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macular function tests ophthalmology PG exam short note

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https://www.ncbi.nlm.nih.gov/books/NBK587444

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Amsler grid macular degeneration test

This four-panel image series illustrates the clinical and diagnostic findings of focal choroidal elevation (FCE) in a patient with atrophic age-related macular degeneration (ARMD). Panel (a) shows an Amsler grid with patient-drawn wavy, irregular lines (metamorphopsia) in the superior-nasal quadrant relative to the central fixation point. Panel (b) presents fundus autofluorescence (FAF) of the right eye, highlighting a pinpoint area of relative hypoautofluorescence (white arrowhead). Panel (c) is a scanning laser ophthalmoscopic (SLO) image with a green arrow indicating the scan location for the subsequent Spectral Domain Optical Coherence Tomography (SD-OCT). Panel (d) displays the SD-OCT cross-section, revealing a focal choroidal elevation (white arrow) characterized by a localized upward protrusion of the choroid. Overlying this elevation, a white arrowhead identifies a subtle disruption of the ellipsoid zone (IS/OS line), which corresponds to the area of metamorphopsia reported on the Amsler grid. The sequence demonstrates the anatomical correlation between deep choroidal structural changes and functional visual distortion in ARMD.

This four-panel image series illustrates the clinical and diagnostic findings of focal choroidal elevation (FCE) in a patient with atrophic age-related macular degeneration (ARMD). Panel (a) shows an Amsler grid with patient-drawn wavy, irregular lines (metamorphopsia) in the superior-nasal quadrant relative to the central fixation point. Panel (b) presents fundus autofluorescence (FAF) of the right eye, highlighting a pinpoint area of relative hypoautofluorescence (white arrowhead). Panel (c) is a scanning laser ophthalmoscopic (SLO) image with a green arrow indicating the scan location for the subsequent Spectral Domain Optical Coherence Tomography (SD-OCT). Panel (d) displays the SD-OCT cross-section, revealing a focal choroidal elevation (white arrow) characterized by a localized upward protrusion of the choroid. Overlying this elevation, a white arrowhead identifies a subtle disruption of the ellipsoid zone (IS/OS line), which corresponds to the area of metamorphopsia reported on the Amsler grid. The sequence demonstrates the anatomical correlation between deep choroidal structural changes and functional visual distortion in ARMD.

TABLE 6 TREATMENT RECOMMENDATIONS AND FOLLOW-UP FOR AGE-RELATED MACULAR DEGENERATION <table><thead><tr><th>Recommended Treatment</th><th>Diagnoses Eligible for Treatment</th><th>Follow-up Recommendations</th></tr></thead><tbody><tr><td></td><td></td><td>• Patients without subfoveal atrophy should be monitored for monocular near vision (reading/Amsler grid).</td></tr><tr><td>Antioxidant vitamin and mineral supplements as recommended in the original AREDS and AREDS2 reports<sup>5, 63</sup></td><td>• Intermediate AMD (AREDS category 3)<br>• Advanced AMD in one eye (AREDS category 4)</td><td>Return examination at 6–18 months if asymptomatic or prompt examination for new symptoms suggestive of CNV<br><br>• Monitoring of monocular near vision (reading/Amsler grid)<br>• Fundus photography and/or fundus autofluorescence as appropriate<br>• Fluorescein angiography and/or OCT for suspicion of CNV</td></tr></tbody></table>

TABLE 6 TREATMENT RECOMMENDATIONS AND FOLLOW-UP FOR AGE-RELATED MACULAR DEGENERATION <table><thead><tr><th>Recommended Treatment</th><th>Diagnoses Eligible for Treatment</th><th>Follow-up Recommendations</th></tr></thead><tbody><tr><td></td><td></td><td>• Patients without subfoveal atrophy should be monitored for monocular near vision (reading/Amsler grid).</td></tr><tr><td>Antioxidant vitamin and mineral supplements as recommended in the original AREDS and AREDS2 reports<sup>5, 63</sup></td><td>• Intermediate AMD (AREDS category 3)<br>• Advanced AMD in one eye (AREDS category 4)</td><td>Return examination at 6–18 months if asymptomatic or prompt examination for new symptoms suggestive of CNV<br><br>• Monitoring of monocular near vision (reading/Amsler grid)<br>• Fundus photography and/or fundus autofluorescence as appropriate<br>• Fluorescein angiography and/or OCT for suspicion of CNV</td></tr></tbody></table>

This diagnostic image displays two comparative grayscale fundus photographs (A and B) overlaid with microperimetry stimulus grids, used to assess macular functional sensitivity. Panel A illustrates a custom stimulus grid consisting of 33 test points arranged in a radial pattern at eccentricities of 0°, 1°, 3°, 5°, and 7° from the foveal fixation point. The points are color-coded (yellow, orange, green) to represent threshold sensitivity values in decibels (dB), superimposed on a macular region showing subtle pigmentary changes and central drusen characteristic of intermediate age-related macular degeneration (iAMD). Panel B shows a higher-density normative database grid (MAIA) with 61 points located at 0°, 1°, 2°, 3°, 4°, and 5° from fixation. In this panel, the points are uniform in color (green) and labeled with numerical sensitivity values. Both grids are centered on the macula, demonstrating the spatial distribution of functional testing relative to retinal vascular landmarks. These visuals serve as educational tools for understanding retinal sensitivity mapping in macular pathology and comparing different perimetric protocols.

This diagnostic image displays two comparative grayscale fundus photographs (A and B) overlaid with microperimetry stimulus grids, used to assess macular functional sensitivity. Panel A illustrates a custom stimulus grid consisting of 33 test points arranged in a radial pattern at eccentricities of 0°, 1°, 3°, 5°, and 7° from the foveal fixation point. The points are color-coded (yellow, orange, green) to represent threshold sensitivity values in decibels (dB), superimposed on a macular region showing subtle pigmentary changes and central drusen characteristic of intermediate age-related macular degeneration (iAMD). Panel B shows a higher-density normative database grid (MAIA) with 61 points located at 0°, 1°, 2°, 3°, 4°, and 5° from fixation. In this panel, the points are uniform in color (green) and labeled with numerical sensitivity values. Both grids are centered on the macula, demonstrating the spatial distribution of functional testing relative to retinal vascular landmarks. These visuals serve as educational tools for understanding retinal sensitivity mapping in macular pathology and comparing different perimetric protocols.

I now have excellent content from Kanski's Clinical Ophthalmology and StatPearls. Let me compile the comprehensive short note.

Macular Function Tests

Introduction

The macula lutea is a 5.5 mm circular area at the posterior pole, lying temporal to the optic disc, subserving the central 15-20 degrees of the visual field. It is the primary area for photopic (daylight) vision and color vision. Macular function tests assess the integrity of this region, particularly to:
  • Detect early or subtle maculopathy
  • Differentiate macular disease from optic nerve disease
  • Predict post-operative visual prognosis (e.g., before cataract surgery)
  • Monitor known macular disease

Classification

Macular function tests are broadly divided into:
A. Subjective Tests
  1. Visual Acuity
  2. Amsler Grid
  3. Photostress Test (Macular Dazzle Test)
  4. Color Vision Tests
  5. Contrast Sensitivity
  6. Entoptic Phenomenon tests
  7. Maddox Rod Test
  8. 2-Point Discrimination Test
  9. Potential Acuity Meter (PAM)
B. Objective Tests
  1. Laser Interferometry
  2. Electroretinogram (ERG) - Pattern ERG (PERG)
  3. Visual Evoked Potential (VEP)
  4. Fluorescein Angiography (FFA)
  5. Optical Coherence Tomography (OCT)
  6. Microperimetry

Detailed Tests

1. Visual Acuity

The simplest and most basic test of macular function. Central visual acuity reflects foveal cone function. Tests include:
  • Distance VA (Snellen chart)
  • Near VA (Jaeger's chart)
  • Color vision
  • Contrast sensitivity

2. Amsler Grid

Amsler grid superimposed on the macula
The Amsler grid, as shown superimposed on the macula, evaluates the central 20 degrees of the visual field - Kanski's Clinical Ophthalmology
Principle: A 10 cm square grid held at 33 cm, each small square subtending 1 degree. Tests the central 20° of the visual field.
Technique:
  • Pupils should NOT be dilated (to avoid photostress effect)
  • Tested before slit-lamp examination
  • Presbyopic correction should be worn
  • Each eye tested separately
Seven Charts Available:
ChartDesignUse
1White grid on black backgroundStandard macular screening
2Grid + diagonal linesCentral scotoma (aids fixation)
3Red squares on blackToxic maculopathy, optic neuropathy, chiasmal lesions
4Random dotsDifferentiates scotoma from metamorphopsia
5Horizontal linesMetamorphopsia, reading difficulty
6White background, closer linesDetailed metamorphopsia evaluation
7Fine central grid (0.5° squares)More sensitive detection
Abnormal findings: Metamorphopsia (distorted lines), scotoma (missing areas), micropsia/macropsia
Uses: Screening for macular neovascularization (MNV), age-related macular degeneration monitoring, home monitoring by patients

3. Photostress Test (Macular Dazzle Test)

Principle: Visual pigments (particularly in the RPE) are bleached by intense light. The time taken for photoreceptors to re-synthesize visual pigment and recover vision is measured. Recovery depends on RPE-photoreceptor function.
Technique:
  • Best-corrected distance VA is first measured
  • A pen torch or indirect ophthalmoscope light is held ~3 cm from the eye for ~10 seconds
  • The Photostress Recovery Time (PSRT) = time taken to read 3 letters of the pre-test acuity line
  • Normal PSRT: 15-30 seconds
  • The fellow (normal) eye is tested for comparison
Interpretation:
  • Macular disease: PSRT is prolonged (>50 seconds) in the affected eye
  • Optic neuropathy: PSRT is normal (photoreceptors are intact)
  • If PSRT of worse eye = better eye, macular disease is NOT the cause - suggests optic nerve disorder
Clinical value: Differentiates macular disease from optic neuropathy - key exam point - Kanski's Clinical Ophthalmology

4. Color Vision Testing

Used to evaluate both macular and optic nerve disease. Tests include:
  • Ishihara's pseudo-isochromatic plates - screening for red-green defects (X-linked, congenital)
  • Farnsworth-Munsell 100 Hue Test - detailed, classifies color defect axis
  • Farnsworth D-15 Panel - quick screening
  • City University Color Vision Test
Key point: Red-green defects are common in optic nerve disease; blue-yellow (tritan) defects are more characteristic of macular disease and glaucoma.

5. Contrast Sensitivity

Principle: Measures the ability to distinguish objects from their background. More sensitive than Snellen acuity for detecting early macular dysfunction.
  • Snellen acuity tests only high-contrast targets
  • Macular disease causes marked impairment for intermediate and higher spatial frequencies
  • Measured using: Pelli-Robson chart, Vistech gratings, Cambridge Low Contrast Gratings
Spatial frequency: Number of dark-light cycles per degree of visual angle. Macular disease selectively impairs mid-to-high spatial frequencies.

6. Entoptic Phenomenon Tests

Based on the patient perceiving features arising from within their own eye.
a) Purkinje Vascular Entoptic Phenomenon (Purkinje tree test):
  • Transilluminate the sclera with a bright light in a dark room; move the light rapidly
  • Patient perceives shadows of the retinal blood vessels (branching tree pattern)
  • Normal macular function = patient perceives the vascular shadow
  • Poor macular function = unable to perceive vasculature
b) Blue Field Entoptic Phenomenon:
  • View a uniform blue light source - patient sees "corpuscles" (white blood cells) moving in perifoveal capillaries
  • Normal: >15 corpuscles seen
  • Abnormal: Partial/complete loss or slowing of corpuscle movement = poor retinal function

7. Maddox Rod Test (2-Point Discrimination)

  • Two small lights are presented close together
  • Normal: Patient perceives 2 separate lights
  • Abnormal: Sees only one light (macular dysfunction)
  • The Maddox rod is a series of parallel cylinders that converts a point of white light into a red line; useful in assessing macular integrity

8. Potential Acuity Meter (PAM)

Principle: Projects a Snellen chart directly onto the retina using a small beam that bypasses media opacities (cataract, corneal opacity).
Use: Predicts potential visual acuity after cataract surgery
Result interpretation: The smallest line where the patient reads 3+ characters is recorded as potential acuity.
Limitation: May overestimate acuity; sensitive to nystagmus and dense cataracts.

9. Laser Interferometry

  • Uses a laser to create interference fringes on the retina, bypassing media opacities
  • Measures retinal resolution ability (spatial frequency)
  • Less affected by refractive errors and cataracts than other tests
  • Expressed as cycles/degree
  • Used to predict post-cataract visual potential

10. Objective Tests

TestWhat it measuresKey notes
Pattern ERG (PERG)Foveal/macular ganglion cell functionReduced in macular disease and glaucoma
Flash ERGGlobal rod and cone functionScotopic ERG: rods; Photopic: cones
Visual Evoked Potential (VEP)Cortical response; neural integrityAffected in optic nerve and cortical disease
MicroperimetryRetinal sensitivity mapped to fundus imageCorrelates structure (OCT) with function
OCTStructural imaging of retinal layersGold standard for macular anatomy
Fluorescein Angiography (FFA)Vascular integrity, leakage, ischemiaIdentifies neovascularization, RPE disease

Exam High-Yield Points

  1. Photostress test differentiates macular from optic nerve disease - prolonged PSRT (>50 s) = macular disease; normal PSRT = optic neuropathy
  2. Normal PSRT = 15-30 seconds (Kanski)
  3. Amsler grid covers central 20 degrees held at 33 cm; Chart 1 is standard, Chart 2 for central scotoma
  4. PAM and Laser interferometry predict visual prognosis before cataract surgery
  5. Entoptic phenomenon - perceiving retinal vessels = normal macula; blue field entoptic: >15 corpuscles = normal
  6. Color vision: tritan (blue-yellow) defects = macular/glaucoma; red-green = optic nerve/congenital
  7. Contrast sensitivity is more sensitive than Snellen for early maculopathy
  8. PERG is the electrophysiological test specifically for macular/foveal function
  9. Amsler grid should be tested before slit-lamp exam and with pupils undilated
Sources: Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed.; StatPearls - Tests for Potential Vision (NCBI)
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