MOC PQA - Optician cheat sheet

Power in diopters: F = 1/f, with f measured in meters; a +2.00 D lens has a focal length of 0.50 m.

Surface power by the lensmaker relation: F = (n_lens − n_medium)/r, so a steeper curve or higher index raises surface power.

Nominal power approximates sphere plus cylinder; effective power changes with vertex distance: F_new = F/(1 − d·F), with d in meters.

Snell's law: n1·sin θ1 = n2·sin θ2; light bending toward the normal occurs when entering a higher-index medium.

Prism diopter: 1 Δ displaces an image 1 cm at 1 m; prism power P = 100·tan θ.

Prentice's rule: prism Δ = decentration in cm × lens power in D; direction follows the base toward the decentration side for plus lenses.

Spherical aberration, coma, and oblique astigmatism are off-axis monochromatic aberrations; chromatic aberration arises from dispersion (Abbe value).

A lens with Abbe number 58 disperses less than one with Abbe 32; lower Abbe values produce more chromatic fringing.

Boxing system: A = lens width, B = lens height, DBL = bridge width, ED = effective diameter; frame size is written A–DBL–temple.

Minimum blank size = ED + 2 × decentration + 2 mm edge allowance; inadequate blank size forces unwanted decentration.

Pantoscopic tilt is typically 8–12°; retroscopic tilt is unusual and is reserved for specific occupational or postural needs.

Face-form (wrap) angle of 5–8° is normal; excessive wrap induces unwanted prism and requires compensated lens design.

Vertex distance is measured from the corneal apex to the back surface of the lens; standard reference is about 12–13 mm.

Temple length should reach the mastoid area and bend downward; a temple that is too short causes pressure and slippage.

Nose pad alignment: pads should contact the sides of the nose symmetrically, with the bridge width matching the nasal profile.

Frame front should sit level; unequal temple bends or a warped front produce a tilted visual axis and patient complaint.

Single-vision lenses have one power; multifocals include bifocal (flat-top, round, executive) and progressive designs.

Progressive addition lenses have a corridor length and add power; shorter corridors suit small B measurements but increase peripheral distortion.

Aspheric designs flatten peripheral curvature to reduce magnification, thickness, and off-axis aberration in higher plus powers.

Refractive index examples: CR-39 ≈ 1.498, Trivex ≈ 1.53, polycarbonate ≈ 1.586, 1.60, 1.67, and 1.74 high-index.

Abbe values: CR-39 ≈ 58, Trivex ≈ 45, polycarbonate ≈ 30, 1.67 ≈ 32; higher index generally lowers Abbe value.

Polycarbonate and Trivex are impact-resistant; polycarbonate is required by many safety standards for children and sports.

Anti-reflective coatings reduce surface reflections and increase light transmission; hydrophobic and oleophobic layers ease cleaning.

Photochromic lenses darken with UV exposure; performance depends on temperature and UV intensity, and they may not darken behind a windshield.

Prescription format: sphere, cylinder, axis (1–180°), add, and prism; a cylinder with no axis is incomplete.

Transposition: add cylinder power to sphere, reverse cylinder sign, and change axis by 90° (axis ≤ 90 add 90; axis > 90 subtract 90).

Optical center is the point where the optical axis meets the lens; the major reference point is the fitting cross for progressives.

Monocular PDs are measured from the bridge of the nose to each pupil; binocular PD is their sum.

Distance PD can be estimated as half the pupillary distance at distance; near PD is reduced by about 3 mm per 10 D of add or by convergence.

Prism notation: base in, base out, base up, base down; resolving compound prism uses vector addition of horizontal and vertical components.

Vertical imbalance tolerance is typically about 1 Δ; horizontal prism tolerance is generally more lenient.

ANSI Z80.1 tolerances for sphere power vary with power range; stronger lenses allow proportionally tighter absolute tolerances.

Soft lens materials are hydrogels or silicone hydrogels; Dk is oxygen permeability and Dk/t is transmissibility through a given thickness.

Higher water content increases oxygen permeability in conventional hydrogels but raises dehydration and deposit risk.

Base curve, diameter, and sagittal depth determine soft lens fit; steep fits show excessive movement and tight fits show limbal impingement.

Rigid gas permeable lenses are lathe-cut or molded; fluorescein pattern shows apical clearance, mid-peripheral bearing, and edge lift.

Keratometry values guide base curve selection; steeper corneas require steeper base curves.

Care systems include multipurpose solutions and hydrogen peroxide systems; peroxide systems require a neutralizing case and full soak time.

Daily disposable lenses eliminate care solutions and reduce deposit-related complications.

Never use tap water or saliva on lenses; Acanthamoeba risk is associated with non-sterile water contact.

Cornea provides about two-thirds of the eye's refractive power (roughly 43 D); the crystalline lens contributes about 15–20 D.

Tear film has lipid, aqueous, and mucin layers; mucin anchors the aqueous layer to the corneal epithelium.

Myopia: light focuses in front of the retina; corrected with minus lenses. Hyperopia: focuses behind the retina; corrected with plus lenses.

Astigmatism results from unequal curvature; regular astigmatism is corrected with cylinder, irregular astigmatism often with RGP lenses.

Presbyopia is age-related loss of accommodative amplitude, typically noticed in the early to mid-40s.

Accommodation is mediated by the ciliary muscle and zonules; the near point recedes with age.

Ametropia is measured in diopters; axial myopia is associated with increased axial length and retinal detachment risk.

Pupil size and depth of focus interact: smaller pupils increase depth of focus and reduce blur from low refractive error.

Lensmeter (focimeter) measures sphere, cylinder, axis, prism, and optical center; calibration should be verified before use.

Auto-refractor and auto-keratometer provide objective starting points; subjective refraction and keratometry refine the result.

Pupillometer measures interpupillary distance; monocular measurement reduces error from head turn.

Corneal topographer maps curvature and is used to detect keratoconus and irregular astigmatism.

Tonometer measures intraocular pressure; Goldmann applanation is a reference method, and non-contact tonometry is common in screening.

Frame adjustment tools: nylon-jaw pliers for delicate work, flat pliers for pads and temples, and a lens edger for sizing.

Screw threads are typically M1.4 for eyewear; stripped threads require a tap or replacement hinge.

Solder repairs require matching metal (monel, nickel silver, titanium) and appropriate flux; titanium requires specialized equipment.

Prescriptions are medical documents; release and retention must follow local privacy rules and professional record-keeping requirements.

A valid prescription includes prescriber information, date, and expiration; dispensing without a current prescription may be unlawful.

Informed consent and clear communication of risks, alternatives, and costs are core ethical obligations.

Conflict of interest must be disclosed; referral arrangements and incentives must comply with anti-kickback and fraud laws.

Patient records should be retained per jurisdiction; typical retention periods range from 5 to 10 years, with longer periods for minors.

Scope of practice defines which tests and fittings an optician may perform; exceeding scope is a licensing violation.

Advertising and claims must be truthful; comparative claims and guarantees require substantiation.

Infection control: hand hygiene, disinfection of trial frames and instruments, and proper handling of contact lens trial sets.

Thin lens combination in contact: F_total = F1 + F2; separated lenses use F_total = F1 + F2 − d·F1·F2, with d in meters.

Magnification of a lens: M = 1/(1 − d·F) for vertex distance effects; plus lenses magnify, minus lenses minify.

Base curve selection affects magnification and aberration; flatter base curves reduce magnification in plus lenses.

Cylinder axis convention: axis is the meridian of least power in minus cylinder form, and the meridian 90° away carries the cylinder power.

Induced prism from decentration is zero at the optical center; for aspheric and progressive lenses, the reference point is not the geometric center.

Light transmission through a lens is reduced by surface reflections; AR coating can raise transmission toward 99%.

Polarized lenses block reflected glare oriented in one plane; they are useful for water and driving but can interfere with some displays.

UV protection: lenses should block UVA and UVB; polycarbonate inherently absorbs most UV below 380 nm.

Frame materials: cellulose acetate (adjustable with heat), titanium (light, corrosion-resistant), stainless steel, monel, and TR-90 (flexible nylon).

Frame fronts should be adjusted for symmetry before lenses are ordered; a warped front changes effective PD and axis perception.

Temple bend position should align with the top of the ear; the bend length is typically 35–45 mm from the hinge end.

For high minus lenses, choose a smaller A and thicker edge or high-index material to reduce edge thickness and weight.

For high plus lenses, a smaller eye size and rounder shape reduce center thickness and weight.

Bridge fit determines vertical position; a slipping frame is often caused by a bridge that is too wide or pads that are misaligned.

Sports and safety frames should meet impact standards and provide retention; strap or cable temples improve hold.

Dispensing verification includes power check, optical center alignment, PD match, and comfort check before delivery.

Scratch-resistant coatings are applied to both surfaces; hard coats differ from anti-reflective stacks, which are multilayered.

Edge treatments: polishing reduces edge glare in high minus; safety bevels reduce chipping and injury risk.

Tints and mirror coatings reduce light transmission; category 3 sunglasses transmit roughly 8–18% of visible light.

Blue-light filtering claims should be evaluated critically; evidence for clinical benefit is limited compared with UV protection.

Impact standards: ANSI Z87.1 applies to safety eyewear; children's eyewear often requires impact-resistant material.

Progressive lens design categories include standard, short corridor, and office/occupational designs with different add distributions.

High-index materials require appropriate AR coating and edge treatment because of higher surface reflections and brittleness.

Lens thickness estimation uses the sagitta formula and edge thickness; center thickness minimums protect against impact failure.

Spherical equivalent = sphere + ½ cylinder; used for contact lens conversion when cylinder is small.

With-the-rule astigmatism has the steeper meridian near 90°; against-the-rule near 180°; oblique is between.

Axis tolerance is typically ±2° to ±5° depending on cylinder power; higher cylinder requires tighter axis control.

Prism base direction in a prescription is specified per eye; compounding horizontal and vertical prism requires vector resolution.

Optical center height for single vision is usually set at the pupil center; for progressives, the fitting cross is placed at the pupil.

Near PD measurement should be taken at the reading distance; using distance PD for near work induces unwanted prism.

Lensmeter prism measurement should be zeroed with no lens; residual prism indicates decentration or lens defect.

Vertex distance conversion is required when a prescription of ±4.00 D or more is fitted at a different vertex distance.

Dk units are barrers; silicone hydrogels achieve Dk values above 100, while conventional hydrogels are typically 20–40.

Replacement schedules: daily, two-week, and monthly; extended wear increases microbial keratitis risk.

Soft lens diameter typically ranges 13.8–14.5 mm; base curves typically 8.3–8.8 mm.

RGP lens fitting uses fluorescein and cobalt blue light; central pooling indicates a steep fit, central bearing indicates a flat fit.

Orthokeratology uses reverse-geometry RGP lenses worn overnight to flatten the central cornea temporarily.

Solution compatibility matters: some multipurpose solutions are incompatible with certain silicone hydrogel materials.

Symptoms of overwear include redness, dryness, and reduced wearing time; persistent symptoms require discontinuation and evaluation.

Contact lens hygiene: wash hands, avoid water, replace cases regularly, and never reuse solution.

Retina layers include photoreceptors, bipolar cells, and ganglion cells; the fovea has the highest cone density.

Rods mediate scotopic vision and are more numerous in the periphery; cones mediate photopic and color vision.

Aqueous humor is produced by the ciliary body and drains through the trabecular meshwork and Schlemm's canal.

Intraocular pressure normally ranges about 10–21 mmHg; elevated pressure is a risk factor for glaucoma.

The optic nerve head is the blind spot; the macula provides central vision and has no blood vessels at the fovea.

Refractive error components: corneal power, lens power, axial length, and anterior chamber depth.

Anisometropia is a difference in refractive error between eyes; aniseikonia is a difference in perceived image size.

Amblyopia results from abnormal visual development and is treated by correcting refractive error and occlusion therapy.

Lens clock (lens measure) reads surface curvature in diopters; it is used to verify base curve and surface power.

Geneva lens measure converts sagitta to surface power using the refractive index setting.

Frame heater softens acetate for adjustment; overheating causes blistering and loss of shape.

Hinge repair options include screw replacement, rivet replacement, and hinge replacement; matching hinge type is essential.

Nose pad arms can be adjusted with pad pliers; silicone pads are used for sensitive skin.

Ultrasonic cleaning removes debris from frames and hinges; it is not suitable for some lens coatings.

Edger calibration affects lens size and shape; a mis-sized lens causes frame stress and lens cracking.

Torque on hinge screws should be moderate; over-tightening strips threads and damages the hinge.

Informed financial disclosure: itemized pricing, insurance coverage, and out-of-pocket costs should be explained before ordering.

Patient autonomy: the patient may request a copy of the prescription and choose where to fill it.

Professional boundaries: do not diagnose or treat ocular disease outside scope; refer when abnormalities are suspected.

Documentation should be contemporaneous, legible, and include measurements, recommendations, and patient responses.

Confidentiality applies to all patient information, including frame and lens choices and payment details.

Continuing education and licensure renewal are required in most jurisdictions; lapsed licensure prohibits practice.

Advertising must avoid misleading claims about lens performance, safety, or guarantees.

Complaint handling should be documented and resolved transparently; unresolved complaints may require regulatory reporting.

Effective power change with vertex distance is clinically significant above ±4.00 D; a plus lens moved closer to the eye increases effective power.

Prism induced by decentration is used deliberately in some fittings, but unintended decentration causes diplopia or asthenopia.

The optical center of a progressive lens is not the fitting cross; prism reference point and fitting cross differ.

Aberration control: aspheric and atoroidal designs reduce oblique astigmatism in wrapped frames.

Refractive index and Abbe value trade off: higher index reduces thickness but can increase chromatic aberration.

Lens thickness at the edge for minus lenses depends on decentration, blank size, and frame shape.

Reflection at a surface increases with index difference; AR coatings reduce reflection and improve contrast.

Polarization axis is usually vertical for sunglasses; crossed polarization can block display visibility.

Frame selection should consider prescription power, facial measurements, occupation, and lifestyle.

For progressive lenses, the fitting cross height should be at the pupil center; too high or low causes adaptation problems.

Vertex distance should be recorded and matched to the refraction; a change of 1 mm is negligible below ±4.00 D.

Frame adjustment sequence: front alignment, bridge fit, temple alignment, and final comfort check.

A frame that sits too low reduces the effective reading area in progressives.

Weight distribution: heavier lenses require a well-fitted bridge and proper temple bend to prevent slipping.

Children's frames require impact-resistant lenses and secure retention; cable temples may be appropriate.

Dispensing should include instructions on cleaning, storage, and when to return for adjustment.

Occupational lenses for computer use often use a reduced add and a shorter corridor to match screen distance.

Photochromic lenses may not perform well in cars because windshields block UV; a separate sunglass pair is often recommended.

Mirror coatings reduce transmission and are available in full or gradient styles; they can scratch and require care.

Edge polishing is cosmetic and reduces glare but can increase edge reflections in high minus lenses.

Impact resistance: polycarbonate and Trivex are preferred for safety and children's eyewear.

Lens thickness minimums: center thickness for plus lenses is typically at least 1.5–2.0 mm for impact safety.

AR coating stacks include hard coat, AR layers, and hydrophobic top coat; cleaning should use microfiber and lens spray.

Progressive lens adaptation is influenced by corridor length, add power, and frame fitting height.

Transposition example: +1.00 −2.00 × 180 becomes −1.00 +2.00 × 090.

Spherical equivalent of +2.00 −1.00 × 90 is +1.50; used for contact lens selection when cylinder is small.

Prism resolution: horizontal and vertical components combine as vectors; resultant prism = √(H² + V²).

Optical center height measurement uses the pupil center or the fitting cross; record the method used.

Monocular PD measurement should be repeated to confirm; a difference of 1 mm or more between eyes is common.

Lensmeter axis reading should be verified against the prescription; axis errors above tolerance require remaking.

Vertex distance conversion formula: F_new = F/(1 − d·F); apply when the fitting distance differs from the refraction distance.

Tolerance for prism in eyewear is typically about 0.33 Δ to 0.67 Δ depending on standards and power.

Silicone hydrogel lenses have high Dk but may be stiffer and require attention to fit and wettability.

Soft lens fit assessment: centration, coverage, movement (typically 0.2–0.5 mm), and comfort.

RGP fit assessment: apical clearance, mid-peripheral bearing, and edge lift; a flat fit shows central bearing.

Keratoconus fitting often uses RGP or scleral lenses; scleral lenses vault the cornea and rest on the sclera.

Care regimen compliance reduces microbial keratitis risk; peroxide systems require the correct case and soak time.

Contact lens prescription includes base curve, diameter, power, brand, and material; it is not interchangeable across brands.

Replace lenses per manufacturer schedule; do not extend replacement intervals.

Remove lenses before swimming or showering; water exposure increases Acanthamoeba and Pseudomonas risk.

Corneal curvature is measured in diopters; average corneal power is about 43 D.

Axial length increase of 1 mm corresponds to roughly 3 D of myopia.

Presbyopia add power typically starts at +1.00 D in the mid-40s and increases with age.

Astigmatism axis orientation affects visual performance; oblique astigmatism is often less tolerated.

Anisometropia greater than 2 D may cause aniseikonia and adaptation problems.

Amblyopia treatment is most effective in childhood; early detection improves outcomes.

Dry eye affects lens tolerance and measurement reliability; tear film quality should be considered.

Pupil size affects depth of focus and night vision complaints; larger pupils increase higher-order aberration effects.

Lensmeter calibration should be checked with a known lens; drift affects power and axis readings.

Auto-refractor results should be refined by subjective refraction; instrument values are a starting point.

Pupillometer measurement should be taken with the patient fixating at the intended distance.

Frame heater temperature should be controlled; acetate softens without blistering at moderate heat.

Hinge screw replacement requires matching thread size and length; mismatched screws damage the hinge.

Nose pad replacement should match material and shape; silicone pads are useful for sensitive skin.

Ultrasonic cleaning should be followed by drying; trapped moisture can corrode hinges.

Edger maintenance includes calibration, blade or wheel condition, and lens chuck pressure.

Record keeping should include prescription, measurements, lens specifications, and patient instructions.

Privacy rules apply to paper and electronic records; secure storage and access control are required.

Informed consent for contact lens fitting includes risks of infection and non-compliance.

Referral for suspected disease should be documented and communicated to the patient.

Scope of practice varies by jurisdiction; verify licensure and permitted tasks.

Advertising claims about lens safety or performance must be substantiated and not misleading.

Conflict of interest disclosure includes ownership interests and referral relationships.

Complaint resolution should be documented; unresolved issues may require escalation to a regulator.

Thin lens combination with separation: F = F1 + F2 − d·F1·F2; d in meters.

Magnification by vertex distance: M = 1/(1 − d·F); plus lenses magnify, minus lenses minify.

Prism induced by decentration: Δ = c·F; direction depends on lens sign and decentration direction.

Aberration control: aspheric surfaces reduce spherical aberration; atoroidal surfaces reduce oblique astigmatism.

Abbe value indicates dispersion; lower Abbe values produce more chromatic aberration.

Refractive index affects surface power and thickness; higher index reduces curvature for the same power.

Polarized lenses block reflected glare; orientation matters for displays and driving.

UV absorption: polycarbonate absorbs most UV below 380 nm; additional UV treatment may be needed for other materials.

Frame fit affects effective vertex distance and optical center alignment; record both at dispensing.

Progressive fitting height should be measured with the frame in place and the patient in a natural posture.

Pantoscopic tilt changes the effective cylinder and axis; compensation may be required in high prescriptions.

Face-form angle affects prism and aberration; wrapped frames require compensated lens design.

Bridge fit determines vertical position; a slipping frame often indicates a bridge that is too wide.

Temple length and bend affect retention and comfort; the bend should align with the top of the ear.

High minus lenses benefit from smaller eye size, high index, and edge treatment to reduce thickness and weight.

High plus lenses benefit from smaller eye size, rounder shape, and aspheric design to reduce center thickness.

Progressive lens corridor length affects reading area and peripheral distortion; shorter corridors suit small B measurements.

Occupational designs distribute add power for near and intermediate tasks; they are not general-purpose progressives.

Photochromic performance depends on UV and temperature; they may not darken behind a windshield.

Mirror coatings reduce transmission and are available in full or gradient styles; they require careful cleaning.

AR coatings improve transmission and reduce glare; multilayer stacks include hard coat and hydrophobic top coat.

Impact standards: ANSI Z87.1 applies to safety eyewear; polycarbonate and Trivex are preferred.

Edge polishing reduces glare but can increase edge reflections in high minus lenses.

Center thickness minimums protect against impact failure; plus lenses typically require at least 1.5–2.0 mm.

Transposition: add cylinder to sphere, reverse cylinder sign, change axis by 90°.

Spherical equivalent = sphere + ½ cylinder; used for contact lens conversion when cylinder is small.

Prism resolution uses vector addition; resultant prism = √(H² + V²).

Vertex distance conversion: F_new = F/(1 − d·F); apply when fitting distance differs from refraction distance.

Axis tolerance is typically ±2° to ±5° depending on cylinder power.

Prism tolerance is typically about 0.33 Δ to 0.67 Δ depending on standards and power.

Monocular PD measurement reduces error from head turn; record both eyes separately.

Optical center height should be recorded with the method used (pupil center or fitting cross).

Dk is oxygen permeability; Dk/t is transmissibility through a given thickness.

Silicone hydrogels achieve high Dk but may be stiffer and require attention to wettability.

Soft lens fit: centration, coverage, movement (0.2–0.5 mm), and comfort.

RGP fit: apical clearance, mid-peripheral bearing, and edge lift; flat fit shows central bearing.

Scleral lenses vault the cornea and rest on the sclera; used for keratoconus and irregular corneas.

Peroxide care systems require a neutralizing case and full soak time; incomplete neutralization causes burning.

Contact lens prescriptions are brand- and material-specific; they are not interchangeable.

Water exposure increases Acanthamoeba and Pseudomonas risk; remove lenses before swimming or showering.

Cornea provides about two-thirds of refractive power; the crystalline lens contributes about 15–20 D.

Axial length increase of 1 mm corresponds to roughly 3 D of myopia.

Presbyopia add power typically starts at +1.00 D in the mid-40s and increases with age.

Anisometropia greater than 2 D may cause aniseikonia and adaptation problems.

Amblyopia treatment is most effective in childhood; early detection improves outcomes.

Dry eye affects lens tolerance and measurement reliability.

Pupil size affects depth of focus and night vision complaints.

Aqueous humor is produced by the ciliary body and drains through the trabecular meshwork and Schlemm's canal.

Lensmeter calibration should be checked with a known lens; drift affects power and axis readings.

Lens clock reads surface curvature in diopters; used to verify base curve and surface power.

Frame heater softens acetate; overheating causes blistering and loss of shape.

Hinge repair requires matching screw thread size and length; mismatched screws damage the hinge.

Ultrasonic cleaning removes debris but trapped moisture can corrode hinges; dry thoroughly.

Edger calibration affects lens size and shape; mis-sized lenses cause frame stress and cracking.

Torque on hinge screws should be moderate; over-tightening strips threads.

Nose pad replacement should match material and shape; silicone pads suit sensitive skin.

Records should include prescription, measurements, lens specifications, and patient instructions.

Privacy rules apply to paper and electronic records; secure storage and access control are required.

Informed consent for contact lens fitting includes infection and non-compliance risks.

Referral for suspected disease should be documented and communicated to the patient.

Scope of practice varies by jurisdiction; verify licensure and permitted tasks.

Advertising claims about lens safety or performance must be substantiated.

Conflict of interest disclosure includes ownership interests and referral relationships.

Complaint resolution should be documented; unresolved issues may require escalation to a regulator.