COA cheat sheet

Snellen fraction 20/40 means the patient identifies at 20 ft a letter a normal eye resolves at 40 ft; larger denominator = worse acuity.

Diopter D = 1/f in meters; a +2.00 D lens has a focal length of 0.50 m (50 cm).

Lens power in air: F = (n_lens - 1)(1/R1 - 1/R2), with R in meters and sign by surface curvature convention.

Two thin lenses separated by distance d: F_total = F1 + F2 - d(F1)(F2); contact lenses add powers directly (d = 0).

Vertex distance matters above about +/-4 D; a minus lens moved closer to the eye needs less minus power (effective power F_new = F/(1 - dF)).

Spherical equivalent = sphere + (cylinder/2); a -2.00 -1.00 x 180 refracts as -2.50 D equivalent.

Prism diopter = 100 x tan(deviation angle); 1 prism diopter displaces an image 1 cm at 1 m.

With-the-rule astigmatism: steepest meridian vertical (near 90 degrees), corrected by minus cylinder axis near 180.

Tear film layers: lipid (meibomian glands), aqueous (lacrimal and accessory glands), mucin (goblet cells); mucin deficiency destabilizes the film.

Cornea has five layers: epithelium, Bowman layer, stroma, Descemet membrane, endothelium; the endothelium does not regenerate and maintains deturgescence.

Aqueous humor is produced by the ciliary epithelium, flows through the pupil, and drains mainly via trabecular meshwork into Schlemm canal.

Ciliary muscle contraction releases zonular tension and increases lens power (accommodation); the lens stiffens with age (presbyopia).

Retina: rods mediate dim-light and peripheral vision, cones mediate acuity and color; the fovea is cone-dense and avascular.

Optic nerve head has no photoreceptors, producing the physiologic blind spot about 15 degrees temporal to fixation.

Extraocular muscles: four recti (superior, inferior, medial, lateral) and two obliques; superior oblique is innervated by CN IV, lateral rectus by CN VI, the rest by CN III.

Normal adult intraocular pressure is roughly 10-21 mmHg; aqueous outflow resistance raises IOP when the trabecular pathway is obstructed.

Mydriatic/cycloplegic duration: tropicamide is short-acting (hours); cyclopentolate intermediate; atropine longest (up to 1-2 weeks).

Phenylephrine is a direct alpha-1 agonist causing pupil dilation without cycloplegia; it can raise blood pressure in susceptible patients.

Topical beta-blockers (timolol) lower IOP by reducing aqueous production; they are contraindicated in asthma and heart block.

Prostaglandin analogs (latanoprost) increase uveoscleral outflow and commonly cause iris darkening and eyelash growth.

Pilocarpine is a direct cholinergic agonist that constricts the pupil and increases trabecular outflow.

Punctal occlusion for 1-2 minutes after instillation reduces systemic absorption via the nasolacrimal duct.

Instill one drop at a time; wait about 5 minutes between different drops to avoid washout of the first agent.

Topical anesthetics (proparacaine) act within seconds for minutes and are not for chronic home use; they can mask injury and delay healing.

Record chief complaint, onset, duration, laterality, associated symptoms, and prior ocular history before testing.

Distance acuity: test at the calibrated 20 ft (6 m) line; pinhole improves refractive blur but not media or retinal disease.

Near acuity uses a card at 40 cm (16 in); record the smallest line read and any add used.

Cover test detects tropia (manifest) versus phoria (latent) deviation; alternate cover breaks fusion to reveal total deviation.

Confrontation visual fields screen peripheral vision by comparing the patient's field to the examiner's at about 1 m.

Ishihara plates screen red-green color deficiency; a normal result does not exclude acquired (blue-yellow) defects.

Amsler grid testing detects central/metamorphopsia changes suggestive of macular disease.

Document acuity with the correction used (sc, cc, or pinhole) and the method (Snellen, ETDRS) for reproducibility.

Clean and disinfect tonometer tips per manufacturer instructions between patients; disposable tips are single-use.

Goldmann applanation tonometry requires fluorescein and topical anesthetic; the prism tip should be cleaned and dried before use.

Keratometry measures corneal curvature in diopters or millimeters and is used to fit contact lenses and estimate IOL power.

Autorefraction gives an objective starting point; manifest refraction and subjective refinement determine the final prescription.

Slit-lamp biomicroscopy: diffuse illumination for general view, optic section for depth, and cobalt blue with fluorescein for corneal staining.

A-scan biometry measures axial length for IOL calculation; B-scan ultrasound images posterior segment when media are opaque.

Position the patient's chin on the chin rest and forehead against the strap for slit-lamp and tonometry; align the canthus to the marker.

Before any procedure, verify patient identity, procedure, and consent, and confirm allergies and current medications.

Hand hygiene with soap and water or alcohol-based rub is the single most effective infection-control measure between patients.

Standard precautions treat all blood and body fluids as potentially infectious; use gloves for contact with tears, blood, or mucous membranes.

Disinfect high-touch surfaces and shared instruments between patients; follow contact time specified by the disinfectant label.

Sharps go into puncture-resistant containers; never recap needles by hand.

Report needlestick or splash exposures immediately per facility protocol; post-exposure prophylaxis may be indicated.

Protect patient confidentiality under HIPAA; disclose protected health information only for treatment, payment, or operations, or with authorization.

Document findings objectively in the medical record; correct errors with a single line and initials, never obliterate entries.

Verify insurance eligibility and obtain prior authorization before procedures when required to avoid claim denials.

Snellen fraction 20/40 means the patient identifies at 20 ft a letter a normal eye resolves at 40 ft; larger denominator = worse acuity.

Diopter D = 1/f in meters; a +2.00 D lens has a focal length of 0.50 m (50 cm).

Lens power in air: F = (n_lens - 1)(1/R1 - 1/R2), with R in meters and sign by surface curvature convention.

Two thin lenses separated by distance d: F_total = F1 + F2 - d(F1)(F2); contact lenses add powers directly (d = 0).

Vertex distance matters above about +/-4 D; moving a minus lens closer to the eye needs less minus power (effective power F_new = F/(1 - dF)).

Spherical equivalent = sphere + (cylinder/2); a -2.00 -1.00 x 180 refracts as -2.50 D equivalent.

Prism diopter = 100 x tan(deviation angle); 1 prism diopter displaces an image 1 cm at 1 m.

With-the-rule astigmatism: steepest meridian vertical (near 90 degrees), corrected by minus cylinder axis near 180.

Tear film layers: lipid (meibomian glands), aqueous (lacrimal and accessory glands), mucin (goblet cells); mucin deficiency destabilizes the film.

Cornea has five layers: epithelium, Bowman layer, stroma, Descemet membrane, endothelium; the endothelium does not regenerate and maintains deturgescence.

Aqueous humor is produced by the ciliary epithelium, flows through the pupil, and drains mainly via trabecular meshwork into Schlemm canal.

Ciliary muscle contraction releases zonular tension and increases lens power (accommodation); the lens stiffens with age (presbyopia).

Retina: rods mediate dim-light and peripheral vision, cones mediate acuity and color; the fovea is cone-dense and avascular.

Optic nerve head has no photoreceptors, producing the physiologic blind spot about 15 degrees temporal to fixation.

Extraocular muscles: four recti (superior, inferior, medial, lateral) and two obliques; superior oblique is innervated by CN IV, lateral rectus by CN VI, the rest by CN III.

Normal adult intraocular pressure is roughly 10-21 mmHg; aqueous outflow resistance raises IOP when the trabecular pathway is obstructed.

Mydriatic/cycloplegic duration: tropicamide is short-acting (hours); cyclopentolate intermediate; atropine longest (up to 1-2 weeks).

Phenylephrine is a direct alpha-1 agonist causing pupil dilation without cycloplegia; it can raise blood pressure in susceptible patients.

Topical beta-blockers (timolol) lower IOP by reducing aqueous production; they are contraindicated in asthma and heart block.

Prostaglandin analogs (latanoprost) increase uveoscleral outflow and commonly cause iris darkening and eyelash growth.

Pilocarpine is a direct cholinergic agonist that constricts the pupil and increases trabecular outflow.

Punctal occlusion for 1-2 minutes after instillation reduces systemic absorption via the nasolacrimal duct.

Instill one drop at a time; wait about 5 minutes between different drops to avoid washout of the first agent.

Topical anesthetics (proparacaine) act within seconds for minutes and are not for chronic home use; they can mask injury and delay healing.

Record chief complaint, onset, duration, laterality, associated symptoms, and prior ocular history before testing.

Distance acuity: test at the calibrated 20 ft (6 m) line; pinhole improves refractive blur but not media or retinal disease.

Near acuity uses a card at 40 cm (16 in); record the smallest line read and any add used.

Cover test detects tropia (manifest) versus phoria (latent) deviation; alternate cover breaks fusion to reveal total deviation.

Confrontation visual fields screen peripheral vision by comparing the patient's field to the examiner's at about 1 m.

Ishihara plates screen red-green color deficiency; a normal result does not exclude acquired (blue-yellow) defects.

Amsler grid testing detects central/metamorphopsia changes suggestive of macular disease.

Document acuity with the correction used (sc, cc, or pinhole) and the method (Snellen, ETDRS) for reproducibility.

Clean and disinfect tonometer tips per manufacturer instructions between patients; disposable tips are single-use.

Goldmann applanation tonometry requires fluorescein and topical anesthetic; the prism tip should be cleaned and dried before use.

Keratometry measures corneal curvature in diopters or millimeters and is used to fit contact lenses and estimate IOL power.

Autorefraction gives an objective starting point; manifest refraction and subjective refinement determine the final prescription.

Slit-lamp biomicroscopy: diffuse illumination for general view, optic section for depth, and cobalt blue with fluorescein for corneal staining.

A-scan biometry measures axial length for IOL calculation; B-scan ultrasound images posterior segment when media are opaque.

Position the patient's chin on the chin rest and forehead against the strap for slit-lamp and tonometry; align the canthus to the marker.

Before any procedure, verify patient identity, procedure, and consent, and confirm allergies and current medications.

Hand hygiene with soap and water or alcohol-based rub is the single most effective infection-control measure between patients.

Standard precautions treat all blood and body fluids as potentially infectious; use gloves for contact with tears, blood, or mucous membranes.

Disinfect high-touch surfaces and shared instruments between patients; follow contact time specified by the disinfectant label.

Sharps go into puncture-resistant containers; never recap needles by hand.

Report needlestick or splash exposures immediately per facility protocol; post-exposure prophylaxis may be indicated.

Protect patient confidentiality under HIPAA; disclose protected health information only for treatment, payment, or operations, or with authorization.

Document findings objectively in the medical record; correct errors with a single line and initials, never obliterate entries.

Verify insurance eligibility and obtain prior authorization before procedures when required to avoid claim denials.