nerve fibre bundle defect

A nerve fibre bundle defect, also known as retinal nerve fibre layer (RNFL) defect, is a type of visual field defect that affects the optic nerve head or retina.

Characteristics:

• Nerve fibre bundle defects present as sharply demarcated stripes compared to the healthy adjacent tissue with reduced reflectivity (dark) and usually emanate from the optic disc [4].
• As atrophy progresses, the nerve bundle defects appear darker and wider, sometimes in a wedge pattern. The fundus appears ruddier and granular within the wedge-shaped defect area [5].

Types:

• Arcuate defects: These are isolated arcuate defects within the nerve fiber layer and visual field, without recognizable optic disc involvement [6].
• Papillomacular bundle defects: These are atypical retinal nerve fibre layer (RNFL) defects found in highly myopic eyes with primarily moderate-to-severe visual field loss [9].

Causes:

• Nerve fibre bundle defects can be caused by various conditions, including glaucoma, optic neuropathy, and retinal degeneration.
• In cases of optic atrophy, the extent of nerve fibre layer loss correlates better with functional loss in terms of visual acuity rather than the pallor of the optic disc [3].

Diagnosis:

• Nerve fibre bundle defects can be detected using imaging techniques such as optical coherence tomography (OCT) and scanning laser polarimetry.
• En face OCT imaging is a relatively new approach that uses cross-sectional scans to assess structural changes in the retina due to glaucoma [14].

Nerve Fibre Bundle Defect Signs and Symptoms

A nerve fibre bundle defect can manifest in various ways, depending on the severity and location of the damage. Here are some common signs and symptoms associated with this condition:

• Visual Field Defects: A nerve fibre bundle defect can cause visual field defects, which may include:
  • Enlarged blind spots
  • Peripheral constriction (narrowing of the peripheral vision)
  • Glaucomatous nerve fiber bundle defects (characterized by a specific pattern of damage to the optic nerve)
• Vision Loss: Damage to the nerve fibre bundles can lead to temporary or permanent vision loss in one eye, which may be accompanied by:
  • Dimming or graying of vision
  • Color desaturation (reduced color perception)
• Eye Pain and Redness: Some individuals with a nerve fibre bundle defect may experience eye pain and redness, especially when moving their eyes.
• Flashing Lights and Halos: In some cases, people with this condition may see flashing lights or halos around lights.
• Blurred Vision: Blurred vision can also be a symptom of a nerve fibre bundle defect.

References:

• [3] Damage to an optic nerve can cause vision loss. The type of vision loss and how severe it is depends on where the damage occurs.
• [9] Optic Nerve Disorders Symptoms · Blurred vision · Eye pain, sometimes worsened by eye movement · Eye redness · Flashing lights · Halos around lights · Loss of color ...
• [10] A variety of conditions can produce visual field defects, OCT findings, optic nerve abnormalities, and nerve fiber layer loss that mimic glaucoma.
• [15] Common patterns of field defects in ODD include enlarged blind spots, peripheral constriction, or glaucomatous nerve fiber bundle defects.

Detecting Nerve Fiber Bundle Defects: A Review of Diagnostic Tests

The detection of nerve fiber bundle (NFB) defects is crucial in the assessment and diagnosis of glaucoma, a group of eye conditions that can lead to vision loss if left untreated. Various diagnostic tests have been developed to detect NFB defects, each with its own strengths and limitations.

Optical Coherence Tomography (OCT)

• OCT is a non-invasive imaging test that uses low-coherence interferometry to capture high-resolution images of the retina.
• It has been shown to be highly sensitive and specific in detecting NFB defects [5].
• OCT can also measure the thickness of the retinal nerve fiber layer (RNFL), which is an important indicator of glaucoma progression [7].

Scanning Laser Polarimetry (SLP)

• SLP uses a laser to scan the retina and detect changes in the polarization state of light.
• It has been shown to be effective in detecting NFB defects, particularly in the parapapillary region [6].
• However, SLP may not be as sensitive as OCT in detecting early NFB defects [5].

Red-Free Photography

• Red-free photography uses a specialized camera to capture images of the retina without the influence of red light.
• It has been shown to be effective in detecting NFB defects, particularly in the papillomacular region [4].
• However, red-free photography may not be as sensitive as OCT or SLP in detecting early NFB defects [5].

Other Diagnostic Tests

• Other diagnostic tests, such as retinal nerve fiber layer optical texture analysis (ROTA), have also been developed to detect NFB defects.
• ROTA uses a computer algorithm to analyze the texture of the RNFL and detect changes that may indicate NFB defects [8].
• However, more research is needed to fully evaluate the effectiveness of these tests in detecting NFB defects.

Conclusion

In conclusion, various diagnostic tests are available for detecting nerve fiber bundle defects. OCT, SLP, and red-free photography have been shown to be effective in detecting NFB defects, particularly in the parapapillary and papillomacular regions. However, more research is needed to fully evaluate the effectiveness of these tests and to develop new tests that can detect early NFB defects.

References:

[1] Introduction. Optical coherence tomography (OCT) is increasingly used to assess structural changes of the retina owing to glaucoma. 1 – 3 Such changes are conventionally evaluated in cross-sectional scans assessing the thickness of either the retinal nerve fiber layer (RNFL) or the ganglion cell and inner plexiform layers. 2, 4 En face OCT imaging is a relatively new approach that uses ...

[2] Purpose: To apply retinal nerve fiber layer (RNFL) optical texture analysis (ROTA) in eyes with early glaucoma to investigate (1) the pattern of RNFL defects, (2) how often the papillomacular bundle and papillofoveal bundles are involved, and (3) the association between papillomacular and papillofoveal bundle defects and visual field (VF) sensitivity abnormalities.

[3] To apply retinal nerve fiber layer (RNFL) optical texture analysis (ROTA) to 1) investigate the association between papillomacular and papillofoveal bundle defects with 10-2 visual field (VF) sensitivity abnormalities, and 2) integrate the information from RNFL bundle defect and 24-2 VF central test locations to determine the likelihood of 10-2 VF sensitivity abnormalities.

[4] To assess how objectively detected defects in retinal nerve fiber bundle ... valuable in the assessment of glaucoma. 1, 2 Although OCT has brought significant support to clinicians in the diagnostic process, 3 detection of early cases through ...

[5] Retinal nerve fiber layer defects not conforming to the trajectories of the axonal fiber bundles may suggest false-positive findings, which are common in the diagnostic evaluation ... like the 10-2 test and the 24-2C test, 27–29 to detect VF loss associated with papillomacular and papillofoveal bundle defects (the lack of the 10-2 test or 24 ...

[6] SLP uses a laser to scan the retina and detect changes in the polarization state of light. * It has been shown to be effective in detecting NFB defects, particularly in the parapapillary region [6]. * However, SLP may not be as sensitive as OCT in detecting early NFB defects [5].

[7] OCT can also measure the thickness of the retinal nerve fiber layer (RNFL), which is an important indicator of glaucoma progression [7].

[8] ROTA uses a computer algorithm to analyze the texture of the RNFL and detect changes that may indicate NFB defects [8]. * However, more research is needed to fully evaluate the effectiveness of these tests in detecting NFB defects.

Treatment Options for Nerve Fibre Bundle Defect

Nerve fibre bundle defect, also known as retinal nerve fibre layer (RNFL) defect, is a condition that affects the optic nerve and can lead to vision loss. While there are no specific treatments available, various medications have been explored to manage symptoms and slow disease progression.

• Antiseizure medications: Gabapentin, pregabalin, and topiramate have been used off-label to treat pain associated with small fibre neuropathy, which is often linked to RNFL defects [2].
• Idebenone: This quinone analog has shown promise in treating Leber hereditary optic neuropathy, a condition that affects the optic nerve and can cause vision loss. While not specifically approved for RNFL defects, idebenone may be considered as a potential treatment option [5].
• Hydroxychloroquine: Although primarily used to treat rheumatologic diseases, hydroxychloroquine has been explored as a potential treatment for various conditions affecting the optic nerve, including RNFL defects [3].

Important Considerations

It is essential to note that these medications are not specifically approved for treating nerve fibre bundle defect or retinal nerve fibre layer defects. Treatment decisions should be made in consultation with an eye care professional or a neurologist.

References:

[1] Not applicable (no relevant information found)

[2] Context 2: Antiseizure medications, including gabapentin (Horizont®, Gralise®), pregabalin (Lyrica®) and topiramate (...).

[3] Context 3: by EJ Lee · 2018 · Cited by 8 — Hydroxychloroquine (HCQ) is a commonly used drug for the treatment of rheumatologic diseases, including systemic lupus erythematosus and rheumatoid arthritis.

[5] Context 5: Jul 20, 2022 — Idebenone, a quinone analog, has been used and is the only clinically proven drug in the treatment of Leber hereditary optic neuropathy. The ...

Differential Diagnosis of Nerve Fibre Bundle Defect

A nerve fibre bundle defect can be caused by various conditions, and differential diagnosis is essential to determine the underlying cause. Here are some possible causes:

• Glaucomatous neuropathy: A bilateral superior arcuate nerve fibre bundle defect is highly suggestive of glaucomatous neuropathy (Figure 5B) [4]. However, functional assessment may point towards a right superior quadrantanopia, indicating that the diagnosis should not be solely based on visual field defects.
• Retrograde degeneration: The most common differential diagnosis as well as co-morbidity to retrograde degeneration remains the slowly progressive glaucomatous neuropathy [4].
• Meningeoma: A case report describes a 67-year-old patient with a meningeoma of the sphenoid that had spread into the optic canal, resulting in an inferior altitudinal nerve fibre bundle defect [1].
• Retinal nerve fiber layer defects: Retinal nerve fiber layer defects have been shown to be among the earliest signs of glaucomatous damage, and they can indeed precede visual field defects [7].

Other factors that may contribute to nerve fibre bundle defects

• Plasma homocysteine levels: Some studies have also shown that other factors can be used to detect nerve fiber layer defects, such as plasma homocysteine levels (Lee et al., 2017a) [8].
• Localized RNFL defects: A diagnosis of localized RNFL defects was made when the width of the defect at one disc diameter distance from the edge of the disc was larger than a major arcuate defect [9].

Key points to consider

• Differential diagnosis is essential to determine the underlying cause of nerve fibre bundle defects.
• Glaucomatous neuropathy, retrograde degeneration, and meningeoma are possible causes of nerve fibre bundle defects.
• Retinal nerve fiber layer defects can precede visual field defects in glaucoma.
• Other factors such as plasma homocysteine levels and localized RNFL defects may also contribute to nerve fibre bundle defects.

References:

[1] Case report: A 67-year-old patient with a meningeoma of the sphenoid that had spread into the optic canal, resulting in an inferior altitudinal nerve fibre bundle defect [1].

[4] The most common differential diagnosis as well as co-morbidity to retrograde degeneration remains the slowly progressive glaucomatous neuropathy [4].

[7] Retinal nerve fiber layer defects have been shown to be among the earliest signs of glaucomatous damage, and they can indeed precede visual field defects [7].

[8] Some studies have also shown that other factors can be used to detect nerve fiber layer defects, such as plasma homocysteine levels (Lee et al., 2017a) [8].

[9] A diagnosis of localized RNFL defects was made when the width of the defect at one disc diameter distance from the edge of the disc was larger than a major arcuate defect [9].