MCQs-11. Lens and Cataract Samer (3)

Lens and Cataract Section 11

2011-2012 (Last major revision 2008- 2009)

t::lD. AMERICAN ACADEMY

\V OF OPHTHALMOLOGY Th" Eye M .D. AUoc;ati(ln

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Study Questions Although a concerted effort has been made to avoid ambiguity and redund ancy in these questions, the authors recogni ze that differences of opinion m ay occur regarding the "best" answer. The discussions are provided to demonstrate the rationale used to derive the answe r. They may also be helpful in confirming that your approach to the problem was correct or, if necessar y. in fixin g the principle in your memory_ 1. The normal , aging human crystalline lens a. develops an increasingly curved shape, resulting in more refractive power b. develops an increasingly flatter shape. result ing in less refractive power c. undergoes an increase in index of refraction as a result of decreasing presence of insoluble

protein particles d. undergoes a decrease in index of refra ction as a result of dec reasing presence of insoluble protein particles e. a and c are correct

f. a and d are correct 2. Terminal differentiation is the process whereby a. lens epithelial cells elongate into lens fibers b. the mass of cellular proteins is decreased c. glycolysis assumes a lesser role in metabolism

d. cell organelles increase their metabolic activity 3. When the ciliary muscle contracts, a. the diameter of the muscle ring is reduced, thereby increaSing tension on the zonular fibers, which allows the lens to become more spherical b. the diam ete r of the muscle ring is increased, thereby increasing tension on the zonul ar fibers, which allows the lens to become more spherical c. the diameter of the muscle ring is reduced, thereby relaxing tension on the zonular fibers, wh ich allows the lens to beco me more spherical d. the diameter of the muscle ring is increased, thereby relaxing tension on the zonular fibers, which allows the lens to become more spherical 4. According to the pump-leak theory, a. sodium ions are actively pumped into the lens b. only active transport is involved in ion movement into the lens c. sodium flows in through the back of the lens with the concentration gradient

d. ouabain can sti mulate the pump cells

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242 • Stud y Question s 5. .' Nhich of the following systemic diseases is not associated with ectopia lentis?

a. homocystinuria b. Ehlers-Danlos syndrome

c. Marfan syndrome d. myotonic dystrophy e. sulfite oxidase defiCiency

6. A lens coloboma a. is usually associated with previous lens trauma b. is typically located sup eriorly c. is typically associated with normal zonu lar attachments

d. is often associated with corti cal lens opacifi cation

7. The epidemiology of cataracts suggests that a. they are more prevalent in those younger than 65 years

b. they are more prevalent in men c. they occur only as a consequence of age

d. they are the leading cause of reversible blindness 8. According to the results of epidem iologic studies, cataracts account for which of the following? a. the removal of2 individuals from the workforce when 1 is blind, if the blind person requires the care of an able adult b. mobll ity problems, including falls c. the number of cataract surger ies performed worldwide will have to triple by the year 2020 in order to keep pace with the needs of the population

d . all of the above 9. Which of the following statements about fun ctional visual impairment caused by cataracts is

false' a. "Second sight" is caused by len ticu lar myopia and improves near vision without correc tion. b. Monocular diplopia caused by cataract cannot be corrected by spectacles.

c. Mild posterior subcapsular cataracts never cause visua l symptoms. d. Cataract can cause greater impairment in co ntrast senSitivity than in Snellen acuity. 10. Which of the following statements about ectopia lentis in Marfan syndrome is false? a. The lens is usually subluxated in an inferior and nasal direction . b. Anterior dislocation is associated with pupillary block glaucoma.

c. Posterior dislocation into the vitreous cavity can occur. d. It occurs in a majority of patients with Marfan syndrome. e. It can cause monocular diplopia.

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Study Qu estions . 243 II . "Vhieh agent is most appropriate for staining the anterior lens capsule in preparation for creating a capsulorrhexis in a patient with a poor red reflex? a. Fluorescein sodium

b. Methylene blue

c. Rose bengal d. Trypan blue 12. While cataract surgery by phacoemulsiflcation is being performed on a patient with exfoliation syndrome, it is noted that the zonules are diffusely loose. If a small capsulorrhexis is performed, al! of the follo wing adverse situa tions may be accentuated except a. anterior capsular ph imosis with further zonular loosening b. increased resistance to nuclear rotation c. increased difficu lty with nuclear chopping d. more rapid opacification of posterior capsule 13. The surgeon may estimate the patient's postoperat ive visual acuity po tential with all of the following methods except a. pinhole visual acuity b. potential acuity meter (PAM) c. laser interferometry d. contrast sensitivity testing e. blue-light entoptoscopy 14 . If a patient has a dense wh ite cataract and the posterior pole is not visible, which of the follow~ ing would be most helpful for the clinician in deciding whether to perform surgery? a. specular microscopy b. B-scan ultrasonography c. laser interferometry d . Maddox rod test e. photostress recovery test 15. What consideration wo uld be least important in the decision to perform cataract surgery? a. difficulties with activities of daily living b. dense nuclear sclerosis c. withdrawal from interactions with others d. recent fall after entering a darkened restaurant e. failure to pass a vision test at the driver's license bureau 16. Which of the follow ing quest ions is (are) impo rtant to answer before a patient is scheduled for cataract surgery? a. Does the lens opacity correspond to the level of visual loss? b. Does the patient have a medical condition that would precl ude surgery? c. Is the patient (or a person responsible for the pat ient) ab le to coo perate with the postoperative regimen and return for (ollow-up care? d . Will the patient's activities of daily living improve after successfu l surgery? e. All of the above.

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244 • Study Questi o ns

. 17. A 56-year-old woman complains of increasing di fficulty reading the newspaper in the morning, especially in bright sunlight. If her only ocul ar abnormality is cataract, which type of lens opacity is she most likely to have? a. posterior subcapsular

b. nuclear c. cortical d. oil droplet e. anterior polar 18. Clear corneal incisions a re associated with all of the following except a. more susceptible to wound burn b. more difficult to construct c. less likely to be watertight d . lower incidence of endophthalm it is 19. In cataract surgery in which the posterior lens caps ule ruptures and vitreous presents in the anterior chamber, anterior vitrectomy is complete when a. vit reous is removed from the wou nd b. a posterior chamber IOL can be placed c. the surgeon can see the ret ina

d. vitreous is removed anterior to the posterior lens capsule 20. The most common complication of retrobulbar anesthesia is a. pe rforation of the globe b. re trobul bar hemorrhage c. anesthesia of the opposite eye

d. perforation of the optic nerve 21. Which of the following preoperative measures has proven most effective in reducing the risk of endophthalmitis? a. administering oral amoxicill in beginn ing 3 days before surgery b. prescribing topical antibiotics for 2 weeks foll owin g surgery c. dec reasing the duration of surge ry

d. administering top ical 5% povidone- iodine solution at the time of surgery e. injecting vancomycin into the infus ionlirrigating solut ion 22. During phacoemulsification, when the surgeon notes a tear in the posterior capsule. the first priority is to a. finish phacoemulsification of the nucleus b. convert to extracapsular extraction c. stabilize the anterior cham ber wi th OVD d. perform a vitrectomy

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Study Questions. 245

23. Appropriate management of seve re retrobu lbar hemorrhage includes all of the following

except a. proceeding with surge ry if th e red reflex is maintained b. promptly applying fir m direct pressure on the globe

c. observing the optic nerve and fundus with an indirect ophthalmoscope d. administering carbonic anhydrase inh ibitors or mannitol intravenously to reduce intraocular pressure (lOP) e. pe rforming a lateral canthotomy if proptos is, increased lOP, and tight eyelids persist after other measures have been undertaken to relieve orbital swelling 24. If the posterior capsule ruptures and nuclear materi al fa lls back into the vitreous during phacoe mui sification, the surgeon should a. immediately termin ate the case b. send immediately for a vitreoretinal surgeon c. make every possible attempt to retrieve the lost piece of nucleus d. remove any rema ining nucl ear and cor tical mate rial from the posterior cham ber and perfo rm a vitrectomy e. never consider placemen t of an IOL in that case 25. All of the following reduce the risk of incis ion burns du ring phacoemu lsifi cation except a. higher aspiration flow rates an d vacuum levels b. ophthalmic viscosurgical device (OV D) asp iratio n prior to applying ultrasound and use of lower power c. occlusion of the phaco tip

d. loose fit between the phaco handpiece and the cataract incision e. use of cohesive OVDs 26. All of the follow ing may result in a shallow or flat anterior chamber in the postoperative period after cataract surgery except a. wound leak

b. pupillary block c. suprachoroidal effusion or hemorrhage d. posterior infusion syndrom e e. ciliary block with aqueous misd irect ion 27. All of the following are risk factors for cystoid macular ede ma after cataract surgery except a. flexible open -loop anterior chamber IOL implantation b. ruptured posterior capsu le c. marked postoperative inflammati on d. vitreous loss e. diabetes mellitus

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246 • Study Questions 28. If ciliary block glaucoma is suspected as the source of a shallow anteri or chamber after cataract surgery, all of the following maneuvers may be useful except a. miotic drops such as piloca rpine to co nst rict the pupil, deepen the anterior chamber, and open up the trabecular meshwork b. aqueous suppressants such as beta-blockers and carbonic anhydrase inhibitors to lower the lOP c. Nd: YAG laser disruption of the anterior vitreous face

d. mechanical vitrectomy to decompress the vitreous and disrupt the ante ri or vitreous face e. laser iridotomy to elimi nate the possibility of pupillary block 29. If the capsulorrhexis tear starts to extend too fa r peripherally, the following maneuver(s) may be used: a. Check for positive vitreous pressure and try to relieve any external pressure on the globe. h. Refill the anterior chamber with OVO. c. In sert a second instrument through t he paracentesis site to press poste riorly on the lens. d. Use the bent cyst ito me to try to redirect the tear centrally.

e. All of the above. 30. Evaluation of the cornea is important pr ior to cataract surgery. Which of the following statements is true? a. In order to speed visual rehabilitation, corneal transplant surgery should be combined with cataract extraction when guttae are present. b. Spec ular microscopy is the best means of determ ining how well the cornea will fare following cata ract surgery. c. Normal corneal pachymetry measuremen ts obtained in the early morning suggest that the cornea will probably remain clear fo ll owing cataract surgery. d. Corneal pachymetry should be perfo rm ed late in the day, after the cornea has had longe r exposure to the environment. e. Other than determining lens implant power, keratometry does not have a role in the preoperative evaluation for cataract surgery. 31. W hich of the following statements is true about the management of cataract associated with ocular trauma? a. After blunt or penetrating trauma in ch ild ren, fibrin can be deposited on the anterior lens capsule that mimi cs the appearance of cataract. b. Cataracts associated with large cornea l laceration s shou ld be removed through the lace ration to avoid making an addit ional corneoscleral wound. c. Ifa cataract does not develop in the injured eye within 10 days of the trauma, the patient is unlikely to develop a cataract late r. d. Phacoemulsification through a small limbal incision is the best approach to the removal of any cataract associated with acute tra uma. e. When a cataract is removed dur ing the repair of a paracentral corneal laceration, the benefits of inserting an IOL at the time of surgery outweigh the risks.

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Study Questi ons. 247

32. A 3-year-old with a dense developmental cataract in the left eye demonstrates poor fixation as and a left esotropia. The right eye appears normal. \¥hich of the following statements is true? a. TaL implantation surgery should not be performed in children. b. The left esotropia should be repaired surgically prior to cataract surgery. c. Amblyopia therapy should begin prior to cataract surger y.

d . Posterior capsulotomy should not be performed at the time of surgery because of the risk of retinal detachment. e. Cata ract surgery with 10L implantation is a reasonable approach toward visual rehabilitation in this case. 33. A SO-year-old woman with myopia presents with complaints of monocular diplopia and difficulty driving at night. Her best-corrected visual acuity with a 2 D myopic shift is 20/30. On slit-lamp examination, she has minimal nuclear sclerosis. Which of the following would be most helpful to evaluate her symptoms? a. retinoscopy b. corneal topography c. flu orescein angiography

d. MRI scan 34. A 76-year-old man complains of difficulty driving because of reduced vision. His bestcorrected visual acuity is 20/70 OD and 20/40 OS. Goldmann visual fields are constricted, more in the OD than in the OS. A moderate nuclear cataract is prese nt OD, and a mild one is seen OS. Hi s lOP is 23 mm Hg OD and 18 mm Hg OS. He uses timolol 0.5% bid OD and dorzolamide tid OD. His cup - disc ratio is 0.8 OD and 0.6 OS. The fundus is otherwise normal. Which of the following statements is true? a. Cataract surgery in this patient carries a high risk of loss of fixation postoperatively. b. Cataract surgery combined with glaucoma filtering surgery is the only approach that should be considered for this patient. c. Medical glaucoma treatment should be maxim ized before cataract surgery is considered.

d. The visual field constriction in this case is probably caused by glauco ma. e. Cataract surgery should be considered in order to improve his vision, and care should be taken to control lOP postoperatively. 35. Systemic use of a lA-antagonists for the treatment of benign prostatic hypertrophy may cause intraoperative floppy iris syndrome (IFIS) by wh ich of the following mechanisms? a. atrophy of th e iris sphincter muscle b. competitive binding to the postsynap tic nerve endings of the iris dilator c. loss of iris stroma

d. atrophy of the posterior pigment epithelium e. metabolic alkalosis of the aqueous humor 36. Epidem iologic studies have identified risk factors for nuclear opacification, which include a. current or past smoking b. non-Hispan ic \-"hite race c. diabetes mellitus

d. all of the above

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248 • Study Questions

37. Which manifestation of pseudoexfoliation syndrome is most related to cataract surgery complications? a. endothelial deposits on the iris and the lens capsule

b. Sampaolesi line c. phacodonesis

d. nuclear sclerosis 38. Which of the following statements is true regarding lens implant power calculations? a. Shorter axial length is obtained with immersion biometry as compared with contact biometry. b. Corneal thickness measurement is needed for regression formulas used to predict the appropriate 10L power. c. The calculated lens implant power fo r a sulcus- supported 10L is less than that for a lens positioned in the capsular bag. d. The calculations for 10L power will differ depending on the 10L material (eg, silicone, acrylic, or polymethylmethacrylate [PMMA]). 39. vVhich of the following statements about temporal clear corneal phacoemulsification is false?

a. It is useful in a patient with a deep orbit. b. It cannot be used in combi nation with trabeculectomy. c. It is useful in a pat ient with a preexistin g, functioning superior trabeculectomy.

d. It can be performed with the pat ient under topical anesthesia.

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Answers 1. a. With aging, the human lens develops an increasingly curved shape, which results in more refractive power. This change may be accompanied by- and sometimes offset by-a decrease in the index of refraction of the lens resulting from an increase in water-insoluble proteins.

2. a. Terminal differentiation involves elongation of the lens epithelial cells into lens fibers. This change is associated with a tremendous increase in the mass of cellular proteins in each celL The cells Jose organelles, including nuclei, mitochondria, and ribosomes. The loss of cell organelles is optically advantageous, and the cells now become more dependent on glycolysis for energy production. 3. c. The ciliary muscle is a ring, but upon contraction it does not have the effect that one would intuitively expect of a sphincter. When this muscle contracts, the diameter of the muscle ring is reduced, thereby relaxing tension on the zonular fibers, which allows the lens to become more spherical. 4. c. The combination of active transport and membrane permeability is referred to as the "pumpleak theory" of the lens. Potassium is actively transported into the anterior lens via the epithelium. It then diffuses out with the concentration gradient through the back of the lens, where there are no active transport mechanisms. Conversely, sodium flows in through the back of the lens with the concentration grad ient and then is actively exchanged for potassium by the epithelium. Experimentally, ouabain can inhibit the sodium-potassium pumps. 5. d. Myotonic dystrophy is not associated with ectopia lentis. 6. d. A lens coloboma is a wedge-shaped defect or indentation of the lens periphery that occurs as an isolated anomaly or is secondary to the lack of ciliary body or zonular development. lens colobomas are typically located inferiorly and may be associated with colobomas of the uvea. Cortical lens opacification or thickening of the lens capsule may appear adjacent to the defect. 7. d. Cataracts increase in prevalence with increasing age and are the leading cause of blindness world\vide. They can occur as a congenital condition or as a result of trauma, metabolic diseases, or medications. Major epidem iologic studies confirm an increased prevalence in women. 8. d. v\Then an individual is incapacitated by blindness and requires the care of an able adult, the caregiver may be removed from the workforce as well. Reduced acuity is a primary factor in the decrease of mobility, and it contributes to falls. With the aging of the population in both the developed and the developing world, the number of individuals needing cataract surgery will increase from 40 million to 120 million in the next 2 decades. 9. c. Posterior subcapsular cataracts (even mild ones) can lead to severe visual impairment, especially when there is bright illumination and while the patient is reading. 10. a. Tn Marfan syndrome the lens is usually subluxated in a superior and temporal location. 11. d. Trypan blue is nontoxic and commercially available as a ready-made solution. Fluorescein is a very weak stain for all intraocular surfaces. Methylene blue is toxic to the corneal endothelium. Rose bengal is not approved for intraocular use and has been shown to be toxic to the corneal endothelial cells in an imal studies.

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250 • Answers

12. d. Opacification of the posterior lens capsule is not dependent on CCC size. A small capsulorrhexis leaves more anterior capsule, which leads to greater resistance in nuclear rotation for quadrant removal techniques, as well as increased difficulty in choppi ng techniques. The zonular laxity all ows the larger anterior capsul e remaining to contract to a much small er opening. YAG anterior capsular relaxing incisions can be made in the early postoperative period to reduce the anterior capsular phimosis, which can further reduce the zonular integrity. 13. d. Patients with cataracts may experience diminished contrast sensitivity, even when Snellen acuity is preserved. Thus, contrast sensitivity may be a very unreliable method for measuring visual poten tial. Although many patients fin d the blue-light entoptoscopy test di ffi cult to comprehend, if they can see the shadows of white blood cells coursing through the perjfoveal capillaries, macu lar function is probably intact. 14. b. B-scan ultrasonography is indicated to evaluate for occult tumors. retinal detachment, or posterior staphyloma or other posterior pathology that could affect visual outcome. Laser interferometry, Maddox rod testing, and photostress recovery are not reliable with such a dense cataract. Specular microscopy would be indicated if signs of corneal endothelial dysfunction were present. 15. b. The presence of dense nuclear sclerosis alone may not prevent the ophthalmologist, by means of a careful refraction, from improving acuity so that activities of dail y living. interactions with others, stability in walking, and vision sufficient to drive (although perhaps in more limited circumstances) may be possible. 16. e. Each of these questions must bear on the decision to operate and be answered for each specific patient. 17. a. Posterior subcapsular cataracts create more difficu lty with glare and nea r vision. Nuclear and cortical cata racts affect distance vision more than near vision. Progressive loss of vision from oil droplet or anterior polar cataracts is not often seen in this age group. 18. d. Studies have shown a higher incidence of endophtha lmitis with clear corneal incisions although the mechanism has not been demonstrated. (McDonnell Pl, Taban M, Sarayba M, et al. Dynamic morphology of clear corneal cataract incisions. Ophthalmology. 2003; 110:23422348.) Both poo rly constructed incisions and wound burns can lead to a leaking wound, which many suspect may be the cause of increased infection rates. Experimental studies have demonstrated that transient reduction in postoperative lO P may also result in poor wound apposition in clear corneal inc isions, with potential for fluid flow across the cornea and into the anterior chamber, with the attendant risk of endophthalmi tis. 19. d . Loss of vitreous is not a problem for the eye; vitreous traction is. The goal of vitreous removal is to reduce the possibility of traction. The clini cian may prevent traction by removing enough vitreous to keep it away from other intraoc ular structures, such as th e lens implant, or away from the incision. Therefore, a vitrectomy is not complete until all vitreous is removed anter ior to the posterior capsule. This ensures a lower ri sk of traction and is also the best way to decrease the risk of postope rative cystoid macular edema (CME). 20. b. The increasing preference for topical or sub-Tenon anesthesia for cataract surgery has been driven by the potential complications of anesthesia in which a needle is placed near the eye without visual confirmation of the needle's pOSition . All of the answers are potential complications, but the most common complication is a retrobulbar hemorrhage. When this occurs, cataract surgery usually needs to be stopped and rescheduled, and other fo rms of anesthesia need to be considered.

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Answers. 251 21. d. Answers c and e are intraoperative measures, and controversy surrounds admixing ant ibiotics into the infusion solution. Oral antib iot ics have poor ocular penetration and are no t recom mended. 22.

Co Early detection of capsula r rupture is critical to th e satisfactory resolution of this unexpected occurre nce. As soon as the surgeon notes a rupture or suspects one, he or she should freeze the action by instilling an OV D to keep the anterior cham ber formed. This maneuver allows removal of the phaco handpiece. prevents fur th er trau ma to the capsule. and enables the surgeon to calmly assess the situation before proceed ing any further. The next step is determined by the exten t of the rupture, the amount of nucleus left to be removed, and the presence or absence of vitreous.

23. a. If a severe retrobul bar hemorrhage occ urs, surgery should be canceled, despite an adequate red reflex. All of the other measures are appropriate in the presence of severe retrobulbar hem orrhage compromising opt ic nerve and retinal blood supply. 24. d. Capsular rupture during phacoemulsification prese nts a risk of nuclear material falling posteriorly into the vitreous cavity. The case does not need to be im mediately terminated. Attempts to retrieve the nuclear remnant from dee p in the vitreous are not recommended, as those maneuvers can result in more serious reti nal co mplicati ons. Nuclear and cortical material remaining in th e posterior chamber should be removed and a vitrectomy performed via an anterio r incision or the pars plana. Conve rsion of a small rent into a posterior continuous curvil inear capsulorrhexis may stabilize the posterior capsular open ing. Surgeons familiar with pars plana techniques may attempt a posterior levitation maneuver for larger nuclear fragme nts present in the anterior or midvitreous. An IOL of choice may be implanted with due consideration to the integrity of the remaining capsule. The pat ient may be referred to a vitreoretinal surgeon, who can wait up to 7- 14 days to remove retained len ticular material without jeopardizing the outcome. 25. c. Occl usion of the phaco tip red uces or interr upts fluid evacuation through the phaco handpiece. This results in an increased buildu p of heat with in th e handpiece and a transfer of thermal energy to the inc ision. Use of lowe r ult raso und powe r reduces heat buildup. Aspiration of OVD, use of more easily aspirated cohesive OVDs, higher aspiration flow rates and vacuu m levels. and a loose fit between the phaco ha ndpiece and the incision all contribute to a more efficient fl uid flow through the handp iece and/o r the in cis ion, reducing the transfer of therma l energy. 26. d. Posterior infusion synd rom e causes shallowing of the anterior chamber duri ng cataract surgery, not in the postope rative period. Th is rare complicat ion typically occurs during hyd rodissection, when fluid may be misdirected into (he vitreous caVity, resulting in forward displacement of the lens. Wound lea kage and suprachoroidal hemorrhage may result in a flat chamber during or follow ing surgery. Su prachoroidal effu sion, pupillary block, and ciliary block with aqueous misdirection occ ur in the postoperative period. Suprachoroidal effusio n is often associated with hypotony and may be associated with a wound leak. Pupilla ry block and ciliary block, as well as suprachoroidal hemo rrhage, are often associated with normal or elevated lOP. 27. a. Flexible open-loop anterior chamber IOL implantation is not associated with an increased risk of eME in the absence of other risk fac tors. CME is almost always the res ult of increased pe rmeability of peri foveal capillaries. typically ind uced by release of inflammatory mediators. Diabetes mellitus, rupture of th e posterior capsul e. postoperative inflammation, and vitreous loss durin g surgery are each associated with an increased risk ofCME.

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252 • Answers

28. a. Management of ciliary block glaucoma is directed at controlling the lOP, shrinking the expanded vi treous volume, and ult imately reestablishing th e normal balance of aqueous circulation. Medical management consists of cycloplegia and mydriasis with atropine 1% and phenylephrine 10% to create a larger anterior hyaloid surface area for perfusion of posterioriy sequestered aqueous. lOP control with aqueous suppressants like beta-blockers, carbonic an hydrase inhibitors, and alpha agonists is very helpful. Miotics are expressly avoided, as they exacerbate the anterior displacement of the middle segment structures and may contribute to the in itiating mechanism of the disease. If pat ients fail to respond to medical therapy, surgery is undertaken to reduce the expanded vitreous volume an d dis rupt the anterior vitreous face with either the Nd:YAG laser or mechanical vit rectomy. 29. e. All of these maneuvers may be helpful in redirecting a capsulorrhexis tear that is extending too far peripherally. Preserving an intact continuous-tear capsulorrhexis is very important to the ultimate success of phacoemulsification surge ry. 30. c. Corneal thickness as measured by ultrasonic pachymetry is an important indicator of corneal endothelial func tion. Because the endotheli um is under greatest stress afte r the eyelids have been closed during sleep, pachymetry should be performed in the early morning. Earlymorning pachymetry is a better predictor of postoperative endothelial function than is specular microscopy. Keratometr y can be helpful in determin ing the quality of the anterior refractive surface-that is, the tear layer. If epithelial irregularity within the visual axis is detected preoperatively, potential visual acuity after cataract surgery may be reduced. 31. a. The surgeon must distingui sh carefully between an actual cataract and an apparent lens opacity due to fibrin coating on the anterior lens capsule of an otherwise clear lens. Cataracts should never be extracted through a corneal laceration; this procedure would cause additional injury to an already traumatized corneal endothelium. Traumatic cataracts can develop long after the actual ocular injury. The use of phacoemulsification through a limbal incision would not be preferred when the view through the cornea is inadequate. Tn this situation, cataract surgery should eit her be postponed or, if necessary, combined with penetrating keratoplasty. When the lens is subluxated as a result of zonular dehiscence, a pars plana approach is preferred . Insertion of an Tal as part of a com bined cataract ext raction and corneal laceration repair procedure is controversial. Preoperative biometry is usually impossible, or the measurements may be inaccurate, which can lead to significant ani sometropia. Zonula r status, as well as capsular integrity, may not be certain. 32. e. Lens implant surgery in a 3-year-old child with a monocular cataract is no longer considered controversial, assuming that the surgeon is fami liar with the special techniques involved in performing such surgery in this age group. Strab ismus surgery and amblyopia therapy should both be postponed until cataract surgery has cleared the visual axis. Posterior capsulotomy and anterior vitrectomy are usually performed at the time of surgery in a child this age. The posterior capsule usually opacifies in children and ca n become quite thick and fibrotic. Td:YAG laser posterior capsulotomy is difficult to perfo rm in this age group even if the capsule has not become fibrotic. 33. a. Patients with lens-induced myopia, symptoms of nighttime glare, and monocular diplopia often have a central nuclear sclerosis that, on sli t-lamp examination, appears insignificant. Although the red reflex can be evaluated with the slit lamp, it is visualized more prominently with the retinoscope or the direct ophthalmoscope. v"hen thi s finding is missed on initial evaluati on, patients may unnecessarily undergo more expensive testing such as fluorescein angiography or magnetic resonance imaging.

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Answe rs. 253 34. e. Cataract surgery alone will address the patient's current visual needs. Tn this case, the visual field constriction is more likely to be the result of the cataract than of glaucoma. There is no mention of field loss approaching fixation, and with a cup-disc ratio of 0.8, fixation is not likely to be threatened by cataract surgery. Although combined glaucoma filtering and cataract surgery is a valid approach, it is not the only surgical approach in this case. Glaucoma filtering surgery could be performed as a subsequent procedure if needed. If combined surgery is performed, no additional glaucoma medications are needed preoperatively. With an TOP of 23 mm Hg, cataract surgery alone can probably be performed without additional medication. The surgeon must be prepared to treat a postoperative pressure spike if it occurs after surgery. 35. b. Systemic al A- antagonists competitively bind to the postsynaptic nerve endings of the iris dilator muscle for long periods. Atrophy of the iris dilator muscle results in intraoperative billowing of the iris and progressive miosis. 36. d. Current smoking, white race, and diabetes mellitus are all risk factors for nuclear opacification. 37. c. Phacodonesis is an om inous sign of zonular incompetence associated with pseudoexfoliation syndrome and requires special strategies to avoid dehiscence of the zonule or dislocation of the lens during surgery. Although the other choices are manifestations of pseudoexfoliation, they do not complicate cataract surgery. 38.

The more anterior the position of the lens implant within the eye, the lower the dioptric power required. Measurements by the contact applanation method may result in falsely shorter axial length. Corneal thickness measurements are not part of the data needed for regression formulas. The material of the 10l does not affect the Tal power calculations. The A constant compensates for the lens location and light transmission.

Co

39. b. A temporal incision for phacoemulsification can be coupled with a superior trabeculectomy in a 2-site procedure. A deep orbit may present challenges for the superior approach; the tem poral approach obviates the need to work over a prominent brow. Keeping the incision away from a functioning filtering bleb reduces the risk of bleb failure. Topical anesthesia may be used with either a superior or a temporal approach .

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