COMT cheat sheet

Cornea has five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, endothelium; central thickness averages about 0.54 mm and the endothelium does not regenerate.

Aqueous humor is secreted by the ciliary epithelium of the pars plicata, passes through the pupil, and exits mainly via trabecular meshwork, Schlemm's canal, and episcleral veins (conventional outflow, roughly 90%).

Tear film has three components: lipid from meibomian glands, aqueous from the lacrimal gland, and mucin from conjunctival goblet cells.

Retina contains about 120 million rods (dim light, periphery) and about 6 million cones (color, acuity, concentrated at the fovea); the foveola contains no rods.

Cranial nerve supply: CN III innervates superior, inferior, and medial rectus plus inferior oblique; CN IV innervates superior oblique; CN VI innervates lateral rectus.

Optic disc cupping greater than 0.6, asymmetry greater than 0.2 between eyes, or progressive cupping with notching or disc hemorrhage suggests glaucomatous optic neuropathy.

Cataract is classified by location as nuclear sclerotic, cortical, or posterior subcapsular; posterior subcapsular opacity causes disproportionate glare and is associated with corticosteroid use.

Nonproliferative diabetic retinopathy shows microaneurysms, dot-blot hemorrhages, and hard exudates; proliferative disease adds neovascularization with risk of vitreous hemorrhage and traction detachment.

Snell's law: n1 sin θ1 = n2 sin θ2, describing the bending of light at an interface between media of differing refractive index.

Thin lens power in diopters equals 1 divided by the focal length in meters (F = 1/f).

Keratometry converts corneal radius to power with F = (1.3375 − 1)/r, using the keratometric index because only the anterior corneal surface is measured.

Refractive indices used clinically: cornea 1.376, aqueous and vitreous 1.336, crystalline lens approximately 1.42.

Vertex distance conversion: Fc = Fs / (1 − d × Fs), with d in meters; the adjustment becomes clinically significant above about plus or minus 4.00 D.

With-the-rule astigmatism has the steeper meridian vertical (plus cylinder axis near 90 degrees); against-the-rule has the steeper meridian horizontal (axis near 180 degrees).

One prism diopter deviates a light ray by 1 centimeter at a distance of 1 meter; prism power quantifies strabismic deviation.

LARS rule for toric soft lenses: if the lens rotates to the clinician's left, add to the cylinder axis; if it rotates right, subtract.

Goldmann applanation tonometry: normal intraocular pressure is about 10 to 21 mmHg; central corneal thickness must be considered because thick corneas overestimate and thin corneas underestimate pressure.

Humphrey field programs: 24-2 tests 54 points at 6-degree spacing, 30-2 tests 76 points, and 10-2 tests 68 points for macular evaluation.

Mean deviation reflects overall field depression (cataract, advanced glaucoma); pattern standard deviation reflects localized loss after adjusting for overall depression.

Glaucomatous field defects respect the horizontal midline and include nasal step, arcuate scotoma, and paracentral defects.

A-scan is a one-dimensional amplitude display used to measure axial length for IOL power calculation; B-scan is a two-dimensional cross-section used to view the posterior segment.

Optical coherence tomography quantifies retinal nerve fiber layer and macular thickness; thinning indicates ganglion cell and axon loss.

Amsler grid testing screens the central 10 degrees for metamorphopsia in macular disease.

Swinging-flashlight testing detects a relative afferent pupillary defect (Marcus Gunn pupil), indicating asymmetric optic nerve or extensive retinal disease.

Pachymetry measures central corneal thickness and corneal topography maps curvature for astigmatism and keratoconus screening.

Cycloplegic duration: tropicamide about 4 to 6 hours, cyclopentolate about 24 hours, atropine 7 to 14 days; phenylephrine 2.5% dilates without cycloplegia.

Topical anesthetics (proparacaine 0.5%, tetracaine 0.5%) last about 15 to 20 minutes; chronic use produces corneal epithelial toxicity.

Fluoroquinolones (moxifloxacin, gatifloxacin) are first-line for bacterial keratitis and conjunctivitis; erythromycin ointment is often used in children.

Topical corticosteroids such as prednisolone acetate 1% can raise intraocular pressure, induce cataract, and mask infection.

Topical beta-blockers such as timolol reduce aqueous production; they are avoided or used cautiously in asthma, COPD, bradycardia, and heart block.

Prostaglandin analogs such as latanoprost increase uveoscleral outflow and can cause iris darkening, eyelash growth, and periorbital pigmentation.

Acetazolamide, a carbonic anhydrase inhibitor, reduces aqueous production and is given orally or intravenously for acute elevations of intraocular pressure.

Sterilization standards: steam autoclave at 121 degrees Celsius and 15 psi for 15 to 20 minutes; tonometer tips may be disinfected with 70% isopropyl alcohol or 10% bleach.

Snellen acuity is tested at 6 meters (20 feet); a 20/20 letter subtends 5 arc minutes total, with each stroke subtending 1 arc minute.

Acuities are recorded as corrected and uncorrected for OD, OS, and OU, with pinhole used to separate refractive from organic vision loss.

Cataract surgery uses phacoemulsification with an intraocular lens whose power is calculated from axial length and keratometry.

10-0 nylon is standard for corneal and cataract incisions; polyglactin (Vicryl) is used for conjunctiva.

Povidone-iodine 5% applied to the cul-de-sac and periocular skin before intraocular surgery reduces the risk of endophthalmitis.

The surgical time-out verifies patient identity, correct eye with site marked, procedure, consent, and antibiotic prophylaxis before incision.

Informed consent is obtained by the physician; the assistant may witness the signature and document the discussion in the record.

Visual acuity procedure: occlude one eye without allowing squinting, test distance and near, and repeat with a pinhole if acuity is reduced.

Instill drops into the lower cul-de-sac without touching the tip to the ocular surface, then have the patient close gently.

Punctal occlusion for 1 to 2 minutes after instillation reduces nasolacrimal drainage and systemic absorption of the drug.

Chemical ocular injury: irrigate with saline or lactated Ringer's for at least 15 to 30 minutes and check conjunctival pH until neutral before further examination.

Vital signs (blood pressure, pulse, respiration) are documented at each visit and during any urgent presentation.

Current medications including over-the-counter and herbal products, plus all drug allergies, are recorded at every visit.

Slit lamp positioning requires chin on the chinrest, forehead against the strap, and the canthal alignment marker level with the outer canthus.

HIPAA permits disclosure of protected health information only with a signed, dated authorization naming the recipient and purpose, except for treatment, payment, or operations.

CPT modifier 25 is appended to an evaluation and management code when a separately identifiable service is performed on the same day as a procedure.

Modifiers LT and RT identify the left or right eye or side on a claim and clarify the structure examined or treated.

ICD-10 diagnosis codes must match the documented clinical findings to establish medical necessity for the billed service.

Insurance workflow sequence: eligibility verification, prior authorization, claim submission, then denial management and appeal.

The OSHA bloodborne pathogens standard requires an exposure control plan, hepatitis B vaccination offer, personal protective equipment, and employee training.

Sterilization logs and inventory par levels are maintained to document autoclave cycles and prevent supply shortages.