Visual Perception Quiz 2

VF and CSF study guide

Define Visual field

The range of area in which we can see.

What is the range of normal monocular visual fields?

150 degrees

What is range of horizontal monocular visual field (without eye movements)?

30 degrees

What is the range of binocular horizontal visual field? How much is the overlap of the visual fields when both eyes are open?

180 degrees, overlap 120 degrees

What is the visual driving requirements to obtain driving license in MA?

20/40 or better, with visual field of 120 degrees

Why test visual fields? What is the advantage of testing visual fields?

Incidence of visual field loss is 3-5% in the general population, and loss of visual field can signify pathologies or other threatening developments Also allows physician to asses integrity of visual pathways with noninvasive means

Describe the 3 levels of visual field testing with clinical test examples.

Visual field screening, qualitative/diagnostic field testing, quantitative field testing

What is Perimetry? Name the 2 types of Perimeter.

Process of plotting visual fields Static Perimeter, Kinetic perimeter

What is Hill of Vision? Describe how the light sensitivity under Photopic and scotopic conditions alters "shape of the hill" ?

3D view of the light sensitivity at different spaces in visual space

under photopic conditions: looks like a hill

under ^^scotopic^^ conditions: flattened and suppressed shape

What are the factors that affect Hill of Vision?

Age, level of light, stimulus sizes stimulus intensity stimulus duration, retinal locus, pathology

What is Visual Field Defect?

reduction of sensitivity compared to the normal hill of vision, can be localized blind spot, or generalized depression

What happens to visual field threshold measurements in senile miosis and nuclear sclerosis cataract? What happens to Weber's fraction?

Visual thresholds measurements in senile miosis and nuclear sclerosis are not affected. Weber's fraction remains constant

Define Isopter and its characteristics.

areas of equal retinal sensitivity

Define the term threshold. How does threshold vary across the visual field?

the minimum quantity of stimulus that can be detected

Define Suprathreshold and Infrathreshold stimulus.

Suprathreshold - stimulus is above threshold, can be seen

Infrathreshold - stimulus is below threshold, cannot be seen

Define Sensitivity. How is it related to threshold?

Inversely related to threshold

Define Decibel & Apostilb. How is decibel value related to visual sensitivity?

Decibel refers to stimulus intensity. Apostilb is an old unit of luminance. Decibels are directly related to sensitivity, the higher the dB values, the better the visual sensitivity.

What is kinetic perimetry? How do you clinically perform it?

Using a moving target

Define static perimetry. How do you clinically perform it?

Using a static target

State the 2 subtypes of static perimetry and their objectives. Provide examples of clinical tests that use this technique.

Threshold testing: determines the minimum stimulus intensity that can be seen at each tested location

Suprathreshold testing: is intended to establish whether or not sensitivity is abnormally low at any location in the visual field

What Psychophysical method does Humphrey perimetry employ?

Method of limits - adaptive stair case procedure

Why is 31.5 apostilb the background illumination of Humphery Perimetry?

It estimates the minimum brightness for photopic vision, vision that depends on cones insteads of rods

What is the stimulus duration of the dim light presented in Humphrey perimetry?

200 ms, this way the patient does not have enough time to look towards the peripheral stimulus

What is SWAP? How is it clinically used? Why does it employ a yellow background?

Short wavelength automated perimetry, it was developed to assess S-system function in certain eye diseases.

A yellow background is used to suppress M and L cones

Define Scotoma. Differentiate Absolute and Relative scotoma.

A small localized or partial visual field defect AKA blind spot

==Absolute: nothing can be seen in the area==

@@Relative: an area where objects of low luminance cannot be seen but larger or brighter ones can@@

Provide some examples of common causes of visual field loss (overall), central & peripheral field loss.

**Overall**: Glaucoma, Retinal conditions, Neurological conditions

**Central**: AMD, Optic neuropathy, Macular holes

**Peripheral**: Glaucoma, retinal detachment, retinitis pigmentosa

Define Spatial vision. Provide an example of clinical application of spatial vision.

The ability of visual system to detect and resolve stimuli of various sizes & contrasts

2. Define Contrast sensitivity.

A psychophysical measure used to assess the sensitivity of the visual system to spatial luminance changes of different spatial frequencies

3. Define Luminance and its unit.

the physical amount of light emitted by a source is reflected from an illuminated object, measure in **cd/m2**

4. Define Brightness. What affects brightness perception.

the perception of a luminous object by the human visual system. adaptation, after effects, and presence or absence of other objects in the visual field

5. Define Contrast.

refers to the difference in luminance between an object (Lmax) and its background (Lmin)

6. Define Modulation. How is it calculated?

the term for the contrast of a repeating pattern AKA grating, M \= (Lmax - Lmin) / (Lmax + Lmin)

Define Contrast Threshold, Contrast Sensitivity and log Contrast Sensitivity

**Contrast threshold**: the least amount of contrast that can be seen in a chart

**Contrast sensitivity**: the reciprocal of contrast threshold

**logCS**: conversion of the CS values to a linear scale

8. How do you calculate Contrast Threshold from log Contrast sensitivity and vice versa?

CS = 1/CT

LogCS = log(CS) or 10^(logCS)

9. The log contrast sensitivity score of a patient in Pelli Robson Chart is 1.65. What is the Contrast Sensitivity and Contrast Threshold?

CS \= 44.67, CT \= 0.022 or 2.2%

10. Name and describe the 3 types of contrast.

**Weber contrast** for letter stimuli

**Michelson contrast** for gratings

**RMS contrast** for natural stimuli

11. What is Weber and Michelson contrast? When would you their respective formula?

Weber contrast; letters = (Lb - Lt) / Lb

Michelson contrast; gratings = (Lmax - Lmin) / (Lmax + Lmin)

12. What is Sine wave? why do we use Sine wave? What are the elements used to describe sine-wave grating?

We use sine wave because they do not get degraded when refracted, and only change in contrast and phase. Sine wave gratings constitute the building blocks of complex periodic waveforms.

13. Why did we learn about Fourier transformation in this topic?

Sine waves of the proper frequency, contrast, phase and orentation can be used to construct complex stimuli

14. What is MTF? How does it change for High and Low spatial frequency?

The ability of an optical system to produce an accurate image of an object.

**Low** spatial frequencies - image blur is hardly noticeable

**High** spatial frequencies - image is almost fully obscured

15. How does SMTF change with Lens in focus, Lens in defocus and translucent lens?

Lens in focus: affect higher spatial frequencies

Lens in defocus: higher spatial frequencies

Translucent lens: equal degradation at all spatial frequencies

1. What is CSF?


2. What is the range and peak of adult CSF?

1. Depicts an observer's sensitivity to sinusoidal bar gratings of widely varied spatial frequencies.
2. Adult range: 2-10cpd, peak 4cpd

17. In the CSF curve what's on x-axis and what's on y-axis.?

x: cpd

y: % contrast sensitivity

18. How does the CSF curve change for Photopic, Mesopic and Scotopic conditions?

Decreases for scotopic, Increases for photopic

19. Name the two types of CSF.

Spatial CSF, Temporal CSF

20. Name the key landmarks of CSF curve and their limitations.

* High SF cutoff: corresponds to best VA, limited by optics and packaging of photoreceptors
* Peak CS: correspond to average receptive field size of retinal ganglion cells
* Low SF cutoff: due to lateral inhibition throughout the visual system

21. What does the shape of CSF reflect? What is CSF high frequency cutoff?

Shape of CSF reflects underlying spatial frequency channels, high frequency cutoff refers to visual system's limited ability to resolve detail when the contrast is 100% (in adults 60cpd)

22. What is the relationship between VA and the CSF?

As CSF increases, then so does VA.

23. Why does the visual system show reduction in sensitivity for high spatial frequencies?

higher contrasts can be resolved until the observer's acuity, it needs high contrast

24. What happens to the high frequency cut-off if the eye is out of focus, such as uncorrected refractive errors (myopia)?

Reduction in high-spatial frequency cut-off

25. How does CS change with aging? How does CS develop in infants?

after a certain age CSF gets worse, this is due to number of photoreceptors and the cortical area devoted to the image

26. How can you determine CSF in the clinic? Provide examples of charts used in the clinic.

MAR chart, 10% EDTRS Chart, Peli-Robson chart

27. Describe the Pelli Robson chart. What are the normal values for adults and above 60 years?

LogCS: 1.68 for 60+ years, 1.84 for 20-39 years

28. Describe MARS CS chart.

Hand-held chart with 48 different contrast levels, declining gradually in 0.04 log unit steps

29. Why measure CS? What are the factors affecting CS?

Sensitive measure to smaller changes in the visual system, complaints of reduced vision not proportionate to the reduction in high contrast acuity, optical factors, drug usage, progress of disease or monitor treatment effect

30. What is the importance of low and middle spatial frequencies for seeing?

low and middle spatial frequencies are important for looking at scarring of the stromal layers and stromal swelling

31. Name few clinical ocular conditions where CS is affected?

Cataract, corneal edema, stromal scarring/swelling, corneal epithelial disruptions

32. Why has the spatial CSF not become a useful diagnostic test for ocular pathology?

snellen only shows a portion of spatial vision

33. How is reading speed impacted by spatial CSF losses?

loss in spatial CSF can cause reduction in reading

34. How is CSF measurement useful in Low Vision?

it has been found that spatial CSF, rather than visual acuity, determines which eye is preferred in situations in which only one eye can be used.

35. Why is the visual system considered as Fourier Analyzer?

because it can deconstruct the retinal image into its individual frequency components

36. What is MACH band?

nonexistent perceptual bands

37. Why does MACH band occur? Which part of the visual system is responsible for that?

its primarily done by lateral inhibition within the retina

38. State some facts about the visual system.

brightness is invariant, brightness is predicted by local contrast

39. Define Brightness Constancy.

The brightness of objects is relatively invariant even though the absolute luminance varies widely

40. What is Simultaneous contrast?

The brightness of an object is not always predicted by its luminance, but by the local contrast with surrounding objects

41. What is Assimilation?

complex version of simultanous contrast, the brightness of a stimulus covaries with the brightness of a surrounding stimulus

42. Which spatial frequency reduction prompts most complaint from patients?

Reduction in high spatial frequencies