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

choice in treating endophthalmitis caused by Propioni- bacterium acnes is vancomycin in the same dose recommended for other forms of bacterial endophthalmitis (1000 μg in 0.1 ml).

STERILE ENDOPHTHALMITIS

(POSTOPERATIVE INFECTION VS INFLAMMATION)

Though infection is the most serious and probably the most common cause of unexpected postoperative inflammation, it is not the only cause. Other factors incriminated in the genesis of postoperative inflammation include retained lens matter, residual chemicals from sterilization, toxicity of residual monomers on PMMA lenses, mechanical irritation of the iris and ciliary body by the lens and rarely inadvertent injection of xylocaine or antibiotics containing high concentration of these drugs. Inflammation caused by these agents are sometimes termed ‘sterile postoperative endophthalmitis’.

The dictum that all unexpected postoperative reaction should be considered as infective until proven otherwise

is useful. However, there are certain clinical features that may aid in making this critical differentiation. These are summarized in Table 35.1.

Table 35.1: Infection vs inflammation

Visual prognosis In the EVS study, the rates of achieving a final visual acuity of 20/100 or more in relation to the organism producing endophthalmitis was as follows: gram-positive, coagulase negative micrococci (84%), Staphylococcus aureus(50%), streptococci (30%), enterococci (14%) and gram-negative organisms (56%). It was found that a positive Gram stain or infection with species other than gram-positive, coagulase negative micrococci is significantly associated with poorer visual outcomes.

•Direct plating is better than sending the sample in transportation media

•If direct plating is not possible, then the sample should be sent at the earliest for plating in the laboratory and immediate Gram and Giemsa staining performed

•Lid margin and conjunctival swab cultures are no longer recommended

•Culture of suture removed in the presence of a suture abscess or infected suture track is a must

•Samples from both aqueous and vitreous must be cultured

•Aqueous and vitreous samples must be obtained with sterile precautions

•Plating should be on all three culture media: aerobic, anaerobic and fungal

•The preferred culture media are:

•Chocolate agar ( 37°C in CO2 )

•Fresh enriched thioglycolate ( 37°C )

•Fresh Sabourauds dextrose agar ( 25°C )

•No culture should be considered negative until two weeks of observation for growth

•Laboratory confirmed growth is defined as:

1.Atleast semiconfluent growth on solid media

2.Any growth on more than or equal to 2 media

3.Growth on one media supported by a positive Gram stain.

1.Vancomycin hydrochloride (1000 μg in 0.1 ml): The drug is available as a powder in a strength of 500 mg. Reconstitute this with 10 ml of sterile solution of injection or saline. This gives a strength of 50 mg in 1.0 ml and hence 10 mg in 0.2 ml. 0.2 ml of the drug is drawn into a tuberculin syringe and this is further diluted with 0.8 ml of sterile saline to give a strength of 10 mg in 1.0 ml and hence 1000 μg (1 mg) in 0.1 ml.

2.Ceftazidime hydrochloride (2.25 mg in 0.1 ml): The drug is available as a powder in a strength of 500 mg. Reconstitute this with 2 ml of sterile solution for injection to give a strength of 250 mg in 1 ml (has 225 mg of active ingredient) and 25 mg (22.5 mg) in 0.1 ml. 0.1 ml of the drug is drawn into a tuberculin syringe and diluted further with 0.9 ml of sterile solution to give a strength of 2 5 mg (22.5 mg) in 1.0 ml and hence 2.25 mg in 0.1 ml.

3.Cefazolin hydrochloride (2.25 mg in 0.1 ml): The drug is available as a powder in a strength of 500 mg. The required concentration is achieved by following the same steps of dilution indicated above for ceftazidime hydrochloride.

4.Ciprofloxacin hydrochloride (150 μg in 0.1 ml): The drug is available as a 100 ml bottle containing 200 mg of ciprofloxacin. 0.15 ml is withdrawn into a tuberculin syringe and this is mixed with 0.1 ml ringer lactate. 0.1 ml of this mixture contains

150 μg of ciprofloxacin

5.Amikacin sulfate (400 μg in 0.1 ml): The drug is available as a solution in a strength of 100 mg in 2 ml vial (50 mg in 1 ml)

and 10 mg in 0.2 ml. 0.2 ml of the drug is drawn into a tuberculin syringe and diluted further with 2.3 ml of sterile solution to give a strength of 10 mg in 2.5 ml and hence 400 μg in

0.1ml.

6.Gentamicin sulfate (200 μg in 0.1 ml): The drug is available as a solution of 80 mg in 2 ml vial (40 mg in 1 ml) and 4 mg in

0.1ml. 0.1 ml of the drug is drawn into a tuberculin syringe and diluted further with 1.9 ml of sterile solution to give a strength of 4 mg in 2 ml (2 mg in 1 ml) and hence 200 μg in

0.1ml.

1.Chloramphenicol (2000 μg in 0.1 ml): The drug is available as a powder in a strength of 1000 mg. Reconstitute this with 10 ml of sterile solution for injection to give a strength of 100 mg in 1 ml and 10 mg in 0.1 ml. Draw 0.1 ml into a tuberculin syringe and dilute further with 0.4 ml of sterile solution to give a strength of 10 mg in 0.5 ml and hence 2 mg (2000 μg) in 0.1 ml.

2.Clindamycin (1000 μg in 0.1 ml): The drug is available as a solution in a strength of 300 mg in 2 ml vial (150 mg in 1 ml) and 15 mg in 0.1ml. Draw 0.1 ml into a tuberculin syringe and dilute further with 1.4 ml of sterile solution to give a strength of 15 mg in 1.5 ml and hence 1 mg (1000 μg) in 0.1 ml.

1.Cefuroxime (50 mg/ml): An injection vial of 1000 mg cefuroxime is diluted with 2.5 ml sterile water. Of this dilution, 2.5 ml is then added to 12.5 ml of artificial tears. This is stable at room temperature for 24 hours and in the refrigerator for 96 hours.

2.Tobramycin (15 mg/ml): Add 2 ml of parenteral tobramycin containing 80 mg of the drug into a commercially available 5 ml vial of tobramycin eyedrops (0.3%)

3.Gentamicin (15 mg/ml): Add 2 ml of parenteral gentamicin containing 80 mg of the drug into a commercially available 5 ml vial of gentamicin eyedrops (0.3%).

*Fortified eyedrops in endophthalmitis is not recommended routinely but only if there is a concurrent corneal ulcer or suture abscess and in bleb associated endophthalmitis.

1. Amphotericin B : 0.7-1.0 mg/kg/day (given slow IV over 2-6 hours after a test dose)

2. Fluconazole : 200 mg/day PO in single or two divided doses

1.Amphotericin B (5 μg): Amphotericin B available as 50 mg powder in a vial. Reconstitute this with 10 ml of dextrose 5% (not normal saline) to give a concentration of 5 mg/ml and

500 μg in 0.1 ml. Take 0.1 ml into a tuberculin syringe and dilute further with 9.9 ml of dextrose 5% to give a concentration of 500 μg in 10 ml and 50 μg /ml and 5 μg in 0.1 ml.

Small incision cataract surgery and phacoemulsification have revolutionized the management of cataract surgery. The main advantages of these procedures over conventional extracapsular cataract extraction (ECCE) with intraocular lens (IOL) implantation are a consequence of the reduced size of the wound required for delivery of the nucleus. Consequently the surgery can be performed in a closed system with out significant alterations in the intraocular pressure (IOP). Furthermore the smaller size of the wound imparts it with greater stability and minimises postoperative morbidity and especially postoperative astigmatism. Today more than ever before, cataract extraction by small incision cataract surgery is being performed as an outpatient office procedure permitting early rehabilitation with minimal to no morbidity. It is therefore important for all small incision cataract surgeons to have a sound knowledge of the posterior segment complications of small incision cataract surgery. In comparison to conventional cataract surgery, especially regarding posterior segment disorders which might occur either during small incision surgery or in the postoperative

period and compromise the final visual outcome.

Pathophysiology of Posterior Segment Disorders

Posterior segment affections in patients undergoing small incision cataract surgeries can be described along four major subheads.

A.Posterior segment surgical complications of small incision surgery.

B.Posterior segment disorders which arise de novo following the surgery in the postoperative period, i.e. cystoid macular oedema.

C.Previously existing disorders which can be aggravated following small incision cataract surgery, i.e. diabetic retinopathy.

D.Associated independent retinal pathologies, i.e. retinal detachment or macular degeneration.

Posterior Segment Surgical Complications

Preoperative Complications These include complications relating to ocular anaesthesia, i.e.:

•Accidental globe perforation

•Central retinal artery occlusion following long time use of superpinky

Intraoperative complications

•Expulsive haemorrhage

•Vitreous loss

•Posterior dislocated nucleus

•Dislocated IOL

Postoperative complications

•Endophthalmitis

•Late retrobulbar haemorrhage

ACCIDENTAL GLOBE PERFORATION

Accidental globe perforations during local anaesthesia are a well documented, but rare complication in experienced hands. The incidence of needle perforations during retrobulbar anaesthesia varies from study to study with figures of 1 in 12000 to 3 in 4000 cases reported by different authors. The incidence is much lower in patients who receive peribulbar blocks. However, accidental globe perforation has been reported following peribulbar injections as well. The possibility of carrying out a small incision cataract surgery and especially a phacoemulsification under topical anaesthesia or without anaesthesia raises the important possibility of total prevention of this complication during this procedure. It is however likely that the use of peribulbar or retrobulbar blocks will continue even in patients undergoing phacoemulsification as topical phaco is likely to be possible only in patients who are extremely co-operative. Further more a peribulbar or retrobulbar block is likely to be used in all patients undergoing a small incision cataract surgery.

Clinical Features

The most important predisposing factors for the occurence of this complication are large myopic eyes and very uncooperative patients. Varying clinical presentations may occur in patients who have had accidental perforations of the globe depending upon the sequence of events that have happened i.e.

1The needle penetrates the globe and the drug is injected into the globe

2The needle penetrates the globe, and is then retracted and the drug is injected into the orbital cavity.

3The needle penetrates the eye anteriorly and then again posteriorly and the drug is injected into the orbital cavity.

In situation one, If the drug is accidentally injected into the globe, the IOP rises to extremely high levels, and the patient may complain of severe pain as the drug is being injected. The cornea becomes hazy and the anterior chamber may become shallow. In situations two and three, the condition is diagnosed when there is sudden hypotony or pupillary constriction, a characteristic “poking through” sensation and loss of the red reflex and pain may be complained by the patient at the time of perforation.

Management

Further management of this complication depends upon the situation. The factors, which influence decision making in this situation, are extent of the cataract, the IOP, media clarity including the clarity of the cornea, presence or absence of vitreous haemorrhage, and presence of a retinal detachment.

If the cataract is total and if the IOP is within normal limits, it is best to go ahead with the cataract extraction in the same sitting. If however the site of the perforation can be visualized due to a moderate or mild cataract, one should ask a retinal surgeon to seal the break with cryopexy or laser photocoagulation using a laser indirect ophthalmoscope before the patient is taken up for cataract extraction. Furthermore it is preferable to wait for 3 to 4 weeks after the prophylactic treatment before going in for the cataract extraction. It is therefore mandatory to do an indirect ophthalmoscopy in all suspected cases of occult perforation.

In patients who have very high IOP, it is probably best to defer surgery to the next operating day to permit the IOP to come down to normal. But immediate paracentesis may be required to prevent permanent visual loss due to central retinal artery occlusion (CRAO) because of very high IOP. The visualization of sponta-

neous or induced central retinal artery pulsations in a clear media and high IOP is a sign of impending CRAO.

Patients who have a vitreous haemorrhage with a hazy media or in cases who have retinal detachments would need to be taken up for prompt vitreous surgery in addition to the cataract surgery.

Since cataract surgery will be needed in most of the cases even to manage the posterior segment pathology, the cataract should be removed in the first sitting if it can be safely done so. The decision to insert an IOL should then be based on the condition of the posterior segment of the eye after nucleus removal and cortical aspiration. If the media is clear and no retinal detachment is present, an IOL may be inserted. If however the media is very hazy and / or a retinal detachment is present, it is best to avoid inserting an IOL. A flow diagram outlining the management of accidental globe perforation is given in Figure 36.1.

Accidental globe perforation: Approach to management

Indirect ophthalmoscopy (If globe perforation is suspected

Fig. 36.1

CENTRAL RETINAL ARTERY OCCLUSION

Central retinal artery occlusion has been reported rarely following peribulbar anaesthesia. This is likely to occur when the superpinky has been kept at high pressure for a long time. The compressing effect of the superpinky could raise the intraocular pressure when it is on and thereby precipitate a central retinal artery occlusion. Hence it is important not to keep the superpinky at too high a pressure. It is even more important to release the superpinky at timely intervals. Generally the pressure exerted by a pressure lowering devise on the eye should be lesser than 30 mm of Hg. This pressure should not be exerted for over 15 minutes at a time. It is important to remember that once central retina artery gets obstructed, we might not be able to diagnose the condition until the postoperative phase when treatment modalities are not likely to be effective in successfully managing the condition.

EXPULSIVE HAEMORRHAGE

Introduction

Expulsive choroidal haemorrhage is a dreaded complication of ocular surgery. Its incidence has been quoted to be 0.05 to 0.5 per cent during cataract surgery by different authors. The incidence of this complication is likely to be lower in patients undergoing phacoemulsification since a closed intraocular cavity is maintained at a near constant intraocular pressure through out the procedure. Whether the risk of this complication is less in patients undergoing small incision cataract surgery is open to question.

It has been shown that axial length > 25.8 mm, a history of glaucoma, preoperative intraocular pressure > 18 mm of Hg, and intraoperative pulse rate >85 beats per minute are all associated with higher risk of expulsive haemorrhage. Long-standing hypertension and arteriosclerosis are also predisposing factors.

The site of haemorrhage is probably a sclerotic choroidal arteriole where the vessel crosses the suprachoroidal space from the scleral canal. It has been postulated that the sudden hypotony following surgical penetration of the globe causes a bending and then a rupture of the arteriole.

Clinical Features

This complication can be diagnosed when in a case, sudden wound gape, iris prolapse, self-delivery of lens and loss of red reflex begin to occur in quick succession. Finally this might even lead to expulsion of the whole intraocular contents. Capsular rent during extension of section and a spontaneous prolapse of a PC IOL into AC in a previously well formed anterior chamber are other early signs of suprachoroidal haemorrhage. (personal experience)

Management

It is quite evident that this complication has to be recognized early and prompt measures taken to reduce the tension and close the wound immediately in order to successfully salvage the eye in these cases. Prompt closure of the wound is the most important step in the management as it can help to salvage the eye and even the vision in a number of patients. The quickest technique to close a wound, which has just begun to gape, is one which has been described by Dr Daljit Singh. A set of 6 or 7 8-0 needles which have been left over after suturing of previous cataract surgeries must always be kept handy on one side of the OT trolley so as to facilitate closure. In

case one suspects impending choroidal haemorrhage, these needles are quickly passed through the corneal and scleral ends of the wound and kept in place till formal suturing can be completed. The needles should be passed as quickly as possible even if iris incarceration into the wound occurs since this can be managed once the wound is secure.

In many cases, the occurence of choroidal haemorrhage is recognized late when the IOP has risen to dangerously high levels. At this time, the technique described previously will no longer work. In this situation, it is best to use a 4-0 or a 6-0 vicryl or silk suture for wound closure since finer sutures are likely to give way due to the high pressure. It is imperative that the wound be closed as quickly as possible in this situation even if iris gets incarcerated in the wound. If the surgeon feels that the tension has to be controlled further, a posterior sclerotomy can be done 4 to 4.5 mm posterior to the limbus. Some surgeons have also advocated retrovitreal fluid aspiration through the pars plana route if possible. Personally we feel that this may not prove to be feasible during the acute crisis confronting the surgeon at that time.

In case the acute event has been successfully managed, the possibility of salvaging the eye and its vision increases significantly. The patient is managed conservatively with all the efforts directed at the control of IOP and intraocular inflammation. Choroidal haemorrhages often regress spontaneously in 2-3 weeks. If kissing choroidal haemorrhagic detachments form it may become necessary to drain them on the 5th to 7th day. The procedure may need to be combined with a vitrectomy for clearing of vitreous haemorrhage. The management of a kissing choroidals is best left to an expert vitreoretinal surgeon to whom the patient should be referred as soon as the condition is detected.

Some times, choroidal haemorrhage develops during the postoperative period in elderly patients with arteriosclerosis, especially those patients who have been engaging in Valsalva maneuvers such as straining at stool or coughing. The possibility of this complication should be explained to the patient and he or she should be warned against coughing or severe straining in the early postoperative period.

VITREOUS LOSS

Vitreous loss is one complication that all cataract surgeons have experienced at one time or the other. This complication occurs even in the best of hands and hence all

cataract surgeons should be well versed with its management. The incidence has been reported to vary from 2 to 5 per cent by different authors. The incidence of posterior capsular tears and vitreous loss is high in the early phases of the learning curve of small incision cataract surgery. The incidence is probably higher during the learning curve of the phaco surgeon than it is of manual small incision cataract surgeon. Vitreous loss most commonly occurs during the nucleotomy and lens matter aspiration.

Clinical Features

The capsule rupture may not be readily visible at times. In this situation, we might have to rely on subtle signs like the inability to aspirate cortex despite adequate suction, a peaked pupil, or posterior movement of lens remnants. Sudden deepening of the anterior chamber and a brightening of the red glow may also be noticed. A cellulose sponge kept at the wound and rolled will show the vitreous strands if there is vitreous in the wound. These clinical features will be more over similar in cases of vitreous loss occurring in small incision manual cataract surgeries and in phacoemulsification.

Management

It is important that all the vitreous is removed from the anterior chamber and the wound as it can lead to traction and later complications. The vitreous at the wound can be cleared by a scissors or by an automated vitrectomy probe (preferred method). Instilling viscoelastic material into the bag may reposit the vitreous if the tear is small and there is only a limited vitreous bulge. If a significant amount of vitreous is present in the anterior chamber, and certainly if it is present in the wound, an automated vitrectomy should be performed using high cutting rates of upto 600 cuts per minute and low aspiration pressures and low irrigation. The endpoint of vitrectomy is a round central pupil with a deep anterior chamber with a posteriorly curved iris surface. Infusion for the vitrectomy should be provided either in the full function vitrectomy probe or through a 20 or 22-gauge cannula attached to the infusion bottle suspended 2 feet above the patients head. The infusion should then be used judiciously as excessive infusion could hydrate the gel vitreous, thereby prolonging the vitrectomy. Finally a vitreous sweep is used to move vitreous stands away from the wound and into the pupillary space.

The management of cases with vitreous loss associated with nucleus drop is dealt with elsewhere. It is quite

important to understand that once a lens has sunk down, no fishing of the lens should be done from the anterior route as it will increase the traction on the vitreoretinal interface.

CHOROIDAL DETACHMENT

When serous fluid accumulates in the suprachoroidal space choroidal detachment can occur. The shunting of fluid into this space is generally precipitated by low IOP, causing hydrostatic pressure to decrease in the anterior uveal veins. The plasma proteins add an osmotic force that draws more fluid into the space, increasing the detachment. Low IOP following cataract surgery can result from a wound leak or ciliary body shutdown. The possibility of this complication is low in cases, which have undergone small incision cataract surgery or phacoemulsification unless the corneal or scleral valve has been made in a faulty manner. Attention to the creation of a good corneal or scleral valve is thus essential in all cases undergoing small incision cataract surgery. Care should also be taken to hydrate or close the sideport which may be a more common cause of leakage . Many a time this is ignored thinking that the opening is very small.

Clinical Features

The characteristic clinical signs are smooth dome like brownish elevations of the peripheral choroid and retina. As a consequence, the ora serrata becomes easily visible in the affected area with an indirect ophthalmoscope. These mounds appear very solid but vary in extent. The differential diagnoses include retinal detachment and retinal mass lesions.

Management

Under most circumstances, a choroidal detachment is managed conservatively. If the anterior chamber is well formed and if the choroidal detachments are small to moderate in size, it is recommended that the patient be maintained on a strong cycloplegic agent, such as atropine ointment, 3-4 times per day or homatropine eye drops 8 times a day along with a topical steroid one hourly, i.e. 16 to 18 times daily. Systemic steroids may be added to this treatment regime if needed. If the cause of the hypotony is from a wound leak, then it must be resutured.

CYSTOID MACULAR OEDEMA (CME)

Introduction and Epidemiology

The accumulation of fluid in the macula resulting in the formation of cystic spaces, after cataract surgery, is referred to as Irvine-Gass syndrome. The fluid may be extracellular in the outer plexiform and inner nuclear layers of the retina, or intracellular causing Muller cell degeneration with intracellular vacuolation. CME is more often seen in association with complicated cataract surgery and is more commonly seen in patients with rupture of the posterior capsule with vitreous loss, vitreous incarcerated in the surgical wound, or in those with a poorly positioned intraocular lens.

The incidence of angiographically documented CME is approximately 50 per cent after intracapsular cataract extraction, 20 per cent after extracapsular cataract extraction and 10 per cent after phacoemulsification surgery. However, studies have reported that the occurrence of clinically significant macular edema varies between 1.5- 2.3 per cent and is probably lesser in patients who have undergone phacoemulsification as compared to those who have undergone conventional ECCE and IOL. There is a paucity of studies, which have evaluated the incidence of this disorder in patients undergoing small incision cataract surgery.

It is important to differentiate clinically diagnosed cystoid macular edema based on biomicroscopic examination, from angiographic cystoid macular edema based on fluorescein angiography since angiographic CME does not necessarily affect visual acuity. Persistent macular edema may however result in foveal receptor damage and macular degeneration.

The common risk factors for the development of CME following cataract surgery are rupture of the posterior capsule, vitreous loss, or insertion of a flexible open-loop anterior chamber IOL. Other causes are secondary lens implantation, intraocular lens exchange, old age, preexisting uveitis and YAG capsulotomy.

Clinical Features

The usual clinical presentation is a history of blurring of vision 2-6 weeks following cataract surgery. The problem of cystoid macular edema comes up earlier in the era of small incision cataract surgery as most patients have begun to gain a very good visual acuity soon after surgery due to minimum astigmatism in comparison to routine ECCE and IOL where sutures are removed only after six weeks. Thus these patients can experience the visual loss caused by CME quite early in their postoperative

course.The patient usually presents with gradually decreasing vision usually in the range of 6/18 and 6/60. Direct ophthalmoscopy reveals the absence of foveal reflex with the presence of cystic spaces in the macular region, the inner walls of which are not appreciable. The pathology can be visualised with greater clarity using a slitlamp biomicroscopy with a 90-D lens, which reveals the characteristic cystic spaces in the foveal region. Evidence of cells or flare may be present in some cases. In most cases, fluorescein angiography reveals parafoveal retinal capillary leakage In the early and mid phases of the angiogram where as a petaloid pattern of leakage in the macula and leakage on or around the optic disc occurs in the late phases of the angiogram. (Fig. 36.2) However, the visual acuity is not related to the amount of leakage.

Fig. 36.2: Fluosescein angiogram of a patient with cystoid macular oedema demonstrahng a petalloid form of dye leakage in the late phase

Management

Prostaglandin release has been implicated in the disruption of the inner blood-retinal barrier after ocular surgery and as a cause of CME. Non steroidal antiinflammatory drugs and topical, periocular or oral corticosteroids are of proven benefit in reducing the immediate postoperative inflammation that presumably contributes to the development of CME. In patients in whom there is a significant visual loss, the first line of management should probably consist of periocular or systemic steroids (Injection kenocort ( triamcinolone) 0.5 cc in the subtenon’s space or tablet prednisolone 1 mg/ kg/ day) orally after breakfast along with an antacid or an H1 blocking agent to prevent gastritis. Topical

diclofenac sodium 4 times daily can be added to this regimen. In case there is evidence of improvement over the following 2 to 3 weeks, the subtenons kenocort injection can be repeated after 3 weeks and slowly tapered off by increasing the duration between the doses. Some authors have also used acetazolamide one tablet twice daily in the management of CME.

The problem with most of the therapies is the high incidence of recurrence following the withdrawal of the treatment. It is therefore necessary to continue the treatment for long enough duration to prevent relapses.

The Vitrectomy-Aphakic Cystoid Macular Edema Study showed that pars plana vitrectomy to release vitreous attachments to the surgical wound was beneficial, significantly improving visual acuity in patients with postoperative CME associated with vitreous incarceration. YAG vitreolysis has also been selectively used to divide vitreous strands adherent to the surgical wound. This is however, possible only if the strand is very localised. Other factors like a poorly positioned lens should also be managed appropriately. Local oxygen therapy using goggles for 6 hours a day for 3 weeks has been shown to have utility in 80 to 90 per cent of patients though we have no personal experience with this mode of treatment. It is important to remember that the successful treatment of chronic CME requires persistence on the part of the treating ophthalmologist and the patient.

Photic Maculopathy

The light of the operating microscope can cause macular damage. Operating microscope maculopathy was seen in 7 per cent of 135 consecutive patients undergoing cataract extraction according to one study.

The greatest risk of photic injury occurs following insertion of an IOL, which focuses the light of the microscope onto the retina. The photic retinopathy of operating microscopes is probably due to shorter-wavelength visible light (blue and blue-green). The probability of operating microscope damage can be reduced by using the lowest illumination needed for a particular procedure, and by filtering out light at wavelengths below 450 nm. The duration of a patient’s exposure to coaxial illumination should be minimised by using an occluder or by using paraxial illumination whenever coaxial illumination is not essential. As the operating time decreases with phacoemulsification and small incision cataract surgery, the incidence of these complications are also bound to decrease.

DIABETIC RETINOPATHY AND CATARACT

Cataract surgery in diabetic patients is more unpredictable due to many factors like difficulty in fundus visualisation, increased incidence of cystoid macular edema, and increased risk of progression of the retinopathy and anterior segment neovascularisation. A history of prior photocoagulation can also influence the clinical course of these patients.

The approach to management is based on adequate visualisation of the fundus and a proper diagnosis of the stage of retinopathy. An indirect ophthalmoscopy and a fluorescein angiography must be included in the preoperative work up of these patients. Preoperative assessment of the magnitude of visual loss caused by cataract is often difficult in the diabetic patient, and a laser interferometry should be performed in such cases to know how much improvement is likely to be achievable with a cataract surgery alone. Even in cases in which the retina is normal, the patient should be warned of the risk of development of diabetic retinopathy following surgery, which could hamper his vision. The variables affecting the progression of diabetic retinopathy after cataract surgery include the stage of the diabetic retinopathy, type of cataract surgery, occurrence of surgical complications and previous laser surgery.

Epidemiology

Those patients, in whom there is no evidence of diabetic retinopathy have minimal risk of progression following cataract extraction. Deterioration of diabetic retinopathy occurs following cataract surgery in 30 to 40 per cent of diabetics. if they had significant pre-existing diabetic retinopathy prior to the surgery. In cases with pre-existing diabetic maculopathy, the progression of maculopathy is seen in 20 to 30 per cent of patients. These patients have a higher than normal incidence of cystoid macular edema also. Pre-existing proliferative diabetic retinopathy is associated with an increase in the risk of vitreous haemorrhage

Approach to Management

The approach to management is based on the sufficient visualisation of the fundus. In mild nonproliferative diabetic retinopathy, no active intervention is done preoperatively for the retinopathy (Fig. 36.3a) Only postoperative observation is needed in such patients. In moderate to severe nonproliferative diabetic retinopathy, pre-operative panretinal photocoagulation should be

considered as a management option, especially in India since the risk of patients being lost during the follow-up is high. In patients with pre-existing proliferative diabetic retinopathy, panretinal photocoagulation should be done to whatever extent is possible preoperatively and completion of the same must be done in the early post-opera- tive period (Fig. 36.3b). Maculopathy detected preoperatively will not only deteriorate, but is also associated with the risk of development of cystoid macular edema in the postoperative period. If focal macular laser is possible, then the same should be carried out and cataract surgery should be carried out 4 to 6 weeks later. However, the role of prophylaxis with nonsteroidal anti-inflam- matory drugs in the pre-operative period to prevent the occurrence of CME is still debated.

Fig. 36.3a: Fluorescein angiography of a patient with early non-proliferetive diabetic retinopathy

It is important that the patient’s glycaemic status is checked before he is taken up for cataract surgery. It is known that the chances of infection in a diabetic eye are no higher than in the normal population, but in cases where infection has occurred, the course is more severe.

IOLs are not contraindicated in diabetics. Surgery as such should be directed so as to insert a larger IOL (6mm optic), which is surface modified and which will help in the early postoperative visualisation of the fundus and laser treatment if necessary. Steps like posterior capsule polishing should be taken to prevent the development of aftercataract. An inferior sphincterotomy may help in increasing the pupil size in the otherwise rigid pupil. It is important that the integrity of posterior capsule be maintained during the surgery. Extra sutures should be applied in patients undergoing small incision nonphaco cataract surgery to permit photocoagulation in the early

Fig. 36.3b: Fluorescein angiography of a patient with proliferative diabetic retinopathy

postoperative period.

The rate of progression of retinopathy is higher following intracapsular cataract extraction (ICCE) than with ECCE. Progression to the stages of rubeosis iridis, vitreous haemorrhage and diabetic maculopathy are known. There is no significant difference in the rate of progression of diabetic retinopathy between uncomplicated ECCE and ECCE and IOL.

The advantage of phacoemulsification in such cases is the watertight compartment formed and the higher wound strength that it offers in the immediate postoperative period, which not only makes it possible to do a vitreous surgery with the cataract surgery in the same sitting if needed, but also makes the laser treatment in early postoperative period easier. This advantage is partially negated if the wound size is large. In advanced cataracts, where the posterior segment cannot be assessed for diabetic changes, it is advisable to carry out an indirect ophthalmoscopy on the operating table following cataract extraction and evaluate the retinal status prior to insertion of the IOL. In cases, which require vitreous surgery, it is best to leave the patient aphakic after the cataract extraction. In these cases, after the completion of the retinal surgery, an IOL can be inserted if needed. In case an IOL is planned, a silicone IOL is best avoided in cases where we contemplate the possibility of a vitreous surgery at a later date.

There is a higher incidence of iris neovascularisation reported following capsular rupture during the surgery. Risk of neovascularisation also increases following YAG capsulotomy. Preoperative photocoagulation can help to reduce the incidence of cystoid macular edema following cataract surgery. The progression of diabetic