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EBOD practice questions

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Question 1Optics, Refraction and Refractive Surgery

A transparent medium has a refractive index of 1.50. What is the approximate speed of light inside this medium?

  1. 3.0 × 10^8 m/s
  2. 4.5 × 10^8 m/s
  3. 2.0 × 10^8 m/s Correct answer.
  4. 1.5 × 10^8 m/s

Explanation

The refractive index is the ratio of the speed of light in vacuum to the speed in the medium (n = c/v). Therefore v = c/n = 3.0 × 10^8 / 1.50, which gives 2.0 × 10^8 m/s.

Question 2Optics, Refraction and Refractive Surgery

Which ocular structure contributes approximately +43 D to the total refractive power of the eye?

  1. The cornea Correct answer.
  2. The vitreous humour
  3. The aqueous humour
  4. The crystalline lens

Explanation

Most of the eye's power comes from the air–cornea interface, where the large difference in refractive index produces about +43 D. The crystalline lens adds roughly +19 D, while the intraocular fluids contribute negligibly.

Question 3Optics, Refraction and Refractive Surgery

In which refractive state is the far point of the eye located at infinity?

  1. Myopia
  2. Astigmatism
  3. Emmetropia Correct answer.
  4. Hyperopia

Explanation

In emmetropia the unaccommodated eye focuses parallel rays from infinity onto the retina, so the far point lies at infinity. Ametropic eyes have a far point that is either in front of or behind the eye.

Question 4Optics, Refraction and Refractive Surgery

What is the approximate total refractive power of the adult emmetropic eye?

  1. +19 D
  2. +60 D Correct answer.
  3. +50 D
  4. +43 D

Explanation

The total power of the eye is about +60 D, made up of roughly +43 D from the cornea and +19 D from the crystalline lens. These components together focus parallel light on the retina.

Question 5Optics, Refraction and Refractive Surgery

A patient's uncorrected far point is 50 cm in front of the eye. What is the spherical refractive error?

  1. Hyperopia of +2.00 D
  2. Myopia of −0.50 D
  3. Astigmatism of 2.00 D
  4. Myopia of −2.00 D Correct answer.

Explanation

A real far point in front of the eye indicates myopia, and its power equals the reciprocal of the far point distance in metres. Since 1/0.50 = 2.00, the error is −2.00 D.

Question 6Optics, Refraction and Refractive Surgery

How is the power of a lens in dioptres defined?

  1. The ratio of image size to object size
  2. The product of focal length and image distance
  3. The reciprocal of the focal length expressed in metres Correct answer.
  4. The focal length measured in centimetres

Explanation

One dioptre is the power of a lens with a focal length of one metre, so power equals 1/f where f is in metres. A shorter focal length therefore corresponds to a higher dioptric power.

Question 7Optics, Refraction and Refractive Surgery

A ray of light in air (n = 1.00) strikes glass (n = 1.50) at an angle of incidence of 30°. What is the approximate angle of refraction?

  1. 30°
  2. 19.5° Correct answer.
  3. 48.6°
  4. 15°

Explanation

Snell's law states n1·sin θ1 = n2·sin θ2. Thus sin θ2 = (1.00 × 0.500)/1.50 = 0.333, giving θ2 ≈ 19.5°; the ray bends towards the normal when entering the denser medium.

Question 8Optics, Refraction and Refractive Surgery

What is the critical angle at a glass–air interface when the glass has a refractive index of 1.50?

  1. 41.8° Correct answer.
  2. 30°
  3. 19.5°
  4. 48.6°

Explanation

Total internal reflection begins when the refracted ray grazes the interface, so sin θc = n2/n1 = 1.00/1.50 = 0.667. This gives a critical angle of approximately 41.8°.

Question 9Optics, Refraction and Refractive Surgery

A spectacle lens of −10.00 D is worn 12 mm in front of the cornea. What is the approximate power required at the corneal plane?

  1. −11.20 D
  2. −10.70 D
  3. −9.50 D
  4. −8.93 D Correct answer.

Explanation

Effective power is converted using Fc = F/(1 − dF), with d in metres. Here d = 0.012 m and F = −10.00 D, so Fc = −10.00/(1 + 0.12) ≈ −8.93 D; minus lenses become less negative as they move closer to the eye.

Question 10Optics, Refraction and Refractive Surgery

A +4.00 D lens is decentred by 5 mm. Approximately how much prism is induced at the optical centre of the eye?

  1. 8 Δ
  2. 0.2 Δ
  3. 2 Δ Correct answer.
  4. 20 Δ

Explanation

Prentice's rule states that induced prism equals decentration in centimetres multiplied by lens power in dioptres. With 0.5 cm × 4.00 D the result is 2 Δ.

Question 11Optics, Refraction and Refractive Surgery

Retinoscopy is performed at a working distance of 50 cm. Which spherical power must be subtracted from the gross finding?

  1. 2.00 D Correct answer.
  2. 0.50 D
  3. 1.00 D
  4. 3.00 D

Explanation

The working distance lens is the reciprocal of the working distance in metres. For 0.50 m this is 1/0.50 = 2.00 D, which must be subtracted from the retinoscopy result.

Question 12Optics, Refraction and Refractive Surgery

A presbyopic patient has an amplitude of accommodation of 2.00 D and reads at 40 cm. If half the amplitude should be kept in reserve, what near addition is required?

  1. +0.50 D
  2. +2.00 D
  3. +1.00 D
  4. +1.50 D Correct answer.

Explanation

The reading demand at 40 cm is 1/0.40 = 2.50 D. Reserving half the amplitude (1.00 D) leaves 1.00 D available, so the addition needed is 2.50 − 1.00 = +1.50 D.

Question 13Optics, Refraction and Refractive Surgery

Keratometry gives corneal radii of 7.50 mm in one meridian and 8.00 mm in the perpendicular meridian. What is the approximate corneal astigmatism?

  1. About 5.6 D
  2. About 1.4 D
  3. About 0.5 D
  4. About 2.8 D Correct answer.

Explanation

Corneal power is derived from the radius using the calibrated index, with powers of about 45.0 D and 42.2 D for 7.50 mm and 8.00 mm respectively. The difference between these meridians gives roughly 2.8 D of astigmatism.

Question 14Optics, Refraction and Refractive Surgery

Which biometric measurement has the greatest influence on the calculated power of an intraocular lens?

  1. Anterior chamber depth
  2. Axial length Correct answer.
  3. Crystalline lens thickness
  4. Corneal diameter

Explanation

Axial length is the dominant determinant of IOL power, and a 1 mm error can change the calculated power by roughly 2.5 to 3 D. Because its effect is so large, accurate axial length measurement is the priority in biometry.

Question 15Optics, Refraction and Refractive Surgery

In which corneal layer is the hinge flap of a laser in situ keratomileusis (LASIK) procedure created?

  1. Corneal endothelium
  2. Anterior stroma Correct answer.
  3. Descemet membrane
  4. Posterior stroma

Explanation

A LASIK flap comprises epithelium, Bowman's layer and a portion of the anterior stroma, leaving a stromal bed for excimer laser ablation. The posterior stroma, Descemet membrane and endothelium are left undisturbed.

Question 16Optics, Refraction and Refractive Surgery

Which finding is a contraindication to corneal laser refractive surgery?

  1. An age of 30 years
  2. A stable refraction for two years
  3. A central corneal thickness of 600 µm
  4. Active keratoconus Correct answer.

Explanation

Keratoconus involves progressive corneal thinning and ectasia, and laser ablation further weakens the cornea, so it is a contraindication. Stability of refraction, adult age and adequate corneal thickness are favourable features.

Question 17Optics, Refraction and Refractive Surgery

A +5.00 D thin lens is placed 2 cm in front of a +10.00 D thin lens. What is the equivalent power of this combination?

  1. 16.00 D
  2. 13.00 D
  3. 15.00 D Correct answer.
  4. 14.00 D

Explanation

For two thin lenses separated by distance d in metres, the equivalent power is F1 + F2 − d·F1·F2. Here it is 5 + 10 − (0.02 × 50) = 14.00 D.

Question 18Optics, Refraction and Refractive Surgery

A 45-year-old myope has a refraction of −8.00 D, a central corneal thickness of 480 µm and inferior corneal steepening on topography. What is the most appropriate management?

  1. Perform corneal cross-linking and then proceed with LASIK
  2. Avoid corneal laser ablation and consider a phakic intraocular lens Correct answer.
  3. Proceed with LASIK using a thin flap
  4. Perform surface ablation with mitomycin C

Explanation

Thin corneas combined with inferior steepening raise suspicion of forme fruste ectasia, in which laser ablation risks progressive ectasia. A phakic intraocular lens avoids removing corneal tissue and is preferred for high myopia in this setting.

Question 19Optics, Refraction and Refractive Surgery

Which factor most limits the accuracy of intraocular lens power calculation after previous myopic laser refractive surgery?

  1. Axial length becomes unreliable
  2. Keratometry overestimates true corneal power Correct answer.
  3. The effective lens position moves posteriorly
  4. Corneal astigmatism is always induced

Explanation

Laser ablation flattens the anterior cornea more than the posterior cornea, altering the normal front-to-back curvature ratio. Standard keratometry therefore overestimates the true corneal power, and eyes tend to become hyperopic after cataract surgery if uncorrected.

Question 20Optics, Refraction and Refractive Surgery

Why does a diffractive multifocal intraocular lens reduce spectacle dependence at the cost of contrast sensitivity?

  1. The lens material has a lower refractive index
  2. Light is split among several foci, reducing energy per image Correct answer.
  3. The haptics induce more astigmatism
  4. The optic has a smaller effective diameter

Explanation

A multifocal optic divides incoming light between a distance focus and one or more near foci. Each retinal image therefore receives only part of the available light, which lowers contrast sensitivity, particularly in dim illumination.

Question 21Cornea and External Disease

Which sequence lists the layers of the cornea in order from anterior to posterior?

  1. Epithelium, Bowman layer, stroma, Descemet membrane, endothelium Correct answer.
  2. Epithelium, Descemet membrane, stroma, Bowman layer, endothelium
  3. Epithelium, stroma, Bowman layer, Descemet membrane, endothelium
  4. Bowman layer, epithelium, Descemet membrane, stroma, endothelium

Explanation

The cornea is organized from anterior to posterior as epithelium, Bowman layer, stroma, Descemet membrane, and endothelium. Each layer contributes distinctly to barrier function, structural strength, and deturgescence.

Question 22Cornea and External Disease

Corneal sensation is mediated primarily by which nerve?

  1. Ophthalmic division of the trigeminal nerve (V1) Correct answer.
  2. Facial nerve (CN VII)
  3. Maxillary division of the trigeminal nerve (V2)
  4. Oculomotor nerve (CN III)

Explanation

Corneal nerves derive from the nasociliary branch of the ophthalmic division of the trigeminal nerve, entering via the long ciliary nerves. This is why corneal lesions produce a V1-pattern referred pain.

Question 23Cornea and External Disease

Which organism is the most common cause of contact lens–associated bacterial keratitis?

  1. Staphylococcus aureus
  2. Moraxella catarrhalis
  3. Streptococcus pneumoniae
  4. Pseudomonas aeruginosa Correct answer.

Explanation

Pseudomonas aeruginosa is the leading cause of contact lens–associated bacterial keratitis and typically produces a rapidly progressive, purulent ulcer with marked stromal melting. Its affinity for damaged epithelium and biofilm formation on lens cases underlie this association.

Question 24Cornea and External Disease

Which slit lamp finding is most characteristic of epithelial herpes simplex keratitis?

  1. A branching epithelial ulcer with terminal bulbs Correct answer.
  2. A raised gelatinous mass at the limbus
  3. A ring-shaped stromal infiltrate with central necrosis
  4. A feathery-edged stromal infiltrate with satellite lesions

Explanation

Epithelial HSV keratitis produces a dendritic ulcer with a central ulcerated bed, club-shaped terminal bulbs, and rose bengal or fluorescein staining along its margins. The dendrite reflects focal epithelial cell destruction by replicating virus.

Question 25Cornea and External Disease

Which statement best describes a pterygium?

  1. A band of calcium deposited within the superficial cornea
  2. A yellow-white conjunctival deposit near the limbus that spares the cornea
  3. A focal nodule of the bulbar conjunctiva with dilated feeding vessels
  4. A fibrovascular growth of conjunctiva that extends onto the cornea Correct answer.

Explanation

A pterygium is a wing-shaped fibrovascular proliferation of conjunctiva that crosses the limbus onto the cornea, usually nasally. Ultraviolet exposure and chronic irritation are the principal risk factors.

Question 26Cornea and External Disease

A positive Seidel test indicates which of the following?

  1. Increased corneal thickness from stromal edema
  2. A break in Descemet membrane without perforation
  3. A full-thickness wound with aqueous leaking through it Correct answer.
  4. Intact corneal epithelium after a healed abrasion

Explanation

In a Seidel test, concentrated fluorescein is applied over a suspicious wound; a positive result shows a dark stream of aqueous diluting the fluorescein, confirming full-thickness leakage. It is used to identify occult perforations and leaking surgical wounds.

Question 27Cornea and External Disease

A patient develops a corneal ulcer after being struck by a piece of vegetable matter. Slit lamp examination shows a dry, raised lesion with feathery margins and several smaller satellite lesions. What is the most likely diagnosis?

  1. Pseudomonas keratitis
  2. Herpes simplex keratitis
  3. Fungal keratitis Correct answer.
  4. Acanthamoeba keratitis

Explanation

Organic matter injury with a dry, raised, feathery-edged infiltrate and satellite lesions is the classic presentation of filamentous fungal keratitis. The satellite lesions represent adjacent foci of fungal proliferation.

Question 28Cornea and External Disease

A contact lens wearer presents with severe pain out of proportion to the visible signs, and slit lamp examination shows a ring-shaped stromal infiltrate with perineural infiltrates. Which organism is most likely responsible?

  1. Herpes simplex virus
  2. Acanthamoeba species Correct answer.
  3. Fusarium species
  4. Pseudomonas aeruginosa

Explanation

Acanthamoeba keratitis classically causes pain out of proportion to signs, radial keratoneuritis, and later a ring infiltrate, most often in contact lens wearers exposed to contaminated water. Corneal scrapings or confocal microscopy may be needed to confirm the diagnosis.

Question 29Cornea and External Disease

Which corneal finding is most characteristic of Fuchs endothelial corneal dystrophy?

  1. Bilateral subepithelial granular opacities with clear intervals
  2. Central corneal guttae with overlying stromal edema Correct answer.
  3. Axial stromal thinning with a cone-shaped protrusion
  4. Deep stromal branching lines that stain with Congo red

Explanation

Fuchs dystrophy is a bilateral, typically asymmetric disorder of the corneal endothelium characterized by central guttae (excrescences of Descemet membrane). Progressive endothelial failure produces stromal and epithelial edema with reduced vision.

Question 30Cornea and External Disease

Which retinoscopic finding is most closely associated with keratoconus?

  1. An absent red reflex with leukocoria
  2. Scissoring of the red reflex Correct answer.
  3. A uniformly dulled red reflex
  4. A bright red reflex with a central dark spot

Explanation

The irregular, cone-shaped anterior corneal surface in keratoconus splits the retinoscopic reflex into diverging bands, producing the classic scissoring reflex. This sign may be present even before marked topographic change is visible on slit lamp examination.

Question 31Cornea and External Disease

A patient reports sharp pain and tearing on waking, with a history of a corneal abrasion several months earlier. Slit lamp examination shows a loose area of epithelium. What is the most appropriate first-line management?

  1. Hypertonic saline ointment at bedtime Correct answer.
  2. Oral acyclovir
  3. Topical corticosteroid drops four times daily
  4. Penetrating keratoplasty

Explanation

Recurrent corneal erosion syndrome results from defective hemidesmosomal adhesion after epithelial injury. First-line treatment is lubrication with hypertonic saline ointment at bedtime to reduce overnight epithelial edema and mechanical shearing.

Question 32Cornea and External Disease

A patient with chronic blepharitis has a peripheral corneal infiltrate separated from the limbus by a clear zone of uninvolved cornea. What is the most likely diagnosis?

  1. Pellucid marginal degeneration
  2. Terrien marginal degeneration
  3. Staphylococcal marginal keratitis Correct answer.
  4. Mooren ulcer

Explanation

Staphylococcal marginal keratitis is an immune-complex hypersensitivity reaction to lid margin antigens, producing peripheral infiltrates that spare a clear interval adjacent to the limbus. Treatment combines lid hygiene with a short course of topical corticosteroid.

Question 33Cornea and External Disease

What is the most important initial step in managing an alkali chemical burn to the eye?

  1. Instilling a topical anesthetic and referring without irrigation
  2. Copious irrigation with balanced salt solution or Ringer lactate Correct answer.
  3. Applying a topical steroid and a pressure patch
  4. Debriding all necrotic conjunctiva before any irrigation

Explanation

Immediate, copious irrigation is the single most important intervention after a chemical burn because it removes the offending agent and limits the duration of tissue injury. Irrigation should begin at the scene and continue until the conjunctival pH normalizes.

Question 34Cornea and External Disease

Which ocular surface stain is most sensitive for detecting devitalized conjunctival and corneal epithelium in keratoconjunctivitis sicca?

  1. Rose bengal Correct answer.
  2. Fluorescein
  3. Alcian blue
  4. Congo red

Explanation

Rose bengal stains dead and devitalized epithelial cells that lack an intact mucin barrier, making it more sensitive than fluorescein for the early ocular surface changes of dry eye. Lissamine green is now often preferred because it is less irritating.

Question 35Cornea and External Disease

A patient has a 6 mm central corneal ulcer with a 2 mm hypopyon. After slit lamp examination, what is the most appropriate next step?

  1. Perform corneal scrapings for smears and cultures, then start fortified antibiotics Correct answer.
  2. Observe for 48 hours before starting treatment
  3. Start topical corticosteroid monotherapy
  4. Proceed directly to penetrating keratoplasty

Explanation

A large suppurative ulcer with hypopyon is sight-threatening and requires corneal scraping for Gram stain, culture, and smear followed by prompt initiation of broad-spectrum fortified topical antibiotics. Scraping guides later adjustment of therapy based on identified organisms and sensitivities.

Question 36Cornea and External Disease

Which corneal dystrophy is characterized by branching refractile lines in the anterior stroma that stain with Congo red and show apple-green birefringence?

  1. Lattice corneal dystrophy Correct answer.
  2. Schnyder corneal dystrophy
  3. Macular corneal dystrophy
  4. Granular corneal dystrophy

Explanation

Lattice corneal dystrophy is a TGFBI-related dystrophy in which amyloid deposits form branching refractile lines in the anterior stroma. Amyloid classically stains with Congo red and demonstrates apple-green birefringence under polarized light.

Question 37Cornea and External Disease

A patient who underwent penetrating keratoplasty develops a line of keratic precipitates advancing across the donor endothelium, with overlying corneal edema. This finding represents which type of graft rejection?

  1. A suture-related infiltrate
  2. Epithelial rejection
  3. Endothelial rejection Correct answer.
  4. Subepithelial infiltrates from adenoviral infection

Explanation

An advancing line of keratic precipitates across the donor endothelium is the Khodadoust line, the hallmark of endothelial rejection. Because the endothelium controls corneal deturgescence, rejection at this layer produces graft edema.

Question 38Cornea and External Disease

Which preoperative finding is the strongest risk factor for corneal ectasia after laser in situ keratomileusis?

  1. Central corneal thickness of 560 µm
  2. Myopia of −2.00 diopters
  3. Patient age of 40 years
  4. Forme fruste keratoconus on corneal topography Correct answer.

Explanation

Abnormal or suspicious topography consistent with forme fruste keratoconus reflects underlying biomechanical weakness and is the strongest predictor of post-refractive ectasia. Normal corneal thickness and low myopia do not confer protection if topographic abnormalities are present.

Question 39Cornea and External Disease

A patient with long-standing rheumatoid arthritis develops a crescent-shaped peripheral corneal epithelial defect with adjacent stromal thinning and overlying scleritis. What is the most likely diagnosis?

  1. Terrien marginal degeneration
  2. Peripheral ulcerative keratitis associated with systemic autoimmune disease Correct answer.
  3. Pellucid marginal degeneration
  4. Mooren ulcer

Explanation

Peripheral ulcerative keratitis in a patient with rheumatoid arthritis represents immune-complex-mediated destruction of peripheral corneal stroma and is frequently accompanied by adjacent scleritis. It requires systemic immunosuppression and urgent rheumatologic co-management because it can progress to perforation.

Question 40Cornea and External Disease

A patient with prior herpes zoster ophthalmicus has a painless, oval corneal epithelial defect with rolled edges and markedly reduced corneal sensation. Which management is most appropriate?

  1. Topical proparacaine for symptomatic relief
  2. Topical fortified tobramycin every hour
  3. Topical corticosteroid drops as monotherapy
  4. Preservative-free lubricants with a bandage contact lens Correct answer.

Explanation

This is neurotrophic keratitis, in which loss of trigeminal innervation impairs epithelial healing and tear production. Treatment is supportive, using preservative-free lubrication, punctal occlusion, bandage contact lenses, or serum tears, with topical cenegermin reserved for refractory cases.

Question 41Cataract and Lens

Which change in refractive error is most typical of an age-related nuclear sclerotic cataract?

  1. Myopic shift Correct answer.
  2. Increased astigmatism only
  3. Hyperopic shift
  4. No change in refraction

Explanation

Nuclear sclerosis increases the refractive index of the lens nucleus, producing an index myopia that can transiently improve near vision ('second sight'). Because the change arises from the lens itself, it occurs independently of corneal astigmatism.

Question 42Cataract and Lens

Which medication class is most strongly associated with the development of posterior subcapsular cataract?

  1. Oral antibiotics
  2. Topical beta-blockers
  3. Topical prostaglandin analogues
  4. Oral corticosteroids Correct answer.

Explanation

Prolonged systemic corticosteroid use is a well-established risk factor for posterior subcapsular opacification, along with smoking, ionizing radiation and chronic uveitis. The opacity forms at the posterior pole of the lens where epithelial cells migrate and swell.

Question 43Cataract and Lens

A white pupillary reflex is noted in a 4-week-old infant. Urgent assessment is required chiefly to exclude which condition?

  1. Optic nerve hypoplasia
  2. Strabismus
  3. Congenital glaucoma
  4. Retinoblastoma Correct answer.

Explanation

Leukocoria in a neonate is a red flag for retinoblastoma, which is life-threatening and requires urgent imaging and specialist referral. Congenital cataract is another common cause of leukocoria but does not carry the same risk of mortality or metastatic spread.

Question 44Cataract and Lens

What is the primary purpose of a continuous curvilinear capsulorhexis in phacoemulsification?

  1. Delivery of the nucleus in a single piece
  2. A tear-resistant capsular opening Correct answer.
  3. Reduction of pre-existing corneal astigmatism
  4. Prevention of vitreous loss during closure

Explanation

A continuous, smooth capsular edge distributes stress evenly, so the opening resists radial extension during hydrodissection, phacoemulsification and IOL implantation. This intact rim also supports in-the-bag fixation of the implant.

Question 45Cataract and Lens

A patient reports slowly progressive blurring of vision three years after uncomplicated cataract surgery with a clear cornea and well-centred implant. What is the most likely cause?

  1. Corneal endothelial decompensation
  2. Posterior capsule opacification Correct answer.
  3. Late bacterial endophthalmitis
  4. Chronic retinal detachment

Explanation

Residual lens epithelial cells proliferate and migrate across the posterior capsule, producing opacification over months to years. The cornea and implant position in this scenario are normal, pointing to the capsule as the source of visual loss.

Question 46Cataract and Lens

Which age-related cataract type typically begins as radial spoke-like opacities in the lens periphery?

  1. Nuclear sclerotic
  2. Anterior polar
  3. Posterior subcapsular
  4. Cortical Correct answer.

Explanation

Cortical cataract forms from fluid-filled clefts and vacuoles between lens fibres, appearing as radial spokes that extend from the periphery toward the centre. These spokes cause glare and produce characteristic shadows on retroillumination.

Question 47Cataract and Lens

Which intraoperative problem is characteristically increased in eyes with pseudoexfoliation syndrome undergoing phacoemulsification?

  1. Corneal epithelial abrasion from instrument contact
  2. Zonular weakness with capsular instability Correct answer.
  3. Thermal wound burn from ultrasound energy
  4. Suprachoroidal haemorrhage during wound closure

Explanation

Pseudoexfoliative material is deposited on the lens capsule, zonules and iris, and the zonular apparatus is structurally weakened. This produces phacodonesis, capsular instability and a higher risk of intraoperative zonular dialysis.

Question 48Cataract and Lens

A man taking tamsulosin for benign prostatic hyperplasia is listed for cataract surgery. Which preoperative plan is most appropriate?

  1. Pre-treat with topical pilocarpine to stiffen the iris
  2. Plan for floppy iris and use pupil support devices Correct answer.
  3. Discontinue the drug 48 hours before surgery
  4. Defer surgery until the drug is stopped permanently

Explanation

Tamsulosin produces long-lasting blockade of iris dilator alpha-1A receptors, so intraoperative floppy iris syndrome may occur even after the drug is withdrawn. Surgeons therefore anticipate billowing iris, progressive pupillary constriction and prolapse, and use pupil expansion devices with low-flow phaco settings.

Question 49Cataract and Lens

Which organism is the most frequently isolated cause of acute postoperative endophthalmitis following cataract surgery?

  1. Streptococcus pneumoniae from the nasopharynx
  2. Aspergillus fumigatus from environmental spores
  3. Coagulase-negative staphylococci Correct answer.
  4. Pseudomonas aeruginosa from contaminated solutions

Explanation

Coagulase-negative staphylococci, chiefly Staphylococcus epidermidis, are normal eyelid and conjunctival commensals and account for the majority of acute postoperative cases. Infection usually arises from perioperative seeding of the anterior chamber.

Question 50Cataract and Lens

A tall, thin teenager has bilateral ectopia lentis with superotemporal lens displacement, a normal homocysteine level and arachnodactyly. Which diagnosis is most likely?

  1. Homocystinuria
  2. Pseudoexfoliation syndrome
  3. Marfan syndrome Correct answer.
  4. Weill-Marchesani syndrome

Explanation

Marfan syndrome results from fibrillin-1 abnormalities and characteristically displaces the lens superotemporally, with a normal homocysteine level. Homocystinuria also causes ectopia lentis but usually displaces the lens inferonasally and elevates homocysteine.