Normal Horizontal Field of Vision
The normal horizontal binocular visual field extends approximately 180-200 degrees, with each eye contributing roughly 150-170 degrees temporally and 60 degrees nasally, creating substantial binocular overlap in the central 120 degrees.
Monocular Visual Field Parameters
The horizontal extent of a normal monocular visual field encompasses:
- Temporal field: Extends approximately 90-100 degrees from fixation 1
- Nasal field: Extends approximately 60 degrees from fixation 1
- Total monocular horizontal extent: Approximately 150-170 degrees 1
Research using Goldmann perimetry (III-4e stimulus) establishes that visual impairment begins when the total horizontal visual field falls below 146 degrees, while more stringent criteria (III-3e stimulus) set this threshold at 109 degrees 1.
Binocular Visual Field Parameters
When both eyes function together normally:
- Total horizontal binocular field: Approximately 180-200 degrees in healthy adults 2, 1
- Central binocular overlap: The central 120 degrees where both eyes' visual fields overlap, enabling stereopsis and depth perception 2
- Normal orthotropic subjects: Demonstrate a mean horizontal binocular visual field of approximately 141 degrees (±6.6 degrees) on Esterman testing 2
The binocular field is not simply the sum of both monocular fields; in normal subjects, the difference between the summation of monocular visual fields and the actual binocular visual field averages approximately 100 degrees, reflecting the overlapping central region 2.
Clinical Thresholds for Visual Impairment
According to the American Academy of Ophthalmology guidelines, visual field diameter thresholds define severity of impairment:
- Severe visual impairment: Visual field diameter of 20 degrees or less 3
- Profound visual impairment: Visual field diameter of 10 degrees or less 3
- Category 3 blindness: Field no greater than 10 degrees but greater than 5 degrees around central fixation 3
- Category 4 blindness: Field no greater than 5 degrees around central fixation 3
Testing Considerations
Standard automated perimetry typically evaluates:
- 24-degree programs: Cover the central 24 degrees from fixation 3
- 30-degree programs: Extend to 30 degrees from fixation 3
- 10-degree programs: Focus on the central 10 degrees for advanced disease monitoring 3
Normal threshold sensitivity values in the central field range from 30-35 dB, decreasing toward the periphery 4.
Common Clinical Pitfalls
Avoid assuming symmetry: The horizontal visual field can be significantly asymmetric in pathologic conditions. Esotropia reduces the horizontal binocular field to approximately 123 degrees (±18.8 degrees), while exotropia maintains near-normal fields at 138 degrees (±8.3 degrees) 2.
Don't overlook amblyopic eye contributions: Even in strabismic patients, the amblyopic eye's horizontal field is significantly reduced compared to normal (approximately 99-105 degrees versus 121 degrees), which impacts overall binocular function 2.