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Fundoscopy (Ophthalmoscopy) - Detailed Overview

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What is Fundoscopy?

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Types of Fundoscopy

1. Direct Ophthalmoscopy

• Magnification: ×15 (significantly magnified, monocular image)
• Field of view: Small (approximately 5°)
• Stereopsis: None
• Key advantage: Portable, can be performed at the bedside

1. Dim room lights; ask patient to fixate on a distant target (minimises miosis from accommodation)
2. Examine the right eye with your right hand/right eye, standing on the patient's right. Reverse for the left eye.
3. Select 'O' on the lens dial
4. Direct the beam at the pupil and approach from the temporal side at a slight angle
5. The optic disc comes into view at approximately 3.5 cm from the eye
6. Adjust focus with the index finger rotating the lens dial:
   • Hyperopes: use plus lens (green numbers)
   • Myopes: use minus lens (red numbers)
7. Examine the disc first (clarity, colour, elevation, cup, vessels), check for spontaneous venous pulsation
8. Follow vessels into the periphery (ask patient to look up/down/sides for the periphery)
9. Locate the macula by moving the light 2 disc diameters temporally from the disc, or ask the patient to look directly at the light

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2. Slit Lamp Biomicroscopy (Indirect Ophthalmoscopy)

• Volk 60 D: ×0.88-1.0
• 90 D: ×1.3

• Slit beam adjusted to ~¼ of full diameter
• Illumination angled coaxial with the viewing system
• Lens held close to the eye with flat surface toward the patient

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3. Head-Mounted Binocular Indirect Ophthalmoscopy (BIO)

• Allows retinal visualisation through greater media opacity than slit lamp
• Readily facilitates scleral indentation
• Image is inverted and laterally reversed, viewed stereoscopically

1. Patient supine (reclining chair preferred, not sitting)
2. Pupils must be dilated
3. Set eyepieces to correct interpupillary distance
4. Examine peripheral fundus first (helps patient adapt to light)
5. Ask patient to move eyes into optimal positions to view periphery

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4. Scleral Indentation

• A cotton-tipped applicator is applied to the outside of the eyelid at the tarsal plate margin
• Indenter kept tangential to the globe at all times (perpendicular indentation causes pain and risks scleral perforation)
• For 3 and 9 o'clock positions: direct scleral indentation with topical anaesthesia

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What to Examine Systematically

1. Red reflex - absent = media opacity
2. Follow a retinal vessel centrally to locate the optic disc
3. Optic disc - assess for:
   • Oedema/papilloedema (blurred disc margins, loss of spontaneous venous pulsation)
   • Pallor (optic atrophy)
   • Cupping (glaucoma - cup:disc ratio; normal ≤0.5)
4. Peripapillary region - look for:
   • Haemorrhages
   • Cotton-wool spots (nerve fibre layer infarcts)
   • Hard exudates
   • Retinal folds
5. Retinal vasculature - arteries and veins from the disc
6. Macula - temporal to the optic disc, the area of finest central vision

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Key Normal Fundus Landmarks

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Common Abnormal Fundoscopic Findings

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Dilation for Fundoscopy

• Preferred when possible - gives a much better view
• Can be done without dilation in a darkened room with patient fixating a distant target
• Mydriatics used: Tropicamide 1% (short-acting), Cyclopentolate 1%
• Contraindications to dilation: Suspected narrow-angle glaucoma, head injury monitoring (obscures pupillary response), certain corneal/anterior segment pathology
• In patients with normal anterior chamber anatomy, risk of precipitating angle-closure glaucoma is minimal

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Fundoscopy in Systemic Disease - At a Glance

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Visual Acuity - Detailed Overview

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Definition and Physiology

• A focused point of light on the retina has a minimum diameter of ~11 micrometres (due to optical imperfections)
• Foveal cone diameter: ~1.5 µm
• Two points can be distinguished when their centres are ≥2 µm apart on the retina
• Normal visual acuity = 25 seconds of arc (the minimum angle between two distinguishable points)
• At 10 metres: two points must be 1.5-2 mm apart to be seen as separate
• VA is maximum at the fovea (<0.5 mm / <500 µm diameter = <2° of visual field)
• VA falls >10-fold toward the retinal periphery due to convergence of multiple rods/cones onto single optic nerve fibres

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Distance Visual Acuity

1. Snellen Chart

• Testing distance: 6 metres (or with a mirror)
• Worse eye tested first, other eye occluded
• Patient uses own glasses or contact lenses (corrected VA)
• Normal corrected VA in young adults is often better than 6/6

• More letters on lower lines creates unbalanced "crowding" effect
• Fewer larger letters reduce accuracy at lower VA levels
• Variable readability between individual letters
• Lines not balanced for consistency
• Letter/row spacing is not systematic
• Lower accuracy and consistency - unsuitable for research

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2. LogMAR Visual Acuity

• If a 6/6 letter subtends 5' of arc, each limb has an angular width of 1' → MAR = 1'
• 6/12 line: MAR = 2'; 6/60 line: MAR = 10'
• LogMAR score = log₁₀(MAR)

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3. LogMAR Chart Types

• Used at 6 m
• 5 letters per line, spacing proportional to letter size
• 6/6 letter = 5' height × 4' width
• Letter and row spacing based on letter dimensions

• Calibrated for 4 m
• Uses Sloan optotypes - equiluminous, equal legibility between letters and rows
• Square letters based on a 5×4 grid
• Standard in diabetic retinopathy and clinical trials

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Special VA Tests

Pinhole (PH) Visual Acuity

• If VA < 6/6, repeat with pinhole
• PH VA improves → reduced VA is due to refractive error (correctable)
• PH VA does not improve (or worsens) → reduced VA is due to pathology (macular disease, posterior lens opacity, amblyopia)

Note: In patients with macular disease and posterior lens opacities, pinhole acuity may be worse than with spectacle correction.

Best-Corrected Visual Acuity (BCVA)

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Very Poor Visual Acuity - Grading Scale

Localising the direction of light in PL vision indicates the cause is a media opacity (e.g. dense cataract) rather than retinal/optic nerve disease.

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Near Visual Acuity

• Patient wears distance correction + presbyopia correction (reading glasses)
• Tested each eye separately, then both together
• Near vision is a sensitive indicator of macular disease (particularly useful for monitoring AMD, diabetic maculopathy)

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Contrast Sensitivity

• Standard VA charts use high-contrast optotypes; contrast sensitivity tests low-contrast function
• Conditions where contrast sensitivity is reduced with normal VA: amblyopia, optic neuropathy, certain cataracts, higher-order aberrations
• Useful when patients report visual symptoms (especially in dim light) but have good Snellen VA

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Amsler Grid - Macular Function Test

• AMD monitoring (especially for macular neovascularisation / MNV)
• Macular oedema, central serous retinopathy
• Central visual field defects of any origin

• Pupils NOT dilated (to avoid photostress effect)
• Do not examine on slit lamp beforehand
• Wear presbyopic correction if needed
• Chart well illuminated at ~33 cm
• Cover one eye
• Fix on the central dot
• Report any distortion (metamorphopsia), waviness, blank areas, or missing squares

• Metamorphopsia (wavy/distorted lines) - macular disease
• Scotoma (blank area) - any cause
• Patients with macular disease often see the central dot only, with surrounding grid area missing

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Photostress Test

1. Record BCVA first
2. Patient fixates on a pen torch held ~3 cm from the eye for ~10 seconds
3. Photostress Recovery Time (PSRT) = time to re-read any 3 letters of the pre-test acuity line

• Prolonged PSRT = macular disease (slow visual pigment regeneration)
• Normal PSRT = optic nerve lesion (photoreceptors intact)

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Light Brightness Comparison Test

1. Shine indirect ophthalmoscope light into the normal eye, then the diseased eye
2. Ask if brightness is symmetric
3. Patient rates the diseased eye on a 1-5 scale relative to the normal eye

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Summary: VA Measurement Hierarchy

Distance VA (Snellen or LogMAR)
    ↓ If < 6/6
    Pinhole VA
        ↓ Improves → refractive error
        ↓ Doesn't improve → pathology
Near VA
    ↓ Sensitive for macular disease
Contrast Sensitivity
    ↓ Reduced with normal VA → amblyopia / optic neuropathy
Amsler Grid
    ↓ Metamorphopsia / scotoma → macular disease
Very poor VA scale: CF → HM → PL → NPL

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