Sia Calculation And Its Importance

SIA CALCULATION AND ITS IMPORTANCE DR MITA JOSHI DR SACHDEV EYE HOSPITAL SURAT

SURGICALLY INDUCED ASTIGMATISM SITE OF INSICION SIZE OF INSICION CAUTERIZATION SUTURING OF INSICION

CHANGES INDUCED BY SURGERY CORNEAL STEEPENING TIGHT SUTURE WOUND EDEMA VERTICAL MISALIGNMENT EXCESSIVE CAUTERY

CORNEAL FLATENNING WOUND GAPE LOOSE SUTURES SUPERFICIAL SUTURES CENTRAL OVERRIDING

CLEAR CORNEAL INCISION 2.7 – 4 MM MINIMAL OR NO EFFECT ON ASTIGMATISM 0.25 - 0.5 D MULTIPLANAR INCISION BEVELLED BIPLANAR SELF SEALING INCISION

PSEUDOPHAKIC ASTIGMATISM TORIC IOLS CYLINDER POWER INCORPORATED IN THE IOL , ACTS AT THE CORNEAL PLANE

MEASURING ASTIGMATISM TOPOGRAPHY MANUAL KERATOMETRY MANIFEST REFRACTION WAVEFRONT REFRACTION

IMPLANTATION OF TORICIOL CONSIDER REF AND KERATOMETRIC ASTIGMATISM IMPLANTED ACC TO KERATOMETRIC ASTIGMATISM CORRECT FOR DISTANCE FROM NODAL POINT

SURPRISE ELEMENT SURGICALLY INDUCED ASTIGMATISM INSICION PLAYS A MOJOR ROLE SITE AND SIZE

Effect of surgically induced astigmatism Why is there almost always a difference?

045°

45.50 D

The problem Q: Why is it that the astigmatic power correction and axis are often different than expected following toric IOL implantation? A: We have not been taking into account a second important influencing factor.

Effect of surgically induced astigmatism Astigmatism is a vector quantity

Because corneal astigmatism has both a magnitude and a direction, it is a vector quantity. Multiple vectors in the same plane can be combined. The sum of multiple vectors will result in a new magnitude and a new direction.

Effect of surgically induced astigmatism Astigmatism is a vector quantity

Airplane flying to Las Vegas 120 knots to the Northeast (036°)

Planned 036° at 120 knots

Effect of surgically induced astigmatism Astigmatism is a vector quantity

Airplane flying to Las Vegas 120 knots to the Northeast (036°)

Planned 036° at 120 knots

Wind 22 knots out of the Northwest (160°)

Wind 160° at 22 knots

Effect of surgically induced astigmatism Addition of two vectors = third vector

Airplane flying to Las Vegas 120 knots to the Northeast (036°)

Planned 036° at 120 knots

Wind 22 knots out of the Northwest (160°) No wind

120 knots at 036°

With wind

110 knots at 046°

Actual 046° at 110 knots Without making a correction

Wind 160° at 22 knots

Actual = Sum of flight vector & wind vector

Effect of surgically induced astigmatism Addition of two vectors = third vector

Airplane flying to Las Vegas 120 knots to the Northeast (036°)

Planned 036° at 120 knots

Wind 22 knots out of the Northwest (160°) No wind

120 knots at 036°

With wind

110 knots at 046°

The sum of the two vectors results in the need for a change in direction combined with an increase in power to maintain same direction & speed.

Correction

Actual 046° at 110 knots Without making a correction

Wind 160° at 22 knots

Actual = Sum of flight vector & wind vector

Effect of surgically induced astigmatism Calculating the new axis of astigmatism

42.25 flat Steep K

43.50 x 135°

Flat K

42.25 x 045°

43.50 steep

Effect of surgically induced astigmatism Calculating the new axis of astigmatism

Steep K

43.50 x 135°

Flat K

42.25 x 045°

Incision

3.0 mm 180°

Induced cyl

0.50 x 090°

Original axis

Right eye

OCULAR RESIDUAL ASTIG

SIA OD <3MM LOCATION

SIA

(D) NO OF PT

TEMPORAL

1.82

1

NASAL

1.17

2

SUPERIOR

0.0

0

INFERIOR

0.0

0

SUP TEMP

0.31

2

INF TEMP

0.0

0

OVERALL SIA

0.96

5

SIA OS <3 MM LOCATION

SIA(D) NO OF PTS

TEMPORAL

0.5

5

NASAL

0.0

0

SUPERIOR

0.0

0

INFERIOR

0.0

0

SUP TEMP

0.3

1

INF TEMP

0.0

0

OVERALL SIA

0.47

6