NBEO TMOD cheat sheet

Pretest probability drives test choice: a test's post-test probability depends on disease prevalence in the population tested, so a positive result in a low-prevalence setting often remains a false positive (positive predictive value falls as prevalence falls; negative predictive value rises).

Sensitivity = TP/(TP+FN); specificity = TN/(TN+FP). A highly sensitive test is best for ruling out (SnNout: high Sensitivity, Negative result rules out); a highly specific test is best for ruling in (SpPin: high Specificity, Positive result rules in).

Likelihood ratios are prevalence-independent: LR+ = sensitivity/(1 − specificity); LR− = (1 − sensitivity)/specificity. LR+ >10 or LR− <0.1 produces large, often conclusive shifts in post-test probability; LR 2–5 or 0.2–0.5 yields only small shifts.

Post-test odds = pretest odds × likelihood ratio; convert probability to odds (odds = p/(1−p)) before multiplying and back afterward.

A diagnostic hypothesis is strengthened by findings with high specificity and by convergence of independent tests; repeated concordant low-specificity findings (e.g., redness, tearing) add little discriminative value.

Red-flag triage precedes diagnosis: sudden painless vision loss, new flashes/floaters with a curtain, painful red eye with decreased vision, or afferent pupillary defect mandate urgent referral before elective workup.

Ocular emergencies by time frame: chemical burn = immediate irrigation before any testing; acute angle closure, giant cell arteritis, retinal artery occlusion, and endophthalmitis require same-day management.

Ancillary testing follows the examination, not the reverse: order visual fields, OCT, or angiography to answer a specific question raised by history and biomicroscopy, and confirm that the result would change management.

Differential diagnosis is narrowed by pattern recognition of onset (sudden vs gradual), laterality, pain, and associated systemic findings; monocular vs binocular diplopia and transient vs persistent vision loss each split the differential in half.

Intraocular pressure is a risk factor, not a diagnosis: normal-tension glaucoma occurs with pressures ≤21 mmHg, and ocular hypertension has elevated pressure without glaucomatous damage; management depends on disc, field, and risk profile.

Glaucoma progression is judged on structural (retinal nerve fiber layer, disc rim) and functional (visual field) concordance; a single field is unreliable, and reliability indices (fixation losses, false positives/negatives) must be checked before acting.

A visual field defect is glaucomatous when it respects the horizontal midline, is present on repeat testing, and corresponds to disc structure; isolated single-point or cloverleaf patterns often reflect artifact.

OCT retinal nerve fiber layer thickness is compared with age-matched normative data and the patient's own baseline; a thin rim with a compatible field defect supports glaucoma, while a suspicious disc alone may need monitoring.

Anterior chamber angle assessment determines management: occludable angles warrant prophylactic laser peripheral iridotomy, while open-angle disease is managed with topical therapy, laser trabeculoplasty, or surgery by target pressure.

Diabetic retinopathy grading drives follow-up: mild nonproliferative disease may be monitored at 6–12 months, while severe nonproliferative or any proliferative disease requires referral for panretinal photocoagulation or anti-VEGF; macular edema is treated regardless of grade.

Amsler grid and OCT findings of subretinal fluid or hemorrhage in age-related macular degeneration indicate conversion to exudative disease; anti-VEGF injection is time-sensitive, and delay worsens visual outcome.

Corneal ulcer management is guided by stain and culture: bacterial ulcers need frequent topical antibiotics with daily review, fungal ulcers need antifungal agents and are slower to respond, and any ulcer with hypopyon or worsening needs urgent ophthalmology input.

Systemic associations change the plan: a patient with anterior uveitis and joint or skin findings needs systemic workup, and long-term topical steroid use requires monitoring for cataract, pressure rise, and infection.

Referral thresholds and follow-up intervals must be documented explicitly, with the reason for referral and the level of urgency stated so the receiving clinician can triage appropriately.