Optics: Tear Film Optics Flashcards
Epithelium
Protects the cornea by providing a barrier against water, larger molecules, and toxic substances
Bowman’s membrane
Consists mainly of randomly arranged collagen fibrils
Stroma
Comprises 90% of corneal thickness and over 200 collagen lamellae
Collagen fibrils within each lamella run _______ to each other and the successive lamellae run _________
Parallel, across the cornea at angles to each other
Desemet’s membrane
The basement membrane of the endothelial cells
Endothelium,
Single layer that regulates the fluid balance of the cornea in order to maintain the stroma at about 78% hydration
Dua’s layer
Located between the stroma and descemet’s membrane, comprised of type-1 collagen bundles
Pre-corneal tear film is the…
Most anterior refractive surface of the eye
Tear film is composed of _______, ___________, and ________ layers
Oily, aqueous, mucous
Refractive index of tear film
1.336
Optical power of the tear film
48.35D
Tear film is essential for…
Clear vision and reduces transparency when the tear film dries out
Stability of tear film is important for the…
Optical quality of the eye
The chief function of the tear film lipid bilayer is to:
-provide smooth optical surface for the cornea
-retard water evaporation from the ocular surface
Tear film stability is measured by its..
Lack of stability
Tear film refers primarily to ….
Evaporation rate
A stable tear film is one in which a…
Minimum amount of tears evaporate
Instability of the tear film occurs due to the…
Depletion of aqueous component of tears
Tear film optics is very significant because…
The change in the refractive index at the air-tear film interface is greater than any other interface in the eye
Due to the large change in refractive index in the air-tear film interface, irregularities in the anterior surface of the tears have potential to…
Significantly degrade the optical quality of the eye
Qualitative assessment of the tear film is realized by using:
-retro-illumination of pupil with slit lamp
-fluorescein
Dry eye is a disorder of the tear film due to…
Tear deficiency or excessive tear evaporation which causes damage to the interpalpebral ocular surface and causes ocular discomfort
High order aberrations are _____ times greater in dry eyes than in healthy eyes
2.5
Contact lenses sit….
In and not on the tear film
The contact lens is about _______ times thicker than the aqueous layer in the tear film
10
Contact lens interaction with the tear film is dependent on the:
-lens material
-individuals tear chemistry
Effects of contact lens wear on the tear film:
-deplete the levels of specific components in the tear film by sorption
-lens can stimulate the biochemical generation of additional components
Factors affecting tear film stability:
-stability decreases significantly w age
-men have longer tear film breakup time (TBUT)
-Caucasian’s have higher TBUT
-generally affected by presence of contact lens
-ocular surgery
-local irregularities
-external environmental conditions
-smoking and alcohol intake
-amount of computer exposure
