DHA Optometrist cheat sheet

Cornea has five layers: epithelium, Bowman's layer, stroma, Descemet's membrane, endothelium; endothelium is non-regenerating and maintains deturgescence via Na+/K+ ATPase pumps.

Trabecular meshwork drains aqueous into Schlemm's canal; obstruction raises IOP and underlies open-angle glaucoma.

Fovea centralis contains only cones and no retinal vessels; it lies temporal to the optic disc and provides maximal acuity.

Optic nerve head carries about 1.2 million axons, lacks photoreceptors, and creates the physiological blind spot.

Ciliary muscle contraction slackens zonules, allowing the lens to thicken for accommodation (Helmholtz theory).

Lens derives nutrients from aqueous; its capsule is thickest anteriorly and thinnest at the posterior pole.

Blood-retinal barrier is formed by tight junctions of retinal capillary endothelium and the retinal pigment epithelium.

Extraocular muscles: four recti and two obliques; superior oblique is innervated by CN IV and acts as intorter in adduction.

Total refractive power of the reduced eye is about +60 D, of which the cornea contributes roughly +43 D and the crystalline lens about +17 D.

Snell's law: n1 sin θ1 = n2 sin θ2; refraction occurs only when refractive indices differ.

Vergence formula: L = n/l, and L' = L + F; thin lens power F = 1/f in dioptres with f in metres.

Myopia corrected with diverging (minus) lenses; hyperopia with converging (plus) lenses; cylinder corrects astigmatism.

Tear film has lipid, aqueous and mucin layers; loss of mucin destabilises the film and shortens break-up time.

Aqueous humour is secreted by the ciliary epithelium at roughly 2–3 µL/min and exits mainly via trabecular outflow.

Phototransduction hyperpolarises photoreceptors; rods mediate scotopic vision and cones photopic and colour vision.

Pupil light reflex afferent limb is CN II and efferent limb CN III; a relative afferent defect indicates optic nerve or retinal disease.

Spherical equivalent = sphere + (cylinder/2); useful when a toric correction cannot be given.

Jackson cross-cylinder at axis ±45° refines cylinder axis; at axis ±90° refines cylinder power.

In duochrome testing, red-before-green suggests myopic overcorrection and green-before-red suggests undercorrection.

Asthenopia plus a small hyperopic refraction favours prescribing the full plus found on cycloplegic refraction.

Anisometropia greater than 1 D in children risks amblyopia and warrants correction and monitoring.

With-the-rule astigmatism has the steeper meridian near 90°; against-the-rule near 180°.

Vertex distance changes effective power: moving a minus lens away from the eye increases its effective minus power.

Prism dioptre = 100 × tan(deviation angle in degrees); Prentice's rule: prism = decentration (cm) × lens power (D).

Working distance in metres converts to dioptres to subtract: 50 cm adds +2.00 D, 67 cm adds +1.50 D, 1 m adds +1.00 D.

With motion indicates neutrality requires more plus; against motion requires more minus in the trial frame.

Neutrality is the endpoint where the reflex fills the pupil and no movement is seen with the sleeve.

Cycloplegic retinoscopy with cyclopentolate 1% is standard in children to reveal latent hyperopia.

Retinoscopy is performed in the primary position with both eyes open where possible to avoid accommodative artefact.

Prescribing rule: give the maximum plus and minimum minus that maintains best visual acuity.

Prism adaptation and tolerances: generally avoid more than 2–3 D of aniseikonia from anisometropic spectacle correction.

High plus lenses magnify and high minus lenses minify; contact lenses reduce aniseikonia compared with spectacles.

Keratometry measures anterior corneal curvature and is used to select the base curve of rigid lenses.

Sagittal depth determines lens fit; steeper base curve gives greater sag and tighter fit.

Oxygen transmissibility Dk/t, not Dk alone, governs corneal oxygenation through a lens.

Rigid lens fluorescein pattern: central pooling means steep fit; central bearing means flat fit.

Soft lens replacement schedules reduce deposit-related complications; daily disposable lenses minimise care burden.

Contraindications include active keratitis, severe dry eye and poor hygiene compliance.

Giant papillary conjunctivitis is linked to lens deposits and mechanical irritation; management is refit and replacement.

Orthokeratology flattens the central cornea to reduce myopia; overnight wear requires strict hygiene and monitoring.

Bacterial keratitis presents with pain, photophobia, hypopyon and stromal infiltrate; urgent topical antibiotic is first-line.

Acute angle-closure glaucoma shows mid-dilated fixed pupil, corneal oedema and high IOP; treat with IOP-lowering agents and laser iridotomy.

Diabetic retinopathy: microaneurysms, dot-blot haemorrhages, hard exudates; proliferative disease needs laser or anti-VEGF.

Age-related macular degeneration: dry form shows drusen and geographic atrophy; wet form shows choroidal neovascularisation.

Cataract is opacity of the crystalline lens; surgery replaces the lens with an intraocular lens implant.

Topical beta-blockers are contraindicated in asthma; prostaglandin analogues increase pigmentation and lashes.

Atropine is a cycloplegic and mydriatic; pilocarpine induces miosis and increases aqueous outflow.

Steroid drops reduce inflammation but raise IOP and risk infection; monitor IOP during prolonged use.

Cover test detects manifest deviation; alternate cover test reveals latent deviation by dissociating fusion.

Amblyopia is reduced acuity without organic cause; treatment includes occlusion or atropine penalisation.

Critical period for visual development is early childhood; screening should occur before school age.

Esotropia with accommodation is managed with plus lenses; intermittent exotropia may need surgery.

Stereopsis is tested with Titmus or TNO; reduced stereoacuity suggests binocular dysfunction.

Convergence insufficiency presents with near exophoria and reduced near point of convergence; treated with exercises.

Suppression and anomalous retinal correspondence are sensory adaptations to strabismus.

Prism cover test quantifies deviation; prism dioptres guide surgical or optical management.

Snellen acuity is recorded at 6 m; 6/6 is normal, and each line represents about 0.1 log unit change.

Goldmann applanation tonometry is the reference standard; normal IOP is roughly 10–21 mmHg.

Visual field testing with Humphrey perimetry maps sensitivity; glaucoma shows arcuate and nasal step defects.

Slit lamp biomicroscopy with a 90 D or 78 D lens allows fundus examination.

OCT provides cross-sectional retinal imaging and detects macular oedema and ganglion cell loss.

Low vision aids include magnifiers, telescopes and electronic devices; magnification = required acuity / present acuity.

Kestenbaum rule estimates magnification needed from best-corrected acuity for reading.

Amsler grid detects central scotoma and metamorphopsia in macular disease.

Dubai Health Authority regulates healthcare professionals; optometrists must hold a valid DHA licence to practise.

Scope of practice: optometrists diagnose and manage refractive and some ocular conditions; surgery is outside scope.

Informed consent must be obtained before examination, dilation or any procedure.

Patient records must be accurate, confidential and retained per DHA requirements.

Infection control: hand hygiene and instrument disinfection are mandatory between patients.

Referral to an ophthalmologist is required for conditions beyond optometric scope, such as suspected malignancy or acute glaucoma.

Advertising and professional conduct must comply with DHA ethics rules; patient confidentiality is paramount.

Continuing professional development is required to maintain licensure and competence.

Cornea power ~43 D plus lens ~17 D gives total ~60 D; loss of lens power is corrected with plus lenses.

Retinoscopy working distance subtraction: divide 1 by working distance in metres to get dioptres to subtract.

Spherical equivalent = sphere + half cylinder; used for toric-to-spherical conversion.

Tonometry normal range 10–21 mmHg; Goldmann applanation is reference standard.

Amblyopia management: correct refractive error, then occlusion or atropine penalisation.

Contact lens Dk/t governs oxygen delivery; higher Dk/t reduces hypoxia risk.

DHA licence and informed consent are prerequisites for optometric practice in Dubai.

Low vision magnification = required acuity divided by present acuity; Kestenbaum rule estimates need.

Snellen 6/6 is normal acuity; each line change is about 0.1 logMAR.

Cover test reveals manifest deviation; alternate cover reveals latent deviation.

Bacterial keratitis: pain, photophobia, hypopyon; urgent topical antibiotics.

Acute angle-closure: fixed mid-dilated pupil, corneal oedema, high IOP; urgent referral.

Prescribing rule: maximum plus, minimum minus maintaining best acuity.

Prism dioptre = 100 × tan(angle in degrees); Prentice's rule: prism = decentration × power.

OCT images retinal cross-sections; Humphrey perimetry maps visual field defects.

DHA licence, informed consent and confidentiality are core regulatory duties.

Vertex distance affects effective power; moving a minus lens away increases minus effect.

Anisometropia >1 D in children risks amblyopia; correct and monitor.

Cycloplegic retinoscopy with cyclopentolate reveals latent hyperopia in children.

Rigid lens fluorescein: central pooling = steep, central bearing = flat.

Giant papillary conjunctivitis from deposits; refit and increase replacement frequency.

Prostaglandin analogues increase pigmentation and lashes; beta-blockers contraindicated in asthma.

Amblyopia critical period is early childhood; screen before school age.

Amsler grid detects central scotoma and metamorphopsia.

Duochrome: red-before-green = myopic overcorrection; green-before-red = undercorrection.

Jackson cross-cylinder refines axis and power of astigmatic correction.

Trabecular meshwork obstruction raises IOP; open-angle glaucoma mechanism.

Fovea has only cones and no vessels; optic disc creates blind spot.

Stereopsis tested with Titmus or TNO; reduced stereo suggests binocular dysfunction.

Convergence insufficiency: near exophoria, reduced NPC; treat with exercises.

Infection control and instrument disinfection mandatory between patients.

Referral to ophthalmologist for conditions beyond optometric scope.

Aqueous secretion ~2–3 µL/min; exits via trabecular meshwork into Schlemm's canal.

Tear film lipid, aqueous, mucin layers; mucin loss shortens break-up time.

Rods mediate scotopic vision; cones photopic and colour vision.

Pupil reflex: afferent CN II, efferent CN III; RAPD indicates optic nerve or retinal disease.

Diabetic retinopathy: microaneurysms, dot-blot haemorrhages, hard exudates; proliferative needs laser or anti-VEGF.

AMD dry form: drusen and geographic atrophy; wet form: choroidal neovascularisation.

Atropine cycloplegic and mydriatic; pilocarpine miosis and increased outflow.

Steroid drops raise IOP and risk infection; monitor during prolonged use.

Keratometry guides rigid lens base curve selection.

Sagittal depth determines fit; steeper base curve = tighter fit.

Soft lens replacement schedules reduce deposit complications.

Contraindications: active keratitis, severe dry eye, poor hygiene.

Orthokeratology flattens central cornea to reduce myopia; overnight wear needs strict hygiene.

Esotropia with accommodation managed with plus lenses; intermittent exotropia may need surgery.

Suppression and anomalous retinal correspondence are sensory adaptations to strabismus.

Slit lamp with 90 D or 78 D lens allows fundus examination.

Snell's law: n1 sin θ1 = n2 sin θ2; refraction only when indices differ.

Vergence: L = n/l; L' = L + F; thin lens F = 1/f in dioptres.

Myopia corrected with minus lenses; hyperopia with plus; cylinder for astigmatism.

With-the-rule astigmatism steeper near 90°; against-the-rule near 180°.

High plus lenses magnify; high minus minify; contact lenses reduce aniseikonia.

Cataract is lens opacity; surgery replaces with intraocular lens.

Low vision aids: magnifiers, telescopes, electronic devices.

Kestenbaum rule estimates magnification from best-corrected acuity for reading.

Retinoscopy neutrality: reflex fills pupil, no movement with sleeve.

Working distance 50 cm = +2.00 D subtraction; 67 cm = +1.50 D; 1 m = +1.00 D.

With motion needs more plus; against motion needs more minus.

Cycloplegic retinoscopy standard in children with cyclopentolate 1%.

Prescribing: maximum plus, minimum minus maintaining best acuity.

Avoid >2–3 D aniseikonia from anisometropic spectacle correction.

DHA licence required to practise; scope excludes surgery.

Informed consent before examination, dilation or procedure.

Cornea five layers; endothelium non-regenerating, maintains deturgescence.

Ciliary muscle contraction slackens zonules; lens thickens for accommodation.

Lens capsule thickest anteriorly, thinnest posterior pole.

Blood-retinal barrier: retinal capillary endothelium and RPE tight junctions.

Superior oblique CN IV, acts as intorter in adduction.

Goldmann applanation tonometry reference standard; normal 10–21 mmHg.

Humphrey perimetry shows arcuate and nasal step defects in glaucoma.

Records confidential and retained per DHA requirements.

Optic nerve head ~1.2 million axons, no photoreceptors, creates blind spot.

Fovea centralis temporal to optic disc, maximal acuity.

Prism dioptre = 100 × tan(angle); Prentice's rule: prism = decentration (cm) × power (D).

Cover test manifest deviation; alternate cover latent deviation.

Prism cover test quantifies deviation for surgical or optical management.

OCT detects macular oedema and ganglion cell loss.

Infection control: hand hygiene and instrument disinfection between patients.

CPD required to maintain licensure and competence.

Aqueous humour secretion by ciliary epithelium; trabecular outflow main route.

Diabetic retinopathy screening: microaneurysms, haemorrhages, exudates.

AMD wet form needs anti-VEGF; dry form drusen and atrophy.

Bacterial keratitis urgent topical antibiotics; hypopyon is a red flag.

Acute angle-closure: mid-dilated fixed pupil, corneal oedema, high IOP; laser iridotomy.

Topical beta-blockers contraindicated in asthma.

Prostaglandin analogues increase pigmentation and lashes.

Referral to ophthalmologist for conditions beyond optometric scope.

Keratometry measures anterior corneal curvature for rigid lens base curve.

Dk/t governs corneal oxygenation through a contact lens.

Rigid lens fluorescein: central pooling steep, central bearing flat.

Giant papillary conjunctivitis from deposits; refit and replace more often.

Orthokeratology flattens central cornea; overnight wear needs monitoring.

Amblyopia: reduced acuity without organic cause; occlusion or atropine.

Critical period early childhood; screen before school age.

Stereopsis Titmus or TNO; reduced stereo suggests binocular dysfunction.

Snellen 6 m; 6/6 normal; each line ~0.1 log unit change.

Goldmann applanation reference standard; normal IOP 10–21 mmHg.

Humphrey perimetry maps sensitivity; glaucoma arcuate and nasal step defects.

Slit lamp with 90 D or 78 D lens for fundus examination.

OCT cross-sectional retinal imaging; macular oedema and ganglion cell loss.

Low vision magnification = required acuity / present acuity.

Kestenbaum rule estimates magnification for reading.

Amsler grid detects central scotoma and metamorphopsia.

DHA regulates healthcare professionals; valid licence required to practise.

Scope of practice: diagnose and manage refractive and some ocular conditions; no surgery.

Informed consent before examination, dilation or procedure.

Records accurate, confidential, retained per DHA requirements.

Infection control: hand hygiene and instrument disinfection between patients.

Referral to ophthalmologist for conditions beyond optometric scope.

Advertising and conduct comply with DHA ethics rules; confidentiality paramount.

CPD required to maintain licensure and competence.

Total eye power ~60 D: cornea ~43 D, lens ~17 D.

Snell's law: n1 sin θ1 = n2 sin θ2.

Vergence L = n/l; L' = L + F; F = 1/f.

Spherical equivalent = sphere + cylinder/2.

Vertex distance changes effective power; minus lens moved away increases minus.

Prism dioptre = 100 × tan(angle); Prentice's rule.

Prescribing: maximum plus, minimum minus maintaining best acuity.

Retinoscopy working distance subtraction: 1/distance in metres.

Jackson cross-cylinder ±45° refines axis; ±90° refines power.

Duochrome red-before-green myopic overcorrection; green-before-red undercorrection.

Anisometropia >1 D in children risks amblyopia; correct and monitor.

Cycloplegic retinoscopy with cyclopentolate 1% in children.

Esotropia with accommodation managed with plus lenses.

Convergence insufficiency: near exophoria, reduced NPC; exercises.

Suppression and anomalous retinal correspondence are sensory adaptations.

Tonometry normal 10–21 mmHg; Goldmann reference standard.

Cornea endothelium non-regenerating; maintains deturgescence via Na+/K+ ATPase.

Trabecular meshwork drains aqueous into Schlemm's canal.

Fovea only cones, no retinal vessels; maximal acuity.

Optic nerve head lacks photoreceptors; blind spot.

Ciliary muscle contraction slackens zonules; lens thickens.

Lens capsule thickest anteriorly, thinnest posterior pole.

Blood-retinal barrier: capillary endothelium and RPE tight junctions.

Superior oblique CN IV; intorter in adduction.

Tear film lipid, aqueous, mucin; mucin loss shortens break-up time.

Aqueous secretion ~2–3 µL/min; trabecular outflow main route.

Rods scotopic; cones photopic and colour vision.

Pupil reflex afferent CN II, efferent CN III; RAPD indicates optic nerve or retinal disease.

Bacterial keratitis pain, photophobia, hypopyon; urgent antibiotics.

Acute angle-closure mid-dilated fixed pupil, corneal oedema, high IOP.

Atropine cycloplegic and mydriatic; pilocarpine miosis and increased outflow.

Steroid drops raise IOP and risk infection; monitor.

Keratometry guides rigid lens base curve selection.

Sagittal depth determines fit; steeper base curve tighter.

Dk/t governs corneal oxygenation.

Rigid lens fluorescein: central pooling steep, central bearing flat.

Soft lens replacement reduces deposit complications.

Contraindications: active keratitis, severe dry eye, poor hygiene.

Orthokeratology flattens central cornea; overnight wear monitoring.

Giant papillary conjunctivitis from deposits; refit and replace.

Snellen 6/6 normal; each line ~0.1 log unit.

Goldmann applanation reference standard; normal IOP 10–21 mmHg.

Humphrey perimetry maps sensitivity; glaucoma arcuate and nasal step defects.

Slit lamp with 90 D or 78 D lens for fundus examination.

OCT cross-sectional imaging; macular oedema and ganglion cell loss.

Low vision magnification = required acuity / present acuity.

Kestenbaum rule estimates magnification for reading.

Amsler grid detects central scotoma and metamorphopsia.

DHA licence required to practise; scope excludes surgery.

Informed consent before examination, dilation or procedure.

Records accurate, confidential, retained per DHA requirements.

Infection control: hand hygiene and instrument disinfection between patients.

Referral to ophthalmologist for conditions beyond optometric scope.

Advertising and conduct comply with DHA ethics rules; confidentiality paramount.

CPD required to maintain licensure and competence.

Patient confidentiality is paramount in professional practice.

Total eye power ~60 D: cornea ~43 D, lens ~17 D.

Snell's law: n1 sin θ1 = n2 sin θ2.

Vergence L = n/l; L' = L + F; F = 1/f.

Spherical equivalent = sphere + cylinder/2.

Vertex distance changes effective power; minus lens moved away increases minus.

Prism dioptre = 100 × tan(angle); Prentice's rule.

Prescribing: maximum plus, minimum minus maintaining best acuity.

Retinoscopy working distance subtraction: 1/distance in metres.

Jackson cross-cylinder ±45° refines axis; ±90° refines power.

Duochrome red-before-green myopic overcorrection; green-before-red undercorrection.

Anisometropia >1 D in children risks amblyopia; correct and monitor.

Cycloplegic retinoscopy with cyclopentolate 1% in children.

Esotropia with accommodation managed with plus lenses.

Convergence insufficiency: near exophoria, reduced NPC; exercises.

Suppression and anomalous retinal correspondence are sensory adaptations.

Tonometry normal 10–21 mmHg; Goldmann reference standard.

Cornea endothelium non-regenerating; maintains deturgescence via Na+/K+ ATPase.

Trabecular meshwork drains aqueous into Schlemm's canal.

Fovea only cones, no retinal vessels; maximal acuity.

Optic nerve head lacks photoreceptors; blind spot.

Ciliary muscle contraction slackens zonules; lens thickens.

Lens capsule thickest anteriorly, thinnest posterior pole.

Blood-retinal barrier: capillary endothelium and RPE tight junctions.

Superior oblique CN IV; intorter in adduction.

Tear film lipid, aqueous, mucin; mucin loss shortens break-up time.

Aqueous secretion ~2–3 µL/min; trabecular outflow main route.

Rods scotopic; cones photopic and colour vision.

Pupil reflex afferent CN II, efferent CN III; RAPD indicates optic nerve or retinal disease.

Bacterial keratitis pain, photophobia, hypopyon; urgent antibiotics.

Acute angle-closure mid-dilated fixed pupil, corneal oedema, high IOP.

Atropine cycloplegic and mydriatic; pilocarpine miosis and increased outflow.

Steroid drops raise IOP and risk infection; monitor.

Keratometry guides rigid lens base curve selection.

Sagittal depth determines fit; steeper base curve tighter.

Dk/t governs corneal oxygenation.

Rigid lens fluorescein: central pooling steep, central bearing flat.

Soft lens replacement reduces deposit complications.

Contraindications: active keratitis, severe dry eye, poor hygiene.

Orthokeratology flattens central cornea; overnight wear monitoring.

Giant papillary conjunctivitis from deposits; refit and replace.

Snellen 6/6 normal; each line ~0.1 log unit.

Goldmann applanation reference standard; normal IOP 10–21 mmHg.

Humphrey perimetry maps sensitivity; glaucoma arcuate and nasal step defects.

Slit lamp with 90 D or 78 D lens for fundus examination.

OCT cross-sectional imaging; macular oedema and ganglion cell loss.

Low vision magnification = required acuity / present acuity.

Kestenbaum rule estimates magnification for reading.

Amsler grid detects central scotoma and metamorphopsia.

DHA licence required to practise; scope excludes surgery.

Informed consent before examination, dilation or procedure.

Records accurate, confidential, retained per DHA requirements.

Infection control: hand hygiene and instrument disinfection between patients.

Referral to ophthalmologist for conditions beyond optometric scope.

Advertising and conduct comply with DHA ethics rules; confidentiality paramount.

CPD required to maintain licensure and competence.

Patient confidentiality is paramount in professional practice.

Total eye power ~60 D: cornea ~43 D, lens ~17 D.

Snell's law: n1 sin θ1 = n2 sin θ2.

Vergence L = n/l; L' = L + F; F = 1/f.

Spherical equivalent = sphere + cylinder/2.

Vertex distance changes effective power; minus lens moved away increases minus.

Prism dioptre = 100 × tan(angle); Prentice's rule.

Prescribing: maximum plus, minimum minus maintaining best acuity.

Retinoscopy working distance subtraction: 1/distance in metres.

Jackson cross-cylinder ±45° refines axis; ±90° refines power.

Duochrome red-before-green myopic overcorrection; green-before-red undercorrection.

Anisometropia >1 D in children risks amblyopia; correct and monitor.

Cycloplegic retinoscopy with cyclopentolate 1% in children.

Esotropia with accommodation managed with plus lenses.

Convergence insufficiency: near exophoria, reduced NPC; exercises.

Suppression and anomalous retinal correspondence are sensory adaptations.

Tonometry normal 10–21 mmHg; Goldmann reference standard.

Cornea endothelium non-regenerating; maintains deturgescence via Na+/K+ ATPase.

Trabecular meshwork drains aqueous into Schlemm's canal.

Fovea only cones, no retinal vessels; maximal acuity.

Optic nerve head lacks photoreceptors; blind spot.

Ciliary muscle contraction slackens zonules; lens thickens.

Lens capsule thickest anteriorly, thinnest posterior pole.

Blood-retinal barrier: capillary endothelium and RPE tight junctions.

Superior oblique CN IV; intorter in adduction.