Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BOARDS > Physiological Optics II > Flashcards

Physiological Optics II Flashcards

1
Q

GUllstrands exact eye model

A
  • made up of the cornea, the humor, the lens.

* In total there are 6 refractive surfaces and 4 chambers.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Reduced eye model

A 
single spherical refraction interface 
• N=1.33
• Cornea to anterior focal point=16.67mm
• Cornea to posterior focal point (axial length)=22.22mm
• Total eye power=60.00D
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Far point of the eye

A

the point conjugate to the axial retinal point. A point object at the far point will result in the formation of a point image on the retina. Where is the eye looking WITHOUT accommodation to have light perfectly focused on the retina. 1/F=far point.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Far point sphere of the eye

A

when the eye rotates, it traces out a spherical surface known at the far point sphere. Center of curvature is the center of rotation of the eye (about 27mm behind the tropical spectacle plane)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Near point of eye

A

point conjugate to the retina when the eye is exerting maximum accommodation. Similar to far point except the eye is fully accommodating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Emmetropia

A
  • incoming plane waves should converge to a point on the retina.
  • Far point is infinity
  • The retina should be located about 22mm from the lens to be emmetropic.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Myopia

A
  • eye is too strong (>60D)
  • Light from incoming plane waves to converge to a point in front of the retina
  • Far point: located between the eye and infinity. It will sit somewhere in front of the retina.
  • L (object vergence) has to be negative (real object)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Night myopia

A

◦ Low light levels
◦ Due to combination of increased spherical aberration as well as light levels which are too low to fully relax accommodation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When is there the highest prevalence of myopia

A

Newborns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Prevalence of myopia with age

A 
◦ 0y=25-50%
	◦ 1y=1%
	◦ 6y=2%
	◦ 20y=20%
	◦ 30y=30%
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Hyperopia

A
  • far sighted
  • Eye too weak (<60D)
  • Plane waves converge somewhere behind the retina
  • Axial distance and refractive power play a role.
  • Far point: located behind the retina=virtual object
  • Optically speaking, a correcting lens should be places so that its secondary focal point coincides with the far point of the ametropic eye
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Latent hyperopia

A

◦ Difference between subjective and objective

◦ Patient may show a lower amount of hyperopia in subjective refraction tha during objective refraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Manifest hyperopia

A

◦ What is present in the refraction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Absolute hyperopia

A

◦ The amount that cannot be overcome with accommodation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Facultative hyperopia

A

◦ Hyperopia that can be neutralized with accommodation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Trends with hyperopia

A 
◦ 5yr >1.50D=hyperopic at 14
	◦ 5yr -0.50-1.25D=emmetropic at 14
	◦ 5yr <0.50D=myopic at 14
	◦ 6% of 6-15yr olds
	◦ Between ages 20-40, hyperopia tends to remain constant
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Interpupillary distance

A

◦ Use a PD ruler or pupillometer
◦ From one edge of one pupil to the same edge of another
◦ Examiner sits 40cm away from pt and closes one eye
◦ Pt fixates on examiners left eye: measure, this is near PD
◦ Pt fixates on other eye while rule remains stationary, this is the distance PD
◦ Pupillometer reduces errors resulting from parallax

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Resolution acuity

A

‣ Teller
‣ Determined by asking a patient to distinguish a pattern from a uniform patch of equal luminance
‣ Normal cut off is 40-60cpd

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Recognition acuity

A

‣ Snellen acuity
‣ Information about our abiltiy to resolve high frequencies
‣ Not good for cataract patients

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Minimum detectable acuity

A

‣ Thinnest possible wire that is detectable (Cardiff?)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Hyperacuity

A

‣ Vernier
‣ Person’s abiltiy to sense directional relationships
‣ Telling if two lines are perfectly aligned or not
‣ Higher cortical processing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

MAR

A

‣ Minimum angle of resolution

‣ Arcminutes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Snellen fraction

A

‣ 1/MAR, multiplied by 20 to get the standard optometry form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

LogMAR

A

‣ Log(MAR)
‣ 20/20=1 MAR=0 logMAR
‣ Each letter on the 20/20 line of snellen chart subtends an angle of 5 arcminutes when viewed at 20 feet. Each distinct bar making up the letter subtends 1 arc minute

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Charts for VA research

A

‣ EDTRS is a common one used in clinical research because the geometrical progression of letters is based on logMAR scaling

26
Q

Acuity in kids

A

◦ Birthday cake slide: recognition, for kids who don’t know letters and numbers
◦ Tumbling E chart: ages 3-6, recognition
◦ Landolt C: simialr to tumbling E, recognition
◦ Allen Vision Test: 2 and older. Child names a series of images on cards while viewing them at close range. Then occlude one eye and determine the longest distance at which the child can resolve the imaged
‣ Acuity expressed as x/30
◦ STYCAR: matching
◦ HOTV: matching
◦ Lea Symbols: Matching
‣ Uncorrected high hyperopes and those with accommodative infacility may have trouble with matching acuity tests

27
Q

Who may have trouble with matching acuity tests

A

‣ Uncorrected high hyperopes and those with accommodative infacility may have trouble with matching acuity tests

28
Q

Corneal curvature

A

◦ Keratometer
◦ Corneal topographer
◦ Central 3mm of cornea

29
Q

Corneal thickness

A

◦ Pachymeter
◦ Measures the distance between the purkinje images
◦ Important for corneal refractive surgery. Also plays an increasingly important role in glaucoma risk assessment

30
Q

Static retinoscopy

A

◦ Determine a patient’s spherocylindrical refractive error
◦ Optical principles
‣ Retinal reflex and the streak
‣ With add plus, against add minus
‣ Myopes will have against motion
‣ Hyperopes will have with motion
◦ Rx=F-working distance
◦ Astigmatism
‣ Use sphere lens to neutralize the most positive meridian of the eye, and then neutralize the perpendicular axis using a minus cyl lens
‣ Remember that horizontal streak scopes the vertical meridian and the vertical streak scopes the horizontal meridian

31
Q

Dynamic retinoscopy

A

◦ Accommodative accuracy/response
◦ MEM
‣ The fixation target is located at a typical reading distance
‣ Lenses are quickly placed in front of the patient to achieve neutrality of the reflex.
◦ Nott’s method
‣ Moving the retinoscope backwards instead of using lenses
◦ Mohindra: near ret. if no cyclo available. In the dark at 50cm. Monocular. 1.25 must be subtracted.

32
Q

Stenopaic slit

A

‣ 1mm rectangular slit
‣ Decreases the diameter of the entrance pupil the meridian perpendicular to the slit.
‣ Rotate until a “best” position is found
• This is perpendicular to the most plus meridian of the eye
‣ use spherical lenses to get information about the astigmatism.

33
Q

JCC

A

‣ Most common method for measuring astigmatic correction
‣ JCC is a lens whose principle meridians have equal power but opposite signs
‣ Red is positive meridian (or negative axis), and white is the negative meridian (or positive axis)
‣ 1. Refine sphere power so that the CoLC falls on the retina. This corresponds to fogging then decreasing plus power until best acuity is achieved
‣ 2. Chase the red
‣ 3. Refine the power
‣ 4. With each +/-0.50D change of cyl power, one must change the sphere power +/-0.25D to maintain a constant spherical equivalent.
‣ A +/-0.25D JCC is typically used for patients with acuity of 20/30 or better, while higher powers (+/- 0.50D or +/-1.00D) are used for patients with poorer vision.

34
Q

Definition of a JCC lens

A

It has to have SE of PLANO!

35
Q

Astigmatic dial

A

‣ Spoke like pattern
‣ 1. Fog the eye to 20/50
‣ 2. Find the lines of the dial that appear the sharpest and darkest
‣ 3. Add minus cyl until all lines appear equal
‣ 4. Add minus sphere until BCVA obtained
‣ Remember that we do not need to adjust the sphere power to maintain the spherical equivalent as we add minus cyl with the astigmatic dial because the added cyl power is collapsing the interval of sturm.
‣ The rule of 30: lowest number on the clock dial x 30 gives the axis in minus cyl

36
Q

Refining the spherical component of subjective refraction

A

◦ 1. Following JCC, add +0.25D increments until acuity is compromised
◦ 2. Subtract 0.25D increments from each eye, checking acuity after each step until max acuity is reached
◦ 3. If an astigmatic dial is used for the astigmatic portion, the patient should be sufficiently fogged that only step 2 is necessary.
◦ 4. Verify spherical endpoint using the duo chrome test

37
Q

Duochrome test

A

◦ If too much minus power is RXed, the patient can accommodate to offset the excess minus spheres. The combination of a minus lens and a plus lens is optical similar to a galilean telescope, and hence the patient will see images that appear increasingly smaller as minus is added
◦ Utilizes chromatic aberrations
‣ Independent of color perception and therefor works with color vision impaired individuals. However, it cannot be used until acuity has been corrected to at least 20/30 or better
◦ Split background (half red, half green)
◦ Green should focus in front of the retina, red should focus behind the retina. We want the retina to be positioned perfectly between these two points.
◦ A fogged patient will perceive the red image to be clearer, while a patient that is overminsued will perceive the green image to be clearer.

38
Q

Fogging technique for equalizing

A

‣ Fog both eyes to reduce acuity to 20/200-20/100. Place a -0.25D lens in front of one eye at a time switching eyes in rapid succession

39
Q

Prism techniques for equalizing

A

‣ Risley prism to dissociate the eyes.
‣ Fog both eyes and look for differences in the images seen by each eye. When they are balanced, they will report equal clarity between the two eyes at any point during the testing

40
Q

Cycloplegic techniques for refraction

A

◦ Ensures that accommodation is fully relaxed
◦ use for
‣ Child with convergent strabismus
‣ Child with significant eso at near
‣ Young adult complaint of HA but with no uncorrected hyperopia (there could be latent)

41
Q

Accommodation

A
  • an object located closer to the eye than the far point results in rays striking the eye that are too divergent.
  • Accommodation must offset the change in vergence which results from moving an object closer to the eye
  • A person uses only about 50% of his/her accommodation ability comfortably
42
Q

A person can use ____ of his/her accommodative demand comfortable

A

50%

43
Q

Ocular acommodative demand

A

amount of accommodation needed to see an object clearly

44
Q

Ocular accommodation

A

accommodation that the eye actually provides

45
Q

Amplitude of accommodation

A

maximum amount of accommodation possible for a given eye

46
Q

Near point of eye

A

point conjugate to the retina when the eye is achieving its maximum accommodation. Exactly like the far point, but now the eye is fully accommodating

47
Q

Range of clear vision

A

refers to all other points analogous to the near and far points, but at varying degrees of accommodation. It covers all points between the near and the far point.

48
Q

Presbyopia

A
  • loss of accommodation abiltiy with age

* Decrease in the amplitude of accommodation

49
Q

Amplitude of accommodation estimated

A

18.5-0.3(age)

50
Q

Measuring add for presbyopia

A

◦ 1. Half amp method: the patient should have half the amplitude of accommodation in reserve in order to maintain clear and comfortable vision. The theoretical add power is the working distance minus one half of the patients AoA.
◦ 2. Balancing NRA/PRA: patients RXed add power is in the middle of the NRA/PRA range
◦ 3. FCC:
‣ Add plus until they report that the vertical lines appear darker
‣ Gradually decrease plus until they say the horizontal and vertical lines are equally dark.
‣ The total plus power over the patient’s subjective refraction that is required to reach the endpoint is the patient’s add power for that given working distance
◦ 4. Age based plus power

51
Q

Aphakia

A

◦ Aphakia=without a lens
‣ Similar to having a large minus error, leading to aniseikonia and diplopia, or reduced VF and puncushion distortion. Correction associated with a ring scotoma resulting in visual stimuli appearing an disappearing briefly as they pass in and out of the scotoma (jumping effect or jack in the box effect). They also have additional aconvergence demands at near, large BO prismatic effects
‣ Mag=-F1/F2

Patient can no longer accommodate

52
Q

Pseudophakia

A

lens has been replaced with an implant
‣ An IOL can be placed at the anteiror chamber
◦ Patient can no longer accommodate

53
Q

Simple astigmat

A

one line falls on the retina, and one line falls in front of or behind the retina.

54
Q

Mixed astigmat

A

one line falls in front of the retina and one line falls behind the retina

55
Q

Compound astigmat

A

both lines fall in front of or behind the retina

56
Q

Equally mixed astigmat

A

CoLC falls on retina

57
Q

Major meridian of the eye

A

the meridian with the most plus power and steepest corneal meridian

58
Q

WTR astigmatism

A

Corneas major meridian is vertical 90+/- 30

59
Q

ATR

A

major meridian is horizontal (0 +/- 30)

60
Q

Oblique astigmatism

A

zone not covered by WTR or ATR

61
Q

In terms of lens RX in minus forms, WTR and WTR..

A

WTR astigmatism corresponds to an axis that’s us appx horizontal, and ATR corresponds to an axis that is approximately vertical (things are opposite in glasses!)

BOARDS (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions