Portland Community College | Portland, Oregon

Introduces mathematics used in optical prescriptions, manufacturing and dispensing. Basic principles governing transmission of light and its interaction with optical media. Includes experimentation to visually inform the student of the laws of geometric optics.

1. Use an understanding of the principles of optics to perform basic lensometry.
2. Apply knowledge of optics to the selection of corrective lenses.
3. Interpret written prescriptions for ophthalmic lenses for visual correction.

The class will be presented by means of lecture/discussion, audio-visual presentations, handouts and demonstrations. There will be comprehensive lab work requiring demonstrated competency to receive a satisfactory grade. Guest speakers and field trips may be utilized by the instructor as a means of assisting the student in mastering course goals and objectives.

At the beginning of the course, the instructor will detail the methods used to evaluate student progress and the criteria for assigning a course grade. The methods may include one or more of the following tools: examinations, quizzes, homework assignments, research papers, laboratory modules, student participation. An assessment of practical skills will be performed at the conclusion of the term.

The student will demonstrate understanding of the following themes, issues, concepts, and development of the following skills:
THEMES, ISSUES, CONCEPTS

1. Physical Description of Models Used to Describe Action of Light
2. Electromagnetic Radiation Spectrum
3. Concepts of Optical Imaging
4. Basic Mathematics for Optics
5. Basic Lens Terms
6. Reflection
7. Ray Tracing to find Image Distances and Characteristics - Curved Surfaces
8. Explaining the Prescription (Rx)
9. Transposition
10. Prescription Axis Notation and Optical Protractors
11. Lens Forms and Base Curves
12. Astigmatic Refractive Errors and Prescriptions
13. Lensometer

COMPETENCIES AND SKILLS

History of Ophthalmics/Medicine

• Explain how optical lenses and spectacles and contact lenses came to be developed and some of the associated historical names.

Physical Description of Models Used to Describe Action of Light

• Describe wave fronts, wave lengths, frequency, speed of light.
• Define parallel light radiation, convergence and divergence of light radiation, polarization, diffraction, dispersion.

Electromagnetic Radiation Spectrum

• Describe wave and particle theories of light.
• Describe electromagnetic spectrum radiation, visible spectrum radiation, ultra-violet radiation, infra-red radiation.
• Describe electromagnetic radiation in terms of nanometers.
• Describe visible spectrum in units of color.
• Describe and define visible, UV and IR as wavelengths/frequency of electromagnetic radiation.

 Prisms and Refraction Through Prisms

• Describe prism shape.
• Locate base and apex of prism.
• Locate and describe images as seen through prisms.
• Describe apex/base designation and direction of light and images seen through prisms.
• Discuss prism use in refractive examinations.
• Define orthoptics and use of prism lenses.
• Define prism diopter.
• Define Prentice's Rule, prism = decentration in cm x Rx, Decentration in cm = prism/Rx, Rx = prism/decentration in cm.
• Figure base direction for plus or minus lenses when the optical centers of lenses are not directly in front of the patient's pupils.
• Use the lensometer to check for unwanted or prescribed prism.
• Using Snell's Law, mathematically predict angle of refraction through prisms.

Concepts of Optical Imaging

• Define formation of a real image and impossibility of formation of virtual image.
• Define and demonstrate image sizes as compared to object sizes: enlarged, same size, minified.
• Define and demonstrate image states as compared to object states: upright, inverted, reverted.
• Define aberration.
• Define and list examples of opaque, translucent, and transparent substances.

Basic Mathematics for Optics

• Compare measuring units: millimeter, centimeter, meter and inches.
• Demonstrate working with positive and negative numbers: addition, subtraction, multiplication and division of positive and negative numbers.
• Review addition, subtraction, multiplication and division of fractions.
• Demonstrate conversion of fractions to decimals and decimals to fractions.

Basic Lens Terms

• Define: meniscus surfaces, plano, spherical, cylinder and toric surfaces and powers.
• Using the words: sphere, cylinder, toric, describe how lenses may be classified into the following combinations: spherical, sphero-cylinder, plano-cylinder, crossed-cylinder.
• Define and/or locate the following descriptive points on a lens: optical center, optical axis.
• Describe a minus and a plus lens: in terms of center and edge thickness, in terms of motion and magnification.
• Define emmetropia, myopia, hyperopia, ametropia, presbyopia.
• Relate ametropia to corrective lens type.
• Define radius of curvature as related to depth of a surface curve of a lens surface.
• Compare flat surface curvature to radius number and steeply curved surfaces to radius number.
• Describe synonyms for front and back lens surfaces.

Reflection

• Define the basic unit of measurement of dioptric power or a lens.
• Define specular (regular) reflection, diffuse (irregular) reflection, angle of incidence, angle of reflection, normal, plane.
• Define/describe law of reflection: angle I = angle R, object plane vs image plane.

Ray Tracing to find Image Distances and Characteristics - Curved Surfaces

• Find image distances and characteristics when object is at defined distances from the vertex of a concave or convex surface by ray tracing: object at infinity, object at any other distance from vertex.
• Give example of reciprocals, showing the focal length of lens in meters can be divided into one to equal diopters and dioptric power can be divided into one to equal focal length in meters.

Explaining the Prescription (Rx)

• Define how spherical and cylinder power components of an Rx are combined to find the power produced at right angles.
• Define and describe optical cross as a device to show placement and location of power on a lens.

Transposition

• Explain transposition as technique used to change from one cylinder format to another without changing the Rx.
• Explain steps needed to transpose an Rx: algebraically combine sphere and cylinder power, change sign of cylinder number, change axis number by adding or subtracting 90 degrees.
• Demonstrate how optical cross is drawn and how powers are noted.

Prescription Axis Notation and Optical Protractors

• Explain why the axis of the  Rx with cylinder must be oriented when placed before the eye for proper alignment of optical powers.
• Explain how meridians of power relate to components.
• Explain how the axis of an Rx describes placement of powers and relate axis to the protractor.
• State difference between protractor used by the optical industry and a normal protractor that is divided into 360 degrees.
• Explain that 0 degrees on convex surface of a lens is on the right side and that 180 degrees on the convex surface is on the left and 90 refers to both top and bottom of the lens.
• Differentiate 0 degree placement on both concave and convex lens surfaces.
• Describe how ost optical protractors used for marking lenses are marked in red numbers for convex surfaces and black numbers for concave surfaces.

Astigmatic Refractive Errors and Prescriptions

• Define astigmatic errors:
• Define corneal, refractive, residual and total astigmatism.
• Explain corneal topography as related to with-the-rule, against-the-rule and oblique astigmatism.
• Define and be able to write a hypothetical Rx in both plus and minus cylinder for the five classifications of toric prescriptions: simple myopic, compound myopic, simple hyperopic, compound hyperopic and mixed astigmatism.
• Define unit of measurement by the keratometer of corneal curves in diopters and/or radius of curvature in millimeters.

Nominal Power Formula to Find Surface Powers of Rx and Lens Graphs

• Explain the nominal power formula's essential items for computations: Rx, front surface power, back surface power.
• Use formula to solve problems for spherical and toric Rxs. Find: Rx, D1 and D2.
• Explain on plus lenses, the absolute power of D1 surface is always higher (larger number).

Lensometer

• Demonstrate correct eyepiece setting procedure.
• Measure spherical and toric lenses and multifocal additions.
• Read power of toric lens in minus and plus cylinder form.
• Write the neutralized power of toric lenses readings in plus and minus cylinder forms.
• Position optical center of lenses according to: Rx with no prism and mark, Rx with prism and mark.