Binocular Vision: Lecture 20: Cortical Phenomenon in Amblyopes

Question 1

Amblyopia

1. Monocular Deprivation has POWERFUL EFFECTS on what?
   a. But STIMULUS DEPRIVATION is also a SEVERE CONDITION, typically seen ONLY in relatively rare cases of what?
2. What type of Amblyopia has a LESS DRAMATIC EFFECT on Vision than does DEPRIVATION?
   a. With LESS CONSISTENT EFFECTS on what?
   b. Some strabismic animals will exhibit an Ocular Dominance Histogram similar to that of what?

Answer 1

1. on BINOCULARITY
   a. of Congenital Cataracts or Corneal Opacities in Children
2. STRABISMIC AMBLYOPIA
   a. on the Ocular Dominance Histogram
   b. of MONOCULAR DEPRIVATION, where most Cortical Cells will be driven by the Nonstrabismic or Fixating Eye

Question 2

Amblyopia (exotropia)

1. Those animals that develop EXOTROPIA are more likely to develop what?
   a. SWITCHING B/W FIXATING and DEVIATING EYE, sometimes at will, their LACK of BINOCULARLY DRIVEN CELLS results in what?
2. In experiments w/monkeys reared w/27 prism diopter Base-in prisms, thereby inducing exotropia, the population of Binocular Neurons is REDUCED from what?
   a. These monkeys EXHIBIT NORMAL VISUAL ACUITY BUT REDUCED WHAT?

Answer 2

1. ALTERNATING STRABISMUS (alternating Fixation):
   a. in a LOSS of NORMAL BINOCULAR VISION AND STEREOPSIS
2. FROM 81% OF NEURONS in AREAS V1 and V2 to 22% of SUCH NEURONS
   a. reduced BINOCULAR SUMMATION and STEREOPSIS

Question 3

Amblyopia (Esotropia)

1. Individuals w/ESOTROPIA tend to fixate how?
   a. Their likelihood of developing Amblyopia is what?
   i. In this case, the patient or animal tends to SUPPRESS which eye?
   b. After a Period of HABITUAL SUPPRESSION, AMBLYOPIA develops in what?

Answer 3

1. CONSTANTLY w/1 Eye, and have a UNILATERAL STRABISMUS in the Other Eye.
   a. it’s VERY HIGH
   i. the ESOTROPIC EYE
   b. in the STRABISMIC EYE

Question 4

Meridional Amblyopia

1. How does it develop in Infant animals?
   a. Following this, most VISUAL CORTEX CELLS develop an ORIENTATION SELECTIVITY (BIAS) for what?

Answer 4

1. by raising infant animals in an environment in which they receive EXPOSURE only to VERTICAL STRIPES
   a. for ONLY THAT ORIENTATION

Question 5

Is the LGN Impacted due to Amblyopia?

1. The size of the SOMA (cell body) of Neurons in the LGN shrinks when Binocularity is disrupted, that is, CELLS SERVING THE DEPRIVED EYE do what?
   a. This reduction in cell size is thought to be SECONDARY to what?
2. The LEVELS of CYTOCHROME OXIDASE, a METABOLIC ENZYME in these CELLS is what?

Answer 5

1. SHRINK
   a. to their CORTICAL METABOLIC DEMANDS, following the loss of cortical binocular cells innervated by those cells.
2. is REDUCED

Question 6

Amblyopia

1. If you monocularly suture the lids in one eye in a kitten, you can still drive cells from the DEPRIVED EYE located in what?
2. P Cells in the LGN are found in normal numbers in the deprived Laminae of the LGN, but single-unit recordings reveal that they have what?
   a. These LGN P cells are reflecting the loss of what?
   b. What about M Cells?

Answer 6

1. In the Appropriate Layers of the LGN
2. Have a LOWER SPATIAL RESOLUTION (a loss of Sensitivity at Higher Spatial Frequencies)
   a. the Loss of ACUITY in AMBLYOPIA
   b. They are relatively Spared by most types of Amblyopia

Question 7

1. At the very extreme of the lateral extent of the LGN are cells that lie in what area?
2. The Binocular Competition model would predict that Binocular Competition would not be possible in an area of visual space that is represented only Monocularly; THESE CELLS MAKE CONNECTIONS to what?
3. Cell loss is restricted to what?

Answer 7

1. lie in the MONOCULAR TEMPORAL CRESCENT of Visual Space (the area of Visual Space that only one eye can see)
2. to CORTICAL CELLS DRIVEN BY ONLY ONE EYE
3. to the BINOCULAR SEGMENT of the LGN

Question 8

Amblyopia

1. In ANISOMETROPIC AMBLYOPIA, decreases in the soma size and metabolic rates of LGN cells occur only within what?
2. The CHANGES in LGN CELL SIZE with AMBLYOPIA CORRELATE WITH the CHANGES in what?
   a. The Degradation of cells in the LGN therefore represents what?

Answer 8

1. within the BINOCULAR Region of the LGN and not in the monocular Crescents
2. in OCULAR DOMINANCE COLUMN WIDTH in the STRIATE CORTEX
   a. RETROGRADE DEGENERATION

Question 9

Brief Deprivation

1. The Ocular dominance Histograms were measured for kittens at what days of age?
   a. These kittens were either with NORMAL VISUAL EXPERIENCE or were what?
2. The normally reared kittens displayed the typical normal distribution with the MAJORITY OF CELLS SHOWING WHAT?
   a. Whereas after Monocular Deprivation for Only 8 Days, CORTICAL CELLS were what?
3. a Slight shift or Asymmetry in the Ocular Dominance Histogram was evident after as little as what?

Answer 9

1. 26-32 days of age.
   a. or were MONOCULARLY deprived for periods up to 8 days in length.
2. showing BINOCULARITY
   a. were TOTALLY DRIVEN by the NONDEPRIVED EYE ALONE
3. after as little as 12 HOURS of DEPRIVATION

Question 10

Reverse Suturing (1)

1. The eye that was previously sutured is opened, and the formerly nondeprived eye is now what?
   a. What happens to the Ocular Dominance Histogram do?
   i. How and When is this possible?

Answer 10

1. is NOW CLOSED
   a. it REVERSES so that MORE CELLS are now driven by the PREVIOUSLY DEPRIVED EYE
   i. It’s Possible only if the Reverse Suturing is Done w/in the CRITICAL PERIOD and not after the conclusion of the Critical Period

Question 11

Reverse Suturing (2)

1. If reverse suturing is then initiated at age of 5 WEEKS, effects on ocular dominance are noted by as LITTLE as how many days after starting REVERSE SUTURING?
   a. After 9 DAYS of reverse suturing, what happens to the Ocular Dominance Pattern?
2. For the visual system of the Kitten, what is still w/in the Critical Period?
   a. 1 day of Occlusion for what?
3. In Reverse-Sutured kittens, the REVERSAL INDEX (measure of shifts in the Ocular Dominance Histogram to favor the now open (previously deprived) eye) is HIGHEST just before what?
   a. It’s highest at what time?
   b. What is the critical period time for a kitten?

Answer 11

1. as little as 3 days of reverse suturing.
   a. It has REVERSED itself so that MOST of the CELLS are now driven by the Previously Deprived Eye
2. From 5 WEEKS of AGE until JUST OVER 6 WEEKS of AGE
   a. for EACH YEAR of LIFE
3. Just BEFORE 8 WEEKS of AGE.
   a. at 4 WEEKS.
   b. 2-12 weeks.

Question 12

Critical Period

1. When does the Critical Period start?
2. Critical Period is that period when Deprivation results in what?
3. Period of Recovery is the time w/in which you can improve what?

Answer 12

1. it starts with a RAPID INCREASE in PLASTICITY soon after birth and Ends with a MORE GRADUAL DECREASE IN PLASTICITY.
   (it doesn’t start immediately at birth and doesn’t commence suddenly)
2. in Loss of Function
3. Visual Function

Question 13

Interocular Transfer (IOT) in Humans

1. In the Interocular Transfer Paradigm, one eye displays what?
   a. The other eye is tested to see whether what can transfer b/w the 2 eyes?
2. Ratio?
   a. a Score of 100% means what?
   b. What about a score of 0%?
3. The Critical Period for BINOCULARITY DOES NOT BEING AT BIRTH, but starts RAPIDLY b/w what ages?
   a. The CRITICAL PERIOD PEAKS when?
   b. However, Strabismus can affect Interocular Transfer of Aftereffects until what ages?

Answer 13

1. the ADAPTING STIMULUS
   a. the Aftereffect
2. (Strength of IOT)/(Strength of Monocular Aftereffect)
   a. means the IOT Effect is as strong as the Monocular Aftereffect.
   b. A Score of 0% means that you have NO TRANSFER
3. 6 MONTHS and 1 YEAR OF AGE
   a. at 1-2 YEARS OF AGE and then GRADUALLY DIMINISHES
   b. until 7 or 8 years of age.

Question 14

Occlusion Therapy

1. REVERSE OCCLUSION Improves the Acuity of what % of Amblyopes before what ages?
2. At what age must ocular alignment be obtained for the best chance to establish (or reestablish) binocular vision?
3. The Earlier the Strabismus Can be detected and treated, so that proper binocular development can be restored, the better what?

Answer 14

1. of 90% of amblyopes before 7 years of age, but is LESS EFFECTIVE AFTER THAT AGE
2. the best opportunity for SURGICAL CORRECTION OF STRABISMUS OCCURS BEFORE 3 YEARS of AGE.
3. The Better the PROGNOSIS for BINOCULAR FUNCTION

Question 15

Amblyopia Therapy

1. 2 Primary approaches: What are they?
2. Both of these therapies share a common feature in that both produce what?
3. Results: Both methods can generate improved visual performance in the amblyopic eye.
   a. Which has a Huge Compliance Advantage?
   b. Which method works for every amblyope?

Answer 15

1. Patching the Non-Amblyopic Eye (removes all retinal image contrast but isn’t 24/7)

and

2. Image Contrast (due to intermittent defocus) and is 24/7. (ATROPINE PENALIZATION)
3. both produce PARTIAL CONTRAST DEPRIVATION in the NON-AMBLYOPIC EYE.
4. a. ATROPINE
   b. NEITHER

Question 16

Dark Rearing (1)

1. The Critical Period begins for dark-reared animals when they’re first brought to what?
   a. Their visual development is arrested while they’re in what?
2. What does this tell us?
   a. The CRITICAL PERIOD SEEMS to be TRIGGERED by what?
   b. So, the CRITICAL PERIOD IS THEREFORE what?

Answer 16

1. into the LIGHT
   a. they’re in the DARK
2. that Visual stimulation is required as a signal to start the critical period of development.
   a. by the RETINA’s BEING EXPOSED TO LIGHT.
   b. it’s NOT HARD WIRED!

Question 17

Dark Rearing (2)

1. The Development of Binocularity is Accompanied by changes in what?
2. The Development of Ocular Dominance Columns may DEPEND on what?

Answer 17

1. in Neurotransmitter Concentrations and NEURAL DENDRITIC RECEPTOR SITE ACTIVITY in the VISUAL CORTEX
2. on POSTSYNAPTIC NEURONAL RESPONSES to the NEUROTRANSMITTER GLUTAMATE!

Question 18

Dark Rearing (3)

1. These responses are, in turn, mediated by postsynaptic receptors that use a MESSENGER called what?
   a. The DENSITY of NMDA-GLUTAMATE RECEPTORS CHANGES in what?
2. As the Ocular Dominance Columns begin to Segregate, the DENSITY of NMDA RECEPTORS will do what?
   a. As the Critical Period comes to an end, what happens?

Answer 18

1. called NMDA.
   a. in DIRECT PROPORTION to the DEGREE of PLASTICITY in VISUAL CORTEX
2. INCREASES w/in NEURONS in STRIATE CORTEX.
   a. the NMDA-Glutamate Receptor Density DIMINISHES

Question 19

Conclusions

1. Amblyopia PRIMARILY AFFECTS what?
2. The underlying NEUROLOGY is what?
3. the NEURAL ANOMALY is LOCATED where?
4. OCCLUSION THERAPY has proven itself to be what?
5. What Experience may be essential for the best outcomes?
6. Improved Vision in the Amblyopic Eye can be achieved by TREATING with what?

Answer 19

1. SPATIAL VISION at HIGH and MEDIUM FREQUENCIES
2. UNKNOWN
3. in V1 (and maybe have additional deficits in V2)
4. Successful, but lack of carefully controlled studies makes definitive conclusions impossible.
5. BINOCULAR EXPERIENCE
6. with Partial Deprivation of the Non-Amblyopic Eye.