Optics II Flashcards
Punctum Remotum
The far point
Conjugate to the axial retinal point.
A point object at the far point will result in the formation of a point image at the retina.
Punctum Proximus
Near point is conjugate to the retina when the eye is exerting max accommodation. Similar to the far point, except when the eye is fully accommodating.
The far point is located where for emmetropes, hyperopes, and myopes
Emmetropes- infinity
Hyperopes- past infinity or behind the retina (virtual)
Myopes- between the eye and infinity (real)
Power of an emmetrope, myope, and hyperope eye
Emmetrope: +60
Myope: Stronger. +65
Hyperope: Weaker. +55
What 2 things can induce night myopia?
Increased spherical aberrations
Light levels are too low to fully relax accommodation when viewing distant objects.
Trends of myopia. Age 1 Age 6 Age 20 Age 30
Age 1: few
Age 6: 2%
Age 20: 20%
Age 30: 30%
Total- between 5-20% of the pop is myopic.
Manifest hyperopia vs latent
Manifest- how much is present at subjective
Latent- difference between subjective and objective
Absolute vs facultative hyperopia
Facultative- the amount of hyperopia that can be neutralized by accommodation.
Absolute-Hyperopia is too large to be neutralized by accommodation.
At age 5, your patient is a hyperope. Based on their refraction, you can guess their refractive error in 10 years.
Greater than +1.50
+0.50-+1.25
Less than +0.50
Greater than +1.50 –> Hyperope
+0.50-+1.25 —> Emmetrope
Less than +0.50 —> Myope
How does amount of hyperopia change from 20-40 and 45+
20-40 stays relatively the same. May uncover more as accommodative ranges decrease.
45+ hyperopes and emmetropes show an increase in plus
Example of resolution acuity
What is the normal cut off range
TAC
Asking a patient to distinguish a pattern from a uniform patch of equal luminance.
Normal adult has a cut off at 40-60 cpd
Example of recognition acuity
Snellen
Only gives info about ability to resolve high frequencies.
The average person has a much better __ than resolution and recognition acuity. About 1 arcsec
Minimum detectable acuity
Hyperacuity
Person’s ability to sense directional relationships. Ex: Whether 2 lines are parallel.
Result of higher level processing.
MAR
Minimum angle of resolution. Measured in arc mins (1/60 of a degree)
A Snellen 20/20 letter subtends an angle of ___ when viewed at 20 feet
5 arc mins
Each distinct bar (think of the letter E) makes up 1 arc min.
Tumbling E is appropriate for children ages
3-6
3 examples of matching recognition acuity tests
Lea, HOTV, STYCAR
Static ret
Patient fixates through phoropter at a distant target
Nott’s Method of dynamic ret
Keep a target in place at 40cm.
Move the ret backward, away from the patient, instead of using lenses. The distance at which neutrality is achieved can be used to determine the lag.
Ex: near card at 40cm, neutrality at 60cm. Lag is 2.50-1.67= 0.83D.
Mohindra technique
In the dark
50cm
Monocular
Can give a closer estimation to cyclo
How to use an astigmatic dial
Put up the dial
Fog the patient
Ask which line is darkest
Take the smaller value x 30 to find axis
Add minus cyl until all lines look equal
Then add minus sphere until BCVA
Can you do the red/green test on someone who is color blind
Yes
The test is based on chromatic aberrations, not our perception of color
It cannot be used unless acuity is 20/30 or better
When to use a cyclo refraction
- Child with convergent strab (must determine if accommodation is contributing)
- Child with significant eso at near
- Suspecting latent hyperopia
A person only uses __% of their accommodative ability comfortably
50%
Correcting aphakia with plus lenses can lead to what
If monocular aphakia–> Aniso and diplopia
If binocular aphakia –>
1. Pincushion (due to high plus lenses)
2. Reduced visual field due to mag. May also cause a ring scotoma.
3. Induced BO at near may cause increased convergence demands
Pt is more at risk for developing AMD due to increased sun exposure. Educate about importance of sunglasses
The major meridian of the eye
Has the most plus power
Will correspond to the steeper meridian
WTR and ATR astig
WTR: Horizontal meridian OF THE EYE has less plus. Steep vertical meridian. x180 rx correction
ATR: Vertical meridian OF THE EYE has less plus. Steep horizontal meridian. x090 rx correction
