11.4 Kinetic Perimetry (Goldmann Perimetry) & Neurological Visual Pathway Defect Localization

Kinetic Perimetry & Neurological Visual Pathway Defect Localization

Core Clinical Mandate: While automated static perimetry excels at quantifying focal threshold depression in the central 24° to 30°, manual kinetic perimetry—epitomized by the Goldmann perimeter—remains indispensable for mapping the peripheral visual limits (up to 90°), plotting deep neurological hemianopic steps, assessing pediatric or cognitively impaired patients, and satisfying legal and occupational driving requirements. Furthermore, mastery of visual pathway neuroanatomy allows the COMT to pinpoint intracranial lesions along the optic nerve, chiasm, tract, optic radiations, and occipital striate cortex with extraordinary precision.

Principles & Technique of Goldmann Kinetic Perimetry

Kinetic perimetry is based on Sir Arthur Traquair's conceptualization of the visual field as an "island of vision in a sea of blindness":

• The foveal center represents the mountain peak of maximum visual sensitivity.
• Sensitivity slopes steeply downward nasally and temporally toward the shoreline (the peripheral boundary of vision).
• Isopters: An isopter is a contour line connecting all retinal locations that possess the exact same differential light sensitivity threshold. In kinetic perimetry, a stimulus of fixed size and luminance is moved along designated meridians from a non-seeing area toward a seeing area to establish isopter boundaries.

1. Goldmann Bowl Standardization

• Bowl Curvature Radius: Standardized at 30 cm, identical to the HFA.
• Background Illumination: Calibrated to 31.5 apostilbs (10 cd/m²), verified prior to each testing session using the internal photometer screen and calibration lever.

2. Stimulus Target Notation: Size, Coarse & Fine Filters

Every Goldmann kinetic target is designated by a three-character alphanumeric code (e.g., I4e, I2e, V4e):

Goldmann Target Hierarchy:
       [ Roman Numeral ] ──> Stimulus Area / Size (0 to V)
       [ Arabic Numeral ] ──> Coarse Intensity Filter (1 to 4; 0.5 log unit steps)
       [ Lowercase Letter ] ──> Fine Intensity Filter (a to e; 0.1 log unit steps)

1. Size / Area: Roman Numerals (0 through V)

• Each sequential Roman numeral represents a four-fold ($4\times$) increase in target surface area (a 0.6 log unit step):
  • Size 0: $0.0625\text{ mm}^2$
  • Size I: $0.25\text{ mm}^2$
  • Size II: $1.00\text{ mm}^2$
  • Size III: $4.00\text{ mm}^2$
  • Size IV: $16.00\text{ mm}^2$
  • Size V: $64.00\text{ mm}^2$

2. Coarse Luminance Attenuation: Arabic Numerals (1 through 4)

• The coarse filter incorporates neutral density filters that attenuate light transmission in 0.5 log unit (5 dB) increments:
  • Filter 4: $100%$ transmission ($0.0\text{ log units}$ attenuation; unattenuated maximum output = 1,000 asb / 143 cd/m²)
  • Filter 3: $31.5%$ transmission ($-0.5\text{ log units}$ attenuation)
  • Filter 2: $10.0%$ transmission ($-1.0\text{ log units}$ attenuation)
  • Filter 1: $3.15%$ transmission ($-1.5\text{ log units}$ attenuation)

3. Fine Luminance Attenuation: Lowercase Letters (a through e)

• The fine filter provides fine-tuning in 0.1 log unit (1 dB) increments:
  • e: $100%$ transmission ($0.0\text{ log units}$ attenuation)
  • d: $79%$ transmission ($-0.1\text{ log units}$ attenuation)
  • c: $63%$ transmission ($-0.2\text{ log units}$ attenuation)
  • b: $50%$ transmission ($-0.3\text{ log units}$ attenuation)
  • a: $40%$ transmission ($-0.4\text{ log units}$ attenuation)

The Principle of Photometric Equivalence: A four-fold increase in target area ($4\times$) provides the same spatial summation energy as a $0.6\text{ log unit}$ increase in luminance. Thus, target I4e is photometrically equivalent to II3e!

Standard Kinetic Perimetry Protocol & Examination Rules

To map an accurate visual field on a Goldmann perimeter, the technologist must execute rigorous kinetic testing protocols:

1. Standard Diagnostic Isopter Selection

• I4e: Maps the outermost peripheral boundaries of vision (normal limits: 60° superior, 60° nasal, 70° inferior, 90°–100° temporal).
• I2e (or I3e): Maps intermediate peripheral sensitivity (typically at 30° to 45°).
• I1e: Maps the steep central slope within 15° to 20° of fixation.
• V4e: The maximum possible target size and intensity. Used to plot remaining visual fields in low-vision patients, outline absolute neurological scotomas, and document peripheral boundaries for disability determinations.

2. Examination Rules for Target Movement

1. Movement Speed: The target must be moved at a continuous, steady speed of 3° to 5° per second. Moving the target too rapidly causes an artificially contracted isopter because of patient reaction time; moving it too slowly causes patient fatigue and visual fading (Troxler effect).
2. Direction of Presentation: The stimulus must always be presented from an area of non-seeing (darkness) toward an area of seeing. For peripheral isopters, move from the far periphery inward toward fixation.
3. Perpendicular Boundary Crossing: Stimuli must cross anticipated isopter boundaries perpendicularly (at a 90° angle). When mapping a neurological vertical step across the 12 o'clock or 6 o'clock meridian, the target must be moved horizontally across the vertical midline, not diagonally!
4. Meridian Spacing: Vectors should be presented every 15° (24 meridians across 360°).
5. Mapping Scotomas: When mapping the physiological blind spot or an interior scotoma, the target must be introduced from inside the non-seeing core moving radially outward in all directions until the patient signals perception.
6. Refractive Correction: Distance correction must be placed in the trial lens holder when testing the central 30°; the lens must be removed when testing beyond 30° to prevent trial lens rim cutoff!

Retinotopic Organization & the Rule of Congruity

Precise neuro-ophthalmic localization rests upon the fundamental architectural laws governing the visual pathway from the retina to the calcarine cortex:

Retinal Decussation Rules:
├── Nasal Retinal Fibers (~53%): Cross (decussate) at the optic chiasm ──> Carry TEMPORAL visual field
└── Temporal Retinal Fibers (~47%): Remain UNCROSSED ──> Carry NASAL visual field

The Rule of Congruity

• Congruity Defined: The degree of morphological symmetry and geometric similarity between the visual field defects of the two eyes.
• The Anatomical Axiom: Axons originating from corresponding retinal points in each eye do not travel in close physical proximity in the anterior visual pathway. As the visual pathways travel posteriorly toward the occipital lobe, fibers from homonymous retinal points become progressively more tightly bound and organized.
• Clinical Law:
  • Lesions of the anterior optic tract produce markedly incongruous (asymmetrical) homonymous defects.
  • Lesions of the optic radiations produce moderately congruous homonymous defects.
  • Lesions of the occipital striate cortex produce exquisitely and highly congruous (identical) homonymous hemianopias.

Systematic Neuro-Ophthalmic Lesion Localization

1. Pre-Chiasmal Lesions (The Optic Nerve)

• Diagnostic Hallmark: Defect is strictly monocular (isolated to one eye). The fellow eye demonstrates a pristine, normal visual field.
• Central Scotoma: Dense loss involving the fovea, preserving peripheral borders. Characteristic of demyelinating optic neuritis, compressive meningiomas, or toxic-nutritional optic neuropathy.
• Cecocentral Scotoma: An elongated defect extending from the fovea to engulf the physiological blind spot. Classical for Leber hereditary optic neuropathy (LHON), ethambutol toxicity, and vitamin B12 / folate deficiency.
• Altitudinal Defect: Dense loss respecting the horizontal meridian across the upper or lower hemifield. Pathognomonic for ischemic optic neuropathy (NAION or arteritic giant cell arteritis) due to infarction of superior or inferior medial/lateral posterior ciliary arteries.
• Junctional Scotoma of von Willebrand:
  • Anatomy: Occurs at the junction where the optic nerve meets the optic chiasm.
  • The Anterior Knee of Wilbrand: Inferonasal axons from the contralateral eye cross in the chiasm but loop forward 1 to 2 mm into the terminal portion of the ipsilateral optic nerve before turning backward into the optic tract.
  • Visual Field Defect: Compression at this junction (e.g., tuberculum sellae or clinoidal meningioma) destroys the ipsilateral optic nerve fibers (producing an ipsilateral central scotoma) AND simultaneously compresses the looped inferonasal fibers of the other eye (producing a contralateral superotemporal visual field deficit).

2. Chiasmal Lesions (The Optic Chiasm)

• Diagnostic Hallmark: Bitemporal hemianopia respecting the vertical meridian.
• Pituitary Macroadenoma: Originates within the sella turcica beneath the chiasm. Expands upward to compress the inferior crossing nasal fibers first $\rightarrow$ produces an asymmetric superior bitemporal quadrantanopia, eventually progressing to complete bitemporal hemianopia.
• Craniopharyngioma / Suprasellar Meningioma: Arises above or behind the sella turcica, compressing the chiasm from above and behind $\rightarrow$ compresses superior crossing fibers first, producing an inferior bitemporal quadrantanopia.

Retrochiasmal Lesions: Tract, Radiations & Occipital Cortex

All retrochiasmal lesions produce homonymous visual field defects (affecting the same side of the visual field in both eyes) that strictly respect the vertical meridian.

1. Optic Tract Lesions

• Incongruous Homonymous Hemianopia: Defects in the two eyes are markedly asymmetric in shape and depth.
• Associated Neuro-Ophthalmic Signs:
  • Contralateral Relative Afferent Pupillary Defect (Wernicke's Pupil): Because the optic tract carries pupillomotor fibers prior to their exit via the brachium of the superior colliculus, and because the nasal retina provides more afferent light input than the temporal retina (53% vs 47%), tract lesions cause a contralateral RAPD in the eye with temporal field loss!
  • Band ('Bowtie') Optic Atrophy: Occurs in the contralateral eye, while the ipsilateral eye displays temporal/nasal disc pallor.

2. Optic Radiations: Temporal vs. Parietal Loops

The optic radiations diverge into two distinct anatomical pathways traversing the deep cerebral white matter:

| Feature | Temporal Lobe Radiation (Meyer's Loop) | Parietal Lobe Radiation (Baum's Loop) | | :--- | :--- | :--- | | | Anatomical Course | Sweeps anteriorly around the temporal horn of the lateral ventricle | Courses directly posterior through the deep parietal white matter | | Retinal Fibers Carried | Inferior retinal fibers (representing superior visual space) | Superior retinal fibers (representing inferior visual space) | | Visual Field Defect | Superior Homonymous Quadrantanopia ('Pie-in-the-Sky') | Inferior Homonymous Quadrantanopia ('Pie-on-the-Floor') | | Congruity | Moderately congruous | Moderately congruous | | Associated Neurologic Deficits | Receptive aphasia (Wernicke), seizures, uncinate fits (olfactory hallucinations) | Hemispatial neglect, Gerstmann syndrome (acalculia, agraphia), asymmetric Optokinetic Nystagmus (OKN) |

3. Occipital Striate Cortex (Area 17 / Calcarine Cortex)

Occipital lobe lesions represent the terminal projection of the visual pathway and exhibit unique perimetric features:

• Exquisite Congruity: The defects in the two eyes are identical mirror images.
• Macular Sparing:
  • Phenomenon: The homonymous hemianopia encompasses the peripheral field but leaves 5° to 10° of central foveal vision completely intact around fixation.
  • Anatomical Mechanism: The occipital pole (which subserves central macular vision) possesses a dual, collateral blood supply from both the Posterior Cerebral Artery (PCA) and the terminal branches of the Middle Cerebral Artery (MCA). Embolic or thrombotic occlusion of the PCA infarcts the anterior striate cortex while MCA collateral flow keeps the occipital pole viable.
• Macular Splitting: True bisection of the fovea (0° sparing), seen in traumatic occipital injury, surgical resection, or combined PCA/MCA hypoperfusion.
• Temporal Crescent Sparing: The anterior-most lip of the calcarine cortex represents the monocular temporal visual field (from 60° to 100° eccentricity). This far anterior zone receives dedicated blood supply from the anterior calcarine artery (an early branch of the PCA), sparing the far temporal crescent even during terminal PCA trunk infarctions.