Clinical Workup of the Optic Nerve

Signs & Symptoms of Optic Nerve Dysfunction

• Reduced VA: non-specific sign, VA may be normal

• Pupil dysfunction: esp in unilateral cases 

• Dyschromatopsia: mainly difficulty with red-green discrimination and acquired disease

• Diminished light brightness sensitivity: ex. reduced red saturation 

• Reduced contrast sensitivity

• VF defects: may vary depending on underlying etiology 

• Pain is NOT common with many types of optic nerve diseases, but can be a very helpful symptom when present

Diagnosis of Optic Neuropathy

Characteristic (PATTERN) combo of findings = VA loss  + color deficiency + VF defect + pupil dysfunction + (possible) abnormal ONH appearance

Workup: Key Tests

• Main testing: case history, VA, pupils, EOMs, color vision, VF, ocular health eval

• Ancillary testing: potential acuity testing, red saturation test, brightness comparison test, contrast sensitivity testing, exophthalmometry, OCT, OCT-A, FA, B-scan ultrasound, visual evoked potential (VEP)

Case History

• Most common complaint = vision loss

  • Acute/rapid: sudden, over a few hours or days 

    • Demyelinating (MS), ischemic, traumatic

  • Subacute: few days to 1-2 weeks

    • Inflammatory, infiltrative, nutritional/toxic, glaucomatous (some)

  • Gradual: over a few weeks or years

    • Hereditary, compressive, nutritional/toxic, glaucomatous

• Transient vision loss? Diplopia? Proptosis? Other? → Pulfrich phenomenon 

  • Pulfrich phenomenon = difference in quality of the 2 eyes; disorder of perception where 2D objects appear 3D

  • Due to delay in visual input of the affected eye 

  • Occurs in unilateral/asymmetric optic neuropathy 

• Aggravating factors: 

  • If transient vision loss w/ eye movement (gaze-evoked amaurosis) → suggests diseases that “deform” the optic nerve (ie. optic nerve sheath meningioma)

  • If vision worse w/ increased body temperature (Uhthoff phenomenon) → suggests demyelinating disease

  • If symptoms worsen w/ changes in posture → suggests papilledema and increased intracranial pressure 

Visual Acuity

• Non-specific for optic nerve disease

• Is the least sensitive of all function tests

Pupil Testing

• Afferent pathway = from the eye to the brain (CN II)

• Efferent pathway = from the brain to the eye (CN III and oculosympathetic pathway) 

• Optic nerve disease can result in an afferent pupil defect (APD) IF the condition is asymmetric (“relative” to each other) 

Abnormal red saturation and Brightness comparison test correlated well with the presence of an APD

Color Vision

• Non-specific for optic nerve disease

• Mismatch of good visual acuity and acquired color vision dysfunction → strongly suggestive of optic nerve dysfunction 

• Kollner’s rule: 

  • Red/Green discrimination difficulty = optic nerve disease 

    • Exceptions: glaucoma, dominant optic atrophy, chronic papilledema

  • Blue/Yellow discrimination difficulty = retinal disease 

    • Exception: cone dystrophy

Visual Field

Contrast Sensitivity Testing

• Contrast sensitivity usually reduced in optic neuropathy, even if good VA

• Charts: Pelli-Robson, low-contrast Bailey-Lovie, Vistech, MARS

• May be the most valuable in terms of long-term monitoring and in clinical trials

Optical Coherence Tomography (OCT)

• Evaluates the peripapillary RNFL and macular Ganglion Cell Layer (GCL)

• May be helpful in diagnosing early disc edema

• Useful to monitor progression 

Subretinal hyporeflective space (SHYPS) 

• Presence occurs in conditions where the optic disc is elevated

• Hyporeflective space on OCT cross-section below the photoreceptors (neurosensory retina)

• Smooth internal contour; lazy V pattern 

• Optic disc edema: smooth internal contour, “lazy V” pattern

• Optic disc drusen: lumpy-bumpy internal contour, abrupt decline in SHYPS

OCT alone CANNOT definitely differentiate optic disc edema from pseudo disc edema