Refractive Media Of Eye Flashcards
What are the primary refractive media of the eye?
Cornea, lens, and vitreous
What is the definition of refraction?
The change in direction of light as it passes from one medium to another, of different optical density
What is the primary role of the cornea?
Refraction of light
How many layers does the corneal epithelium consist of?
5 layers
What is the thickness of Bowman’s layer?
8-12 micrometers
What is the main component of the stroma?
Collagen fibrils
What is Descemet’s membrane?
A strong and uniform layer that lies on the posterior aspect of the stroma
What is the primary function of the corneal endothelium?
To transport fluid from the anterior chamber to the cornea via active transport
True or False: The cornea is avascular.
True
What are the factors that contribute to corneal transparency?
- Avascular * Smooth epithelium * Regular stromal arrangement * Relatively ‘dry’ structure
What factors reduce the transparency of the cornea?
- Significantly increased IOP * Oedema due to any cause * Fibrosis after trauma * Inflammation and infection
What percentage of the total refractive power of the eye does the cornea account for?
2/3 of total refractive power
What is the normal refractive index of air?
1
What changes occur in the lens with age?
- No cells are lost from the lens * Lens fibers migrate to the center * Capsule thickens * Central portion becomes sclerosed and yellowish
What is the primary function of the lens?
To change its shape to change its refractive power through accommodation
What is the anatomical structure that connects the lens to the ciliary body?
Zonules
What is the role of the vitreous in the eye?
To maintain the shape of the eye and support the retina
Fill in the blank: The cornea comprises ______ layers.
5
What is the typical refractive index of the lens?
1.41
What is the refractive index of the vitreous?
1.33
True or False: The central cornea receives oxygen from the air via diffusion through the tear film.
True
What is the typical size of the cornea?
10.5mm to 11.5mm
What are Hassel and Hanle bodies?
Small peripheral projections into the anterior chamber that increase in number over time
What nerve supplies sensation to the cornea?
Long ciliary nerve
