Iran Ophthalmology Specialty Board cheat sheet

Vergence after a thin lens: V' = V + F, where V = n/l (object side) and V' = n'/l' (image side); F is lens power in diopters when distances are in meters.

Spherical equivalent = sphere + ½ cylinder; used for retinoscopy, IOL power estimation in irregular astigmatism, and judging refractive error tolerance.

Knapp's rule: for axial ametropia, place a spectacle correction at the anterior focal plane (vertex distance ~13 mm) so the retinal image size is matched to that of an emmetropic eye.

Vertex distance conversion: F_new = F_old / (1 − d·F_old), d in meters; a −10.00 D lens moved 12 mm closer to the eye becomes about −8.93 D.

Jackson cross-cylinder: cross-cylinder at 45° to the axis identifies axis error; cylinder power changes are assessed with the cross-cylinder axis aligned to the trial cylinder axis.

Duochrome (red-green) test relies on longitudinal chromatic aberration: in myopia the red side is clearer, in hyperopia the green side is clearer; it refines spherical endpoint, not cylinder.

Hard (RGP) lens flexure and corneal astigmatism: rigid lenses neutralize most corneal astigmatism; soft toric lenses require stable axis marking and adequate lens thickness for stabilization.

Contact lens oxygen: Dk/t (barrier-corrected transmissibility) governs corneal hypoxia; extended wear requires higher Dk/t than daily wear, and closed-eye oxygen demand is far lower than open-eye.

Astigmatism types: with-the-rule = steep vertical meridian (minus cylinder axis near 180°); against-the-rule = steep horizontal meridian (minus cylinder axis near 90°); oblique = axis 30–60° or 120–150°.

Corneal layers: epithelium (non-keratinized, 5–7 layers), Bowman's layer, stroma (~90% thickness, collagen type I), Descemet's membrane (type IV), endothelium (non-replicating, pump function).

Keratoconus diagnosis: inferior steepening on topography, posterior elevation on tomography, thinnest point displaced inferotemporally, and epithelial thinning; progression is monitored by Kmax and pachymetry change.

Corneal ulcer empiric therapy: for bacterial keratitis, start fortified cefazolin 5% plus tobramycin 1.3–1.5% hourly; for contact-lens-related ulcers add anti-Pseudomonas coverage and consider antifungal if risk factors are present.

Acanthamoeba keratitis: ring infiltrate, radial keratoneuritis, severe pain out of proportion to signs, contact lens with tap-water exposure; culture on non-nutrient agar with E. coli overlay, confocal microscopy.

Fuchs endothelial dystrophy: guttae on specular microscopy, corneal guttata, decreased endothelial cell density; hypertonic saline for early edema, endothelial keratoplasty (DSEK/DMEK) for advanced disease.

Dry eye (aqueous deficient): Schirmer I < 5 mm/5 min, tear break-up time < 10 s, rose bengal or lissamine green staining; Sjögren's requires sicca symptoms plus autoantibodies or positive labial biopsy.

Ocular surface squamous neoplasia: gelatinous or leukoplakic limbal lesion; impression cytology, anterior segment OCT, and excisional biopsy with cryotherapy or topical mitomycin C/interferon.

Corneal abrasion management: topical antibiotic prophylaxis, cycloplegic for pain, no patching for contact-lens-related or organic injuries; re-examine for infiltrate if pain worsens after 24–48 h.

Biometry: optical biometry (partial coherence interferometry) is preferred; use immersion or optical for axial length, keratometry for corneal power, and IOL formulas - SRK/T, Hoffer Q, Holladay 1 for normal eyes, Barrett or Hill-RBF for long/short eyes.

Phacoemulsification steps: clear corneal incision (2.2–2.8 mm), continuous curvilinear capsulorhexis (~5–5.5 mm), hydrodissection, nucleus disassembly, cortex removal, IOL implantation in the capsular bag.

Endophthalmitis prophylaxis: intracameral cefuroxime (1 mg/0.1 mL) or moxifloxacin at end of surgery reduces risk; postoperative pain out of proportion with hypopyon requires vitreous tap and intravitreal antibiotics.

Posterior capsule rupture management: stop phaco, maintain anterior chamber with viscoelastic, avoid vitreous traction, consider anterior vitrectomy; sulcus IOL or ACIOL if capsular support is lost.

Pediatric cataract: surgery within the first 6–8 weeks for unilateral dense cataract and within ~10 weeks for bilateral to prevent amblyopia; leave posterior capsule open or perform posterior capsulotomy plus anterior vitrectomy in infants.

IOL power calculation after refractive surgery: use historical data, no-history formulas (Haigis-L, Barrett True-K), and adjust for altered anterior/posterior corneal curvature ratio.

Cataract grading: LOCS III grades nuclear color/opalescence, cortical and posterior subcapsular opacities on standardized photographs; PSC and nuclear sclerosis affect contrast sensitivity more than visual acuity early.

Intraoperative floppy iris syndrome: associated with tamsulosin (alpha-1 antagonist); use preoperative atropine, intracameral phenylephrine, cohesive viscoelastic, and iris hooks or pupil expanders.

Goldmann applanation tonometry: pressure = force/area with a 3.06 mm diameter applanated area; corneal thickness affects readings - thin corneas underestimate and thick corneas overestimate true IOP.

Gonioscopy: Shaffer grading (0 closed to 4 open); identify Schwalbe's line, trabecular meshwork, scleral spur, ciliary body band; indentation gonioscopy distinguishes appositional from synechial closure.

Open-angle glaucoma treatment: prostaglandin analogs (latanoprost) first-line, then beta-blockers, alpha-2 agonists, carbonic anhydrase inhibitors; combination therapy or laser trabeculoplasty (SLT) as alternatives.

Acute angle-closure: topical beta-blocker, alpha-agonist, pilocarpine, systemic acetazolamide, osmotic agents (mannitol), then laser peripheral iridotomy to relieve pupillary block.

Optic disc glaucoma signs: increased cup-to-disc ratio, neuroretinal rim thinning (ISNT rule), disc hemorrhage, beta-zone peripapillary atrophy, retinal nerve fiber layer defect; correlate with visual field.

Visual field defects in glaucoma: nasal step, arcuate scotoma, paracentral scotoma, altitudinal defect; field loss follows nerve fiber layer bundle anatomy and respects the horizontal midline.

Angle-closure risk: shallow anterior chamber, short axial length, thick lens, hyperopia, plateau iris; prophylactic iridotomy for fellow eye in acute angle-closure and for high-risk occludable angles.

Trabeculectomy: guarded filtration surgery with mitomycin C to reduce scarring; complications include hypotony, choroidal effusion, bleb leak, and late blebitis/endophthalmitis.

Diabetic retinopathy grading: nonproliferative (microaneurysms, dot-blot hemorrhages, hard exudates, cotton-wool spots) versus proliferative (neovascularization at disc or elsewhere, vitreous hemorrhage, tractional detachment).

Diabetic macular edema: center-involving edema treated with anti-VEGF (ranibizumab, aflibercept, bevacizumab) or focal/grid laser for non-center-involving; OCT is the monitoring standard.

Retinal detachment: rhegmatogenous (break with subretinal fluid), tractional (fibrovascular membranes), exudative (no break, fluid from tumor/inflammation); rhegmatogenous requires scleral buckle, vitrectomy, or pneumatic retinopexy.

Central retinal artery occlusion: sudden painless monocular vision loss, cherry-red spot, boxcarring, afferent pupillary defect; retinal survival ~90 min; evaluate for carotid and cardiac embolic source.

Central retinal vein occlusion: blood-and-thunder fundus, disc edema, macular edema; anti-VEGF for macular edema; check for hypertension, diabetes, glaucoma, and hypercoagulability in young patients.

Age-related macular degeneration: dry type with drusen and geographic atrophy; wet type with choroidal neovascular membrane treated by anti-VEGF; Amsler grid and OCT for monitoring.

Retinopathy of prematurity: screening for infants ≤30 weeks gestation or ≤1500 g birth weight; zone, stage, extent, plus disease; treat type 1 ROP with laser or anti-VEGF.

Vitreous hemorrhage causes: proliferative diabetic retinopathy, retinal tear/detachment, posterior vitreous detachment with break, trauma, Terson syndrome; B-scan ultrasound when fundus is obscured.

Anterior uveitis: cells and flare in the anterior chamber, ciliary flush, photophobia; HLA-B27-associated in seronegative spondyloarthropathies; treat with topical corticosteroids and cycloplegics.

Granulomatous uveitis: mutton-fat keratic precipitates, iris nodules (Koeppe at pupillary margin, Busacca on stroma); consider sarcoidosis, tuberculosis, syphilis, VKH, sympathetic ophthalmia.

Posterior uveitis: vitritis, retinitis, choroiditis; infectious workup includes syphilis (FTA-ABS/TPPA), tuberculosis (IGRA, chest imaging), toxoplasmosis (serology), and HIV testing.

Toxoplasma retinochoroiditis: focal necrotizing retinitis adjacent to a pigmented scar, 'headlight in the fog' vitritis; treat with pyrimethamine plus sulfadiazine and folinic acid, or trimethoprim-sulfamethoxazole.

Vogt-Koyanagi-Harada disease: bilateral granulomatous panuveitis with serous retinal detachments, meningismus, vitiligo, poliosis, hearing loss; treat with high-dose systemic corticosteroids.

Sympathetic ophthalmia: bilateral granulomatous panuveitis after penetrating trauma or surgery in the exciting eye; enucleation within 2 weeks of injury reduces risk; immunosuppression is the mainstay.

Cytomegalovirus retinitis: in advanced HIV (CD4 < 50), 'pizza-pie' or brushfire hemorrhagic retinitis; treat with ganciclovir, valganciclovir, foscarnet, or cidofovir; immune reconstitution with ART.

Behçet uveitis: recurrent hypopyon, occlusive retinal vasculitis, oral/genital ulcers; treat with systemic corticosteroids and immunosuppressants (azathioprine, cyclosporine, anti-TNF agents).

Relative afferent pupillary defect: detected with swinging flashlight test; indicates optic nerve or severe retinal disease on the affected side; not caused by media opacity or mild cataract.

Optic neuritis: painful vision loss, decreased color vision, afferent pupillary defect, visual field defect; MRI of brain/orbits with contrast; treat with IV methylprednisolone for recovery speed, not final acuity.

Papilledema: bilateral disc edema from raised intracranial pressure; preserves visual acuity early, enlarges blind spot, may cause transient visual obscurations; neuroimaging then lumbar puncture.

Third nerve palsy: ptosis, eye down and out, mydriasis; pupil-involving palsy requires urgent angiography/MRA to exclude posterior communicating artery aneurysm.

Horner syndrome: ptosis, miosis, anhidrosis; topical apraclonidine or cocaine test confirms; localization with hydroxyamphetamine; Pancoast tumor and carotid dissection are key causes.

Internuclear ophthalmoplegia: impaired adduction on the side of the lesion with abducting nystagmus in the fellow eye; MLF lesion; bilateral in multiple sclerosis, unilateral in brainstem stroke.

Giant cell arteritis: age > 50, headache, jaw claudication, scalp tenderness, elevated ESR/CRP; start high-dose corticosteroids immediately and confirm with temporal artery biopsy within 2 weeks.

Cortical blindness: bilateral occipital lesions, normal pupils and fundi, macular sparing if occipital pole is spared; Anton syndrome is denial of blindness.

Ectropion: involutional (horizontal laxity) treated with lateral tarsal strip; cicatricial (scarring) requires grafting; paralytic from facial nerve palsy requires support and lubrication.

Entropion: involutional from lower lid retractor dehiscence and horizontal laxity; repair with retractor reattachment plus lateral tarsal strip; trichiasis treated by epilation, cryotherapy, or lid margin rotation.

Ptosis: levator function > 10 mm suggests levator resection; < 5 mm suggests frontalis sling; check for Marcus Gunn jaw-winking, Horner syndrome, and myasthenia gravis.

Orbital cellulitis: fever, proptosis, pain with eye movement, restricted motility; children often from ethmoid sinusitis; treat with IV antibiotics and imaging; watch for cavernous sinus thrombosis and abscess.

Thyroid eye disease: lid retraction, proptosis, restrictive strabismus, optic neuropathy; smoking cessation is critical; treat active disease with steroids or teprotumumab; orbital decompression for compressive optic neuropathy.

Dacryocystorhinostomy (DCR): for nasolacrimal duct obstruction; external or endoscopic approach creating a fistula between lacrimal sac and nasal cavity; silicone stents may be used.

Basal cell carcinoma: most common eyelid malignancy, pearly nodule with telangiectasia, lower lid predilection; Mohs micrographic surgery for margin control; rare metastasis.

Orbital compartment syndrome: acute proptosis, pain, vision loss after trauma or surgery; emergent lateral canthotomy and cantholysis; retrobulbar hemorrhage is a common cause.

Amblyopia types: strabismic, anisometropic, deprivational, isoametropic; treat by correcting refractive error, patching or atropine penalization of the better eye; critical period is early childhood.

Esotropia: infantile (onset < 6 months, large angle, treat with surgery), accommodative (hyperopia, responds to glasses), partially accommodative, and divergence insufficiency in older patients.

Exotropia: intermittent exotropia is common; assess control, stereopsis, and suppression; surgery for deterioration or poor control; overminus lenses can be used short-term.

Strabismus surgery: recession weakens a muscle, resection strengthens; adjustable sutures for adult strabismus; risk of anterior segment ischemia with multiple muscle surgery.

Leukocoria differential: retinoblastoma, congenital cataract, persistent fetal vasculature, Coats disease, toxocariasis, retinal detachment; urgent evaluation with fundus exam and imaging.

Congenital glaucoma: buphthalmos, corneal edema, photophobia, tearing, elevated IOP; treat with goniotomy or trabeculotomy, then medical therapy; examine under anesthesia.

Retinopathy of prematurity screening: first exam at 4–6 weeks postnatal age or 31–33 weeks postmenstrual age; follow until vascularization is complete; treat type 1 disease with laser or anti-VEGF.

Nasolacrimal duct obstruction: tearing and discharge in infants; conservative management with massage; probing if persistent beyond 6–12 months; dacryocystocele may require early intervention.

Retinoblastoma: leukocoria and strabismus, calcification on CT, RB1 gene mutation; treat with systemic chemotherapy, intra-arterial chemotherapy, focal therapy, enucleation, or radiation depending on stage.

Uveal melanoma: most common primary intraocular malignancy in adults; risk factors include light iris color, UV exposure, and BAP1 mutation; treat with plaque brachytherapy, proton beam, or enucleation.

Choroidal nevus versus melanoma: thickness > 2 mm, subretinal fluid, orange pigment, acoustic hollowness, and margin within 3 mm of optic disc favor melanoma.

Squamous cell carcinoma of conjunctiva: UV exposure, limbal location, leukoplakia; treat with excision with cryotherapy, topical mitomycin C, or interferon; monitor for orbital invasion.

Rhabdomyosarcoma: most common orbital malignancy in children; rapid proptosis, ptosis; biopsy and systemic chemotherapy plus radiation; embryonal subtype most common.

Lymphoma of the orbit: older adults, salmon-patch conjunctival lesion, bilateral involvement; biopsy for flow cytometry and molecular studies; systemic staging required.

Sebaceous carcinoma: eyelid tumor often misdiagnosed as chalazion or blepharitis; pagetoid spread; requires wide excision or Mohs surgery with map biopsies.

Histopathology basics: melanoma shows atypical melanocytes with mitoses; basal cell carcinoma shows peripheral palisading and clefting; squamous cell carcinoma shows keratin pearls and intercellular bridges.

Prevalence versus incidence: prevalence is proportion with disease at a point in time; incidence is new cases per population at risk over a period; both depend on the denominator and case definition.

Sensitivity and specificity: sensitivity = true positives / (true positives + false negatives); specificity = true negatives / (true negatives + false positives); both are independent of prevalence.

Positive predictive value depends on prevalence: PPV = (sensitivity × prevalence) / [(sensitivity × prevalence) + ((1 − specificity) × (1 − prevalence))].

Randomized controlled trial: randomization reduces confounding; intention-to-treat analysis preserves randomization; blinding reduces observer bias; power depends on effect size, variance, and sample size.

Odds ratio versus relative risk: odds ratio approximates relative risk only when the outcome is rare; cohort studies estimate relative risk directly; case-control studies estimate odds ratio.

Screening criteria: disease must be important, have a detectable preclinical phase, an acceptable test, and effective early treatment; lead-time bias and length bias inflate apparent survival.

Confounding: a variable associated with both exposure and outcome that distorts the exposure–outcome relationship; addressed by randomization, stratification, or multivariable adjustment.

Age-standardized rates: adjust for differences in age distribution between populations to compare disease burden fairly; direct standardization applies study age-specific rates to a standard population.

Vision 2020 / WHO global eye health: cataract, uncorrected refractive error, glaucoma, age-related macular degeneration, diabetic retinopathy, and trachoma are major causes of avoidable blindness.

Trachoma: caused by Chlamydia trachomatis serovars A–C; SAFE strategy (surgery for trichiasis, antibiotics with azithromycin, facial cleanliness, environmental improvement); WHO grading uses TF, TI, TS, TT, CO.

Cataract surgical coverage: proportion of people with operable cataract who have received surgery; a key indicator of eye care service delivery and equity.

Diabetic retinopathy screening: annual dilated fundus exam or retinal photography for all diabetics; frequency depends on type and duration; telemedicine programs improve access in underserved areas.

Refractive error correction: uncorrected refractive error is a leading cause of visual impairment globally; school screening and affordable spectacles are cost-effective interventions.

Onchocerciasis: caused by Onchocerca volvulus transmitted by blackflies; ivermectin mass drug administration; can cause river blindness and anterior segment inflammation.

Vitamin A deficiency: causes xerophthalmia, Bitot spots, and keratomalacia; supplementation programs reduce childhood blindness and mortality in deficient populations.

Blindness definition: WHO uses visual acuity < 3/60 in the better eye with best correction; low vision is < 6/18 but ≥ 3/60; legal blindness definitions vary by country.

Corneal transparency depends on uniform collagen fibril spacing and relative dehydration maintained by endothelial pump; stromal edema disrupts regular lattice and causes scatter.

Aqueous humor production: ciliary epithelium (pars plicata) via active secretion (carbonic anhydrase, Na+/K+-ATPase); outflow via trabecular meshwork and Schlemm's canal (conventional) and uveoscleral route.

Retinal layers: photoreceptors, outer limiting membrane, outer nuclear layer, outer plexiform, inner nuclear, inner plexiform, ganglion cell layer, nerve fiber layer, internal limiting membrane; Müller cells span the retina.

Phototransduction: light isomerizes 11-cis-retinal to all-trans-retinal; rhodopsin activates transducin, which activates phosphodiesterase to hydrolyze cGMP, closing cGMP-gated sodium channels and hyperpolarizing the cell.

Visual pathway: retina → optic nerve → chiasm (nasal fibers cross) → optic tract → lateral geniculate nucleus → optic radiations → primary visual cortex (V1) in the occipital lobe.

Pharmacology: topical beta-blockers reduce aqueous production; prostaglandin analogs increase uveoscleral outflow; pilocarpine increases trabecular outflow; atropine and cyclopentolate are antimuscarinic cycloplegics.

Microbiology: common ocular pathogens include Staphylococcus aureus, Pseudomonas aeruginosa (contact lens), Streptococcus pneumoniae, and Neisseria gonorrhoeae (hyperacute conjunctivitis).

Genetics: retinoblastoma follows Knudson's two-hit hypothesis with RB1 tumor suppressor; Leber hereditary optic neuropathy is mitochondrial (m.11778G>A in ND4); Marfan syndrome is FBN1 autosomal dominant.

Cross-sectional studies measure prevalence and associations but cannot establish temporality; cohort studies measure incidence and relative risk; case-control studies are efficient for rare diseases.

Number needed to treat = 1 / absolute risk reduction; number needed to harm = 1 / absolute risk increase; both depend on baseline risk and should be reported with confidence intervals.

Bias types: selection bias (non-random sampling), information bias (measurement error), recall bias (case-control), and observer bias (lack of masking); each threatens validity differently.

Confidence interval interpretation: a 95% CI excluding the null value (1 for ratios, 0 for differences) corresponds to statistical significance at the 0.05 level; it also conveys precision.

Screening program evaluation: lead-time bias, length bias, and overdiagnosis can make screening appear to improve survival without reducing mortality; mortality endpoints are required.

Random error versus systematic error: increasing sample size reduces random error but not systematic error; calibration and standardization address systematic error.

Cataract surgery outcomes: benchmark indicators include postoperative visual acuity, complication rates (endophthalmitis, posterior capsule rupture), and patient-reported outcomes; registries support quality improvement.

Preventive care: control of diabetes and hypertension reduces retinopathy and vascular events; smoking cessation reduces thyroid eye disease progression and AMD risk.