Free ABO Advanced Exam Flashcards

Formula P = c x F that calculates induced prism when gaze is decentered from a lens optical center, where c is decentration in centimeters and F is lens power in diopters. A +5.00 D lens decentered 0.4 cm induces 2 prism diopters; this rule underlies both prescribed prism calculations and unwanted-prism tolerance checks.

Effective lens power changes as a lens moves closer to or farther from the eye, so for prescriptions beyond about +/-4.00 D the dispensed power must be adjusted when vertex distance differs from the refracted distance. Use F_new = F_old / (1 - d * F_old) with d in meters. Closer, add plus: a plus lens moved closer acts weaker and needs more plus; a minus lens moved closer acts stronger and needs less minus.

Tilting a spherical lens off-axis induces a cylinder power along the axis of tilt, with magnitude proportional to tilt squared and lens power. Consequence: pantoscopic tilt must be matched to the drop of the eye behind the lens center, or unwanted oblique astigmatism degrades acuity.

Approximated as sag = y^2 / (2r), where y is half the chord diameter and r is the surface radius of curvature; the exact form is s = r - sqrt(r^2 - y^2). Sag determines finished lens thickness, the minimum blank size that fits a frame, and whether a chosen base curve is compatible with the lens diameter.

A curve that plots the optimal base curve against lens power so that marginal (oblique) astigmatism is minimized as the eye rotates behind the lens. Choosing base curves outside the ellipse forces peripheral blur; modern corrected-curve lens series are designed to sit on or near it across the common prescription range.

Converting between plus-cylinder and minus-cylinder notation: new sphere = old sphere + old cylinder, new cylinder = -old cylinder, new axis = old axis +/- 90 degrees. The two forms are optically identical; laboratories usually fabricate in minus-cylinder even when the Rx is written in plus-cylinder.

Total lens power F = F1 + F2, the sum of the front and back surface powers. This lets an optician compute total power from surface curves without measuring the finished lens; base curve choice and surfacing calculations flow from it.

A prism specified 'base at theta' decomposes into horizontal (P * cos theta) and vertical (P * sin theta) components, and compounding multiple prisms requires vector addition. A 5 prism-diopter base at 30 degrees yields 4.33 horizontal and 2.5 vertical; fabrication and verification are done on the resolved components.

Ring-shaped muscle and vascular tissue behind the iris that produces aqueous humor and drives accommodation through its attachments to the lens. Cycloplegic drugs paralyze it to block accommodation (used in pediatric refractions), and chronic dysfunction can raise intraocular pressure.

Fibrillin-rich fiber strands running from the ciliary processes to the crystalline lens equator. When the ciliary muscle contracts, the zonules slacken and the lens bulges for near vision (accommodation); when it relaxes, the zonules pull the lens flat for distance vision.

A single layer of cells on the posterior cornea that runs the active fluid pump maintaining corneal deturgescence and clarity. Endothelial cells do not regenerate, so loss from trauma, surgery, or disease causes permanent corneal swelling and clouding.

Innervates the lateral rectus muscle, which abducts the eye. A VI palsy prevents the affected eye from turning outward, producing an esotropia (inward turn) and horizontal diplopia that worsens when the patient looks toward the affected side.

The macula is the central retina area responsible for sharp detail and color vision; the fovea is its cone-only center pit. Macular disease destroys central acuity while sparing peripheral vision, so a patient may still navigate but cannot read faces or print.

Progressive thinning and conical bulge of the cornea that produces irregular astigmatism and increasing myopia. Spectacle acuity lags behind the apparent Rx. Vision is managed with spectacles, then rigid, hybrid or scleral contact lenses; corneal cross-linking is used early to slow progressive disease, and a transplant is for cases where contact lenses no longer give adequate vision.

Opacification of the crystalline lens that reduces acuity, contrast, and color perception. Large Rx shifts late in life are a warning sign; surgery removes the lens and replaces it with an IOL, after which the patient is pseudophakic and needs UV protection.

A group of optic neuropathies frequently associated with elevated intraocular pressure that first damages the peripheral visual field. Patients lose side vision before noticing it, so a sudden Rx change or field complaint warrants referral rather than just a stronger pair of glasses.

Microvascular damage to the retina from chronic hyperglycemia, including dot-blot hemorrhages, exudates, and neovascularization. Early disease often has no symptoms, so people with diabetes need a dilated eye exam at least once a year. Separately, high blood sugar can change the shape of the eye's lens and blur vision, so new blur in a person with diabetes should prompt referral before dispensing.

Age-related loss of accommodation from crystalline lens hardening and reduced ciliary force, beginning clinically around age 40. The prescriber sets the near add, which rises as accommodation declines with age; the optician should know why it rises, not set it.

Refractive error in which the two principal meridians focus at different distances because the cornea or lens is toric rather than spherical. A cylindrical lens is prescribed to equalize the meridians, and axis accuracy is critical because rotation shifts the entire correction.

Lens surface whose curvature varies progressively from center to edge, reducing spherical aberration and flattening the profile. High-plus lenses are thinner and lighter with less magnification distortion, but the design requires precise centration on the pupil or peripheral blur worsens.

Computer-controlled point-by-point grinding of the lens back surface, allowing personalized corridor geometry and power maps. A single progressive design can be tuned to the patient's actual PD, vertex, pantoscopic tilt, and viewing distances, expanding the usable intermediate and near fields.

A material's reciprocal chromatic dispersion; higher values mean less wavelength spread and less transverse chromatic aberration. Polycarbonate (V about 30) produces more color-fringe complaints than CR-39 (V about 58), especially in high minus powers.

Refractive index governs how strongly a material bends light (higher index = thinner lens for the same power); specific gravity governs weight per unit volume. Trivex (n = 1.53, low SG) is lighter than high-index 1.74 even though 1.74 is thinner; trade thickness against weight when matching material to patient.

High-index materials shrink lens thickness but typically lower the Abbe value and raise surface reflectance. High-index wearers more often report chromatic fringes and reflections, so AR coating is essentially mandatory on 1.67 and 1.74 to control glare.

The narrow channel of gradually increasing plus power that connects the distance zone to the near zone in a progressive lens. Short corridors build power faster and react more to head and eye movement; the frame must still be deep enough for the full range of powers.

Vertical distance from the pupil center (or boxed lens center) to the lowest point of the lens or frame rim. Too low and the near zone is cut off; too high and the distance field narrows; most progressive designs specify a minimum fitting height below which the lens cannot be ordered.

Perception of peripheral sway when turning the head in new progressive lenses, caused by the prismatic gradient across the periphery. It usually adapts within days, but is more pronounced with steep adds, narrow corridors, and wrap frames, so warn the patient before they drive home.

Sudden displacement of the image at the top edge of a flat-top or round segment bifocal, produced by the prismatic effect of the segment itself. The patient notices a 'jump' as gaze crosses the segment top; progressives eliminate it through the corridor, but executive bifocals still show it.

A difference in refractive error between the two eyes, usually considered significant above 1.00 D. When the patient reads below the optical centers, unequal induced vertical prism can cause diplopia and asthenopia; multifocal anisometropia is a prime indication for slab-off.

A difference in perceived image size between the two eyes, often caused by anisometropia. Spectacles magnify plus images and minify minus images, so the more anisometropic the Rx, the worse the binocular fusion; contact lenses reduce the magnification disparity and are preferred for high anisometropia.

A technique that corrects vertical imbalance at near in anisometropic multifocal wearers. Bicentric grinding adds base-up prism to the reading area of the lens with the most minus or least plus power; on modern plastic lenses, a reverse slab adds base-down prism to the most plus or least minus lens.

The amount the eyes must converge to fuse a near target, increased by base-out prism and reduced by base-in prism. A 4 prism-diopter base-out lens in each eye adds 8 prism diopters of total convergence demand: each base-out prism moves the image toward the nose, so each eye converges 4. Excessive demand causes asthenopia.

An afocal telescope made with a plus objective and a minus eyepiece, producing an upright magnified image; magnification = F_eyepiece / F_objective. It has a shorter tube length than Keplerian designs and a narrower field, making it useful for spot reading and distance spotting tasks.

The power factor is 1/(1 - hF), with h the vertex distance in meters (the form used for iseikonic lens design); a +4.00 D lens at 12 mm gives about 5%. For estimating aniseikonia, clinicians measure to the eye's entrance pupil instead (vertex distance plus about 3 mm, so about 15 mm), which gives about 6% for that lens, about 1.5% per diopter. High-plus reading glasses for low vision deliver high magnification but demand a very close working distance, with reduced field and depth of focus.

Near tasks use high-add bifocals, stand magnifiers, and telemicroscopes; distance tasks use handheld monoculars and bioptic telescopes. Choose the aid by the patient's task distance and mobility needs rather than by acuity number alone, because a mismatched aid is quickly abandoned.

Optical instrument that measures back vertex power, axis, prism, and segment placement of a finished lens. It is the standard verification device for ANSI Z80.1 tolerance checks; the distance reference point on a progressive is where the power is read.

A mechanical three-pin instrument that reads surface curvature and converts it to diopters assuming a crown-glass index of 1.53. Readings are accurate for crown glass but must be recalculated for any other material; using the clock on polycarbonate understates the surface power.

Instrument that measures corneal curvature in the two principal meridians by reflecting a mire off the tear film. It outputs K-readings used for contact lens base-curve selection, astigmatism quantification, and keratoconus screening; corneal distortion makes the mires irregular.

Small spring-loaded caliper that measures vertex distance from the closed eyelid to the back surface of the spectacle lens. It is essential before dispensing high-power lenses (> +/-4.00 D) so the lab can compensate the power; a wrong vertex compensation can throw the effective Rx out of tolerance.

Subjective, Objective, Assessment, Plan - the structured sequence for analyzing a patient complaint about eyewear. Opticians diagnose before adjusting; jumping straight to tweaks (tightening temples, changing pads) often trades one complaint for another and never fixes the root cause.

Standard dispensing sequence: temple spread, bridge fit, pantoscopic tilt, then temple length and behind-ear bend. Each step changes the next; fixing tilt before the bridge can throw off PD alignment, so the order matters and is rarely skipped.

The tilt of the spectacle plane away from vertical. The ideal tilt for standard lenses is about 8 degrees, with the optical center about 4 mm below the pupil center: about 2 degrees of tilt per millimeter of drop, so the optical axis points at the center of rotation; mismatched tilt induces unwanted cylinder by Martin's formula.

For a patient with one functional eye, prioritize impact resistance and protection of the good eye above cosmetic symmetry. Polycarbonate or Trivex lenses, sturdy frames, and avoidance of rimless drill-mounts are standard; cosmetic imbalance between the two sides is acceptable because binocular fusion is irrelevant.

The American National Standard for prescription ophthalmic lenses, specifying tolerances for sphere power, cylinder power, cylinder axis, prism, base curve, and segment position. It defines the pass/fail line for laboratory verification; a lens outside tolerance fails verification and is normally remade.

The American National Standard for occupational and educational eye and face protection; 'Z87' marks basic-impact and 'Z87+' marks high-impact. Dress eyewear is not safety eyewear; safety frames require side shields, marked lenses, and impact-resistant materials, and using a dress frame for safety work is a liability.

Federal regulation (21 CFR 801.410) requiring eyeglass and sunglass lenses to be impact-resistant, unless the prescriber finds such lenses will not meet the patient's visual needs and directs other lenses in writing; it does not apply to contact lenses. Each finished glass prescription lens is drop-ball tested; plastic lenses are tested by statistical sampling of each batch. The rule names no lens material for children.

Federal rule requiring prescribers to give patients a copy of their prescription immediately after the exam, free of charge and without a release form. Opticians may fill any Rx the patient brings; withholding the Rx to capture the sale is illegal, and the patient is free to shop anywhere.

Multi-layer thin-film coating that uses destructive interference to reduce surface reflections from ophthalmic lenses. It improves transmission, contrast, and cosmetic appearance, and is essentially mandatory on high-index materials (1.67 and above) where reflectance is high; it requires careful cleaning to avoid scratches.

Lenses that darken when exposed to UV and clear indoors; the darkening is driven by UV-activated silver-halide or organic photochromic dyes embedded in or on the lens. Most windshields block UV, so most photochromics darken little inside a car; warm temperatures make them fade back faster and darken slightly less, so they are not a substitute for true sunglasses.

Laminated lenses with a built-in polarizing filter that blocks horizontally reflected glare (the kind that bounces off water, roads, and snow). They dramatically reduce glare for driving, fishing, and snow sports, but cannot be used with most cockpit LCD instruments (which disappear at certain angles) and may interfere with reading some ski-goggle LCDs.