. |
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Term
| What is amblyopia often associated with? |
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Definition
| Often associated with esotropia |
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Term
| When did Ben Franklin make the first bifocal |
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Definition
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Term
| What's another term for exec bifocals? |
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Definition
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Term
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Definition
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Term
| What is the seg or segment in terms of bifocals? |
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Definition
| The portion of the lens that provide near vision |
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Term
| What is the bifocal base curve? |
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Definition
| The curve on the same side as the segment. This curve is always a sphere |
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Term
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Definition
| The amount of additional correction required for close work. It is always plus power and is usually contained in the segment |
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Term
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Definition
Chang diverging light into parallel light. Objects viewed 16-20 inches are casting very divergent light.
The eye needs help to converge this light into a point focus. |
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Term
| What are the two types of bifocals? |
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Definition
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Term
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Definition
| The bifocal has a segment of different index material (flint, barium, etc.) inserted into the main or carrier lens that is usually crown glass. The front and back curves of the distance Tx stay the same |
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Term
| Who invented the first fused bifocal? |
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Definition
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Term
| When John Borsch in 1908 invented the first fused bifocal in 1908 what was it made of and what was it called? |
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Definition
| Made of flint glass segment and was called Kryptok or TK bifocal |
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Term
| What is one piece bifocal? |
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Definition
Obviously one piece either glass or plastic.
ALL plastic bifocals are one piece in construction. The strength of the ADD is determined by the thickness of the segment and it's curvature |
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Term
| All bifocal lenses have what three optical centers? |
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Definition
The distance O.C.
The segment O.C
The resultant optical center. This is what we see when we view the lens segment through the lensometer |
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Term
| What are the types of fused bifocals? |
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Definition
| All are glass are glass and all have their segment optical centers at the geometric center of the segment (at least initially) |
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Term
| TK or Krpytok segment is? |
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Definition
| 22mm round with the O.C. at 11mm below the top of the segment B.T.S - it has a small reading area - slightly better cosmetics then a flat top --- plus base curve and minus cyl. form |
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Term
| What are the mm and O.C. of TK or Kryptok? |
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Definition
| 22mm round with the O.C. at 11mm below the top of the segment |
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Term
| What are the widths of Flat tops AKA Straight tops or D -- Shape? |
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Definition
Widths
22mm
25mm
28mm
35mm
40mm
Measured at the widest part of the segment, not at the top line. The optical center is almost always 5mm b.t.s This is the most common bifocal and perhaps the easiest for patient adaptability. Plus base curve and minus cyl. form |
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Term
| What are the dimensions for Flat top widths? |
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Definition
22mm = 22 x 16
25mm = 25 x 17.5
28mm = 28 x 19
35mm = 35 x 22.5 |
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Term
| Always assume the O.C. of flat tops what below the top? |
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Definition
| 5mm unless you are given other dimensions for a flat top |
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Term
| What is the formula if you are given other dimensions for a flat top? |
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Definition
1/2 width of seg -- the height of the seg = O.C. B.T.S
This is the physical height of the seg, uncut, NOT the finished seg height |
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Term
| What does emmetropia mean? |
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Definition
| Normal refractive condition of the eye |
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Term
| If you see an RX get more minus it indicates what? |
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Definition
| A cataract. This is because the lens swells making it more plus so that shifts the Rx into a minus position |
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Term
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Definition
Eye too strong
Real focus inside eye
Minus power
Usually occurs after age 7
Globe too long
usually cornea too steep
Globe stays constant |
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Term
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Definition
Eye too weak
Virtual focus beyond retina
Plus power
Globe usually gets weaker as they grow
Cornea too flat
Starts at birth and gets less and less |
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Term
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Definition
| Identical Rx between both eyes OU |
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Term
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Definition
Same refractive error exists between both eyes, but with significant variation in amount
(more than 1 diopter on the sphere) |
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Term
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Definition
| Each eye has opposite refractive error, one is myopic, and the other is hyperopic |
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Term
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Definition
Difference in retinal image size between the eyes
Caused by the spectacle correction: Anti + Aniso
Inhibits fusion
Tremendous eye asthenopia (severe eye strain-causes nausea, vomiting, frontal brow and occipital headaches) |
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Term
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Definition
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Term
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Definition
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Term
| Straight Superior Rectus? |
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Definition
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Term
| Straight Inferior Rectus? |
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Definition
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Term
| Crooked Inferior Oblique? |
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Definition
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Term
| Crooked Superior Oblique? |
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Definition
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Term
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Definition
General term for muscle imbalance
If not caught before age 7. eye is permanently damaged
Visual Accuity of 20/200ish |
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Term
| What is the cause of Strabismus? |
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Definition
Uncorrected refractive error
Weak/Strong muscle
Nerve damage |
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Term
| What does Amblyopia mean? |
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Definition
| Loss of vision without any obvious disease to eye or muscles |
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Term
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
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Term
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Definition
Eyes turned in by accommodation
Accounts for 5% of all cases of strabismus |
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Term
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Definition
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Term
| What is suppression in accommodative esotropia? |
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Definition
Up to age 7 the brain turns off one eye
When we suppress we end up with a new condition called amblyopia (perfectly healthy eye that can no longer see) |
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Term
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Definition
| A perfectly healthy eye that cannot see |
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Term
| What happens in accommodative esotropia? |
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Definition
Hyperopia
CN3 (Cranial nerve 3, oculomotor)
Ciliary muscle: controls accommodation
Pupillary constriction: Controls sphincter muscle of the iris causing pupils to constrict
Medial Recti Muscles that creates the double vision
Diplopia (Double vision)
Fusion confusion - Brain can't make sense because the images are so misaligned
Suppression up to age 7 the brain turns off one eye
We end up with amblyopia
Amblyopia is a perfectly healthy eye that can no longer see
Age 7 becomes permanent |
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Term
| How does one treat accommodative esotropia? |
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Definition
Occlusion therapy: Patching the eye so child cannot peek, occlude eye they are using to force the other eye to turn on. You know it's working because visual acuity improves, usually over a couple of months
Orthoptics: Vision training (VT), exercises in office or at home. Can use polarization or red/green
Prism: Reliving or Adverse
Surgery: LAST RESORT. Lengthen muscle by moving back or taking piece out, requires 2-3 surgeries before they get it right |
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