Kuwait MOH Optometrist cheat sheet

Cornea: 5 layers (epithelium, Bowman, stroma, Descemet, endothelium); epithelium and endothelium regenerate, Bowman and Descemet do not.

Corneal nutrition: avascular; derives oxygen from tears and limbal vessels, glucose from aqueous; endothelial Na+/K+ ATPase pump maintains deturgescence.

Aqueous drainage: trabecular meshwork → Schlemm canal → collector channels → episcleral veins (major); uveoscleral route ~10-15%.

Embryology: surface ectoderm → lens and corneal epithelium; neural ectoderm → retina, RPE, iris epithelium, optic nerve; neural crest → corneal stroma/endothelium, sclera, trabeculum, ciliary muscle.

Retinal layers: photoreceptors outermost; fovea has only cones, no rods, and is avascular (foveal avascular zone).

Optic nerve: ~1.2 million axons; myelination begins behind the lamina cribrosa (hence no myelin in the nerve head).

Tear film: lipid (meibomian), aqueous (lacrimal and accessory glands), mucin (goblet cells); mucin layer converts hydrophobic epithelium to hydrophilic.

Ciliary body: pars plicata produces aqueous; parasympathetic stimulation and beta-2 agonists increase secretion; carbonic anhydrase inhibitors reduce it.

Vergence formula: L' = L + F; thin lens power F = 1/f (metres); additivity applies to thin lenses in air in contact.

Snell's law: n1 sin θ1 = n2 sin θ2; critical angle sin θc = n2/n1 when n1 > n2.

Reduced vergence: L = n/l; effective power change on vertex distance d: Fnew = F/(1 − dF).

Schematic eye (Gullstrand reduced): power ~60 D, axial length ~22.2-24 mm; 1 mm axial change ≈ 3 D refractive change at the eye.

Astigmatism: Jackson cross-cylinder; with-the-rule = steeper vertical meridian (minus cylinder axis near 180°).

Prentice's rule: prism dioptres = decentration (cm) × power (D); used for prism thinning and tolerance checks.

Spectral transmission: CR-39 transmits to ~380 nm; polycarbonate blocks UV below ~380 nm; high-index 1.74 has lower Abbe value (~33) than CR-39 (~58).

ANSI tolerance example: spectacle cylinder power tolerance ±0.13 D for powers ≤ 2.00 D (verify against current standard).

Glaucoma: open-angle diagnosis requires optic disc cupping/R NFL loss plus field defect, not IOP alone; IOP is a risk factor, not a criterion.

Amsler grid and confrontation fields are screening tests; Humphrey 24-2 SITA is the standard automated perimetry for glaucoma follow-up.

Diabetic retinopathy: ETDRS grading; clinically significant macular oedema = thickening within 500 µm of fovea, hard exudates within 500 µm with adjacent thickening, or lesion ≥ 1 disc area within 1 disc diameter of fovea.

ARMD: dry = drusen and RPE change; wet = choroidal neovascularisation with subretinal fluid/haemorrhage; anti-VEGF is first-line for wet.

Keratoconus: inferior steepening, Fleischer ring, Vogt striae, Munson sign; topography/tomography (e.g., Belin/Ambrósio) is diagnostic.

Anterior uveitis: cells and flare in anterior chamber, ciliary flush, photophobia; HLA-B27 and sarcoidosis are common associations.

Cataract grading: LOCS III uses nuclear colour/opalescence, cortical and posterior subcapsular grading from standard photographs.

Red-flag symptoms: sudden painless vision loss, flashes/floaters with field loss, painful red eye with reduced acuity, and monocular diplopia warrant urgent referral.

Dk/t is the key oxygen parameter; extended wear requires higher Dk/t than daily wear (commonly ≥ 125 for overnight silicone hydrogel use).

Base curve selection: steeper BC on steep corneas; fluorescein pattern should show even, aligned distribution, not excessive central pooling or bearing.

Sagittal depth and diameter determine fit more than BC alone; larger diameter increases sag and tightness.

Rigid lens optics: tear lens between cornea and lens contributes power; a flat fit creates a minus tear lens, a steep fit a plus tear lens.

Keratometry conversion: BC ≈ average K + 0.7-0.8 mm for alignment in rigid lenses (adjust per design).

Solution compatibility: multipurpose solutions contain preservatives (e.g., PHMB, polyquaternium-1); hydrogen peroxide systems require neutralisation before insertion.

Prosthetic eye: custom PMMA or silicone; polished surface and regular removal/cleaning reduce discharge and socket inflammation.

Complications: microbial keratitis risk rises with overnight wear; CLARE is a sterile infiltrative response to hypoxia and lens deposits.

Cover test: alternate cover reveals total deviation; uncover test detects phoria recovery; prism neutralisation quantifies the deviation.

Hirschberg: 1 mm corneal light reflex displacement ≈ 7° or ~15 prism dioptres.

Krimsky: prism over the fixing eye until reflexes align; useful when fixation is not alternate.

AC/A ratio: normal 4-6 Δ/D; high AC/A suggests convergence excess esotropia, low AC/A suggests divergence excess exotropia.

Amblyopia: critical period early childhood; occlusion or atropine penalisation is first-line; treat refractive error first.

Esotropia with onset after 6 months without accommodative component is infantile; onset after 2 years with hyperopia is often accommodative.

Suppression and ARC (anomalous retinal correspondence) develop in constant strabismus; Worth 4-dot and Bagolini striated lenses assess sensory status.

Stereopsis: Titmus fly ~3000 sec arc; TNO uses random-dot with red-green glasses; normal stereoacuity is ≤ 60 sec arc.

Mydriatics: tropicamide 0.5-1% (short, 4-6 h), cyclopentolate 1% (24 h), atropine 1% (7-14 days); phenylephrine 2.5% is a dilator without cycloplegia.

Topical anaesthetics (proparacaine, oxybuprocaine) are for examination only; chronic use causes epithelial toxicity and masking of disease.

Fluorescein: stains epithelial defects and assesses tear break-up; Seidel test detects aqueous leak in corneal perforation.

Chemical injury: irrigate copiously with saline or Ringer's for at least 30 minutes, check pH, evert lids for particulate matter; alkali injuries are worse than acids.

Steroid use: monitor IOP (steroid response), infection risk, and cataract; taper to avoid rebound inflammation.

Beta-blockers (timolol) are contraindicated in asthma and heart block; prostaglandin analogues cause iris darkening and periorbital fat atrophy.

Pilocarpine causes miosis, accommodative spasm and brow ache; it is less used now but effective in angle-closure prevention.

Anaphylaxis: adrenaline IM 0.5 mg (1:1000) into anterolateral thigh, repeat after 5 minutes if needed; call emergency services.

OCT: cross-sectional retinal imaging; macular thickness normative databases; used for glaucoma RNFL and macular GCC analysis.

Visual field: Humphrey 24-2 covers central 24°; 10-2 for macular/advanced field loss; reliability indices are fixation losses, false positives and false negatives.

OCT-A detects flow without dye; useful for CNV, diabetic ischaemia and glaucoma perfusion; artefacts from motion and projection must be excluded.

Fundus fluorescein angiography: phases are choroidal, arterial, arteriovenous, venous; leakage, staining and pooling are interpreted by timing.

B-scan ultrasound: axial length, intraocular tumours, dense cataract and vitreous haemorrhage where fundus is obscured.

Pachymetry: central corneal thickness affects Goldmann applanation; thinner corneas underestimate IOP and are a glaucoma risk factor.

Gonioscopy: Shaffer grading 0-4; grade 0-1 indicates narrow/closed angle; indentation gonioscopy distinguishes appositional from synechial closure.

Topography: Placido-based (curvature) vs Scheimpflug (elevation); elevation maps detect ectasia earlier than curvature alone.

Consent: valid consent requires capacity, adequate information and voluntariness; document discussion of risks and alternatives.

Confidentiality: disclosure without consent is permitted where required by law, for public safety, or to prevent serious harm; record the justification.

Record keeping: contemporaneous, legible, signed and dated; retain per local regulation (commonly 7-10 years, longer for minors).

Screening vs diagnostic testing: screening requires high sensitivity and acceptable specificity; positive screens need confirmatory testing.

Diabetic retinopathy screening intervals: annual photographic screening is standard; more frequent if sight-threatening changes are present.

Public health: prevalence of refractive error is the leading cause of correctable visual impairment; uncorrected error dominates globally.

Advertising and claims: avoid misleading or comparative claims; only claim qualifications actually held and registered.

Referral duty: urgent same-day referral for retinal detachment, acute angle closure or chemical injury; routine referral for stable cataract.

Hand hygiene: alcohol-based rub for routine; soap and water when hands are visibly soiled or after contact with spores (e.g., C. difficile).

Tonometer prisms: wipe with alcohol or use disposable tips; do not reuse without disinfection; follow manufacturer contact time.

Contact lens trial sets: single-use or disinfected between patients; never use tap water on lenses or cases.

Standard precautions apply to all patients; additional transmission-based precautions for known infections.

Sharps and waste: segregate at point of use; never recap needles; report needlestick injuries immediately.

Incident reporting: near-misses and adverse events are reported through the local system; root cause analysis informs system change.

Prescription writing: include patient identifiers, drug, strength, directions, quantity, date, prescriber signature and registration number.

Equipment safety: electrical equipment requires periodic testing; calibration of tonometers, keratometers and perimeters is documented.