Cataract surgery

1. Prophylactic antibiotic topical and systemic started one day before surgery

2. Patient should take his medications for diabetes and hypertension as usual

3. Pupil dilation with mydriatic as tropicamide plus phenylephrine and diclofenac/ketorolac. The latter inhibit prostaglandin release from the iris on mechanical stimulation during surgery and prevent intraoperative miosis.

Most of cataract surgery is done under local anesthesia except children and uncooperative patients

Topical : 0.5 %  propracaine is used in phacoemulsification in cooperative patient

Block—2% xylocaine 0.5% bupivacaine.

i. Facial nerve block

a. O’ Briens’ method—5 cc of anaesthetic is injected on the neck of the mandible just  below the condyle. The facial nerve is paralysed so that the patient is unable to squeeze the eyelids during operation due to orbicularis oculi muscle paralysis. 

b. Van Lints method—Local anaesthetic is injected near the outer canthus of the eye.

ii. Ciliary block by retrobulbar injection

1-2 cc of anaesthetic is injected into the neighbourhood of ciliary ganglion behind the eyeball. It causes anaesthesia of deeper structures like iris and lowers the intraocular pressure. It also results in mydriasis and akinesia of extraocular muscles. It is associated with risk of causing retrobulbar haemorrhage and bulbar penetration.

iii. Peribulbar anaesthesia—It is a much safer alternative method. The patient looks up straight at the ceiling and 5 ml of local anaesthetic is injected from the lateral part of the lower lid. A 23 G needle measuring 2.5 cm is directed almost straight into the deeper issues and not in the muscle cone. The anaesthetic infiltrates into the retrobulbar space by the application of 30 mm Hg pressure for 15-20 minutes. Facial block is not required/necessary.

Complications of anaesthesia include:

• Retrobulbar or peribulbar haemorrhage

• Accidental globe perforation

• Accidental injection into optic nerve sheath with intracranial spread

• Anaphylactic shock

• Vasovagal reflex resulting in collapse and death

These days only indication is dislocated or subluxated lens

 Technique

 1. Intracapsular forceps cataract extraction

 After the corneoscleral section is made, a small peripheral buttonhole iridectomy is performed at 12 O’ clock position to avoid pupillary block.

Intracapsular forceps are introduced and the lens capsule is grasped just in front of the equator either above or below (capsule is thick at these sites). 

2. Cryoprobe cataract extraction

Alternatively, the cornea is lifted by an assistant, anterior chamber is dried by spontex or cotton swab and cryoprobe is applied to the upper part of lens to form an iceball. The lens is lifted, rotated and removed through the wound by sliding method.

1. Eye is cleaned with 5% povidone  iodide applied to the skin of the eyelids and allowed to dry. One drop of 5% povidone iodide is instilled into the conjunctival sac to eliminate local microbiological flora.

2. A sterile, self adhesive plastic drape is applied to the skin on and around the eyelids and the eyelashes are excluded from the operative field by folding the edges of the drape around them and inserting a self-retaining speculum to hold the lids open.

3. Superior rectus bridle suture is passed to fix the eye in down gaze.

4. A fornix based conjunctival flap is raised and limbus exposed.

5. Haemostasis is achieved by applying gentle cautery.

6. A circumferential vertical partial thickness groove or gutter is made at the limbus through about two-thirds depth from 10 to 2 O’ clock and the anterior chamber entered.

7. Viscoelastic substances (ocular viscosurgical device OVD) such as methylcellulose, healon is injected in the anterior chamber specially to protect the endothelium and deeper tissues and to maintain the anterior chamber. 

8. A cystitome or bent 26 G needle makes a series of small radial cuts in the anterior capsule (can opener). This is known as “can-opener” technique. Anterior capsulotomy can also be done by tearing off a flap in a continuous curvilinear fashion (continuous curvilinear capsulorrhexis) for 360° in shape of a ring.

9. Hydrodissection—Balanced salt solution (BSS) is injected under the lens capsule to separate the cortex from the capsule.

10. Corneoscleral section is then enlarged (8-10 mm) using the corneoscleral section enlarging scissors.

11. Nucleus is delivered by pressing the scleral lip of the wound with an irrigating vectis and applying counter pressure at the opposite pole by gently pushing with a lens hook at the 6 O’ clock position. (Pressure and counter pressure technique).

12. Residual cortical matter is aspirated using a two-way irrigation aspiration cannula  Simcoe aspiration irrigation cannula, using balanced salt solution (BSS), Ringer’s lactate or normal saline.

13. The capsular bag is inflated with viscoelastic substance.

14. Posterior chamber intraocular lens implant is gently inserted behind the iris with angled forceps (of Kelman and McPherson) under the lens capsule at 6 O’ clock.

15. IOL is gently dialed with dialling hook (Sinskys) so that the haptics are placed at 180°.

16. Viscoelastic substance is aspirated and incision is sutured by 3 to 5 interrupted or continuous 10.0 nylon sutures.

17. Conjunctival flap is reposited back and subconjunctival injection of dexamethasone and gentamicin is given.

18. Patching of the eye is done with a pad and a bandage may be applied.

It is becoming very popular due to its merits over conventional ECCE. In this technique IOL implantation is done through a sutureless self-sealing valvular sclero-corneal tunnel incision.

1. Sclero-corneal tunnel incision—It consists of three components:

• Extenral scleral incision: A 1/3 or 1/2 thickness external groove is made 1.5 - 2 mm behind the limbus. It varies from 5.5 - 7 mm in length depending on the size of the nucleus. It may be straight or semi-circular in shape.

• Sclero-corneal tunnel: It is made with a crescent knife. It usually extends 1 - 1.5 mm into the clear cornea.

• Internal corneal incision: It is made with a sharp 3.2 mm angled keratome.

2. Side-port entry is made at 9 O’ clock position with a Stiletto or MVR (micro vitreal retinal) blade.

A valvular self sealing incision about 1 mm wide is made at the limbus. This helps in aspiration of the sub-incisional cortex and increasing the depth of anterior chamber.

3. Anterior capsulotomy—It can be either a ‘can-opener’, envelop shaped or continuous circular capsulotomy (CCC). However, a large sized CCC is preferred.

4. Hydrodissection is essential to separate cortico-nuclear mass from the posterior capsule.

5. Removal of nucleus

i. Prolapse of nucleus from the capsular bag into the anterior chamber is done during hydrodissection and completed by rotating the nucleus with Sinskey’s hook.

ii. Delivery of nucleus through the corneo-scleral tunnel is done by

• Irrigating wire vectis method. 

• Fish hook

• Visco expression.

6. Aspiration of the cortex is done by a two way irrigation and aspiration cannula from the main incision and side port entry.

7. A posterior chamber IOL is implanted in the capsular bag after filling it with viscoelastic substance (OVD).

8. Viscoelastic substance is then removed thoroughly from the anterior chamber and capsular bag with the help of a two way irrigation aspiration cannula.

9. Wound closure—The anterior chamber is deepened with balanced salt solution or Ringer’s lactate (through side port entry). This results in self sealing the valvular incision. The conjunctival flap is reposited back.

i. Irrigation—It is done by a gravity flow system. Balanced salt solution (BSS) is allowed toflow to the handpiece, which is controlled by foot switch.

ii. Aspiration—The emulsified material is aspirated through peristaltic or venturi pump as irrigation maintains normal depth of the anterior chamber.

iii. Fragmentation—It is performed through a piezo-electric ultrasonic mechanism which activates a hollow 1 mm titanium needle, vibrating at the frequency of 40,000/sec (40 kilo- hertz ultrasonic energy). The amplitude of vibration is 0.038 mm from the resting point of the tip and the total to and fro motion is 0.076 mm (stroke length).

Technique of Phacoemulsification

The technique is constantly changing and has many variations. The basic steps are described as

follows:

1. Phaco Incision

i. Scleral tunnel incision

ii. Clear corneal incision

At present scleral tunnel approach is most popular. Initially, incision is placed through half the scleral thickness, 1.5 to 2.0 mm away from the clear cornea. The length of the incision is about 3 mm. Dissection is carried out in the sclera and upto atleast 1 mm inside the cornea. The incision heals quickly, ambulation is quick and there is no induced astigmatism.

2. Anterior Capsulotomy [Continuous Curvilinear Capsulorrhexis (CCC)]

Continuous curvilinear capsulorrhexis of 4-6 mm is performed with bent needle cystitome or capsulorrhexis forceps after filling the anterior chamber with viscoelastic substance. Capsulorrhexis is started by making a small cut at the centre of the lens, pulling directly towards the 12 O’clock position and curving towards the left. This creates a central flap that tears in a circular pattern to the right. The flap is folded over and pulled by forceps in a circular motion and capsulorrhexis is complete.

3. Hydroprocedures

These procedures facilitate nucleus rotation and manipulation during phacoemulsification.

i. Hydrodissection—It is the seperation of the capsule from the cortex by slowly injecting balanced saline solution between the two.

ii. Hydrodelineation—A 26 gauze needle is inserted between the hard central nucleus and epinucleus and slowly balanced saline solution is injected. Thus cleavage is done between nucleus and epinucleus.

4. Nucleus Emulsification

The different densities of cataracts have created different methods of sculpting or breaking the nucleus in small fragments.

i. In soft to moderately hard nucleus—A vertical ‘trench’ is sculpted and the procedure is called ‘trench divide and conquer’ (TDC).

ii. In moderately hard to very hard nucleus—A deep central crater is sculpted and the procedure is called ‘crater divide and conquer (CDC).

The other common methods are ‘chip and flip technique’ and ‘phaco chop technique’. The nucleus is finally emulsified and aspirated.

5. Aspiration of the Residual Cortex

It is performed using the irrigation aspiration handpiece with a 0.3 mm aspiration port. The posterior capsule is polished with the same handpiece using very low aspiration pressure. The incision is then enlarged to a width sufficient to introduce the lens implant into the capsular bag.

6. Intraocular Lens Implantation

The intraocular lenses which may be used after phacoemulsification are,

i. Single piece PMMA IOL—The rigid IOL used in phacosurgery should have an optic diameter of 5.5 mm or less.

ii. Foldable IOL is made of soft acrylic, hydrogels or silicone materials. The design can be either 3 piece lenses or single piece plate haptic design. Presently, the 3 piece lenses are used and plate haptic design is used for toric IOLs to correct astigmatism of < 3 D.

Advantages of Phacoemulsification

1. Intraoperatively, phacoemulsification allows excellent control of each phase of the operation for cataract removal.

2. The small incision technique involving a self-sealing ‘no stitch’ or ‘sutureless’ incision produces very secure and stable wound. There is rapid wound healing and shorter convalescence.

3. Removal of the nucleus occurs through a continuous circular capsulotomy (CCC) with the closed chamber. Aspiration of the cortex also occurs within a closed anterior chamber, with low risks of damaging the endothelium, iris and posterior chamber.

4. Phacoemulsification and small incision surgery are compatible with small size implants, i.e. foldable lenses. There is minimum or no astigmatism with early return of binocular vision.

Disadvantages of Phacoemulsification

1. It is a difficult technique to master.

2. It requires expensive instrumentation.

1. Diagnostic Procedures

i. Gonioscopy

ii. Three mirror examination

iii. Laser procedures

2. In Surgery

i. For creating and maintaining surgical space as during insertion of intraocular lens during cataract surgery.

ii. Protecting the endothelium from damage due to handling in keratoplasty and phacoemulsification.

The common viscoelastic substances

 are 1%, 2% hydroxy propyl methyl cellulose, 1% chondroitin sulphate, 1% sodium hyaluronate (Healon) and combinations of these like Viscoat (3% Sodium hyaluronate and 4% chondroitin sulphate). Sodium hyaluronate (1%, 1.4%, 5%) is obtained from rooster combs and most closely resembles the natural vitreous gel.

• Cohesive OVDs are used to create and maintain intraocular spaces, for example to maintain the AC during capsulorhexis and inflation of the capsular bag to facilitate introduction of an IOL. Higher molecular weight variants maintain intraocular space more effectively, but tend to promote iris prolapse in shallow ACs and confer a more sustained postoperative IOP rise. example is healon.

• Dispersive OVDs are more adherent to surfaces than cohesive OVDs and are typically used to protect the endothelium. They are more difficult to remove from the eye than cohesive viscoelastics, but are less likely to cause an IOP spike. The major practical disadvantage of dispersive OVDs is their tendency to retain air bubbles and lens fragments, compromising the surgical view. example is viscoat.

Adaptive OVDs display mixed characteristics.

uses:

1. Soft shell’ technique involves the injection prior to the capsulotomy stage of an outer dispersive layer followed by an inner cohesive nucleus. Some surgeons use this routinely, others only for eyes at higher risk of corneal decompensation (e.g. cornea guttata).

2. • Pupillary manipulation. In an eye with a small pupil, a high molecular weight cohesive viscoelastic (e.g. Healon GV) will push the iris away from the lens and help to induce mydriasis. Adaptive OVDs’ cohesive effect can be used to dilate a pupil intraoperatively and their dispersive effect to maintain the dilatation. OVDs can be used to break posterior synechiae with minimal trauma.

3. • Cortical manipulation. OVDs can be useful to dissect cortex away from the lens capsule to minimize traction on fragile zonular ligaments.

4. • Capsulorhexis rescue. If a capsulorhexis shows signs of running out to the periphery, injecting a cohesive viscoelastic will flatten the anterior capsule, aiding the exertion of a centrally directed vector and helping to expand the pupil.

5. • Capsular rupture. In a small posterior capsular tear, a dispersive viscoelastic will push the vitreous back into the posterior chamber and maintain plugging of the capsular defect, facilitating completion of lens removal.

spectacles

Aphakia is treated by prescribing suitable spherical convex lens (+ 10 D approximately) and convex cylindrical lens (+1 to +2D at 180°) 6 weeks after the operation, i.e. when the corneo-scleral scar has healed completely and the refraction has become stable.

problems with aphakic correction

1. They are heavy and give a cosmetically poor appearance.

2. There is 25% retinal image magnification hence it causes diplopia in unilateral aphakia.

3. Spherical aberration can cause ‘pin-cushion’ effect. There may be chromatic aberration. This leads to visual distortion.

4. There is ‘jack in the box’ ring scotoma and reduction in peripheral visual field.

5.  Physical invonvenience and cosmetic deficiency are usually present.

2. Contact Lens

Advantage

There is minimum retinal image magnification therefore it is specially useful in case of unilateral aphakia. It also looks good cosmetically.

Disadvantages

• Daily cleaning and maintenance is essential.

• Their insertion and removal is cumbersome.

• Corneal epithelial oedema, erosion and vascularization may occur due to hypoxia

• Conjunctivitis, intolerance and foreign body sensation are common complaints.

• Loss, breakage and deterioration of the contact lens leads to financial loss.

3. Intraocular lens

Biometry

Removal of the crystalline lens substracts approximately 20D from the refracting system of the eye. Modern cataract surgery therefore involves the implantation of an intraocular lens (IOL). Biometry offers calculation of the lens power likely to result in emmetropia or a desired postoperative refraction.

Two ocular parameters are involved in biometry

i. Keratometry—The curvature of anterior corneal surface (steepest and flattest meridians)

ii. Axial length—The anteroposterior dimension of the eye measured using A-scan ultrasonography.

SRK formula—It is the most commonly used mathematical formula to calculate the IOL power. It

 states that

P = A – 2.5L – 0.9K, where;

• P is the power of IOL

• A is a constant, which is specific for each lens type

• L is the axial length of eyeball in mm (A-scan ultrasonography)

• K is the average corneal curvature (Keratometry)

Other formulas are holladay, hoffer Q, SRK-T

RIGID IOLs

POLYMETHYLMETH ACRILATE

FLEXIBLE IOLs

1.          Acrylic IOLs. Hydrophobic (water content <1%) acrylic materials have a greater refractive index than hydrophilic      lenses and  are consequently thinner.

additional features

1.           blue light filters: avoid harmful ultraviolet light

2.           Aspheric optics:  counter corneal spherical aberrations 

3.           heparin coated: in uveitic eyes

4.           toric IOLs for astigmatism

5.            bifocal IOLs: for near and far vision

6.             adjustable IOLs: for variable distance

Femtosecond lasers, used in refractive surgery for several years, have recently been adopted by some surgeons, replacing several of the manual steps of phacoemulsification with an automated process. 

1. The corneal incisions 

2. the capsulorhexis  

3. initial fragmentation of the crystalline lens

4. astigmatism-relieving incisions 

Potential advantages

1. greater precision and integrity of incisions

2. reduced phacoemulsification energy 

3. possibly improved refractive outcomes due to more precise capsulorhexis placement

Disadvantages 

1. substantially higher cost

2. longer total operating time 

3. difficulties with technically challenging cases (e.g. small pupils).

4. There is a substantial learning curve.