OPT505 Lecture 10: Visual Fields Overview

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Lecture Recording

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OPT505 Lecture 10: Introduction to Visual Fields

• The lecture is on visual fields, and is given by Ellie Livings.
• The presentation outlines the concepts of visual fields.

Intended Learning Outcomes

• Students will learn the terminology for describing visual fields and concepts like the "hill of vision."
• Students will apply knowledge of ocular anatomy and the visual pathway.
• Students will interpret visual field defects and identify potential lesion locations.
• Students will compare different perimetry techniques and visual field programs.
• Students will learn how to reduce visual field assessment errors.
• Students will interpret visual field plots and determine their reliability.

Fields: Overview

• Visual field is the area you can see, either with one eye (monocular) or two eyes (binocular).
• Visual fields are normally discussed monocularly unless in special cases.
• Visual field integrity reflects the overall health of the visual system.
• Testing is used for screening, diagnosis, localizing visual loss, and determining functional vision.

The Normal Field: Extent

• Normal monocular fields overlap.
• Normal visual fields include about 120° vertically and 160° horizontally.
• Blind spots are located temporally in field plots.

The Normal Field: The Blind Spot

• Blind spot is the area of the field occupied by the optic nerve.
• There's no vision in the blind spot.
• The blind spot is a useful landmark on visual field plots and is located temporally.

Visual Pathway

• Visual field defects help pinpoint lesions within the visual pathway.
• The visual pathway begins in the retina and progresses through the optic nerve, optic tract, lateral geniculate nucleus (LGN), optic radiations, and ends at the primary visual cortex.
• Visual pathway defects can occur along any segment of that pathway.

Visual Pathway: Chiasm

• Nasal fibers from each eye cross at the optic chiasm.
• Fibers from the left and right visual fields project to the same side of the brain.
• Fibers from the temporal side do not cross at the optic chiasm.

Visual Pathway: Topographic Organization in Striate Cortex

• Adjacent points in the visual field are mapped adjacently in the striate cortex, showing a one-to-one relationship
• The macula has more cortical representation in the striate cortex.
• Information about a central 30 degrees of vision occupies around 83% of the cortex.

What does this mean for the retinal fibres?

• Retinal fibre organization along the visual pathway impacts resulting visual field defects.
• Lesions affect visual field differently depending on their location.
• Examples of lesions and resulting visual defects in the visual field are mentioned.

Describing the Defect

• Visual field defects can be described based on their relationships to the horizontal and vertical midline.
• Common defect classifications are quadrantanopia, hemianopia, altitudinal defects, and scotomas.
• Comparison between the left and right visual fields are important for understanding the extent and location of a defect

Pre-chiasmal

• Visual problems in the pre-chiasmal segment, such as optic nerve disorders, glaucoma or trauma, lead to ipsilateral and monocular defects.
• Pupil function may be affected as part of the defect (e.g., afferent pupillary defect)

Chiasmal

• Visual problems in the chiasmal segment, like tumors at or near the crossing point, may result in binocular defects.
• Defects often involve both temporal visual fields (bitemporal hemianopsia).

Post-chiasmal

• Visual problems after the optic chiasm lead to a defect on the same side of both visual fields.
• Visual defects respect the vertical midline and are typically more congruent.
• Lesions can be stroke or tumor.

Pupilomotor fibres (mid-brain connections)

• Pupil light reflex is mediated by retinal ganglion cells projecting directly to the pretectum.
• Lesions in the optic nerve, chiasm, or tract cause loss of both visual perception and pupil light response.

Lesions along the visual pathway

• Visual pathway lesions affect visual field assessment according to their location.
• Visual deficits can be detected at any stage in the visual pathway, including prechiasmatic (before the optic chiasm), chiasmatic (at the optic chiasm), and postchiasmatic (after the optic chiasm).

Mapping the Field: Kinetic and Static Perimetry

• Kinetic perimetry maps visual field sensitivity using moving stimuli.
• Static perimetry uses stationary stimuli at various intensities to chart the visual field.

Kinetic perimetry: Types

• Bjerrum screen, Octopus 900, Goldmann bowl perimeter machines are commonly used machines (hardware) for kinetic perimetry tests with their specific uses and benefits in clinical practice.

Kinetic perimetry: Goldmann

• The Goldmann visual field test is the most common manual kinetic perimetry instrument.
• It uses calibrated stimuli on a bowl-shaped perimeter with variable intensity and size.
• Data interpretation is logarithmic and expressed as degrees or decibels.

Kinetic perimetry: Used when

• Used for suspected neurological visual field defects, especially large areas of absolute loss, and previous findings of unrepeatable tests.

Mapping the field: Kinetic perimetry

• Gross or confrontation visual fields tests are a type of kinetic perimetry test.
• This test involves comparing a patient's visual field with the examiner's own.

Static Automated perimetry

• Automated visual field testing uses programmed visual stimuli (usually light) presented at various points in the visual field.
• Results can be quantified in decibels (dB).
• Common methods include SITA.

Frequency of seeing curve

• The frequency of seeing curve plots the proportion of times a target is seen at different light intensities.
• 50% of the time is used to define a threshold.

Full threshold

• Full threshold tests (e.g., Humphrey visual field analyser) precisely measure the smallest stimulus (light) intensity to produce a successful response (detection).

Staircase method

• Staircase method is a specific technique used in threshold estimations in visual-field testing.
• It has particular properties for increasing and decreasing intensities.

Supra-threshold Test

• Supra-threshold testing evaluates a larger section of the visual field than standard threshold tests.
• By measuring the sensitivity to higher light intensities, this technique pinpoints the shape of the hill of vision.

Background learning

• The normal visual field, various instruments and strategies are detailed to provide a comprehensive background of the subject matter for study.

Factors influencing visual field measurements

• Visual field measurement is influenced by patient performance, stimulus type and the testing environment.
• Patient and testing factors are provided for the evaluation.

How bright is the light, how sensitive is the retina?

• Light intensity used in visual field testing is measured using apostilbs as the absolute units of light intensity to assess retinal sensitivity.
• Logarithmic scales (e.g., decibels with a scale of 0-40dB) are used to measure the intensity.

Mapping the field

• The shape and features of the visual field are analysed through different techniques with varying advantages and disadvantages.

Explore the key concepts of visual fields in this informative lecture by Ellie Livings. Students will learn important terminology, apply their knowledge of ocular anatomy, and interpret visual field defects. Prepare to enhance your understanding of visual fields.