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The normal (monocular) human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) from the vertical meridian in each eye, to 107 degrees temporally (away from the nose, or outwards) from the vertical meridian, and approximately 70 degrees above and 80 below the horizontal meridian. [7] [1] [8] [9]
Figure 1 - Humphrey field analyser. Humphrey field analyser (HFA) is a tool for measuring the human visual field that is commonly used by optometrists, orthoptists and ophthalmologists, particularly for detecting monocular visual field. [1] The results of the analyser identify the type of vision defect.
For example, myogenic ptosis results from a direct injury to the levator muscle and/or Müller's muscle. On the other hand, neurogenic ptosis is caused by closed head injuries or traumatically introduced neurotoxin (wasp/bee/snake venom) or botulinum toxin due to the effect of those factors on the CNIII or the sympathetic pathway.
Ideally, when the patient covers their right eye, the examiner covers their left eye and vice versa. The examiner will then move his hand out of the patient's visual field and then bring it back in. Commonly the examiner will use a slowly wagging finger or a hat pin for this. The patient signals the examiner when his hand comes back into view.
This is a partial list of human eye diseases and disorders. The World Health Organization (WHO) publishes a classification of known diseases and injuries, the International Statistical Classification of Diseases and Related Health Problems, or ICD-10. This list uses that classification.
As the ptosis worsens, the individual commonly extends their neck, elevating their chin in an attempt to prevent the eyelids from occluding the visual axis. Along with the insidious development of ptosis, eye movements eventually become limited causing a person to rely more on turning the head side to side or up and down to view objects in the ...
At the low end of the range is the absolute threshold of vision for a steady light across a wide field of view, about 10 −6 cd/m 2 (0.000001 candela per square meter). [22] [23] The upper end of the range is given in terms of normal visual performance as 10 8 cd/m 2 (100,000,000 or one hundred million candelas per square meter). [24]
For example, binocular vision, which is the basis for stereopsis and is important for depth perception, covers 114 degrees (horizontally) of the visual field in humans; [7] the remaining peripheral ~50 degrees on each side [6] have no binocular vision (because only one eye can see those parts of the visual field). Some birds have a scant 10 to ...