American Career College Optical Technician Study Guide

Visible Light and Electromagnetic Energy

• Visible Light Definition: A form of energy that behaves according to two primary theories:     * Corpuscular or Quantum Theory: States light is composed of particles called Photons that travel in straight lines.     * Electromagnetic Wave Theory: States light travels in the form of waves.
• Light Synthesis: Light is described as an electromagnetic wave motion containing photon units that travel as a wave.
• Wave Anatomy:     * Crest: The highest point of a wave.     * Trough: The deepest/lowest point of a wave.     * Amplitude: The height or depth of the wave.     * Wavelength: The distance between two consecutive crests, two troughs, or from the beginning to the end of one wave cycle.
• Measurement Units: Visible light wavelengths are measured in nanometers (nm). $1\,\text{nm} = 10^{-9}\,\text{meters}$ (one billionth of a meter).
• Speed of Light: In air, light travels at approximately $186,000\,\text{miles per second}$.
• The Visible Spectrum: Visible light occupies the middle of the electromagnetic spectrum, ranging from $380\,\text{nm}$ to $760\,\text{nm}$.     * Violet: $380-440\,\text{nm}$     * Blue: $440-500\,\text{nm}$     * Green: $500-560\,\text{nm}$     * Yellow: $560-590\,\text{nm}$     * Orange: $590-650\,\text{nm}$     * Red: $650-760\,\text{nm}$
• Invisible Radiation: Components outside the visible range. Shorter wavelengths are generally more dangerous.     * Ultraviolet (UV): Starts below $400\,\text{nm}$.         * UV-C ($200-290\,\text{nm}$): Most dangerous to living cells; absorbed by the ozone layer.         * UV-B ($290-320\,\text{nm}$): Causes sunburn, corneal burns, cataracts, and retinal damage.         * UV-A ($320-400\,\text{nm}$): Causes suntan and cataracts.     * Infrared (IR): Wavelengths from $760\,\text{nm}$ to $10^6\,\text{nm}$. It induces heat. Sources include direct sunlight, molten glass/metal, and arc lamps.

Reflection, Refraction, and Light Transmission

• Refraction: The bending of light as it enters a substance of different density. The chemical composition of the substance determine the speed of travel.
• Index of Refraction (n): A ratio comparing the speed of light in a vacuum/air to the speed in a specific substance.     * Formula: $n = \frac{\text{Speed of Light in Air}}{\text{Speed of Light in Material}}$     * Examples:         * Water: $186,000 / 140,000 = 1.33$         * Crown Glass: $186,000 / 122,000 = 1.52$         * Standard Index (Optical Industry): $1.530$ (calibration standard for lens clocks).         * Polycarbonate: $1.586$         * High Index: Up to $1.74$ (Plastic) or $1.90$ (Glass).
• Reflection: The "bouncing back" of light from a surface.     * Regular (Specular) Reflection: Occurs on smooth surfaces.     * Irregular (Diffuse) Reflection: Occurs on rough surfaces.
• Absorption: The amount of light that remains within the lens material.
• Transmission: The ratio of light entering to light exiting the material after reflection and absorption.     * Crown Glass/CR-39: Approximately $91\%$ transmission (approx. $8\%$ reflection, $1\%$ absorption).     * Polycarbonate: Approximately $88\%$ transmission (approx. $10\%$ reflection, $2\%$ absorption).
• Dispersion: The breaking down of white light into its component colors (e.g., through a prism).     * Primary Colors for the Eye: Blue, Green, Red.     * Focusing: Green focuses on the retina; Red focuses behind (Hyperopic for red); Blue focuses in front (Myopic for blue).

Clinical UV and Infrared Hazards

• Ocular Damage from UV: Welder's burn (UV-C), Snow blindness (exacerbated by sand/snow reflection), Cataracts, Macular degeneration, Eclipse burns, Pterygium, and Pinguecula.
• High-Risk Groups: Individuals with beginning cataracts, Aphakia (missing lens), Pseudophakia (implanted lens), workers around UV lamps (dentists), or those mid-day outdoors.
• Medication Sensitivity: Tetracyclines, Sulfonamides, Tranquilizers, and Oral contraceptives increase UV damage risk.
• UV Blocking Standards (FDA): Sunglasses should transmit no more than $5\%$ UV-A (below $380\,\text{nm}$) and no more than $1\%$ UV-B.
• Note: Tint does not block UV. Dark tints cause pupils to dilate, potentially admitting more UV if the lens lacks a dedicated UV absorbing coating.

Lens Coatings and specialized treatments

• Anti-Reflective (AR) Coating: Clear layers designed to reduce reflection and increase transmission.     * Chemical: Magnesium Fluoride ($MgF_2$).     * Physics: Ideal thickness is $\frac{1}{4}$ of a light wavelength.     * Effect: Single layer transmits $98\%$, multilayer transmits over $99\%$. Highly recommended for high-index materials to reduce glare.
• Blue Blocking AR: Designed to reduce digital eye strain by reflecting up to $80\%$ of High Energy Visible (HEV) Blue Light.
• Scratch-Resistant Coating (SRC): Necessary for plastic lenses. Increases CR-39 transmission from $91\%$ to $96\%$.
• Mirror Coatings: Applied for sun protection; act as a two-way mirror. Effective reflectors of both UV and IR.
• Specialty Coatings: Anti-fog (cooks, skiers), and Edge coating (reduces concentric rings in high minus lenses).

Specialized Lens Technologies

• Photochromic / Transitions™: Lenses that darken when exposed to UV radiation using chemicals like silver halide.     * Optical Bleaching: Red light or IR radiation lightens the lenses.     * Thermal Bleaching: Heat causes the lenses to lighten (they stay darker on cold, sunny days).     * Transitions™ Variants: Signature® Gen8™, XTRActive® (darkest, activates behind windshields), Vantage®, and Acuvue® Oasys with Transitions™.
• Polarized Lenses: Block reflected glare from horizontal surfaces (water, highways) by admitting only vertically vibrating light. Constructed with a sheet of polyvinyl alcohol.
• Cathode Ray Tube (CRT) Lenses: Specifically for computer users to combat "Transient Myopia," eyestrain, and dry eyes.     * Tints for CRT Monitors: Blue (for Amber screens), Violet (for Green screens), Gray (for Black/White screens).

Basic Optical Math and Dioptric Power

• Optical Infinity: Considered to be $20\,\text{feet}$ (approximately $6\,\text{meters}$), where light rays become parallel.
• Prisms: Wedge-shaped material with an Apex (thin) and Base (thick). Bends light toward the base and displaces objects toward the apex.
• Diopter (D): The unit of lens power. $1.00\,D$ focuses light at $1\,\text{meter}$.
• Focal Length Formulas:     * $D = \frac{1}{f\,(\text{meters})}$     * $D = \frac{100}{f\,(\text{cm})}$     * $D = \frac{1000}{f\,(\text{mm})}$
• Lens Anatomy:     * Convex: Bulging out (+ value).     * Concave: Caved in (- value).     * Plano: Zero power/straight surface.     * Base Curve: The front/outside curve.     * Ocular Curve: The inside/back curve.
• Lens Power Factors: Radius of curvature (steeper curve = more power), refractive index (higher index = more power), lens thickness, and vertex distance.

Vertex Distance (VD)

• Definition: The distance between the ocular curve and the eye. Measured with a Distometer.
• Movement Rules:     * Plus Lens: Moving closer to the eye loses power (compensate by increasing power). Moving away gains power (compensate by decreasing power).     * Minus Lens: Moving closer to the eye gains power (compensate by decreasing power). Moving away loses power (compensate by increasing power).
• VD Rule of Thumb: A $10.00\,D$ lens moving $10\,\text{mm}$ changes power by $1.00\,D$.
• Prescription Thresholds: Compensate for VD if the Rx exceeds $7.00\,D$ for spectacles or $4.00\,D$ for contact lenses.

Spherocylinder and Toric Lenses

• Cylinder Lenses: Used to correct astigmatism. Features an Axis (meridian of no power) and a Power Meridian (90 degrees from axis).
• Toric / Spherocylinder Lenses: COMBINE sphere and cylinder powers. They have two "True Powers" 90 degrees apart.
• Spherical Equivalent: The average power of a toric lens.     * Formula: $\text{Sphere} + \frac{1}{2}(\text{Cylinder})$
• Transposition: Changing an Rx from plus-cylinder to minus-cylinder form (and vice-versa).     * Step 1: Combine sphere and cylinder algebraically for the new sphere.     * Step 2: Change the sign of the cylinder.     * Step 3: Rotate the axis by 90 degrees (If $< 90$, add 90; if $> 90$, subtract 90).

Lens Materials and Physical Properties

• Crown Glass: Very scratch-resistant but heavy ($SG: 2.54$) and brittle. Hardened via heat or chemical tempering.
• CR-39 (Colombian Resin): Standard plastic ($n: 1.49, Abbe: 58$). Lightweight and easily tinted.
• Polycarbonate: Soft and impact-resistant ($n: 1.598, Abbe: 30$). Preferred for children and safety glasses. Inherently blocks UV.
• Trivex: High clarity and high impact resistance ($n: 1.52, Abbe: 43$).
• Abbe Value: Measures chromatic aberration (distortion). Higher Abbe = lower distortion.
• Specific Gravity (SG): Measures density/weight of the material.
• Safety Standards (FDA):     * Dress Lenses: Must withstand a $\frac{5}{8}\,\text{inch}$, $16\text{-gram}$ steel ball dropped from $50\,\text{inches}$.     * Safety Lenses: Must withstand a $1\text{-inch}$ steel ball and have a minimum thickness of $3.0\,\text{mm}$ (or $2.5\,\text{mm}$ for high plus).

Anatomy and Physiology of the Eye

• Outer Layer: Sclera (tough white part), Cornea (clear plus lens, $+43.00\,D$), and Limbus (transition zone).
• Middle Layer (Uvea): Choroid (vascular), Ciliary Body (produces aqueous humor/controls accommodation), and Iris (colored part regulating the pupil).
• Inner Layer: Retina with the Macula (central vision/cones) and Optic Disc (blind spot).
• Photoreceptors:     * Cones: Located in macula; for color and detail; function in daylight.     * Rods: Located in periphery; for peripheral vision and motion; function in low light.
• Crystalline Lens: Provides accommodation ($+13.00\,D$ to $+19.00\,D$).
• Common Conditions:     * Glaucoma: High intraocular pressure ($IOP$). Normal range: $10-24\,\text{mmHg}$.     * Cataracts: Opacification of the lens.     * Age-Related Macular Degeneration (ARMD): Loss of central vision.     * Strabismus: Muscle imbalance (Exotropia: out, Esotropia: in, Hypertropia: up, Hypotropia: down).

Refractive Errors and Deficiencies

• Emmetropia: Normal eye, no correction needed.
• Myopia: Eye too long/strong; focuses in front of retina. Corrected with Minus Sphere.
• Hyperopia: Eye too short/weak; focuses behind retina. Corrected with Plus Sphere.
• Astigmatism: Corneal irregularity (football-shaped). Corrected with Cylinder/Toric lenses.
• Presbyopia: Age-related loss of accommodation. Requires an ADD power.
• Anisometropia: Difference in power between eyes of $2.00\,D$ or more.
• Antimetropia: Eyes have opposite signs (one plus, one minus).
• Aniseikonia: Image size difference between eyes (exceeding $5\%$ prevents fusion).

Multifocal Lens Types and Fitting

• Bifocals:     * Flat Top (FT): Most common; least image jump. OC is $4.5-5\,\text{mm}$ below the line.     * Round Seg: Cosmetically pleasing but high image jump. OC is at the center of the segment.     * Executive: Full width segment; no image jump (OC on the line).
• Trifocals: Have three powers (Distance, Intermediate, Near). Intermediate is normally $50\%$ of the ADD.
• Progressive Addition Lenses (PALs): Invisible power increase. Requires monocular PD and fitting heights.     * Hard Design: Aberrations concentrated in periphery; wider/higher near zone.     * Soft Design: Gradual power progression; narrower near zone.

Prismatic Imbalance and Vertical Compensation

• Prentice's Rule: $\Delta = P \times d$, where $P$ is power in diopters and $d$ is decentration in centimeters.
• Yoked Prism: Both eyes looking through same direction/base; usually comfortable.
• Image Jump: The displacement of image when crossing the bifocal line.
• Vertical Imbalance: Discrepancy in prismatic effect between eyes when looking down. If > 1.50\,D, it typically requires correction.
• Slab-Off (Bi-Centric Grinding): Used for vertical imbalance. Adds Base Up prism to the more minus lens.

Frame Anatomy and Materials

• Bridge Styles: Saddle (for comfort/long noses), Keyhole (for short noses), Modified Saddle.
• Temple Types: Skull, Library, Comfort Cable (wraps around ear), Riding Bow.
• Materials:     * Zyl (Cellulose Acetate): Standard plastic; cotton/wood flake based.     * Optyl (Epoxy Resin): Lightweight ($30\%$ less than Zyl); thermoelastic properties (retains memory).     * Carbon Fiber: Strength of metal; extremely thin.     * Monel: Common metal composed of nickel, copper, and iron.     * Titanium: Ultra-light; corrosion-resistant; hypoallergenic.     * Memory Metal: Titanium/Nickel alloy; returns to shape after bending.

Health and Billing Standards (HIPAA, Medicare, Billing)

• HIPAA (1996): Five titles governing privacy of Protected Health Information (PHI).
• PHI Identifiers: Name, Address, DOB, SSN, Health plan numbers, etc.
• Medicare Parts: Part A (Hospital), Part B (Medical). For ages $65+$ or disabled.
• Coding Systems:     * ICD-10-CM: Identification of diseases/diagnosis.     * CPT: Procedure/service codes (e.g., $92014$ for existing patient exam).     * HCPCS: Equipment/supplies (e.g., $V2020$ for frames).
• Claim Form: CMS-1500. Contains 33 boxes; must be submitted with valid ICD and CPT codes.
• VSP (Vision Service Plan): Most popular vision insurance in California ($80\%$ of patients).

Optical Laboratory and Fabrication

• Lensometer (Focimeter): Measures power, axis, and prism.
• Standard Alignment (Truing): 4-point touch test check for X-ing or variant planes.
• Boxing System:     * A dimension: Horizontal length of lens.     * B dimension: Vertical depth.     * DBL: Distance Between Lenses.     * ED: Effective Diameter (twice the longest radius).     * GCD (Frame PD): $A + DBL$.
• ANSI Z80.1 Standards:     * Power Tolerance ($-6.50\,D$ to $+6.50\,D$): $\pm 0.13\,D$.     * Cylinder Axis Tolerance: Varies by power ($\pm 2^\circ$ for high cylinder to $\pm 14^\circ$ for low cylinder).     * Prism Tolerance: Normal limit is $0.33\Delta$ vertical.