2. 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
3. • 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°).
5. SOURCES OF POST OPERATIVE
CATARACT SURGERY ASTIGMATISM
• Preexisting astigmatism
• INCISION CHARACTERISTIC
Incision Length
Location
Shape and cross section
• SUTURE CHARACTERISTICS
Suture - length
Tightness
Depth
Material
Orientation
• Cauterization
• Post operative steriods
6. 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.
7. 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.
8. • An incision, relaxates
meridian which is
vertical to the incision
11. 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.
12. • 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.
13. 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
14. 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
15.
16. SUTURE STRENGTH
tight/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.
18. • Any loose suture
(wound gap)
flattens it’s own
meridian
19. • 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.
20. SUTURING TECHNIQUE
• Steinert et al said - Induced
astigmatism in the first 1–2 weeks
after a 6.5mm wound, is dependent
on suture technique.
21. • Running sutures
produce numerous
force components
• Rotational ,oblique
and bowstring
components are
contributed by each
suture.
• Cummulatively
produce – apposition
and compression
and bowstring.
23. • Any non radial
suture, produces
lateral
displacement and
induces irregular
Ast. (None
predictable)
24. TYPE OF SUTURING TECHNIQUE
Interrupted ,10-0 nylon,
Posterior , ½ depth
Fine suture disintegrates late
WTR….(1: 1)GOOD
Interrupted , 10-0 nylon,
Anterior, ¾ depth
Fine suture, disintegrates late.
WTR(4:1)
9 – 0 silk ,
Posterior, ½ depth
Fine 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)
25. 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
26. • Vertical mismatch, induces
predictable astigmatism:
- Deep corneal to superficial
scleral bite, flattens corneal
curvature
- Superficial corneal to deep
scleral bite, steepens
corneal curvature
27.
28. 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.
29. 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.
30. • Non biodegradable nature of suture ( nylon)
accounts for its long-term instability in ECCE.
• The use of nylon sutures prevents drift
towards ATR astigmatism .
31. 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.
32. 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.
33. • 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.
34. 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
35. 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
36. 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
