Page 92 - 84 human physiolofy part-1

Chapter 5

and eventually their day-time vision may also be affected. In congenital stationary night
blindness the rods do not work from birth, but as the name implies, sufferers do not get worse.
Another cause of night blindness is a deficiency of retinol, or vitamin A, found in fish oils, liver
and dairy products.

Day Blindness
Also known as Hemeralopia is the inability to see clearly in bright light. The daytime vision gets
worse and worse. Nighttime vision remains unchanged due to the use of rods as opposed to cones
(during the day), which get affected by hemeralopia and in turn degrade the daytime optical
response.

Floater
Also known as "Muscae Volitantes" are deposits of
various size, shape, consistency, refractive index, and
motility within the eye's normally transparent vitreous
humour. Floaters are suspended in the vitreous humour,
the thick fluid or gel that fills the eye. Thus, they
generally follow the rapid motions of the eye, while
drifting slowly within the fluid. Floaters are visible only
because they do not remain perfectly fixed within the
eye. The shapes are shadows projected onto the retina by
tiny structures of protein or other cell debris discarded
over the years and trapped in the vitreous humour. They
are also common after cataract operations or after
trauma. In some cases, floaters are congenital.
Impression of floaters, as seen against a blue
Glaucoma sky. (GFDL - Acdx)
A group of diseases of the optic nerve involving loss of
retinal ganglion cells in a characteristic pattern of optic
neuropathy. Although raised intraocular pressure is a
significant risk factor for developing glaucoma, there is no set
threshold for intraocular pressure that causes glaucoma. One
person may develop nerve damage at a relatively low
pressure, while another person may have high eye pressures
for years and yet never develop damage. Untreated glaucoma
leads to permanent damage of the optic nerve and resultant
visual field loss, which can progress to blindness.

Visual Agnosia Picture of children holding a ball as
Visual agnosia is the inability of the brain to make sense of or seen by someone with glaucoma.
make use of some part of otherwise normal visual stimulus,
and is typified by the inability to recognize familiar objects or faces. This is distinct from
blindness, which is a lack of sensory input to the brain due to damage to the eye or optic nerve.
Visual agnosia is often due to damage, such as stroke, in posterior parietal lobe in the right
hemisphere of the brain. Careful analysis of the nature of visual agnosia has led to improved
understanding of the brain's role in normal vision.

Deadly Nightshade
Deadly Nightshade is a plant oil that can potentially kill you. Atrophine taken from this plant

92 | Human Physiology