General shape, size and position of the eye Flashcards
What is photoreception?
the process by which light energy from the environment produces changes in specialised nerve cells in the retina- the rods and cones
the changes result in nerve action potentials which are relayed to the optic nere and then to brain where information processed and consciously appreciated as vision
What are all the structures within the eye other than the photoreceptors (rods and cones) for?
- may be aprt of the system for focusing and transmitting light onto the retina (cornea, lens, iris, ciliary body)
- may be necessary for nourishing and supporting tissues of eye (choroid, aqueous outflow system, lacrimal apparatus)
What is the approximate shape and size of the eye?
approximately a sphere 2.5cm in diameter with volume of 6.5ml
in reality more of the parts of two spheres - smaller one anteriorly, cornea, and the sclera which constitutes large sphere
What proportion of the circumference of the globe is formed by the cornea?
one sixth
How does the curvature of the cornea compare with the sclera?
the cornea has a greater curvature than the sclera
What is the raidus of the cornea?
7.8mm
What is the radius of the sclera?
11.5mm
What is the average axial lenngth of the globe of the eye?
24mm (range 21-26mm varies between individuals)
What is the diameter of the globe?
23mm
What is the horizontal length of the globe?
23.5mm
Are small eyes hyperopic (hypermetropic) or myopic?
hyperopic (aka hypermetropic)
What is the cut off axial length of the globe to be consider a small eye?
<20mm
Are large eyes hyperopic (hypermetropic) or myopic?
myopic
What is the the cut off axial length of an eye to be consiered a large eye?
26mm - 29mm
Where within the orbit is the eye situated?
anterior portion, closer to the lateral than the medial wall and nearer the roof than the floor