Ординатура / Офтальмология / Английские материалы / Small Incision Cataract Surgery (Manual Phaco)_Singh_2002

own immunity and the quality of surgery. Prolonged surgery (longer than 60 minutes),40 use of prolene haptics intraocular lenses, inadvertent ocular penetration during extraocular surgery and vitreous loss have been specifically documented to be risk factors for the development of endophthalmitis.41 The risk of developing infection is high if the integrity of posterior capsule is lost, since it allows an easy access for microorganisms into the vitreous cavity.37 Vitreous loss requires introduction of additional instruments into the eye, which contributes to the increased risk of infection.

Postoperative risk factors include poor wound construction or closure leading to a wound leak, iris prolapse, vitreous incarceration in the wound, exposed sutures,sutureremovalunderinadequateasepticconditions and the presence of a thin filtering bleb.41-43

Irrigating Fluids and Viscoelastic Agents

Contaminated fluids, tubings, intraocular lenses and viscoelastics are known to have caused cluster infec- tions.8,44-48 The fluids for intraocular and intravenous use such as balanced salt solution, Ringer’s lactate, etc. should be inspected for its intact packing and also for any obvious bacterial or fungal contamination. Any visible particulate matter should render a bottle unsafe for use even if its sterile packing seems undisturbed. Cluster postoperative infection usually occur as a result of breach in the OR asepsis. Most common causes are irrigating fluids,44-48 contaminated viscoelastics,44 defective ventilation.11 In cluster infection microbiological surveillance culture specimens for bacterial or fungi are obtained from environmental sites, OR floor and wall, water source, operating room team, irrigating fluids, viscoelastics, intraocular lenses, surgical equipments49 and autoclave equipment.

Even with a sterile surgical technique, infection may occur from many other sources. Studies have shown that bacteria may be recovered from culture of anterior chamber aspirates at the end of cataract surgery in upto 43 per cent of cases even in the presence of preoperative antibiotic prophylaxis and aseptic techniques.50 Lacunae in our knowledge include how many bacteria are required to cause endophthalmitis and how low the bacterial counts have to be in order to ensure a negligible risk of postoperative infection. The role of antibiotics in irrigating solutions such as balanced salt solution or Ringer’s lactate is controversial.51 The antibiotic protocol is aimed at providing protection against gram-positive bacteria, which are the most prevalent organisms, cultured in

isolated endophthalmitis cases. For prophylaxis, half of the maximum non-toxic dose of the antibiotic is recommended in the infusion bottle. Vancomycin 10 mg in a 500 ml bottle has been recommended.52 However, there are reports that this practice makes no difference to the incidence of postoperative endophthalmitis.53 Another concern is the emergence of vancomycinresistant coagulase negative Staphylococcus and Enterococcus strains.53 Other considerations to be kept in mind are the cost implications and the risk of human error during constitution of the required solution. This is especially true when using aminoglycosides, as inadvertent injection of toxic doses could result in macular infarction and endothelial toxicity.

Subconjunctival Antibiotics

Subconjunctival injection of antibiotics at the end of surgery helps in reducing postoperative infection particularly in the setting of the developing world. A single injection of high doses of most antibiotics maintains therapeutic aqueous levels for 4-6 hours.54 The definite efficacy of this practice is still questioned.55

Surgery of Infected Cases

All infected cases must be operated in a separate OR. After performing surgery on the infected cases, the tubings, instruments and sheets used for infected cases must be cleaned thoroughly and sterilized adequately before reuse. An added concern is the need for sterilization or high level disinfection of medical devices contaminated with blood from patients infected with HIV or HBV, or with respiratory secretions from a patient with pulmonary tuberculosis. Experiments have shown that HIV, HBV, and M.tuberculosis are inactivated by commonly used chemical germicides such as 2 per cent glutaraldehyde, 70 per cent isopropyl alcohol, 0.3 per cent hydrogen peroxide and 50 ppm chlorone.56

For ensuring safe surgery, each member of the OR team must perform his/her assigned role faithfully. All staff working in the OR should be well-versed with sterilisation norms and techniques being followed in their own theatre. Abiding by a few rules and ensuring OT discipline no doubt goes a long way in providing safe ocular surgery to patients.

MANAGEMENT OF POSTOPERATIVE

ENDOPHTHALMITIS

All patients must be examined postoperatively at the slit lamp at least twice in the first 72 hours after surgery, at

the end of one week and finally at 4-6 weeks after surgery. At each visit, the ophthalmologist must objectively record visual acuity, cornea clarity, intraocular pressure and the media clarity.

Any increasing postoperative inflammation, presence of a hypopyon and decreasing media clarity should be considered as infective endophthalmitis unless proved otherwise and managed as an emergency. An USG may be obtained if media is hazy. If the visual acuity is HM+ or better, a combination of intravitreal antibiotics such a vancomycin 1 mg in 0.1 ml and ceftazidime 2.25 mg in 0.1 ml in separate syringes should be injected through the pars plana. The sample should be processed for smear and cultures for aerobic and anerobic bacteria and more importantly, also for fungi as the incidence of postoperative fungal endophthalmitis is high in developing countries. Most gram +ve organisms are sensitive to vancomycin and more than 90 per cent of gram-negative to ceftazidime. If the visual acuity is less than HM, the patient should undergo pars plana vitrectomy, essentially consisting of clearing of the anterior chamber of any inflammatory exudates or fibrin and a core vitrectomy as far as it can be comfortably done and intravitreal injection of antibiotic is repeated at the end of surgery. Other indications of pars plana vitrectomy include deterioration despite initial intravitreal antibiotics, no improvement at 48 hours, delayed onset of endophthalmitis and fungal infection.

REFERENCES

1.Forster RK: Endophthalmitis. In Tasman W, Jaeger EA (Eds): Clinical Ophthalmology. Philadelphia: JB Lippincott: 4: 3- 15, 1987.

2.Bohigian GM: Postoperative infection. In Waltman SR, Krupin T (Eds): Complications in Ophthalmic Surgery. Philadelphia: JB Lippincott, 28-31, 1980.

3.Allen HF, Mangiaracine AB: Bacterial endophthalmitis after cataract surgery: A study of 22 infections in 20000 operations.

Arch Ophthalmol 72: 454-62, 1964.

4.Kattan HM, Flynn HW, Pflugfelder SC et al: Nosocomial endophthalmitis survey: Current incidences of infection after intraocular surgery. Ophthalmology 98: 227-38, 1991.

5.Petitt TH, Olson RJ, Foos RY: Fungal endophthalmitis following cataract surgery: A surgical epidemic. Arch Ophthalmic 98:1025-39, 1980.

6.Roy M, Chen JC, Miller M et al: Epidemic Bacillus endophthalmitis after cataract surgery I: Acute presentation and outcome. Ophthalmology 104(11): 1768-72, 1997.

7.Han DP, Wisniewski SR, Wilson LA et al: Spectrum and susceptibilities of microbiologic isolates in the endophthalmitis vitrectomy study . Am J Ophthalmol 122: 1-17, 1996.

8.Tabbara KF, al Jabarti AL: Hospital construction associated outbreak of ocular aspergillosis following cataract surgery.

Ophthalmology 105: 522-26, 1998.

9.Ram J, Kaushik S, Brar GS et al: Prevention of postoperative infections in ophthalmic surgery. Ind J Ophthalmol 49: 5969, 2001.

10.Laufman H: The operating room. In Benett JV, Brachman PS (Eds): Hospital Infections. Boston: Little Brown and Co., 315-24, 1986.

11.Fridkin SK, Kremer FB, Bland LA et al: Acremonium kiliense endophthalmitis that occurred after cataract extraction in an ambulatory surgical center and was traced to an environmental reservoir. Clin Infect Dis 22(2): 222-27, 1996.

12.Senior BW: Examination of water, milk, food and air. In Collee JG, Fraser AG, Marmion BP et al (Eds): Mackie and McCartney Practical Medical Microbiology Churchill Livingston, New York, London 204-39, 1989.

13.Rutala WA: APIC guidelines for selection and use of disinfectants. Am J Infect Control 18: 99-117, 1990.

14.Kramer SG, Char D: Microscope sterility system. Trans Am Acad Ophthalmol Otolaryngol 83(5): 869-71, 1977.

15.Gupta M, Gupta AK: Modern ophthalmic operation theatre. In Gupta AK (Ed): Current Topics in Ophthalmology-III. BI Churchill Livingstone Pvt Ltd: New Delhi, 2-4, 1995.

16.White AB: Sterilization and disinfection in the laboratory. In: Collee JG, Fraser AG, Marmion BP et al (Eds): Mackie and McCartney Practical Medical Microbiology. Churchill Livingston: New York, London 64-88, 1989.

17.Austin GC: Efficient storage of sterilized surgical instruments.

Am J Ophthalmol 93(4): 518-19, 1982.

18.Duguid JP, Marmion BP, Swain RHA: Sterilization and disinfection. In Duguid JP, Marmion BP, Swain RHA (Eds):

Medical Microbiology: A Guide to the Laboratory Diagnosis and Control of Infection (13 edn): Microbial infections. The English Language Book Society and Churchill Livingstone. Wilture Enterprises (International) Ltd., 1: 59-76, 1983.

19.Perkins JJ: Principles and Methods of Sterilization in Health Sciences (2nd edn): Springfield: Charles C Thomas, 1969.

20.Gills JP: Intraocular irrigating solutions with cataract surgery. In Masket S, Crandall AS (Eds): Atlas of Cataract Surgery. London: Martin Duntiz, 21-30, 1999.

21.Gills JP: Filters and antibiotics in irrigating solutions for cataract surgery. J Cataract Refract Surg 17: 385, 1991.

22.Courtright P, Lewallen S, Holland SP et al: Corneal decompensation after cataract surgery. An outbreak investigation in Asia. Ophthalmology 102 (10): 1461-65, 1995.

23.Rutala WA: Disinfection and flash sterilization of the operating room. J Ophthal Nur and Technol 10(3): 106-15, 1991.

24.Drews RC: Acetone sterilization in ophthalmic surgery. Ann Ophthalmol, 9(6): 781-84, 1977.

25.Aggarwal V, Sharma S: The efficacy of acetone in the sterilization of ophthalmic instruments. Ind J Ophthalmol 41: 20-22, 1993.

26.Basu RN: Issues involved in hospital waste management— an experience from a large teaching hospital. J Acad Hosp Adm 7-8(2-1): 79-83, 1995-96

27.Phillips G: Microbiological aspects of clinical waste. J Hospital Infect 41: 1-6, 1999.

28.Wright P: Diagnosis and management of dry eyes. Trans Ophthalmol Soc UK. 91: 119-28, 1971.

29.Johnson MW, Doft BH, Kelsey FL et al: The Endophthalmitis Vitrectomy Study Group: Relationship between clinical presentation and microbiologic spectrum. Ophthalmology 104: 261-72, 1997.

30.Phillips WB, Tasman WS: Postoperative endophthalmitis in association with diabetes mellitus. Ophthalmology 101: 50818, 1994.

31.Good WV, Hing S, Irvine AR et al: Postoperative endophthalmitis in children after cataract surgery. J Paediatr Ophthalmol Strabismus 27: 283-85, 1990.

32.Speaker MG, Milch FA, Shah MK et al: Role of external bacterial flora in the pathogenesis of acute postoperative endophthalmitis. Ophthalmology 98: 639-49, 1991.

33.Christy NE, Lall P: A randomized controlled comparison of anterior and posterior periocular injection of antibiotic in the prevention of postoperative endophthalmitis. Ophthalmic Surg 17: 715-18, 1986.

34.Christy NE, Lall P: Postoperative endophthalmitis following cataract surgery: Effects of sub-conjunctival antibiotics and other factors. Arch Ophthalmol 90: 361-66, 1973.

35.Speaker MG, Menikoff JA: Prophylaxis of endophthalmitis with povidone-iodine. Ophthalmology 98: 1769-75, 1991.

36.Boes DA, Lindquist TD, Fritsce TR et al: Effects of povidoneiodine chemical preparation and saline irrigation on the perilimbal flora. Ophthalmology 99: 1569-74, 1992.

37.Ram J: Reducing cataract-related complications. Ind. J. Ophthalmol 47: 153-54, 1999.

38.Doebbeling BN, Stanley GL, Sheetz CT et al: Comparative efficacy of alternative hand-washing agents in reducing nosocomial infections in intensive care units. N Engl J Med. 327(2): 88-93, 1992.

39.Karcioglu ZA, Aran AJ, Holmes DL et al: Inflammation due to surgical glove powders in the rabbit eye. Arch Ophthalmol 106(6): 808-11, 1988.

40.Kresloff MS, Castellarin AA, Zarbin MA: Endophthalmitis.

Surv Ophthalmol 43(3): 193-224, 1998.

41.Menikoff JA, Speaker MG, Marmon M et al: A case control study of risk factors for postoperative endophthalmitis. Ophthalmology 98: 1761-68, 1991.

42.Katz KJ, Cantor LB, Spaeth GL: Complications of surgery in glaucoma. Early and late bacterial endophthalmitis after glaucoma filtering surgery. Ophthalmology 92: 959-63, 1985.

43.Mandelbaum S, Forster RK, Gelender H et al: Late onset endophthalmitis associated with filtering blebs. Ophthalmology 92: 964-72, 1985.

44.McCray E, Rampell N, Solomon SL et al: Outbreak of Candida parapsilosis endophthalmitis after cataract extraction and intraocular lens implantation. J Clin Microbiol 24: 62528, 1986.

45.Arsan AK, Adisen A, Duman S et al: Acute endophthalmitis outbreak after cataract surgery. J Cataract Refract Surg 22: 1116-20, 1996.

46.O’Day DM, Head WS, Robinson RD: An outbreak of Candida parapsilosis endophthalmitis: Analysis of strains by enzyme profile and antifungal susceptibility. Br J Ophthalmol 71(2): 126-29, 1987.

47.Stern WH, Tamura E, Jacob RA et al: Epidemic of postsurgical Candida parapsilosis endophthalmitis. Clinical findings and management of consecutive 15 cases. Ophthalmology 92: 1701-09, 1985

48.Swaddiwudhingpong W, Tangkitchot T, Silarug N: An outbreak of Pseudomonas aeruginosa postoperative endophthalmitis caused by contaminated intraocular irrigating solution.

Trans R Soc Trop Med Hyg 89: 288, 1995.

49.Zaluski S, Clayman HM, Karsenti G et al: Pseudomonas aeruginosa endophthalmitis caused by contamination of the internal fluid pathways of a phacoemulsifier. J Cataract Refract Surg 25: 540-45, 1999.

50.Samad A, Solomon LD, Miller MA et al: Anterior chamber aspirates cultures after uncomplicated phacoemulsification and intraocular lens implantation. Am J Ophthalmol 120: 143-50, 1995.

51.Alfonso EC, Flynn HW: Controversies in endophthalmitis prevention: The risk of emerging resistance to vancomycin.

Arch Ophthalmol 113: 1369-70, 1995.

52.Gimbel HV, Sun R, De Brof BM: Prophylactic intracameral antibiotics during cataract surgery: The incidence of endophthalmitis and corneal endothelial loss. Eur J Implant Ref Surg 6: 280-85, 1994.

53.Schwalbe RS, Stapleton JT, Gillign PH: Emergence of vancomycin resistance in coagulase-negative staphylococci. N Eng J Med 316: 927-31, 1987.

54.Aaberg TM Jr, Flynn HW Jr, Schifman J et al: Nosocomial acute onset postoperative endophthalmitis survey. Ophthalmology 105:1004-10, 1998.

55.Forster RK, Abbott RL, Gelender H: Management of infectious endophthalmitis. Ophthalmology 87: 313-19, 1980.

56.World Health Organization. Guidelines for preventing HIV, HBV and other infections in the health care setting. WHO Regional office for South Asia, New Delhi, 52-58, 1996.

The Manual 13

Small Incision:

Surgical Aspects–I

Mahipal S Sachdev

P Mishra

S Thanikachalam

The scleral tunnel incision was introduced in early eighties in an attempt to provide better wound healing with less surgically induced astigmatism.

This became the most favoured incision technique in the recent past for sutureless, small incision, non-phaco cataract surgery. Although the length of external incision in this technique varies from 5 to 8 mm still it is called small incision cataract surgery (SICS) since the architectural design renders sutureless, selfsealing property to this incision. This is in contrast to the standard ECCE incision that is approximately 11-12 mm, made in posterior limbal area, which requires number of sclerocorneal stitches.

Richard Kratz, in 1983 was the first surgeon to move the cataract incision from the limbus to the sclera thereby increasing the surfaces of apposed wound to produce enhanced wound healing and less astigmatism. Girard and Hoffman in 1984 were the pioneer to call this posterior incision as scleral tunnel incision.

Jack A Singer in 1991 conducted a prospective clinical trial to evaluate induced astigmatism with PMMA IOL

implantation through a modified pocket incision, curved opposite to the limbus, which was named, “Frown incision”, because of its appearance to the surgeon. They also pointed out that frown incision group consistently had a lower standard deviation from the mean induced astigmatism than the scleral pocket incision group.

Paul H Ernest introduced the concept of an internal corneal lip (triplanar incision); acting as a one-way valve and imparting self-sealing wound properties.

Surgery has evolved from being just a small incision technique for cataract extraction to being a sutureless way of ending the procedure, thereby causing minimal distortion of the corneal curvature. In some cases a choice of incision may also help in reducing a pre-existing toricity in the cornea. So, all the vital parameters that go into the creation of a reproducible leak proof and astigmatic neutral incision have assumed great importance today.

The classical incision is a three-step incision, shaped like a Z. One limb of the Z is the vertical gutter at the external site of the incision, the second limb is the horizontal dissection and the third limb is the angled entry into the anterior chamber (Fig. 13.1).

The vital statistics that go into the making of a manual phaco incision include:

l. Site of the external incision.

2.Placement of the incision.

3.Style of the external incision.

4.The length of the external incision.

5.Length of the sclerocorneal tunnel.

6.Depth of tunnel dissection.

7.Size of initial opening.

8.Size of incision for IOL insertion.

9.Paracentesis opening.

Site of the External Incision

Scleral Pocket Incision (Fig. 13.2a)

In scleral pocket variety of incision, the external incision should be based 2.00 mm posterior to the limbus.

Clear Corneal Incision

In this the corneal incision should start just anterior to the insertion of the conjunctiva to the limbus, i.e. just ahead of the limbal vascular arcade. If the conjunctiva gets punctured, it may lead to massive ballooning of the conjunctiva due to the fluid egressing from the incision.

Placement of the External Incision

The scleral tunnel incisions are usually placed at 12.00 O’clock position. Clear corneal incisions may be placed anywhere around the limbus keeping in view the following:

•The superior limbus is usually anteriorly placed. To make an effective corneal valve incision, the internal opening of the incision then goes too anterior

•The corneal incision is usually associated with flattening of the meridian in which it is given, hence depending on the pre-existing cylindrical condition of the cornea, this side effect can be used to an advantage by placing the incision on the steepest meridian.

Advantages and Disadvantages of

Temporal Incision

The temporal location allows greater access to the incision than when over the brow; for the same reason the eye does not need to be turned down, this does away with a bridle suture and postoperative ptosis. As the iris plane is parallel to the microscope light, the red glow is excellent and hence visualisation is enhanced. Being furthest from the visual axis, theoretically, it is claimed to be more refractively stable.

Its disadvantages are a higher risk of complications and being an uncomfortable position to work from surgically.

Style of the External Incision

The external incision may be in the form of a straight line or shaped like a frown. The frown incision is most stable and is supposed to prevent sliding between the roof and floor of the tunnel, thereby minimising astigmatic shift. This incision is highly recommended. External incision parallel to the limbus should be avoided.

Length of External Incision

The length of the external incision should equal the size of the IOL that has to be introduced through it. Although a small entry is to be made for the initial process, the incision is opened to its full dimension for IOL implantation, or even before that while beginning the surgery.

Thickness of the Roof of the Tunnel

The thickness of the roof of the tunnel should be about 300 microns. Thickness more than this may lead to inadvertent entry into the anterior chamber. Thin tunnel roof may lead to buttonholing of the tunnel roof during dissection or tearing of the thin tissue during the surgery.

Length of the Tunnel Incision

•In clear corneal incision, the recommended tunnel length is, 1.75 mm. Too long tunnel lengths compromises visibility peroperatively because of distortion of the corneal dome. In manual phaco we prefer scleral tunnel except in very soft cataracts when phacotrisection can be done.

Too short tunnel lengths tend to make the incision leaky.

Size of Opening for IOL Implantation

Generally the incision needs to be extended for implantation of the IOL.

For the rigid varieties of single piece PMMA IOLs The extension of the incision should be equal to the diameter of the optic. Some people like to extend 0.5 mm smaller than the size of the diameter of the IOL but the passage of the IOL becomes tight if the length of the tunnel is longer.

For the foldable/injectable lenses The length of the incision depends on the type of IOL and the design of folder/injector being used. Depending on this, the final incision may vary between 3.5 and 4.0 mm.

Paracentesis Opening(s)

In addition to the main incision, a paracentesis opening is required for the introduction of the second instrument for bimanual techniques of phacoemulsification. This opening is usually preferred on the left side of the main incision. The incision is 0.6 to 1.0 mm in breadth and may be in the form of a simple stab or shelved incision.

Instruments required for the incisions:

1.A 15-degree freehand (preset depth 1.300 micron) blade for the initial groove to start the tunnel incision.

2.A 2.0 mm broad crescent blade for dissecting the tunnel with the shaft bent at 45 degrees.

3.A suitable breadth keratome (2.5 mm, 3.0 mm, 3.2 mm, 3.4 mm) with a 90-degree angle at the tip. The bevel should face the surgeon and the shaft of the blade should be bent 45 degrees.

4.A 0.6 to 1.0 mm broad blade for the paracentesis opening.

5.A blunt tipped extender blade for increasing the incision for IOL insertion of suitable size (3.5 mm, 4.0 mm, 5.0 mm, and 5.5 mm). The bevel of the blade should be on the undersurface. The shaft should again be bent 45 degrees.

6.A caliper to measure the intended incision size.

Technique of Making a Incision

Scleral Tunnel (Figs 13.3a and b)

First of all the conjunctiva is reflected from the limbus and mild bipolar cautery applied for haemostasis. Vigorous cautery may make the scleral tissue stiff.

A caliper is used to mark the length of the incision that is needed for IOL implantation at a suitable distance from the limbus. A depth-preset knife (300 microns) is used to make the initial incision into the sclera. If one intends to make a frown incision, and intends to keep 2.0 mm behind the limbus, then the centre of the frown should be at the level of 2.0 mm whereas the ends of the frown

Fig. 13.3a: Scleral tunnel dissection with crescent angled blade

lie more posterior.

A crescent blade is taken and the dissection is begun. It is of utmost importance to begin dissection at the correct depth and then to maintain the same depth throughout the length and breadth of the incision. This is possible if one starts the incision from one side and ends at the other side. If you start from both sides, there is a chance of dissecting at different levels. Multi-planer incisions create confusion during every occasion of introduction of instruments into the anterior chamber and must be avoided. With experience, you get to know the depth of dissection by the visibility of the crescent blade through the roof of the tunnel. The roof is much more transparent if the dissection is superficial and vice versa. Care should be taken to preserve the continuity of the edge of the

Fig. 13.3b: Technique of scleral tunnel incision and its extension

external incision. The dissection is carried forward across the limbus into the clear corneal tissue, again maintaining the same depth of dissection. An inadvertent opening into the chamber at this stage may complicate matters. The scleral incision is usually between 6.0 and 6.5 mm. Although we have shown that even extension up to 8.0 mm does not cause any problem and does not need any sutures. The corneal end should be dissected 2 mm longer than the scleral incision, 1.0 mm on either side (Fig. 13.2b).

Once the tunnel is made, paracentesis stabs are made at the 10 O’ clock and the 2 O’ clock positions (Fig. 13.4). It may or may not be needed and depends on the surgeon’s choice.

Viscoelastic material is introduced through one incision and the aqueous is allowed to escape from the other. Viscoelastic is filled just enough to make the eyeball firm, not hard.

A suitable sized keratome is taken and introduced into the tunnel in the central position of the frown and

advanced along the dissected tunnel. Care should be taken to prevent formation of new tracks. When the tip of the keratome reaches the end of the tunnel, the tip is advanced into the corneal stroma, again remaining in the same plane. One should get this right in the first attempt and re-entry should be avoided to prevent formation of multiple passages.

At the intended point of entry into the anterior chamber, the tip of the blade is dipped posteriorly and advanced slowly until the tip of the blade just appears inside the chamber (Figs 13.5a and b). At this point, the direction of the tip of the blade is again turned horizontal and the entry completed. This particular manoeuvre is carried out to obtain a straight-line internal incision. If the direction of the blade is not turned horizontal, the shape of the internal incision will resemble the shape of the tip of the keratome.

Viscoelastic present in the chamber prevents sudden shallowing of the chamber when the keratome entry is made, thus preventing inadvertent hitting of the lens.

Fig. 13.5a

Clear Cornea Incision

As the name indicates, the incision is purely corneal in nature.

There are two ways to start this incision:

•By making an initial partial thickness vertical incision

•Without an initial incision.

A straight partial thickness vertical incision of the required length is made in the corneal tissue, just anterior to the conjunctival vascular arcades. Then a keratome of the required breadth is taken and the tip introduced into the exposed corneal stroma just short of the full depth of the incision. The blade is to be held parallel, relative to the corneal surface and advanced into the corneal stroma up to the desired length. Then the hilt of the blade is lifted and the tip pointed towards the anterior chamber. Pressure is applied gently for the blade tip to emerge into the chamber, when the blade is again turned into a horizontal direction. This is done to produce a straightline internal opening. For making a same length tunnel every time, one has to note a reference point on the keratome in relation to the point of entry, so that once

you are familiar with a particular keratome, you should always get the tunnel length right. Some keratomes have markings on them to indicate the reference point and make this step easy.

In certain diamond keratomes, the reference point for entry into the anterior chamber is when the shoulder of the keratome reaches the external incision line.

Some keratomes are shaped like a trapezoid, i.e. the tunnel they form will be just right for the phaco probe at the internal incision, while shall be a little loose at the external incision to facilitate easy right-left movement.

When the clear corneal incision has to be made without an initial groove, the tip of the keratome should first dip into the corneal tissue to the desired level before traversing the cornea. This kind of incision should preferably be made with a keratome with a tip angle of 90 degrees, otherwise a tongue-shaped tag is formed at the starting point of the roof of the corneal tunnel.

The limbal incision In order to have a longer tunnel and valve, some surgeons advocate the initiation of the incision from the limbus instead of the clear cornea.

Of these three described tunnel methods scleral tunnel is the most preferred tunnel for manual SICS. The other two methods are usually used in phacoemulsification.

The hinged wound When pressed on the posterior lip a clear corneal paracentesis can leak. The wound can however be made more secure and entirely self-sealing by creating a hinge before the corneal tunnel is dissected. The hinge can be made with both a clear corneal and a limbus-based incision. David WI Angerman, one of the advocates of a hinged incision creates a 600 μm deep groove that is 3.2 mm wide and then a tunnel in the anterior one-third of the corneal stroma with a special 3.2 mm diamond keratome. The groove must be perpendicular to the corneal curvature and the tunnel perpendicular to the groove to obtain a totally self-sealing wound. He has designed a single-hinge diamond knife system for making a hinged incision (Fig. 13.6).

Advocates of this incision are convinced about its greater safety but emphasize that what contributes to this

Fig. 13.6: Creation of the special sclero-corneal pocket incision. The anterior chamber maintainer (A) is in place, introduced through a tunnel in clear cornea which is 1 mm wide and at least 2 mm in length, near and parallel to the limbus (A-arrow). The height of the BSS bottle connected to the maintainer, controls the intraocular pressure. Two 1 mm paracentesis incisions (D) are made at 10:30 and 2:30 just anterior to the limbus, for instrument access. The main external incision. 0.3 mm indepth and 4-5 mm long, is made 1 mm behind the limbus. A crescent knife (C) dissects the tunnel, First 1 mm in sclera, then 2-3 mm forward into clear cornea (1), then extending laterally (2) to produce the pockets (P) on both sides. While performing the pockets, the crescent knife is retracted laterally and backward (3), creating the external incision extensions (E) on both sides. (Below) A keratome (K) enteres the anterior chamber to accomplish the internal incision (I), curved in shape, parallel to the limbus. The keratome must be moved in a direction slightly away form the surgeon while moving it laterally (4-arrow). The distance form the external to internal incision is about 3.5 to 4 mm. Internal incision (I) lengthis about 7 mm. (Courtesy:

Benjamin Boyd, MD issue No. 1, 2000 of Highlights of Ophthalmology)

Comparison of scleral tunnel and corneal tunnel incisions

is not just making the groove but also ensuring that it is maintained by avoiding forceful lens insertion.

Extension of the Incision

The extension of the primary incision is done using a blunt tipped extension keratome. The size of the keratome should equal the diameter of the IOL optic that needs to be implanted through it or the required size for a foldable lens design. The extender keratome should have a bevel away from the surgeon, while extending the incision; care should be taken to prevent the edges of the incision from being cut inadvertently by keeping the blade absolutely horizontal and in the plane of the original incision.

Closing of the Incision

One thing that should not be forgotten about these self sealing incisions is that their typical structure makes them vulnerable to ingress of infectious agents to the inside of the eye if the valve is leaky. So the closure of the incision becomes even more important, than its making. It should remain sutureless only as long as it does not compromise the safety of the eye.

The corneal valve is put into function by inflating the anterior chamber from the paracentesis opening with the irrigating fluid. The high pressure inside the chamber forces the two lips of the internal opening against each other and closes them (Fig. 13.7). Depressing the posterior