Photoreception Anatomy
• Transparent layer covering the anterior eye chamber
• Provides physical protection as well as refracting (focusing) the incoming light (fine-tuning is provided by the lens)
• The iris is composed of smooth muscles, surrounding a circular hole, the pupil
• Signals from autonomic nerves stimulate the smooth muscles of the iris in order to change the pupil diameter, which
regulated the amount of light entering the eye
• Transparent, refractive tissue
• The transparent and refractive properties of the lens are created by tightly packed
proteins called crystallins
• The body's only dispensable tissue (removed and replaced in cataract surgery)
• Attached by zonular fibres to the ciliary membrane
AQUEOUS HUMOUR
• Fills the anterior compartment in front of the lens
• Low-protein, plasma-like fluid
• If more aqueous humour is formed than what is removed, the result is increased ocular pressure,
glaucoma
• Glaucoma can damage nerve fibres and lead to loss of vision
VITREOUS [HUMOUR]
• Fills the much larger compartment behind the lens
• Clear gelatinous matrix
• The light rays that approach the eye are linear - they need to be bent to project them onto the retina through
refraction
• Cornea - first and strongest refraction
• Lens - fine-tuning by accommodation to perceive objects closer than 9m
• Accommodation is accomplished by retracting ciliary muscles
• HYPEROPIA = farsightedness --> focus behind retina
• MYOPIA = near-sightedness --> focus in front of retina
• ASTIGMATISM = uneven curving of cornea
• PRESBYOPIA (gr= "old eye") = hardening of lens
Integration of Physiological Systems Page 1
• Transparent layer covering the anterior eye chamber
• Provides physical protection as well as refracting (focusing) the incoming light (fine-tuning is provided by the lens)
• The iris is composed of smooth muscles, surrounding a circular hole, the pupil
• Signals from autonomic nerves stimulate the smooth muscles of the iris in order to change the pupil diameter, which
regulated the amount of light entering the eye
• Transparent, refractive tissue
• The transparent and refractive properties of the lens are created by tightly packed
proteins called crystallins
• The body's only dispensable tissue (removed and replaced in cataract surgery)
• Attached by zonular fibres to the ciliary membrane
AQUEOUS HUMOUR
• Fills the anterior compartment in front of the lens
• Low-protein, plasma-like fluid
• If more aqueous humour is formed than what is removed, the result is increased ocular pressure,
glaucoma
• Glaucoma can damage nerve fibres and lead to loss of vision
VITREOUS [HUMOUR]
• Fills the much larger compartment behind the lens
• Clear gelatinous matrix
• The light rays that approach the eye are linear - they need to be bent to project them onto the retina through
refraction
• Cornea - first and strongest refraction
• Lens - fine-tuning by accommodation to perceive objects closer than 9m
• Accommodation is accomplished by retracting ciliary muscles
• HYPEROPIA = farsightedness --> focus behind retina
• MYOPIA = near-sightedness --> focus in front of retina
• ASTIGMATISM = uneven curving of cornea
• PRESBYOPIA (gr= "old eye") = hardening of lens
Integration of Physiological Systems Page 1
