sia calculation and its importance
TRANSCRIPT
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