Optics and Image Formation

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Questions and Answers

What is the term used for the material suggested by Professor Otto Wichterle and Dr. Drashoslav Lim?

Resin (correct)
Glass
Metallic elements
Plastic

What is the purpose of high Dk in extended wear lenses?

To prevent hypoxia (correct)
To improve oxygen permeability
To prevent microbial keratitis
To prevent corneal ulcers

Who introduced the concept of a hybrid lens composed of glass and plastic?

Professor Otto Wichterle
Heinrich Wohlk
William Feinbloom (correct)
Istvan Gyorffy

What is the advantage of RGP lenses in reshaping the cornea?

It does not follow the contour of the cornea (A) Signup and view all the answers

What is the term for contact lenses that are used on an abnormal cornea?

Extended wear (B) Signup and view all the answers

Who produced the first fully plastic contact lens?

Istvan Gyorffy (B) Signup and view all the answers

Why are contact lenses used in trichiasis patients?

To prevent contact between eyelashes and cornea (D) Signup and view all the answers

What is a potential complication of contact lens use?

Microbial keratitis (D) Signup and view all the answers

What occurs when the Cornea lacks oxygenation?

Neovascularization (D) Signup and view all the answers

What is the primary function of Meibum?

To prevent evaporation of the eye's tear film (C) Signup and view all the answers

What happens to the production of lactic acid in conditions of oxygen deprivation?

It increases (C) Signup and view all the answers

Which of the following is NOT a layer of the eyelid?

Sclera (A) Signup and view all the answers

What is the comparison made when describing contact lens wear?

Wearing a face mask (C) Signup and view all the answers

What is the consequence of accumulation of lactic acid in the cornea?

Detrimental consequences for vision (A) Signup and view all the answers

What is the relationship between the power of the prescription (Rx) and the thickness of the contact lens?

Higher Rx, thicker CL (D) Signup and view all the answers

What is the name of the glands squeezed every time you blink?

Meibomian glands (D) Signup and view all the answers

What is the primary purpose of the base curve in a contact lens?

To ensure proper alignment and stability of the lens on the cornea (C) Signup and view all the answers

What is the significance of the Back Optic Zone Radius (BOZR) in contact lens fitting?

It coincides with the cornea (D) Signup and view all the answers

Why do contact lenses require more than one curve?

To accommodate the ellipsoidal shape of the cornea (B) Signup and view all the answers

What is the relationship between the base curve and the optic zone?

The base curve becomes the optic zone (A) Signup and view all the answers

What is the result of fitting a contact lens exactly as the patient's cornea?

Poor alignment and stability (C) Signup and view all the answers

What is the purpose of the multiple curves in a contact lens design?

To ensure balance and stability of the lens on the cornea (C) Signup and view all the answers

What is the size of a therapeutic contact lens compared to a scleral lens and a basic corneal lens?

Smaller than a scleral lens but bigger than a basic corneal lens (C) Signup and view all the answers

What is the primary purpose of a therapeutic contact lens?

To prevent epithelial erosions and enhance epithelial healing (D) Signup and view all the answers

What is the typical power of a therapeutic contact lens?

Plano power (A) Signup and view all the answers

What is the advantage of using therapeutic contact lenses for drug delivery?

Increased contact time compared to eye drops (A) Signup and view all the answers

What is the material used to make rigid non-gas permeable contact lenses?

Polymethyl methacrylate (PMMA) (C) Signup and view all the answers

What is the characteristic of a rigid gas permeable contact lens?

Rigid and permeable to gas (C) Signup and view all the answers

What is the advantage of rigid non-gas permeable contact lenses?

They are lighter than glass (B) Signup and view all the answers

What is the characteristic of a soft contact lens with low water content?

Nonionic polymers (A) Signup and view all the answers

What is the main characteristic of SCL in terms of its behavior on the cornea?

It has a flat fit and conforms to the cornea (C) Signup and view all the answers

What is the composition of the post-lens tear film if it is very thin?

Mainly lipids and mucin (C) Signup and view all the answers

What is the effect of lid forces on the apparent fit of a contact lens?

It influences the apparent fit (A) Signup and view all the answers

What is the characteristic of RGP lenses in terms of their fit?

They have a steep fit and do not conform to the cornea (C) Signup and view all the answers

What is the effect of lens thickness and profile on the fit of a contact lens?

It influences the fit of a contact lens (A) Signup and view all the answers

What is the effect of material properties on the fit of a soft lens?

It has a significant influence on the fit of a soft lens (A) Signup and view all the answers

Why can soft lenses be fitted with any available BOZR, even if it is not the computed value?

Because soft lenses have low rigidity (C) Signup and view all the answers

What is the effect of changes in measurement on the fit of a soft lens?

It has no effect on the fit of a soft lens (A) Signup and view all the answers

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Study Notes

History of Contact Lenses

William Feinbloom introduced a hybrid lens composed of glass and plastic in 1936
Istvan Gyorffy produced the first fully plastic contact lens in 1939
Heinrich Wohlk produced his own version of plastic lenses in 1940
Professor Otto Wichterle and Dr. Drahoslav Lim suggested using plastic that simulates living tissue for orbital implants in 1954

Contact Lens Types

Rigid Gas Permeable (RGP) lenses do not follow the contour of the cornea
Soft contact lenses are typically 13mm in size
Corneal contact lenses exactly fit the size of the cornea
Therapeutic Contact Lenses (bandage CL) enhance epithelial healing, prevent epithelial erosions, and control surface-generated pain

Lens Properties

Lens thickness and profile are important for proper fitting
Material properties affect lens movement and stability
Lack of lens movement can cause hypoxia and produce lactic acid, leading to detrimental consequences for vision

Fitting Principles

Fitting principles for soft contact lenses are similar to those for RGP lenses
Base curve is critical for corneal fitting and stability
Back Optic Zone Radius (BOZR) affects power in the optic zone
Multi-curve lenses provide better corneal fitting and stability

Eye Anatomy

The palpebral aperture is the opening between the eyelids
The eyelids have 5 layers: skin and subcutaneous tissue, orbicularis oculi, tarsal plates, levator apparatus, and conjunctiva
Meibomian glands produce meibum, an oily substance that prevents evaporation of the eye's tear film

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