POSTOP ASTIGMATISM AFTER CATARACT SURGERY

PRESENTER – DR TANIA JAIN MODERATOR – DR RINKY ANAND GUPTA

Postoperative astigmatism• Astigmatism is a refractive anomaly in which no point

focus is formed because of unequal refraction of light rays in different meridians by the diopteric system of the eye.

• Regular astigmatism consists of meridians of greatest and least curvature at right angles to each other.

• Irregular astigmatism consists of meridians of greatest and least curvature occurring at other than right angles

• With-the-rule (WTR) astigmatism has its meridian

with the least radius of curvature (steepest) or

greatest refracting power in a vertical direction

(usually 90° ± 30°).

• Against-the-rule (ATR) astigmatism is the converse,

with the curvature of least radius or most refracting

power in a horizontal meridian (usually 0° or 180° ±

30°).

Youth - WTR astigmatism predominates Elderly - ATR astigmatism

Pseudophakia - ATR myopic astigmatism better tolerated than WTR .

SOURCES OF POST OPERATIVE CATARACT SURGERY ASTIGMATISM

• Preexisting astigmatism• INCISION CHARACTERISTICIncision Length Location Shape and cross section • SUTURE CHARACTERISTICSSuture - length Tightness Depth Material Orientation • Cauterization• Post operative steriods

CORRELATION BETWEEN INCISION LENGTH AND ASTIGMATISM

• Samuelson – There is a nearly linear increase in corneal flattening with increasing incision length.

• Corneal astigmatism is directly proportional to the cube of the length of the external incision

• The maximal incision length that prevents flattening greater than 0.25 D is 3.0 mm.

• Larger incisions (6.0-10.0 mm) show an ATR shift early after surgery.

Minimizing incision length decreases surgically induced astigmatism with both scleral and clear-corneal incisions (CCIs).

The incisional length of ECCE is generally 10-11 mm.

• An incision, relaxates meridian which is vertical to the incision

Clear-corneal incision

2.0–2.5 0.05–0.10

3.0–3.5 0.25–0.70 4.0 0.40–0.75 5.0–5.5 0.60–1.25

*

INCISION LOCATION AND ARCHITECTURE

• Superior incisions produce more postoperative astigmatism than temporal incisions.

• Astigmatism with temporal (0.74 D) is less than with nasal (1.65 D) 3.5 mm CCIs.

• More anterior incision induce more astigmatism than posterior.

• More peripheral and shorter cataract incisions induce less astigmatic change.

• CCI are sufficiently small that they induce little astigmatism despite their anterior location.

• For incisions longer than 4 mm, the limbal or scleral approaches with sutures offer greater astigmatic stability.

CONFIGURATION OF INCISION

• The configuration of the incision may also influence wound stability and eventual astigmatic drift.

• With scleral approach, a straight or frown-incision appears to induce less astigmatic change than the traditional curved incision parallel to the limbus

Astigmatic funnel • The concept of astigmatic funnel came from two

relations . • Corneal astigmatism is directly proportional to the

cube of the length of the external incision and inversely proportional to the distance from the limbus

• Incisions made within this funnel will be for all purpose astigmatically equivalent

• Curvilinear limbal parrallel incisions fall outside and our unstable.

• Incision within funnel cause negligible astigmatism

SUTURE STRENGTHtight/loose

• Sutures placed at the superior limbus induced early WTR astigmatism.

• This is reversible on removal of the sutures.• Suture placed at two-thirds depth at the 12 o'clock

limbus steepened the vertical meridian and flattened the horizontal meridian, decreasing the vertical diameter of the cornea and increasing the horizontal diameter.

• INFERENCE - sutures induce central steepening, or plus cylinder, in the meridian placed.

• A tight suture, steepens it’s own meridian

• Any loose suture (wound gap) flattens it’s own meridian

• Sutures should be left tight in recognition of a fairly rapid reduction in WTR astigmatism in the initial weeks after large-incision surgery (cylinder regression).

• Talamo and associates recommended a goal of 2 D ∼of WTR astigmatism at the first month.

• High WTR astigmatism -managed by suture removal

• Early ATR, may need re-suturing of the incision with tighter knots to avoid late high ATR.

SUTURING TECHNIQUE

• Steinert et al said - Induced astigmatism in the first 1–2 weeks after a 6.5mm wound, is dependent on suture technique.

• Running sutures produce numerous force components

• Rotational ,oblique and bowstring components are contributed by each suture.

• Cummulatively produce – apposition and compression and bowstring.

• Radial interrupted sutures have apposition and compression components only.

• Any non radial suture, produces lateral displacement and induces irregular Ast. (None predictable)

TYPE OF SUTURING TECHNIQUEInterrupted ,10-0 nylon, Posterior , ½ depth Fine suture disintegrates late

WTR….(1: 1)GOOD

Interrupted , 10-0 nylon, Anterior, ¾ depthFine suture, disintegrates late.

WTR(4:1)

9 – 0 silk ,Posterior, ½ depthFine suture , disinegrates late

WTR …(1:1)GOOD

9-0 silk,Anterior ¾ depth,(More astigmatism as more anterior)

WTR(3:1)

7-0 silk ATR(3:1)

7-0 chromic catgut ATR (11:1)

7-0 chromic collagen ATR (5:1)WTR(8:1)

DEPTH OF SUTURE • Ideal depth should be up to two third of

corneal and scleral depth

• Too superficial – slough too soon leading to posterior gaping of wound

• Too deep – may reach Anterior chamber

• Vertical mismatch, induces

predictable astigmatism:- Deep corneal to superficial

scleral bite, flattens corneal curvature

- Superficial corneal to deep scleral bite, steepens corneal curvature

LENGTH OF SUTURE

• Long sutures are thought to induce more steepening (with the incision) than short bites, because of the greater forces needed to secure the former.

• Length of suture bite should be equal in both sides otherwise wrinkling occurs.

• Wrinkling occurs with too long and tight sutures.

SUTURE MATERIAL • Sutures that disintegrate early – catgut –

cause wound to gape – ATR

• Fine sutures – 10-0 nylon and 9-0 silk remain in situ for long time – WTR

• The elasticity of suture - nylon allows it to partially accommodate the wound edema and minimize subsequent changes in corneal curvature.

• Non biodegradable nature of suture ( nylon)

accounts for its long-term instability in ECCE.

• The use of nylon sutures prevents drift

towards ATR astigmatism .

Post operative steroids • Manipulation of the duration of action of

corticosteroids has been advocated to tailor the postoperative course to a desired astigmatic end point.

• Prolonged use of steroids may allow great wound slippage to help treat preexisting WTR astigmatism.

• A short course of postoperative steroids may help minimize astigmatic decay from a superior scleral pocket incision in a patient who has preoperative ATR astigmatism.

SUTURE REMOVAL

• Recommended to remove suture at 12 weeks

• More than 3D of WTR astigmatism if present 3–5 weeks postoperatively suture removal is recommended , Talamo et al.

• Selective cutting or removal of interrupted sutures in the axis of steepest curvature has proven utility in reducing postoperative WTR astigmatism.•A single tight suture is recognized by the axis of plus cylinder and the axis of higher keratometric measurement. •An observed keratometric axis may also represent the summation of several suture vectors.•Early suture removal, especially in older patients, may result in progressive ATR.

PRESCRIBING GLASSES

• It is advocated to prescribe glasses 1 month

after suture removal

• Suture cutting may turn WTR astigmatism into

unwanted ATR astigmatism over time

INCISION CRITERIA

• An incision may be centered on the steepest

axis (‘on-axis incision’)

• Posterior incisions decrease against-the-rule

wound drift

• Smaller incision – decrease astigmatism

• Straight or frown incisions decrease against-

the-rule drift

CRITERIA FOR GOOD SUTURE • Radial interrupted sutures

• Fine non biodegradable suturing material used

• Corneal : scleral bite should be ratio of 2;1

• Deep sutures up to 2/3 of depth should be

places

• Equidistant sutures

• Required tension . not loose not very tight

THANK YOU