Ординатура / Офтальмология / Английские материалы / The Art of Phacoemulsification_Mehta, Alpar_2001

The use of dispersive viscoelastics is supposed to significantly diminish the propensity towards endothelial cell loss (e.g. Viscoat). It must however be clearly understood that the primary aim of viscoelastic substances (VES for short) is that they are space occupying, and maintain the chamber.

Steve Arshinoff divided it into two basic groups. An understanding of these groups goes a long way in appreciation of their protection abilities. He divided into:

•High viscosity and cohesive ability with zero shear rate and possessing a high molecular weight (examples are Healon, Healon GV, Provisc, Amvisc and Biolon)

•Lower viscosity with low cohesive ability but with exceptional dispersive ability, possessing a low molecular weight (examples are Viscoat, Vitrax, HPMC).

The high cohesive viscoelastic substances with high viscosity are very useful for the creation and maintenance of space in the anterior chamber. In addition they enable stabilization of the nucleus and the torn capsule during the capsulorrhexis procedure. They can also be used as a tool to separate and dissect tissue like reopening adhesions or reforming a flat chamber. They also act as a inertial energy control when the IOL is shot out of an injector and the viscoelastic substances damp down the speed of silicone unfolding, preventing damage to the tissues, in addition they act as a tamponade for the vitreous in the unlikely event of a capsular rupture.

The high cohesive viscoelastic substances have the advantage that they are very easy to remove during the final irrigation or aspiration phase.

The high dispersive viscoelastic substances have the advantage that they break down (or disperse) into their components (hence the term dispersive). This group of products forms an adherent layer, which clings onto the endothelium, literally acting as a second skin, and protects the endothelium from the effect of deleterious substances. It is this group which is very useful in performing phacoemulsification on eyes with a poor endothelial cell count. It also has the advantage that it traps the nuclear fragments, preventing them from bouncing off the endothelium during phacoemulsification.

The dispersive viscoelastic substances have the disadvantage that at the end of the procedure, they have to be literally, vacuum aspirated.

A combination of these substances is now available—Amvisc Plus (Bausch and Lomb). It is said to combine the advantages of both, and is moderately cohesive as well as dispersive.

Use of Freezing Solutions

Both the viscoelastic as well as the infusion solutions, if used ice-cold are said to have a preservative action on the endothelium (Edelhauser, 1998). In addition the use of freezing solutions also minimizes the incidence of corneal burns from the phaco tips, especially when high ultrasound energies are used with the very hard (suprahard) cataracts.

CORNEAL ENDOTHELIUM AND ITS PROTECTION IN PHACOEMULSIFICATION 373

Pulse Phaco Usage

Diminishing the phaco power by using the pulsed phaco method, and a more sensitive control with better tuning capabilities have both helped to diminish the cell loss. The only problem with pulsed phaco is that it is difficult to really get a good hold on the lens for chopping and thus can only be used after the primary phaco procedure of nuclear chopping is over. A modified version of pulse mode is the Burst mode (the AMO Diplomax and the Alcon Legacy), which, in essence, gives a fixed series

of pulses and stops so that the lens can be held. It however has the problem that if attempted, just a bit carelessly, the burst will, in a medium cataract, go all the

way through, promptly rupturing the capsule

Proper Tip Placement

Though newer techniques like tangential or vertical chop have helped further, by decreasing operative time and diminishing intracameral acrobatics, the modern techniques of phacoemulsification depend much more on the ability to properly position the tip to be in an optimal position to hold a lens and chop it down into smaller parts, permitting easy emulsification using negligible ultrasound energy. The problem only comes about if the cataract is very hard. Now the number of times the lens has to be held with bursts of ultrasound power increases. Since the fragments are very hard, the energy required to engulf and emulsify them also increases. Naturally the endothelium exposure to ultrasonic energy will increase.

THE ADVENT OF THE CONCEPT OF PHYSICAL ENDOTHELIAL CELL PROTECTION

The obvious answer is to protect the endothelium from the deleterious effects of ultrasound, the turbulence of the irrigation fluid, the noxious effects of the irrigating solution and/or intracameral injections (like Xylocard) on the cornea and the accidental touch with the endothelium during intracameral maneuvers. The barrier should be for functional reasons, a physical barrier.

The obvious solution in providing a physical protection for the endothelium is the “Hema Hood”. Here a Hema membrane is used to protect the endothelium of the cornea by placing it in direct contact with the endothelium. Thus, in essence, it functions as an endocorneal contact lens. The method devised acts as a physical barrier literally like a corneal endothelial umbrella.

Hema Intracameral Endothelial Contact Lens

The Hema material used in the Hood has also been used by the author for fashioning Hema soft IOL from 1977 onwards and has been in usage for over 18 years, first as an Iris Clip lens and later as a Disc P/C. It is a proven concept that a soft IOL touching the endothelium of the cornea lead to virtually no deleterious effect. (Packer, 1978, Mehta, 1997,98).

374 THE ART OF PHACOEMULSIFICATION

The Design of the Hema Hood

The Hema Hood is designed with a front surface curve of 8.20 mm, of plano power, 9.00 mm total diameter. The central thickness is 0.18 mm. The edge is made with a reverse bevel, which prevents the hood from being dislodged by a stream of BSS from the phaco needle.

The Material of the Hema Hood

Wohlk (German) soft contact lens material

Hexa methyl meth-acrylate with cross-polymers and EGDA

Temperature resistance: No change in parameters after boiling for 24 hours

Ash content.0.1 mg in 3.00 gm ashed

Preparation of the Hood for Usage

The endothelial Hood is presented in a metal foil sealed bottle filled with BSS, sterilized by autoclaving, and sealed in a sterile (ETO gas) double pouch. The surgeon takes the bottle on the table utilizing full sterile facilities. The hood is removed from the bottle using a toothless forceps or simply floated out. It is then put in the jaws of a box folder, normally used for folding silicone lenses prior insertion. Using a standard silicone lens insertion forceps the hood is grasped making sure that the entire lens is engulfed in the lips of the holder. It is imperative that the lens be always kept moist. It is then coated with viscoelastic solution prior insertion.

Insertion of the Hood

The correct time for insertion of the hood in the anterior chamber is after completing the rhexis, finishing the hydrodissection and making sure the nucleus rotates well. The anterior chamber is inflated with viscoelastic (HPMC works best).

The Hood is now inserted in a folded stage, held in the holder (Fig. 34.1). Once the lens crosses the ¾ mark of the hood, the forceps is released which permit the hood to unfold (Fig. 34.2). Be sure to release the hood keeping the convex side towards the dome of the cornea. Next, viscoelastic is again injected between the hood and the iris, thus, pushing the hood into intimate contact with the endothelium. The hood sticks by itself to the endothelium. Wait for about 30 seconds, which allows the hood to settle itself, and the phaco procedure may be commenced.

The data is transferred to a Pentium III computer and analyzed with the Topcon “ImageNet” Cell Analysis software which give good, reproducible, stable readings. Initial data would seem to confirm what we had originally conceived. The cell protection ability of the Hood seems very good.

To really know if the system works, two independent observers did a series of evaluation of the author’s cases. All cell counts were done with the Topcon Noncontact Specular Microscope SP-2000P. The data being analyzed with the Topcon “ImageNet” Cell Analysis software.

The authors’ average cell loss, using the tangential chop for medium cataracts, vertical phacoemulsification for hard cataracts, and the side chop/saddle-hump technique for suprahard cataracts, without the use of the endothelial cell protection

Note The accuracy of the Topcon non-contact endothelial camera technique has a maximum accuracy of (+/-) 2 to 3 percent.

With the usage of the Hema hood, three types of cataracts were considered and analyzed: medium density, hard cataracts and suprahard cataracts and their cell counts were done individually. Representative analyses are displayed in Tables 34.1 to 34.3.

Table 34.1: Endothelial cell difference in medium density cataracts with the Hema Hood

Endothelial cell loss as evaluated by a Topcon non-contact endothelial camera:

Average Variation = 2.36 percent

Hema Intracameral Contact Lens Endothelial Cell Loss: Average Cell Loss in Phaco with the Hema Hood

With any type of lens density, irrespective of the length of the procedure, the cell loss stays in the narrow range of 3 to 5 percent.

Subsequently, endothelial cells evaluations were done using the Hood. The cells differences showed that whether a hard or a suprahard cataract was done, the

378 THE ART OF PHACOEMULSIFICATION

Table 34.2: Endothelial cell difference in hard cataracts with the use of the Hema Hood

Endothelial cell loss as evaluated by a Topcon non-contact endothelial camera:

Average variation = 2.74 percent

Table 34.3: Endothelial cell difference in suprahard cataracts with Hema Hood

Endothelial cell loss as evaluated by a Topcon non-contact endothelial camera:

Average variation = 4.19 percent

difference remained virtually identical. Even in suprahard cataract, which in the authors, own series showed a gross variation, in the Hood series showed a very stable cell count, which, hardly varied. With any type of lens density, irrespective of the length of the procedure, the cell loss stays in the narrow range of 3 to 5 percent.

Note The accuracy of the Topcon non-contact endothelial camera technique has a maximum accuracy of (+/-) 2-3 percent.

Interestingly in a number of cases of suprahard cataracts after the surgery was over, and the hood was removed a clear demarcation line, almost like a watermark was left. The area protected by the Hood was very clear but a diffuse haze was visible outside the boundaries of the Hood. The haze was there the next day and then gradually faded off.

It would thus seem that the Hema protection device is functional. It is particularly useful where the cells are compromised either in quantity or even quality and where the surgeon feels that the endothelium is at risk. It is particularly useful to use when phaco is been done on a case, which has been grafted before.

It also makes for an excellent teaching device, as even with prolonged ultrasound power being used in the chamber the endothelium is not at any risk.

CORNEAL ENDOTHELIUM AND ITS PROTECTION IN PHACOEMULSIFICATION 379

CONCLUSION

In the long Odyssey of phaco, the Hema Hood is an effective technique in preserving the vital endothelial cells in the phaco procedure. Usage of the Hood permits phaco even in endothelially compromised corneas, with safety.

FURTHER READING

1. Bourne WM, Kaufman HE: Specular microscopy of human corneal endothelium. Am J Ophthalmol 81: 219-33, 1975.

2.Glaser JS, Savino PJ, Sumers KD et al: The photostress recovery test in the clinical assessment of visual function. Am J Ophthalmol 83: 255-260, 1977.

3.Glasser DB, Matsuda M, Ellis JG et al: Effects of intraocular irrigation solution on the corneal endothelium following in-vivo anterior chamber irrigation. Accepted for publication. Am J Ophthalmol 1985.

4.Alpar JJ: Endothelium protection using Healon, serum or air in cataract extraction and intraocular lens implantation. J of Ocular Therapy & Surgery 3(5): 229-33, 1984.

5.Mishima S: Clinical investigations on the corneal endothelium, XXXVIII Edward Jackson Memorial Lecture. Am J Ophthalmol 1982;93: 1-29.

6.Winkler BS, Simson V, Benner J: Importance of bicarbonate in retinal function. Invest Ophthalmol Vis Sci 167: 766-68, 1977.

7.Moorhead LC, Redburn DA, Merritt J et al: The effects of intravitreal irrigation during vitrectomy on the electroretinogram. Am J Ophthalmol 88: 239-245, 1977.

8.Whikehart DR, Edelhauser HF: Glutathione in rabbit corneal endothelia—the effects of selected perfusion fluids. Invest Ophthalmol Vis Sci 17: 455-64, 1978.

9.McDermott ML, Edelhauser HF, Hack HM et al: Ophthalmic irrigants—a current review and update.

Ophthalmic Surg 19: 724-33, 1988.

10.Edelhauser HF, Gonnering R, Van Horn DL: Intraocular irrigating solutions—a comparative study of BSS Plus and lactated Ringer’s solutions. Arch Ophthalmol 96: 516-20, 1978

11.Edelhauser HF, Van Horn DL, Schultz RO et al: Comparative toxicity of intraocular irrigating solutions on the corneal endothelium. Am J Ophthalmol 81: 473-81, 1976.

12.Edelhauser HF, Van Horn DL,Hynduiuk RA et al: Intraocular irrigating solutions—their effect on the corneal endothelium. Arch Ophthalmol 93: 648-57, 1975

13.Edelhauser HF, Rosenfeld SI, Waltman SR et al: Discussion of comparison of intraocular irrigating solutions in pars plana vitrectomy. Ophthalmology 93: 114-15, 1986.

14.Edelhauser HF: Intraocular irrigating solutions. In Lamberts DW, Potter DE (Eds): Clinical Ophthalmic Pharmacology. Little, Brown and Co: Boston, 431-44, 1987.

15.Binkhorst CD: Five hundred planned extracapsular extractions with irido-capsular and iris clip lens implantation in senile cataract. In Boyd BF (Ed): Highlights of Ophthalmology, 20: 267-308, 1978-1979.

16.Cotlier E: The cornea. In Moses RA (Ed): Adler’s Physiology of the Eye. CV Mosby: St. Louis, 35, 1970.

17.Forstor SL, Blackwell WL, Jaffe NS et al: The effect of intraocular lens implantation on the corneal endothelium. Trans Am Acad Ophthalmol Otolaryngol 83: 195-203, 1977.

18.Glasser DB, Matsuda M, Ellis JG et al: Effects of intraocular irrigation solution on the corneal endothelium following in-vivo anterior chamber irrigation. Accepted for publication. Am J Ophthalmol, 1985.

19.Hoffer KJ, Philippi G: A cell membrane theory of endothelial repair and vertical cell loss after cataract surgery. Am Intra-Ocular Implant Soc J 4: 18, 1978.

20.Maurice DM: Cellular membrane activity in the corneal endothelium of the intact eye. Experientia 24: 1094-95, 1968.

21.Maurice DM: The location of the fluid pump in the cornea. J Physiol 43: 221, 1972.

22.Blatt HL, Rao GN, Aquavella JV: Endothelial cell denstiy in relation to morphology. Invest Ophthalmol 18:856, 1979.

23.Eisner G: Biomicroscopy of the Peripheral Fundus: An Atlas and Textbook, Springer: Heidelberg, 1973.

24.Sherrard ES, Novakovic P, Speedwell Z: Age-related changes of the corneal endothelium and stroma as seen in vivo by specular microscopy. Eye 1: 197, 1987.

25.Tripathi RC, Tripathi BJ: Functional anatomy of the anterior chamber angle, In Duane TD, Jaeger EA (Eds): Biomedical Foundations of Ophthalmology Lippincott: Philadephia, 10: 1, 1982.

26.Tripathi RC, Tripathi BJ: Anatomy of the human eye, orbit and adnexa. In Davson H (Ed): The Eye, (3rd ed) Academy Press: London, 40:157, 1984.

380 THE ART OF PHACOEMULSIFICATION

27.Mehta KR, Sathe SM, Karyekar SD: Intra-Ocular Lens Manufacturing Quality Assessment, Xth Congress APAO Soc Proc 1:419-20,1985.

28.Mehta KR: Progressive corneal endothelial decompensation—extended wear contact lenses with aphakia.

All India Ophthl Soc Proc 109-14,1989.

29.Mehta KR: The new clover leaf stabiliser (CLS) for the safe and effective insertion of posterior chamber IOL over a broken capsular face. All India Ophthl Soc Proc 251-53,1995.

30.Mehta KR, Sathe SM, Karyekar SD: New soft posterior chamber implant. Xth Congress APAO Soc Proc 1:421-23, 1985.

31.Mehta KR: When not to do an anterior chamber implant. All India Ophthl Soc Proc 164-65,1986.

32.Mehta KR: Posterior capsular capsulorrhexis with shallow core vitrectomy following implantation in

paediatric cataracts. All India Ophthl Soc Proc 207-10,1995.

33.Mehta KR: Tangential chop (MTC Technique) for phacoemulsification. All India Ophthl Soc Proc (Chandigarh) 1996.

34.Mehta KR: Combined astigmatic annular keratotomy and phaco—a corneal topographic analytical technique. All India Ophthl Soc Proc (Chandigarh) 1996.

35.Mehta KR: Hema intracameral Hood—corneal turbulence control in phaco. All India Ophthl Soc Proc (Chandigarh) 1996.

36.Mehta KR: Intralenticular “hubbing” technique for simple eye camp phacoemulsification—a simple technique. APIIA Conference, 1997.

37.Mehta KR: Newer techniques for eye camp safe phaco techniques. APIIA Conference, 1997.

38.Mehta KR: Intralenticular “hubbing” phaco technique for safe phaco. Proc of SAARC Conference, Nepal, 1994.

39.Mehta KR: Effective endothelial cell protection during phacoemulsification with Hema intracameral contact lens (HICL). Proc of SAARC Conference, Nepal, 1994.

40.Mehta KR: Methylcellulose induced sterile endophthalmitis following phacoemulsification. Proc of SAARC Conference, Nepal, 1994.

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I Howard Fine

Richard S Hoffman

Phacoemulsification

in the Presence of

Pseudoexfoliation: 35

Challenges and Options

INTRODUCTION

Cataract surgery in the presence of pseudoexfoliation of the lens presents surgeons with unusual challenges. In addition to a higher incidence of glaucoma, these patients have loss of zonular integrity occasionally associated with lens subluxation and pupils that dilate poorly. Although the use of phacoemulsification in experienced hands has resulted in a low incidence of intraoperative and postoperative complications such as zonular dialysis, capsule tears, vitreous loss, and IOL decentration;1 special care should still be exercised when performing cataract surgery in these patients. Improvements in phacoemulsification technology, technique, and new capsular supporting rings will ultimately enable these patients to undergo cataract surgery with even fewer complications.

Technique

Glaucoma

Poorly controlled glaucoma with concomitant cataract and pseudoexfoliation is best managed by a glaucoma triple procedure. We prefer the utilization of a limbal conjunctival incision without vertical releasing incisions and a self-sealing scleral tunnel incision (without vertical releasing incisions) located superiorly through which phacoemulsification is performed. A Crozafon-De Laage Punch (Moria # 18069) is used to disrupt the posterior corneal lip creating a fistula which usually results in a diffuse shallow bleb that filters posteriorly. The conjunctival incision is sutured to the limbus at the conclusion of the procedure. Although this is our preferred method, any combined technique can be used with or without the use of antimetabolites.