Ординатура / Офтальмология / Английские материалы / Moorfields Manual of Ophthalmology_Jackson_2007

Box 6.1: Limbal relaxing incision

1.Mark the limbus at the 90° position preoperatively, with the patient sitting upright at the slit lamp (avoids alignment error from cyclotorsion when supine after orbital block). Perform LRI at the start of surgery when the eye is firm and there is less risk of ‘dragging’ the corneal epithelium (if a large LRI is required at the site of the main wound, extend the LRI at the end of surgery).

2.Align a degree gauge (e.g. Mendez ring) on the cornea using the limbal reference marks (Fig. 6.4). Locate and mark the steep meridian. Confirm with intraoperative keratoscopy (reflected mires appear closer on the steep axis).

3.Define the required arc length centred on the steep meridian using either ink marks or a fixation ring with increment markers (e.g. Fine-Thornton-Nichamin).

4.Use a guarded diamond knife-style blade set at a depth of 600 microns (according to nomogram). Make accurate incisions at the most peripheral clear cornea (irrespective of vessels), keep the blade perpendicular and pull towards you. Wait 4–6 weeks for stable refraction.

temporal CCI. Measure the axis and amount of corneal astigmatism by keratometry or topography. Identify requisite LRI length (degrees of arc) from preferred nomogram, e.g. modified Gills or Nichamin (Table 6.3A, 6.3B). Complications include: wrong axis, perforation (rare), infection, misalignment, induced irregular astigmatism, decreased corneal sensation, and weakened globe.

Toric intraocular lenses Toric IOLs incorporate a cylindrical correction on a spherical optic for correction of preexisting regular keratometric astigmatism. They are useful when an LRI is inadequate or less predictable, e.g. astigmatism >3.00–3.75 D or in young patients (beware a forme fruste of keratoconus). Successful outcome relies on careful lens power calculation and selection, minimizing surgically induced astigmatism, meticulous cortical clean-up/capsule polish, and precise alignment of IOL cylindrical correction axis with the steep corneal meridian. Corneal reference marks should be made preoperatively as described above for LRIs. The greatest clinical

experience exists with the STAAR single-piece silicone plate haptic toric IOL; available in astigmatic powers of 2 and 3.5 D (correcting approximately 1.5 and 2.25 D of astigmatism, respectively) and 2 lengths (TF 10.8 mm and TL 11.2 mm). However, significant IOL

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Fig. 6.4: Limbal relaxing incision.

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Management of astigmatism

Local Anaesthesia

Background Most modern cataract surgery is performed under local anaesthesia (LA) with the advantage of reduced morbidity and mortality, reduced hospital stays, and increased patient satisfaction compared to general anaesthesia (GA). Anaesthesia can be achieved by topical means alone, but akinesia (paralysis of ocular movements) requires regional orbital block (sub-Tenon’s, peribulbar, or retrobulbar). The choice of LA technique must be tailored to surgery, the patient’s expectations, and the comfort of both patient and surgeon.

■Patient selection : Good communication before and during surgery reduces anxiety and improves cooperation. The patient should be able to lie still and relatively flat for the duration of surgery.

■Monitoring : all patients must be monitored (pulse oximetry, BP, ECG) by suitably trained personnel; if using sharp needle technique, an anaesthetist must be available and i.v. access in place.

■Sedation : Useful in certain patients (e.g. anxious or claustrophobic, may improve mild head tremor, but not for pain relief). Risks include inducing confusion, restlessness, and airway compromise. Requires postoperative monitoring and appropriate escort/transport arrangements.

■General anesthesia : preferred if the patient is unable to comply with instructions (e.g. confusion, learning difficulties), very severe claustrophobia, history of panic attacks, significant psychiatric disease, marked resting head tremor, young patient, previous adverse reaction, allergy or complication associated with LA, or if the patient declines LA.

Topical anaesthesia Increasingly popular, although regional block remains the standard in cataract surgery. Select wellmotivated patients, routine cases, and an experienced surgeon. Avoid if there is a language barrier, hearing impairment, ‘lid squeezers’, extreme anxiety, dementia/confusion, nystagmus, combined or long surgical procedures. Warn the patient of pressure sensation and preservation of vision during surgery. Avoid unnecessarily bright illumination.

■Advantages : Noninvasive and quick, rapid visual recovery, avoids complications of orbital blocks/GA, inexpensive, useful if anticoagulated or long axial length.

■Disadvantages : Not suitable for all, limited to short

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Local anaesthesia

epithelial haze/impaired view, without akinesia surgery may be challenging if the patient is uncooperative or if complications arise.

■Technique : Apply G. proxymetacaine 0.5% (or G. benoxinate 0.4%) initially (less stinging than amethocaine) then 2–3 drops G. amethocaine 1% (better anaesthesia during surgery than proxymetacaine or benoxinate) 5 minutes preoperatively. Ensure application to the cornea, bulbar conjunctiva, inferior and superior fornices (to reduce speculum discomfort). Also instill G. proxymetacaine 0.5% once to the fellow eye. Instill a further three drops during surgery: before the first corneal incision, before intraocular lens insertion, and before subconjunctival antibiotic/steroid injection. Give additional drops at any stage as required, remembering that amethocaine can cause epithelial haze.

Adjunctive intracameral anaesthesia is not used routinely but is useful in eliminating the pressure sensation/pain sometimes experienced under topical alone: irrigate the AC with 0.5 mL preservative-free 1% lidocaine in BSS (without epinephrine) after the first incision.

Sub-Tenon’s block

■Technique : see Box 6.2 and Figure 6.5.

■Agents : Use shorter-acting lidocaine 1 or 2% (without epinephrine), or longer-acting bupivacaine 0.5%, or a mixture

Box 6.2: Sub-Tenon’s block

1.Position the patient supine, apply G. benoxinate 0.4% then one drop 5% povidone iodine, and insert the lid speculum. Button-

hole the conjunctiva and Tenon’s capsule 4 mm from the limbus in the inferonasal quadrant using spring scissors and forceps. Apply conjunctival cautery if required (Fig. 6.5A).

2.Blunt dissect to open sub-Tenon’s space (Fig. 6.5B) then insert a curved blunt sub-Tenon’s cannula between Tenon’s and sclera. Gentle hydrodissection assists passage (Fig. 6.5C).

3.Keep the tip adjacent to the globe and pass posteriorly; there is usually some resistance at the equator (Fig. 6.5D).

4.Push beyond equator and inject 3–5 mL of LA to spread around globe and into the intraconal space. This often causes proptosis. If there is resistance to injection, reflux, or subconjunctival

A

B

C

D

Fig. 6.5: How to perform a sub-Tenon’s block. See Box 6.2.

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Local anaesthesia

of both, with or without hyaluronidase diluted to 15 i.u./mL (Hyalase® may prevent loculation of fluid behind the globe, reducing the risk of increased posterior pressure and its complications). The maximum safe dose of lidocaine without epinephrine is 3 mg/kg and bupivacaine 2 mg/kg

(0.5% = 5 mg/mL, 1% = 10 mg/mL, 2% = 20 mg/mL) e.g. maximum safe dose of 2% lidocaine for a 70 kg patient is (3 × 70)/20 = 10.5 mL.

■Advantages : safest orbital block (avoids sharp needle), relatively rapid action.

■Disadvantages : less effective akinesia if poorly administered, subconjunctival chemosis or haemorrhage, and difficult to perform if previous buckle/conjunctival surgery.

Peribulbar block A sharp needle technique, but safer than retrobulbar. Check axial length, as long eyes are at higher risk of inadvertent perforation (use topical or sub-Tenon’s instead).

■Technique : Position the patient supine with gaze in the primary position. Apply G. benoxinate 0.4% then one drop 5% povidone-iodine. Usually only one conjunctival injection in the inferotemporal quadrant is required (Fig. 6.6A). Use a short 25-gauge needle (25–31 mm length), and carefully advance posteriorly to the hilt of the needle. Gentle side-to-side movement of the needle should not displace the globe, else suspect scleral puncture. Withdraw the plunger to ensure there is no reflux of blood before injecting 3–8 mL of LA into the extraconal space. Wait 10–15 minutes with digital massage or Honan’s balloon to aid dispersion. An additional medial canthal injection via the caruncle may be given if needed (avoid the superonasal quadrant).

Retrobulbar block Avoid if inexperienced. Apply G. benoxinate 0.4% then one drop of 5% povidone-iodine. Give a single inferotemporal injection via the conjunctiva or lower lid skin at the junction of the outer and middle thirds of the inferior orbital rim. Use a short 25-gauge needle directed toward the occiput, then angle upwards when past the equator of the globe up to the needle hilt (Fig. 6.6B). Use manoeuvres as described for peribulbar block to check needle tip position before injecting a small volume (<3 mL) of LA into the intraconal space.

Basic surgical techniques

Basic Surgical Techniques

A ‘standard’ method of phako surgery is described, recognizing that surgeons will evolve their own techniques.

Preparation and draping

Antiseptic preparation of the surgical field (ocular surface, lids, lashes, cheek, and forehead) with aqueous povidone-iodine 5% (or chlorhexidine) and draping of the eyelashes reduces the risk of postoperative endophthalmitis.

Main incision

Construct small self-sealing clear (or near-clear) corneal incision as either a single plane stab or two or three step incisions (three step is more secure). Stabilize the globe using Thornton-Fine ‘C- ring’ or micro-grooved forceps (Fig. 6.7):

Step 1: Groove the cornea anterior to the limbus using a diamond or steel keratome (avoid incising the conjunctiva to prevent chemosis during phako).

Step 2: Create a stromal tunnel about 1 mm long using a 2.8 mm keratome (a longer tunnel is less likely to leak and essential if the AC is shallow).