What is ocular misalignment?
When the visual axes of both eyes do not intersect at fixation
Define orthophoria.
Alignment in the absence of a stimulus for fixation; even without fixation, the eyes are always straight
What is heterophoria/phoria?
A latent tendency for the eyes to deviate when fusion is broken; eyes will wander without any action
A posture slight INWARD is _____ and a posture slightly OUTWARD is ______.
Esophoria; exophoria
What is heterotrophia/tropia?
A manifest deviation of the eyes (can be seen); a tendency of the eyes to deviate when fusion is blocked
What does a tropia cause visually?
-diplopia
-suppression of the deviated eye
What are the causes of a tropia?
-anisometropia
-abnormality of the extraocular muscles
-eye disease
What is cover test done to determine?
-presence of a phoria or tropia
-laterality/which eye (unilateral or alternating)
-frequency of deviation (constant or intermittent)
-direction of the phoria or tropia
-magnitude of the deviation
What is the order of the cover test?
1. Unilateral cover test (cover-uncover)
2. Alternating cover test
What is the unilateral cover test used to determine, specifically?
-presence of deviation
-laterality
-frequency of deviation
What is the alternating cover test used to determine, specifically?
-direction of the phoria or tropia
-magnitude of the deviation
T/F: Cover test is done at distance only.
False; CT is done at both distance AND near
Describe phoria.
The visual axis of both eyes are aligned at the target with both eyes open (latent)
Describe tropia.
The visual axis of one eye is aligned on the target while the other is misaligned with both eyes open (manifest)
Which eye is evaluated during the cover test?
The unoccluded eye
The "cover" in the cover-uncover shows what?
The presence of a deviation
The "uncover" in the cover-uncover shows what?
Laterality (alternating or unilateral) and frequency
What is a unilateral tropia?
One eye usually fixates when both eyes are open
What is an alternating tropia?
When the patient is able to keep either eye on a target with both eyes open
What equipment is used for cover testing?
-visual acuity chart
-occluder
-near point fixation target
-prism bars
-habitual correction
-well lit room
For distance and near cover testing, what size should the target be?
2 lines larger than the BCVA in the POORER seeing eye; ex: 20/20 BCVA �> target should be 20/30 (20/25 is in between)
For cover test, when is the deviation neutralized?
At the amount of prism where both eyes appear aligned and there is no movement on alternate CT
Where is the prism placed for CT alignment?
The base of the prism is placed in the direction you want the pts eye to move; ex: if esotropic, base is outward
How do you document a phoria or tropia?
-w/ or w/o glasses
-distance or near (prime)
-amount of deviation
-type of phoria or tropia
-constant or intermittent
-unilateral or alternating
CT cc 20? RX(T)' at N
CT sc 35? RXT with 10? RHT at D
What are versions?
movement of both eyes in the same direction (conjugate)
What is duction?
Movement of one eye
What is it called when both eyes are simultaneously cooperating to give a single perception?
Normal binocular vision
What is sensory fusion?
Integration of similar images at the cortex
What is motor fusion?
Motor alignment to sustain binocular vision
What are some heterophoric abnormalities?
-convergence insufficiency
-convergence excess
-divergence insufficiency
-divergence excess
For horizontal phoria, the grooves on the maddox rod are oriented horizontally. What direction will the streak be seen in for the patient?
Vertical
If the red light in a Maddox rod is through the light, what is the diagnosis?
Ortho
If the red light in a Maddox rod is to the right of the light, what is the diagnosis?
Uncrossed diplopia (eso)
If the red light in a Maddox rod is to the left of the light, what is the diagnosis?
Crossed diplopia (exo)
If the red light in a Maddox rod is below the light, what is the diagnosis?
Right hyper
If the red light in a Maddox rod is above the light, what is the diagnosis?
Left hyper
When the patient has uncrossed diplopia in eso deviation, where does the light hit?
Nasal retina
When the patient has crossed diplopia in exo deviation, where does the light hit?
Temporal retina
T/F: A Maddox rod cannot differentiate phoria from a tropia.
True
What are the testing methods for visual fields?
-confrontation visual field
-tangent screen
-amsler grid
-automated perimetry
What do confrontation visual fields detect?
GROSS visual field loss
What is the Amsler grid used for?
to detect macular degeneration by determining if there are central visual deficiencies
At what distance is an amsler grid held for testing?
Whatever distance the card recommends
How is amsler grid recorded?
Monocularly, "normal" if no defects, and describe or draw if there are defects
What is the Hirschberg test?
-rough, objective, estimate and measurement of a deviation/strabismus
-useful to identify tropia in young and uncooperative pts
What is the visual axis?
Connects fovea to target
What is the pupillary axis?
Line passing through the center of pupil, perpendicular to the cornea
What is angle kappa?
angle between pupillary axis and visual axis
Nasal to the pupil is ____ angle kappa/ ____ posture, which is the most common type of corneal reflex position
Positive, exo
Temporal to the pupil is a _______ angle kappa/ ____ posture.
Negative, eso
What is the equivalent number of prism diopters for 1 mm of deviation of the reflex in Hirschberg's test?
22??
________ tries to eliminate discrepancies of the 2 images and tries to make images from each eye fuse to one as best as possible.
Motor fusion
What is the purpose of determining the near point of convergence (NPC)?
To determine the ability to converge while maintaining fusion
What is the normal range for NPC?
Break: 2.4-2.9 cm
Recovery: 4.2-5 cm
If the NPC is abnormal, what are the next steps?
-repeat w/ red glass over right eye
-repeat a 3rd time with an accommodative target
What is accommodation?
Ability to change focus of crystalline lens in response to near stimulus
What is amplitude of accommodation?
Measure a pts ability to accommodate (in diopters)
When testing accommodation, what is the expected result?
Both eyes should be within 1D of each other
What is Hofstetter's formula?
Min: 15 - 0.25(age)
Avg: 18.5 - 0.30(age)
Max: 25 - 0.40(age)
T/F: accommodation is tested monocularly.
True
What are the advantages of binocular vision over monocular?
-depth
-more precise
-quicker
What is the purpose of stereopsis?
Measure fine depth perception by evaluating the ability to fuse stereoscopic targets
What is the worth 4 dot test?
-assess flat fusion at distance and near
-detects small unilateral central scotoma at near
When do you perform a worth 4 dot?
When stereopsis is below normal (40 sec of arc)
If a pt sees 2 red dots during W4T, what is the diagnosis?
Only red eye is used, OS is suppressing
If a pt sees 3 green dots during W4T, what is the diagnosis?
Only OS sees, OD is suppressing
If a pt sees 5 dots during W4T, what is the diagnosis?
Diplopia
The eye's secondary focal point is where?
Located inside the eye, about 22 mm
Where is the far point of an emmetropic eye?
At infinity
In a myopic eye, the vergence is negative because the far point is ____ the eye.
In front of
In a hyperopic eye, the vergence is positive because the far point is ____ the eye.
Behind
What is the optical lens cross?
States the individual spherical power values required for the correction along each principal meridian
In a thick lens, where is the effective focal length measured from and what is is associated with?
-measured from the principal plane/point
-associated with he effective power
In a thick lens, where are the front and back focal lengths measured from and what are they associated with?
-measured from the front/back vertex point
-associated with the front/back vertex power
What contributes to the two-lens system?
Cornea and crystalline lens
The retinal image is....
Real, inverted, minified, and formed at the retina (hopefully)
T/F: Meridians are different in both eyes and start clockwise.
False, they are the same in both eyes and start counterclockwise
What is power transposition?
The re-writing of the astigmatic prescription from one for to another (plus to minus and vice versa)
How do you correct myopia?
By bringing the image of a distant object to the far point of the myopic eye (with a concave lens)
How do you correct hyperopia?
By bringing the image of a distant object to the far point of the hyperopic eye (with a convex lens)
What is neutralizing?
Determining the prescription in a pair of unknown spectacle lenses
What is verifying?
Determining the accuracy in the production of spectacle lenses
Where do we measure lens power?
Optical center
What is the back vertex power?
-the power of a spectacle or contact lens measured at the back surface of a lens with a lensometer
What is the front vertex power?
-the power of a spectacle or contact lens measured at he front surface of a lens with a lensometer
-usually used to determine the add power in a pair of flat top bifocal
Where does a minus lens move the target image?
In the same direction as the lens
Where does a plus lens move the target image?
In the opposite direction to the lens
How is the axis found for a spherocylindrical lens?
Rotational motion
How is prism power determined?
Ray deviation (cm)/distance measured (m)
How is induced prism calculated?
lens power (D) x distance from optical axis (cm)
T/F: the cornea is a minus lens.
F, it is a very strong plus lens.
What is the largest contributor to ocular optical power?
The cornea
Which surface curvature is the main contributor of ocular optical power?
Anterior surface
The corneal power is too strong in which kind of eye?
A. Emmetropic
B. Myopic
C. Hyperopic
B. Myopic
People below age 50 usually have which kind of astigmatism?
With-the-rule astigmatism
People above age 70 usually have which kind of astigmatism?
Against-the-rule astigmatism
The images displayed on the cornea as a mirror are ALWAYS:
-minified
-erect
-virtual
What is used to determine the anterior cornea radius of curvature?
The measurement of image size
What does keratometry do?
-measures reflected image size
-calculates anterior cornea radius of curvature
-estimates corneal optical power
What is the keratometric technique?
-project an image on the cornea
-line up
-compare magnifications
-measure radius of curvature