sia calculation and its importance

SIA CALCULATION AND SIA CALCULATION AND ITS IMPORTANCEITS IMPORTANCE

DR MITA JOSHIDR MITA JOSHI

DR SACHDEV EYE HOSPITALDR SACHDEV EYE HOSPITAL

SURATSURAT

SURGICALLY INDUCED ASTIGMATISM SURGICALLY INDUCED ASTIGMATISM

SITE OF INSICION SITE OF INSICION

SIZE OF INSICIONSIZE OF INSICION

CAUTERIZATIONCAUTERIZATION

SUTURING OF INSICION SUTURING OF INSICION

CHANGESCHANGES INDUCEDINDUCED BYBY SURGERYSURGERY

CORNEAL STEEPENINGCORNEAL STEEPENING

TIGHT SUTURETIGHT SUTURE

WOUND EDEMAWOUND EDEMA

VERTICAL MISALIGNMENTVERTICAL MISALIGNMENT

EXCESSIVE CAUTERY EXCESSIVE CAUTERY

CORNEAL FLATENNINGCORNEAL FLATENNING

WOUND GAPEWOUND GAPE

LOOSE SUTURES LOOSE SUTURES

SUPERFICIAL SUTURES SUPERFICIAL SUTURES

CENTRAL OVERRIDING CENTRAL OVERRIDING

CLEARCLEAR CORNEALCORNEAL INCISIONINCISION

2.7 – 4 MM2.7 – 4 MM

MINIMAL OR NO EFFECT ON MINIMAL OR NO EFFECT ON ASTIGMATISM 0.25 - 0.5 DASTIGMATISM 0.25 - 0.5 D

MULTIPLANAR INCISION MULTIPLANAR INCISION

BEVELLED BIPLANAR SELF SEALING BEVELLED BIPLANAR SELF SEALING INCISIONINCISION

PSEUDOPHAKIC ASTIGMATISMPSEUDOPHAKIC ASTIGMATISM

TORIC IOLS TORIC IOLS

CYLINDER POWER CYLINDER POWER INCORPORATED IN THE IOL , ACTS AT INCORPORATED IN THE IOL , ACTS AT THE CORNEAL PLANE THE CORNEAL PLANE

MEASURINGMEASURING ASTIGMATISMASTIGMATISM

TOPOGRAPHYTOPOGRAPHY

MANUAL KERATOMETRYMANUAL KERATOMETRY

MANIFEST REFRACTIONMANIFEST REFRACTION

WAVEFRONT REFRACTIONWAVEFRONT REFRACTION

IMPLANTATIONIMPLANTATION OFOF TORICIOLTORICIOL

CONSIDER REF AND KERATOMETRIC CONSIDER REF AND KERATOMETRIC ASTIGMATISM ASTIGMATISM

IMPLANTED ACC TO KERATOMETRIC IMPLANTED ACC TO KERATOMETRIC ASTIGMATISM ASTIGMATISM

CORRECT FOR DISTANCE FROM CORRECT FOR DISTANCE FROM NODAL POINTNODAL POINT

SURPRISE ELEMENT SURPRISE ELEMENT

SURGICALLY INDUCED ASTIGMATISM SURGICALLY INDUCED ASTIGMATISM

INSICION PLAYS A MOJOR ROLE INSICION PLAYS A MOJOR ROLE

SITE AND SIZE SITE AND SIZE

Effect of surgically induced astigmatismWhy is there almost always a difference?

045°

45.50 D

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.

The problem

Effect of surgically induced astigmatismAstigmatism 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 astigmatismAstigmatism is a vector quantity

Airplane flying to Las Vegas

120 knots to the Northeast (036°) Planned036° at 120 knots

Effect of surgically induced astigmatismAstigmatism is a vector quantity

Airplane flying to Las Vegas

120 knots to the Northeast (036°)

Wind

22 knots out of the Northwest (160°)

Wind 160° at 22 knots

Planned036° at 120 knots

Effect of surgically induced astigmatismAddition of two vectors = third vector

Airplane flying to Las Vegas

120 knots to the Northeast (036°)

Wind

22 knots out of the Northwest (160°)

No wind 120 knots at 036°

With wind 110 knots at 046°

Wind 160° at 22 knots

Planned036° at 120 knots

Actual = Sum of flight vector & wind vector

Actual046° at 110 knots

Without making a correction

Effect of surgically induced astigmatismAddition of two vectors = third vector

Wind 160° at 22 knots

Planned036° at 120 knots

Actual = Sum of flight vector & wind vector

Airplane flying to Las Vegas

120 knots to the Northeast (036°)

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.

CorrectionActual

046° at 110 knotsWithout making a

correction

Effect of surgically induced astigmatismCalculating the new axis of astigmatism

Steep K 43.50 x 135°

Flat K 42.25 x 045°

43.50 steep

42.25 flat

Effect of surgically induced astigmatismCalculating 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°

Originalaxis

Right eye

OCULAR RESIDUAL ASTIGOCULAR RESIDUAL ASTIG

SIA OD <3MMSIA OD <3MMLOCATIONLOCATION SIA (D)SIA (D) NO OF PTNO OF PT

TEMPORALTEMPORAL 1.821.82 11

NASALNASAL 1.171.17 22

SUPERIORSUPERIOR 0.00.0 00

INFERIORINFERIOR 0.00.0 00

SUP TEMPSUP TEMP 0.310.31 22

INF TEMPINF TEMP 0.00.0 00

OVERALL SIAOVERALL SIA 0.960.96 55

SIA OS <3 MMSIA OS <3 MMLOCATIONLOCATION SIA(D)SIA(D) NO OF PTSNO OF PTS

TEMPORALTEMPORAL 0.50.5 55

NASALNASAL 0.00.0 00

SUPERIORSUPERIOR 0.00.0 00

INFERIORINFERIOR 0.00.0 00

SUP TEMPSUP TEMP 0.30.3 11

INF TEMPINF TEMP 0.00.0 00

OVERALL SIAOVERALL SIA 0.470.47 66