Ординатура / Офтальмология / Английские материалы / The Art and the Science of Cataract Surgery_Boyd, Barraquer_2000

values change very rapidly during the first six months. Thus keratometry may be replaced by the mean adult average keratometry value of 44.00 D. Children less than two years old may be incompletely corrected +3.00 D to even +4.00 D; between three and four years old incompletely correct them +3.00 D in those closer to three and +2.50 D in those closer to four. In children closer to six or seven, who have little chance of recovering from any amblyopia present but who are the ones that more

frequently suffer from a unilateral traumatic cataract, overcorrect them by +1.00 D.

3) A new method of management in pediatric cataracts is to render the eyes emmetropic from the very start and when axial length grows and makes the eye myopic, proceed to implant a second IOL with negative or minus power utilizing the piggyback technique and placing the new IOL in front of the primary IOL (Fig. 25- B).

IOL Power Calculation

Following Vitrectomy

For the most part, IOL power calculation in eyes that develop a cataract following vitrectomy is straightforward. The intravitreal gas is reabsorbed and slowly replaced by aqueous. If silicone oil was used instead of perfluorocarbons, when the oil is removed, aqueous fills the vitreous cavity. Since the refractive indices of aqueous and vitreous are identical (1.336), no corrections are needed in the calculation of the IOL power.

But what if silicone oil is present in the vitreous cavity? Lihteh Wu, M.D., has pointed out that anywhere from 60% to 100% of eyes have been reported to develop cataract following silicone oil tamponade. Up to 25% of eyes with silicone oil tamponade, especially those with retinal detachment secondary to necrotizing retinitis, will require permanent tamponade. Several authors have reported unpredictable refractions following cataract extraction in silicone-filled eyes when traditional formulas are used. In one study the axial length was measured prior to silicone oil tamponade, and the IOL power was calculated using the traditional formulas. In these eyes the average postoperative refraction was about +4.00 diopters (with a range of +2 to +6 D). These results were more hyperopic than had been predicted and the change is associated with the different refractive index of silicone oil. If the silicone oil was later removed then the postoperative refraction was only off by 0.5 to 1 D.

Drs. Melissa Meldrum, Tom Aaberg, Anil Patel, and Janet Davis have described and proposed correction factors for

the calculation of an intraocular lens implant in a silicone filled eye (Fig. 32). They recommend: (1) the use of a modified ultrasound velocity in silicone oil in the calculation of axial length, (2) the use of convexoplano IOL's, and (3) the addition of a constant to compensate for the refractive index of silicone oil.

The velocity of sound in a medium is inversely related to the medium’s refractive index. Since silicone oil has a higher index of refraction than vitreous, it slows down sound velocity. For instance, sound velocity in silicone oil is 986 m/s compared to 1532 m/s in aqueous. If we recall, the velocity of sound is preset in the computer in the ultrasound machine. If no modification is made, the eye appears to be longer than it actually is. Consequently, the wrong IOL may be implanted.

Drs. Meldrum, Aaberg, Patel, and Davis also explain why the choice of IOL is important. When convexoplano lenses are used, the anterior surface of the lens is solely responsible for the refractive power of the lens. Thus the presence of silicone oil in the vitreous cavity has no effect on the refractive power of the IOL. On the other hand, when biconvex lenses are used, the posterior surface also contributes to the refractive power of the lens. The refractive power of the posterior surface depends on the difference between the refractive indices of the IOL and the vitreous or vitreous substitute. Since silicone oil has a higher index of refraction than vitreous, the posterior refractive power of the lens is reduced. The use of a biconvex lens requires further correction.

Meldrum, Aaberg, Patel, and Davis make the following recommendations.

•Measure the axial length using the velocity of sound in silicone oil.

•Calculate the IOL power to achieve emmetropia using the traditional formulas. To this IOL power, a correction factor must be added to obtain the IOL power to achieve emmetropia in silicone oil. The correction factors range from 2.79 D to 3.94 D, for axial lengths from 20 mm to 30 mm.

•Choose a convexoplano IOL if possible. If another type of le1ns is used, another correction factor must be added to obtain the total power of the IOL in the presence of silicone

oil. For a convexoplano lens no additional correction factor is required.

For instance, let us suppose that a patient requires indefinite intraocular tamponade with silicone oil and develops a cataract. Using the traditional formulas, assuming that the IOL power is calculated to be 22 D based on a measured axial length of 23 mm. To this 22D we must add a correction factor of 3.64D (Meldrum et al) to correct for the axial length. Thus, for this patient a 25.5 D convexoplano lens should be implanted in order to achieve emmetropia in the presence of silicone oil. No additional correction factor for the IOL design is necessary.

RECOMMENDED READING

Mendicute J, Cadarso L, Lorente R., Orbegozo J, Soler JR: Facoemulsificación, 1999.

BIBLIOGRAPHY

Boyd, BF.: Undergoing cataract surgery with a master surgeon:apersonalexperience.HighlightsofOphthalm. Bi-monthly Journal, Volume 27, Nº 1,1999;3.

Brady, KM., Atkinson, CS., Kilty, LA., Hiles, DA: Cataract surgery and intraocular lens implantation in children. Am J. Ophthalmol, 1995;120:1-9.

Buckley, EG., Klombers, LA., Seaber, JH., et al: Management of the posterior capsule during intraocular lens implantation. Am J Ophthalmol, 1993;115:722-8.

Dahan, E., Drusedan, MUH.: Choice of lens and dioptric power in pediatric pseudophakia. J Cataract Refract Surg, 1997;23:618-23.

Gayton,JL.:Implantingtwoposteriorchamberintraocular lenses in microphthalmos. Ocular Surgery News, 1994:64-5.

Gayton JL., Apple DJ., Peng Q., Visessook N., Sanders V., Werner L., Pandey SK., Escobar-Gomez, M., Hoddinott D., Van Der Karr M.: Interlenticular opacification: Clinicopathological correlation of a complication of posterior chamber piggyback intraocular lenses.

J Cataract Refract Surg, 2000; 26:300-336 ©ASCRS and ESCRS.

Gimbel, HV: Posterior continuous curvilinear capsulorhexis and optic capture of the intraocular lens to prevent secondary opacification in pediatric cataract surgery. J Cataract Refract Surg, 1997;23:652-656.

Gimbel, HV., Basti, S., Ferensowicz, MA., DeBroff, BM.: Results of bilateral cataract extraction with posterior chamber intraocular lens implantation in children. Ophthalmology, 1997; 104:1737-1743.

Grinbaum A., Treister G., Moisseiev J.: Predicted and actual refraction after intraocular lens implantation in eyes with silicone oil. J Cataract Refract Surg, 1996; 22:726-729.

Grusha YO., Masket, S., Miller, KM: Phacoemulsification and lens implantation after pars plana vitrectomy. Ophthalmology 1998;105:287-294.

Holladay, JT: Intraocular lens power in difficult cases.

Atlas of Cataract Surgery, Edited by Masket & Crandal, Published by Martin Dunitz, 1999, 19:147-158.

Holladay JT., Gills, JP., Leidlein, J., Cherchio, M.: Achieving emmetropia in extremely short eyes with two piggyback posterior chamber intraocular lenses. Ophthalmology, 1996; 103:1118-1123.

Hoffer, KJ: Intraocular lens power calculation for eyes after refractive keratotomy. J Refract Surg, 1995;11:490-3.

Hoffer, KJ.: The Hoffer Q formula: A comparison of theoretic and regression formulas. J Cataract Surg., 1993; 19:700-711.

Hoffer, KJ: Ultrasound velocities for axial length measurement. J Cat Refract Surg, 1994;20:554-562.

Kora, Y., Shimizu, K., Inatomi, M., et al: Eye growth after cataract extraction and intraocular lens implantation in children. Ophthalmic Surg, 1993;24:467-75.

Lacava AC., Centurion, V.: Cataract surgery after refractive surgery, Faco Total, Editora Cultura Medica, 2000;269-276.

Lyle WA, Jin GJC.: Intraocular lens power prediction in patients who undergo cataract surgery following previous radial keratotomy. Arch Ophthalmol 1997; 115:457-61.

McCartney, DL., Miller, KM., Stark, WJ., et al: Intraocular lens style and refraction in eyes treated with silicone oil. Arch Ophthalmol 1987; 105:1385-1387.

Use of Antiseptics, Antibiotics

and Antiinflammatory Agents

Endophthalmitis following cataract surgery is a rare complication. When it occurs, however, it becomes the most serious postoperative complication. We will discuss its prevention in this chapter and its management in the chapter on Complications from Cataract Surgery.

The use of preoperative, intraoperative and postoperative antibiotics and antiinflammatory agents and the very careful cleaning of the lids are generally accepted as the standard of care in patients undergoing cataract surgery.

Effective Preoperative Antibiotic

Treatments

There is no agreement as to which is the most effective type of antibiotic as well as the dosage and route of administration to prevent postoperative infectious endophthalmitis. We do know, however, that aminoglycosides are toxic to the healing cornea while fluoroquinolones are not. The former have also gaps in the antibacterial spectrum of activity and the latter (i.e. ciprofloxacin and ofloxacin) are more potent for a wide spectrum of bacteria with less toxicity.

With regard to prophylaxis in an era of increasing use of small incision cataract surgery where corneal incision without conjunctival protection over it is becoming the proce-

dure of choice for a large number of surgeons well trained in phaco, the key factors to consider are that most infections come from the patient's own flora. Consequently, we must effectively kill bacteria in the skin, lids and ocular surface before making an incision in the eye itself. For this purpose, you may place 5% Betadine solution inside the fornix and leave it there for 2 minutes before washing it out of the eye. This is followed by painting the lids with 10% povidone-iodine solution.

Peter McDonnell, MD., has pointed out that endophthalmitis is difficult to study scientifically, because it occurs so rarely. Al Sommer, M.D., the Dean of the School of Public Health at Johns Hopkins University, has emphasized that to do a prospective, randomized trial in order to prove that a specific management lowers the risk of endophthalmitis, is close to impossible. There are almost no scientific data proving that various strategies clearly reduce the risk of this complication. Such data are even harder to obtain now because, asincisionsizeshavegottensmaller,the risk of endophthalmitis has dropped. But as incision sizes have dropped, so has the time that it takes for surgery. This, of course, reduces the risk.

Henry Perry, M.D., has also brought out another important point: In patients where the posterior capsule breaks or there is need for a vitrectomy, those patients should be treated withextraantibioticsbecausetheriskforinfection significantly increases depending on whether it is just the capsule that has ruptured or whether you actually had to do a vitrectomy.

Regimens Recommended

Considering that there are so many alternative regimens for minimizing the development of infection, depending on the personal choices of different successful surgeons, I am hereby presenting what I consider two alternatives that appear to be effective and safe.

Gills Formulas to Prevent Infec-

tion

1) For High Volume Cataract

Surgery

As proposed by James Gills, M.D., after years of profound clinical analysis of this subject on many thousands of his own patients. Gills' regime is complex particularly when it comes to the preparation of two antibiotic mixtures with two antiinflammatory agents (NSAIDS) for injection into the anterior chamber at the end of the operation. The accurate preparation, mixture and exact dilution of a variety of medications that needs to be done with absolute accuracy and in very small doses for injection routinely into the anterior chamber isabigstepforwardinminimizingendophthalmitis, based on Gills' extensive experience. The disadvantage is, however, that such multiple steps of preparing these mixtures by operatingparamedicalpersonnelinsome large institutions where not only ophthalmic surgery is performed may be somewhat risky. A small human error is feasible, particularly on the side of mistakenly applied larger doses, which may lead to toxicity of the ocular tissues. In large private eye centers, where the paramedical personnelisexclusivelydedicatedtohightech-

nologyocularsurgery,Gillsoutlineisanexcellent measure to follow. The following is his step by step procedure.

1)Gills considers that filtering all the irrigating solutions through a 0.2 micron millipore filter is a major step forward in minimizing infection, particularly endophthalmitis. Following his use of filtration, the incidence of endophthalmitis at Gills Institute has significantly reduced from 1-2 per 1000, which was the same as the national average in the U.S. to an overall incidence of 1 in 8000 to 10,000.

2)After years of successfully using antibiotics(gentamicinandvancomycin)inthe irrigating solution, Gills has changed to what he considers maximum security, which is as follows:

A) Preoperatively, 15 minutes prior to transfer to the operating room:

a) Neosynephrine 10% one drop.

b) Ocuflox 0.3% mixed with Indocin, one drop.

This combination of Ocuflox (a fluoroquinolone) and Indocin (a non-steroidal) is prepared as follows: Reconstitute 1 mg of Indocin with Ocuflox. Reinject into Ocuflox bottle and use one drop of this mixture.

B) In the Operating Room

a)Tetracaine: 0.5% 1 gtt x 3 (3 min. apart with final drop instilled just prior to beginning).

b)Betadine BSS: 1 gtt x 3 (2 gtts at the beginning of the case, 1 gtt at the end).

Preparation: Draw up into the syringe 5 cc of BSS followed by 5 cc of Betadine solution 10%.

Change needle to 18 gauge filter needle wil filter and inject into sterile empty vial. Use the drops on the eye as outlined above but obtained from this prepared mixture.

c)Cyloxan (antibiotic): Instill one drop at the end of the operation.

d)Intraocular anesthesia (Intracameral): Irrigated inside the anterior chamber (see Chapter 6).

Gills no longer uses antibiotics in the irrigating solution. Instead, he feels there is a more effective control by using a combination of antibiotics and antiinflammatory drugs directly injected into the anterior chamber at the end of the operation. This combination of drugs is obtained as follows:

f)Post-op Anterior Chamber Injection of Indomethacin, Solucortef and Two Antibiotics

• Draw up 14.4 ml BSS into a syringe and inject 12.4 ml of this BSS into an empty sterile bottle.

• Use the remaining 2 ml to reconstitute two 1 mg vials of Indomethacin.

• Add both of the 1 ml vials of Indomethacin solution to the 12.4 ml bottle containing BSS making 14.4 ml of total volume.

•Add 8 gtts of Solucortef 125 mg/ml (8 minims using TB syringe), 0.06 Cephtazidime 50 mg/ml.

•0.1 ml Vancomycin 500 mg/10 ml to the 14.4 ml bottle of Indomethacin solution.

•Dosage per patient: 0.50 ml of this mixture is injected into the anterior chamber at the end of the operation.

g)Recovery Room: Polytracin ointment x 1.

In doses higher than those described in this outline, Vancomycin and Cephtazidime would interact and precipitate out of solution. Gills states that he has no problems with the minute concentrations used for intraocular injection. At the end of the operation, topical Betadine® drops are instilled in the eye. Betadine eliminates flora in the cul-de-sac so

they cannot enter the soft eyes that may occur within the first hour after surgery. During this critical period it is important to make sure that the eye is clear and clean.

C) Oral Medications: These are instilled before the antibiotic ointment.

Ibuprofen 200 mg tablet given pre-op and tablet postop unless contraindicated.

2) Non-Complex, Effective and Safe Alternative for Prevention of Infection

The regimen that follows is practical and effective, one which every ophthalmic surgeon may use with excellent results.

1) Asepsis

Followthesameroutinepreviously outlined for thorough cleaning of lids and skin with soap and 10% povidone iodine solutions. The sameappliesforuse of5%Betadine 1drop topically, Betadine 5% solution inside the fornix leaving it there for 2 minutes before washing it out of the eye.

2)Preop antibiotics: none.

3)Filtration of irrigating solution

If the micropore filter is available, by all means use it as recommended by Gills.

4) Intracameral irrigation at end of operation

Yes. Irrigate the anterior chamber with an effective mixture of:

A) One antibiotic and one steroidal antiinflammatory mixture containing:

a) Gentamicin 0.5 ml drawn from a vial containing 40 mg / ml.

b)Prednisoloneacetate(Depomedrol) 0.5 ml solution from a vial containing 40 mg / ml.

This combination is easy to use, it provides very little risk of confusion and is most effective.

5) Topical instillation after intracameral irrigation

In cataract surgery there are many ways to reduce the ocular surface flora which is the main source of contamination that may lead to endophthalmitis. It is also quite clear the usefulness of Povidone-Iodine as an antiseptic in the skin and lids and Betadine gtts topically preoparatively as outlined previously. The use of preoperative antibiotics has never been a subject of consensus essentially because there is no fundamental evidence that they really contribute to minimize the risk of infection.

Antibiotics Most Commonly Used

As to the use of postoperative antibiotics which is the subject we discuss here, the subconjunctival injection of antibiotics is not recommended by the majority of experts.

The general consensus, however, is that immediately following cataract surgery, the postoperative use of antibiotics and antiinflammatory agents applied topically is an important component of the formula for successful results. Antibiotic ointment used immediately at the end of surgery is certainly the preference of most surgeons.

The antibiotics most commonly used today in the form of drops are Ciprofloxacine (Ciloxan from Alcon) or Ofloxacine (Ocuflox in some countries or Oslox in others , manufactured by Allergan). The routine use of antibiotic drops q.i.d. for seven days is the dosage

T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y

recommended. Both of these antibiotics are very effective. You may use one or the other. They may be instilled immediately following surgery and started four times a day within one hour of surgery.

Antimicrobials should be used only for the shortest period of time needed to obtain the desired effect and should never be tapered but simply discontinued. Do not prescribe them at a frequency of less than four times daily.

Antibiotics in the first seven days may be used in combination with a steroid. However, once you discontinue the topical application of the antibiotic within seven days, if everything looks well, the patient has to continue with steroids.

Most Frequently Used Anti-in- flammatory Agents

The most frequently used antiinflammatory agents applied topically are Prednisolone Acetate1%,commerciallyknownasPrednefrin Forte by Allergan or Econopred by Alcon. These may be started promptly following surgery, so that the medication starts its effects immediately and continued depending on the clinical findings and the surgeon's individual preference.

In cataract surgery, there is an inherent difficultyinestablishingconsensusguidelines. Those outlined above are the most generally accepted by advanced surgeons. It is important that the antibiotics, particularly the fluoroquinolone family, which are indeed very effective as an antimicrobial medication, be used no more than seven days, unless there is a specific indication to continue the antibiotic.

AntibioticsinIrrigatingSolutions

The previously widely used practice of using antibiotics in irrigating solutions are of questionable value. Their use has not been proven to be effective, mainly because the concentration and the duration or the exposure of the antibiotic to the bacteria is insufficient to achieve a killing effect. A much better procedure is to instill within the anterior chamber a combination of antibiotic and antiinflammatory agent as outlined previously. There also seems to be a general consensus not to use Vancomycin in the irrigating solutions or for irrigation of the anterior chamber immediately followingsurgery. Prospectivestudiesseemto indicate some potential toxicity particularly a clinical significant cystoid macular edema and decreased best corrected visual acuity in cataract patients receiving Vancomycin in the irrigating solutions as compared with controls. This is not a proven fact but it is a potential for concern that has been expressed by the Centers of Disease Control in the United States.

Patching

Following phacoemulsification, patching is not used unless the patient lives very far away and may be at risk for trauma during his trip back home. Practically all patients today are operated in outpatient surgical centers or eye clinics that have their own operating room and they go home without patching and start using the topical antibiotics and antiinflammatory agents immediately after getting home so that the medication will start with their effect immediately.

Postoperative Antiinflammatory

Agents

We already described the use of antiinflammatory agents by irrigation into the anterior chamber immediately following the operation. Gills uses a combination of nonsteroidalantiinflammatoryagents(Indomethacin) and a steroidal medication within the anterior chamber, mixed with two antibiotics. In the other more simple and very effective alternative which we have outlined, 0.5 ml of PrednisoloneAcetate(Depomedrol)combinedwith 0.5 ml of antibiotic (Gentamycin) are irrigated intracamerally immediately following the operation.

Postoperatively, the most effective antiinflammatory agents is a combination of Prednisolone Acetate 1% q.i.d. gradually tapered over eight weeks and a non-steroidal antiinflammatory drug such as Voltaren® q.i.d. for twoweeks. EitherVoltarenorAcular®aretwo commonly used and effective medications. It is also known that topical diclofenac can reduce pain, burning and inflammation. It may also be effective in reducing photophobia after pupil dilation. The mechanism is not known. However, the use of diclofenac alone is not sufficienttoeradicateallinflammation. Supplemental topical steroid is necessary to completely control inflammation.

Thiscombinationofpostoperativemedications applied topically not only contribute to the prevention of inflammation and infection but also significantly contribute in the patient's postoperative comfort.