Cataract surgery revisited

CATARACTREVISITED

INDOREDRISHTI.WORDPRESS.COM

DR DINESH MITTAL DR SONALEE MITTAL

DRISHTI EYE HOSP VIJAYNAGAR INDORE

1 Cataract surgery has evolved into a refractive procedure with the goal of eliminating or significantly reducing the need for spectacle dependence.• 2. One must consider not only the astigmatism induced by the cataract incision itself, but also the correction of preexisting astigmatism.

• 3. Incision length, depth, and distance from visual axis all affect astigmatism.

•4. LRIs are commonly used to correct preexisting astigmatism, and

•published nomograms are helpful in tailoring a surgical approach.

•5. Toric IOLs and excimer laser ablation are alternative approaches to correcting astigmatism in the patient for refractive cataract surgery.

•No single approach is best suited for all patients.

INTRAOCULAR LENS CALCULATIONS• Choosing the appropriate IOL power is a major determinant of patient satisfaction with cataract surgery.

•3 main factors • accurate measurements (biometry), • selecting calculations (formulas),• and assessing the patient’s needs to determine postoperative refractive target (clinical considerations).

BIOMETRY•At minimum, 2 measurements reqd to calculate implant power:

•axial length & corneal curvature (keratometry)

•Precise measurements critical •error of 0.3 mm in axial length will result in a 1-D error in IOL power.

Axial Length• Axial length has been obtained utilizing A-SCAN ULTRASOUND.

• This measurement is determined by calculation;• an ultrasound pulse is applied and the transit time through the eye is measured. Using estimated velocities of ultrasound waves through various media (ie, cornea, aqueous, lens, and vitreous) the distance travelled through the eye is calculated.

• The instrument should have an oscilloscope screen to differentiate a good measurement from a poor one. Characteristic echo peaks or spikes should be observed when the probe is aligned properly

• These include the following: a tall peak for the cornea, tall peaks for the anterior and posterior lens capsule, tall peak for the retina, mod-erate peak for the sclera, and moderate-to-low peaks for orbital fat. If these spikes are not well seen, then the probe may be misaligned.

A SCAN ULTRASOUND

•The contact A-scan technique must be performed carefully, as com-pressing the cornea will result in a shorter-than-expected measurement and multiple measurements should be taken and averaged.

• If several are taken and differ by a significant amount, they should be discarded until consistent readings can be obtained.

• It is also prudent to measure both eyes for comparison

•the machine should be regularly calibrated, checking measurements against an eye of known axial length.

Immersion techniqueThe immersion technique may more accurately represent the true axial length because there is no corneal compression.

In this technique, the patient lies in the supine position and a scleral shell is placed on the eye and filled with Goniosol. The ultrasound probe is placed in this solution and the beam is aligned with the macula by having the patient look at the probe tip fixation light.

Although the immersion method may be strongly advocated by some users, applanation A-scan is the more commonly used method

IMMERSION TECHNIQUE SHOWING PROBE IN OSSOINIG SHELL

Optical biometry: IOLMaster• In the last decade, the technique of optical coherence biometry was in-troduced by Haigis, which utilizes light rather than ultrasound to measure the length of the eye. The first device introduced was the IOLMaster (Zeiss), based on the principle of partial coherence interferometry using a 780-nm multimode laser diode.

•Measurements taken without contact to eye, thus eliminating variability due to an examiner technique.

•The distance measured lies between the anterior surface of tear film & retinal pigmented pigment epithelium (rather than the anterior surface of the cornea and internal limiting membrane ), which may be more physiologically accurate (refractive rather than anatomic axial length).

2 advantages to the IOLMaster

patient asked to focus on a small red fixation light, & examiner maneuvers focusing spot within the measurement reticule, sampling areas until the best peak pattern is obtained. 5 to 20 measurements obtained until the readings differ by less than 0.1 mm. Maximal axial length measured 40 mm.

IOLMASTER USE

IOL MASTER DISADVANTAGE

The primary disadvantage of this optical device is that any significant axial opacity, such as a corneal scar, dense posterior subcapsular plaque, darkly brunescent cataract, or vitreous hemorrhage, will reduce the signal-to-noise ratio (SNR) to the point that reliable measurements are not possible.

A-scans should be remeasured under the following conditions• 1. Axial length is less than 22 mm or greater than 25 mm in either eye.

• 2. The difference between the 2 eyes is greater than 0.3 mm.

• 3. The measurements do not correlate with the patient’s refraction (ie, hyperopes should have shorter eyes, and myopes should have longer eyes).

IOL CALCULATION BEST IN UNOPERATED EYES

IOL CALCULATION BEST POST KERATOREFRACTIVE SURGERY

ASCRS SITE FOR IOL POWER CALCULATION

SPECULAR MICROSCOPY

SCLERAL TUNNEL VS CLEAR CORNEAL

• 1. The 2 most common types of wounds for phaco are the scleral tunnel and clear corneal incisions.

•2. Advantages of the scleral tunnel incision include conjunctival coverage and a greater vertical distance from the corneal endothelium to the phaco probe

• 3. Advantages of the clear corneal incision include an undisturbed conjunctiva and the potential avoidance of a retrobulbar block.

• 4. Choice of wound location is influenced by astigmatic considerations, preexisting ocular disease states, and ergonomic comfort of the surgeon.

• 5. Incision characteristics such as width, shape, and tunnel length may all be modified, affecting astigmatic outcome, endothelial cell loss, and self-sealing properties of the wound.

SCLERAL TUNNEL VS CLEAR CORNEAL

INITIATION OF GROOVE OR EXTERNAL INCISION

INITIATION OF TUNNEL WITH CRESCENT BLADE

DISSECTION OF SCLERAL TUNNEL INTO CLEAR CORNEA

DIMPLING OF CORNEA BY DEPRESSING THE POINT OF KERATOME

STRAIGHT LINE INCISION IN DECEMET’S MEMBRANE .5 MM ANTERIOR TO VASCULAR ARCADE

ENLARGEMENT OF 3.5 MM INCISION TO 4 MM WITH BLUNT TIPPED KERATOME

CAPSULORRHEXIS•1. it confines the IOL to the capsular bag as the capsule fibroses and contracts around the lens.

•2. Start the capsulorrhexis by making the initial puncture with a bent 30-gauge needle and flopping the tear toward the incision so that it can be grasped using capsulorrhexis forceps

A central puncture with a cystotome followed by a arched curve creates a slit . The capsular flap is lifted and pulled in a circular fashion by cystotome or capsular forceps

A central puncture with a cystotome followed by a arched curve creates a slit . The capsular flap is lifted and pulled in a circular fashion by cystotome or capsular forceps

• 3. Always pull tangentially when tearing the capsulorrhexis to maintain optimum control.

• 4. If you start to lose control, inject more viscoelastic material and begin tearing tangentially again. If the capsulorrhexis extends beneath the pupil margin, repuncture the capsule and tear it in the reverse direction

• 5. It takes practice to become good at creating a uniformly consistent capsulorrhexis

• 1. Keep the cannula tip beneath the anterior capsule while injecting fluid.

• 2. Apply slow, constant pressure on the syringe so that the fluid wave will propagate.

• 3. Watch for a complete fluid wave to ensure adequate hydrodissection.

• 4. Watch for the “golden ring” sign as confirmation of hydrodelineation.

• 5. Confirm rotation of the lens before proceeding to phacoemulsification.

HYDRODISSECTION AND HYDRODELINEATION

•1. Flow (aspiration rate) and vacuum are controlled independently in a peristaltic pump system.

•2. Aspiration flow rate and vacuum are not independent in a vacuum pump system (Venturi).3 Inflow should be adequate to maintain the anterior chamber volume even as the outflow through the incisions and the pump varies.4 Surge effects can be minimized by using lower vacuum, lower aspiration rates, and higher infusion bottle height.

Aspiration Flow Rate

• By aspiration flow rate, or simply “aspiration,” I mean the rate at which fluid and particles come to the ultrasound tip.

• Higher aspiration means faster flow and faster movement of nuclear and epinuclear pieces to the tip.

• Aspiration flow rate determines how quickly fluid and materials come to the tip.

• Vacuum occurs only when the tip is occluded and helps to remove material at the tip.

•Ultrasound Power• Once the nucleus is at the tip, ultrasound power is responsible for emulsifying it into a small enough piece to fit through the tip and travel through the

• bore of the ultrasound handle. • The surgeon must choose a power level that is• just enough to break up the nuclear fragment into small enough chunks to be vacuumed through the tip.

• The surgeon must also choose between longitudinal• ultrasound power and torsional ultrasound. •Longitudinal ultrasound• delivers an axial cutting force that will tend to push nuclear piece away from the tip and create a “tunnel-like” cavity into the tissue, much like a jackhammer.

•Torsional ultrasound, • is produced by side-to-side oscillation of phaco tip, and delivers ultrasound force to a larger region of tissue.

•More the angulation, the lesser the holding power but cutting power is more.

•60° tip is a sharper tapered tip making occlusion difficult. But is useful for grooving hard cataracts.

•Entering into the anterior chamber is easy with the 60° tip and progressively harder with a 15° or a 0° tip.

Mechanism of Emulsification•actual mechanism of emulsification is Jack-hammer & Cavitation

• jackhammer effect is physical striking of the needle against the nucleus.

• It requires that the nucleus should be fixed as for the bombarding action to be effective.

Cavitation• phaco needle, moving through a liquid medium at ultrasonic speeds, gives rise to intense zones of high and low pressure.

• Low pressure, created with backward movement of the tip, pulls dissolved gases out of solution, producing micro bubbles.

• Forward tip movement then creates an equally intense zone of high pressure.

• This initiates compression of the micro bubbles until they implode.

•At the moment of implosion, the bubbles create a temperature of 7204˚C degrees and a shock wave of 5,171,100 mbar.

•Of the micro bubbles created, 75% implode, amassing to create a powerful shock wave radiating from phaco tip in direction of bevel with annular spread.

•The energy created by cavitation exists for no more than 4 milliseconds and is present only in the immediate vicinity of the phaco tip and within its lumen.

• cavitation is instrumental in clearing nuclear fragments within phaco needle, preventing repetitive needle clogging.

• angle of the bevel of the phaco needle governs direction of generation of shock wave and micro bubbles.

• disadvantage of this wave is that it may push nuclear pieces away if the hold is not good and thus decrease the Jack-hammer effect.

• Phacoemulsification is most efficient when both the jackhammer effect and cavitation energy are combined.

•Once the ultrasound has “handled” the nuclear fragment, it is the vacuum that determines how quickly the fluid or particle will make its way through

•the tip. •Softer nuclear and epinuclear pieces need less vacuum to pull the tissue through the ultrasound tip.

• Harder and denser nuclei need higher vacuum levels to draw them through tip.

•Vacuum rise occurs when the ultrasound hand piece tip is occluded. Maximum vacuum is generated when the tip is completely occluded

• Use the pulse setting when you want slower, more controlled nuclear removal.

•Use burst mode for maximum speed and efficiency.

•Use the epinuclear setting for epinucleus removal.

DIVIDE AND CONQUER PHACO•Nuclear fracturing techniques, have facilitated cataract surgery immensely, allowing for safer and more efficient means of nucleus removal.

•fundamental principle underlying all nuclear-fracturing techniques is the creation of “breaks” to divide the lens into smaller fragments for controlled removal through a small incision.

•Gimbel first to propose a Approach with the “divide and conquer” nucleofractis phaco technique.

• This method involves the creation of 2 deep grooves in nucleus that Intersect centrally and are then cracked into 4 quadrants.

•These smaller sections of lens can be brought away from the capsule into a “safe zone” for emulsifi cation and removal

DIVIDE-AND-CONQUER TECHNIQUE•Phaco Settings•The initial nuclear groove formation requires the use of a moderate degree of phaco energy with low aspiration and vacuum settings.

•Quadrant removal requires higher aspiration and vacuum settings to allow the phaco tip to engage the lens fragments.

Grooving Technique• Goal: Deep sculpting to facilitate cracking•create a sulcus that is 90% of the depth of the lens. The sulcus depth is the most important aspect for facilitating a complete crack at the base of the lens.

•Groove length is not as important and should not extend into the far lens periphery. A good rule of thumb is to limit the length of the groove to the length of capsulorrhexis.

•Creation of the initial sulcus is best achieved using a moderate degree of phaco energy with low aspiration and vacuum settings.

•phaco power setting of 20% to 60%, vacuum of 60 mm Hg, and aspiration setting of 25 to 30 mm Hg

•create a groove that is•1.5 phaco tips wide and 3 TIPS deep. •The standard phaco tip is 1.2 mm in diameter, thus yielding a groove that is 1.8 mm × 3.6 mm centrally.

•The average lens has a diameter of 9 mm and a thickness of 4.5 mm centrally. The rationale for limiting the length of the initial groove is that the lens thickness and the proximity of the posterior capsule decrease in the periphery.

•The goal of grooving should be to achieve 90% depth centrally with a length of approximately 6 mm

Cracking Technique &Bisection of Two Halve

• Goal: Nucleofractis of the nuclear plate and rim and the remaining nuclear material

• It is important to achieve a complete separation of the posterior nucleus.

• A complete crack of the periphery is not as important (leaving a portion of the cortex and epinucleus intact is not problematic).

• The phaco tip and second instrument must be positioned deep in the groove, and the second instrument is rotated to simulate a paddle-like movement while the phaco tip is moved in the opposite direction to create a crack

INITIAL SCULPTING OF A TRENCH OR TROUGH

DOWN SLOPE TECHNIQUE STARTS WITH TRENCH OR TROUGH SCULPTED TO JUST PAST THE CENTER OF LENS SURFACE AND THEN NUDGE THE LENS INFERIORLY AND CONTINUE SCULPTING OF MORE SUPERIOR PART

POSTERIOR PLACEMENT OF TWO INSTRUMENTS FOR BIDIRECTIONAL FRACTURING

INAPPROPRIATE ANTERIOR PLACEMENT OF INSTRUMENTS , RESULTING IN INEFFECTIVE FRACTURING

• Achieving a consistent, even crack of the posterior cataract is an important piece in mastering the divide-and-conquer technique. complete posterior crack reflects that entire nuclear component of the lens has been thoroughly bisected. Extension of crack into far periphery is not nearly as vital because peripheral cortex and epinucleus can be easily divided with a second instrument during quadrant removal

• initial crack described here is performed after formation of the initial groove

CRATER DIVIDE AND CONQUER TECHNIQUE IN DENSE AND BRUNESCENT CATARACTS IS FACILITATED BY EMULSIFICATION OF A DEEP AND WIDE CENTRAL CRATER OF NUCLEUS

USING THE CYCLODIALYSIS SPATULA AND THE PHACO TIP , RESULTANT PERIPHERAL NUCLEAR RIM IS FRACTURED

NUCLEUS IS ROTATED AND A SECOND FRACTURE IS MADE . THE SECTION IS LEFT IN PLACE ENSURING STABILISATION OF NUCLEUS AND CAPSULE

Quadrant Removal•Goal: Rotation, reposition, and removal of nucleus

•Engage the quadrants in the region of the nucleus (the middle portion of the cataract). Occlude the tip and pull the fragment centrally. Once the phaco tip and nuclear fragment are positioned centrally and at the level of the Iris , quadrant can be safely removed

• settings for quadrant removal are phaco power setting of 20% to 60%, vacuum of 350 mm Hg, and aspiration of 25 mm Hg

• present posterior edge of the fragment to the phaco tip by gently lifting fragment with second instrument & engaging piece with higher vacuum and higher flow rates and drawing it into the pupillary center

• The phaco tip is used to impale the fragment, the vacuum is then allowed to increase, and piece is drawn into pupillary plane. The second instrument remains under segments being emulsified in order to protect posterior capsule

PHACO SUMMARY• 1. Create a nuclear groove that is 90% of the depth of the lens. sulcus depth is the most important aspect for facilitating crack at the base of the lens.

• 2. Groove length is not as important as groove depth and should not extend into the far lens periphery. A good rule of thumb is to limit the length of the groove to the length of the capsulorrhexis.

• 3. Cracking of the posterior aspect of the lens is more important than cracking the periphery.

• 4. In general, create a groove that is 1.5 phaco tips wide and 3 deep.

• 1. Aspiration flow rate determines how quickly fluid and materials come to tip.

• 2. Vacuum occurs only when the tip is occluded and helps to remove material at the tip.

• 3. Use the pulse setting when you want slower, more controlled nuclear removal.

• 4. Use burst mode for maximum speed and efficiency.

• 5. Use epinuclear setting for epinucleus removal

BIMANUAL IRRIGATION AND ASPIRATION IS BETTER

ECCEIN VERY HARD CATARACTS ORIF PHACO CAN NOT BE COMPLETED BECAUSE OF SOME COMPLICATION

ECCE TECHNIQUE

CAUTERISE SURFACE VESSELS POSTERIOR TO INCISION SITE

DISSECTION OF SCLERAL TUNNEL USING CRESCENT BLADE

PLANE THREE OF INCISION PENETRATION INTO ANTERIOR CHAMBER USING A DISPOSABLE PHACO BLADE

ANTERIOR CAPSULOTOMYBEND A 27 G DISPOSABLE NEEDLE ANTO CONFIGURATION SHOWN IN INSET . ATTACH THE NEEDLE TO A SMALL SYRINGE , WHICH SERVES AS A HANDLE

EXTEND PLANE THREE OF INCISION WITH CRESCENT BLADE

FEMTOSECOND LASER ASSISTED CATARACT SURGERY

•Femtosecond laser provides an ultrafast burst of energy.

•Argon, excimer, and Nd: YAG lasers: nanosecond (10 -9 ) pulses

•Femtosecond: 10 -15 second

FEMTOSECOND LASER ASSISTED CATARACT SURGERY• Excimer: “photoablates”• Argon: “photocoagulates”• Nd: YAG and Femtosecond: “photodisrupt”.• Their light energy can be absorbed by optically clear tissue and create “microcavitation bubbles” that cause an acoustic shock wave that incises the target tissue.

Femtosecond laser first FDA approved for LASIK flaps in 2001

and then approved for cataract surgery In 2010.

Optimedica catalys

With guidance systems OCT or Scheimpflug-like technology FEMTO

CATARACT is used to make: Cataract clear corneal incisions and limbal relaxing incisions Capsulorhexis

Lens fragmentation/softening; a pretreatment prior to phaco &/or irrigation /aspiration

Status of femto catarct• Does only 3 steps • incision , capsulorhexis and nucleus softening

•Even in phaco itself first two steps incision and capsulorhexis are done by blade or needle or forceps .

•3rd step actual nuclear emulsification it is not better than phaco and for aspiration anyway phaco has to be used ; then why not the 3rd complete step to be done completely by one time tested , economical and time efficient phaco machine

Status of femto catarct

• femtolaser is practically not useful at this juncture .

• So phaco is superior to femto phaco

THANK YOUDR DINESHDR SONALEE