Welcome to Seminar

Welcome to seminar

POST OPERATIVE POST OPERATIVE ASTIGMATISMASTIGMATISM

Moderator: Dr.Arvind TenagiModerator: Dr.Arvind Tenagi

Presenter: Dr. Chaitra K.L.Presenter: Dr. Chaitra K.L.

Astigmatism is a condition wherein Astigmatism is a condition wherein an optical system has different foci an optical system has different foci for rays which propagate in two for rays which propagate in two perpendicular planes.perpendicular planes.

It is derived from Greek.It is derived from Greek.

A: withoutA: without

Stigma: a mark, spot or puncture.Stigma: a mark, spot or puncture.

Thomas Young was the first person Thomas Young was the first person to describe astigmatism in his own to describe astigmatism in his own eyes in 1801.eyes in 1801.

Astigmatism following cataract Astigmatism following cataract surgery was first described by surgery was first described by Donders in 1864.Donders in 1864.

Meridians:Meridians:

Locations on the corneal Locations on the corneal surface are designated along surface are designated along meridians, lines that span the meridians, lines that span the diameter of cornea from one point diameter of cornea from one point on the limbus to the opposite point. on the limbus to the opposite point. They are designated from 0-180°.They are designated from 0-180°.

AxisAxis

Designates the direction in a Designates the direction in a cylindrical lens along which there is cylindrical lens along which there is no power. It is parallel to the focal no power. It is parallel to the focal line. line.

The eye is not able to bring an image to point focus

Regular astigmatism:Regular astigmatism:

The refractive power changes The refractive power changes uniformly from one meridian to uniformly from one meridian to another, i.e. there are 2 principal another, i.e. there are 2 principal meridia.meridia.

With the rule.With the rule. Against the rule.Against the rule. Oblique astigmatism.Oblique astigmatism. Bioblique astigmatism.Bioblique astigmatism.

With the rule With the rule astigmatismastigmatism

Against the rule Against the rule

Oblique astigmatism Oblique astigmatism

Irregular astigmatism:Irregular astigmatism:

There is an irregular change of There is an irregular change of refractive power in different refractive power in different meridia.meridia.

Causes Causes

Cataract extraction with iol Cataract extraction with iol implantation.implantation.

Penetrating and lamellar Penetrating and lamellar keratoplasty.keratoplasty.

Trabeculectomy.Trabeculectomy. Radial keratotomy.Radial keratotomy. LASIK.LASIK.

Cataract surgeryCataract surgery

Astigmatism of more than 3 D was Astigmatism of more than 3 D was found by Jaffe and colleagues in a found by Jaffe and colleagues in a study done over 6 years in 1557 study done over 6 years in 1557 eyes.eyes.

The causes of astigmatism occurring The causes of astigmatism occurring after cataract surgery are due to after cataract surgery are due to either corneal causes or lenticular either corneal causes or lenticular causes. causes.

Lenticular causesLenticular causes

Tilting of the lens.Tilting of the lens. Decentered lens.Decentered lens.

Proper surgical technique by the Proper surgical technique by the operating surgeon and use of operating surgeon and use of multifocal intra ocular lenses have multifocal intra ocular lenses have helped to significantly reduce the helped to significantly reduce the incidence of astigmatism occurring incidence of astigmatism occurring due to lenticular causes.due to lenticular causes.

Corneal causesCorneal causes

IncisionIncision

Sutures Sutures

Incision Incision

Length Length ShapeShape Position Position Edges Edges

LengthLength

Phaco phaconit Phaco phaconit

Dough Koch, MD,performed studies Dough Koch, MD,performed studies on cadaver eyes to evaluate incision on cadaver eyes to evaluate incision length and astigmatism.length and astigmatism.

Jim Gills, MD, analysed that corneal Jim Gills, MD, analysed that corneal astigmatism is directly proportional astigmatism is directly proportional to the cube of the length of the to the cube of the length of the incision.incision.

ShapeShape

Astigmatic funnel is bounded by a Astigmatic funnel is bounded by a pair of curved lines whose shape is pair of curved lines whose shape is based on the relationship between based on the relationship between astigmatism and the 2 astigmatism and the 2 characteristics of incision i.e. characteristics of incision i.e. incision length and distance from the incision length and distance from the limbus.limbus.

Incisions made within this funnel Incisions made within this funnel will be astigmatically equivalent.will be astigmatically equivalent.

PositionPosition

Clear corneal incisions cause more Clear corneal incisions cause more scarring and result in greater scarring and result in greater astigmatism.astigmatism.

Scleral incisions have been found to Scleral incisions have been found to cause comparatively less cause comparatively less astigmatism.astigmatism.

EdgesEdges

Wound with jagged edges tends to Wound with jagged edges tends to heal more slowly and with scarring.heal more slowly and with scarring.

These type of wounds cause more These type of wounds cause more astigmatism.astigmatism.

Sutures

material technique number

Suture materialSuture material

Larger sutures- early removal- Larger sutures- early removal- wound gaping-flattens the vertical wound gaping-flattens the vertical meridian- against the rule meridian- against the rule astigmatism.astigmatism.

Finer sutures-compress the wound- Finer sutures-compress the wound- with the rule astigmatism.with the rule astigmatism.

Suturing techniqueSuturing technique

Continuous Continuous Interrupted Interrupted

Number Number

More sutures- more astigmatismMore sutures- more astigmatism

KeratoplastyKeratoplasty

If rejection is the limiting factor in If rejection is the limiting factor in corneal transplants, post operative corneal transplants, post operative astigmatism causes the greatest astigmatism causes the greatest disappointment to the patient, disappointment to the patient, particularly in simple cases such as particularly in simple cases such as keratoconus where patient expects keratoconus where patient expects more than clear graft.more than clear graft.

Factors causing Factors causing astigmatismastigmatism

Graft over sizing / under sizing.Graft over sizing / under sizing. Donor or host corneal pathology.Donor or host corneal pathology. Unequal suture tension.Unequal suture tension. Irregular wound healing.Irregular wound healing. Imprecise trephination.Imprecise trephination. Sutures.Sutures.

Image of continuous Image of continuous suturessutures

Image of interrupted Image of interrupted suturessutures

Cardinal suturesCardinal sutures

Placement of 4 cardinal sutures is Placement of 4 cardinal sutures is important.important.

In his, the 2In his, the 2ndnd, 6 0 clock suture , 6 0 clock suture should be exactly in line with the 12 should be exactly in line with the 12 o clock suture. If not , it can result in o clock suture. If not , it can result in torsion and cause irregular torsion and cause irregular astigmatismastigmatism

Irregular astigmatism Irregular astigmatism

Radial keratotomyRadial keratotomy

The axis of this astigmatism may The axis of this astigmatism may change from day to day towards change from day to day towards ‘with the rule’, but may change ‘with the rule’, but may change course.course.

Hence called as Hence called as

““Pre ambulatory or Wandering”Pre ambulatory or Wandering” astigmatism.astigmatism.

Residual astigmatism after surgery Residual astigmatism after surgery is most often due to incomplete is most often due to incomplete correction or residual myopia either correction or residual myopia either through failure to correct for through failure to correct for astigmatic portion or ignoring it.astigmatic portion or ignoring it.

TrabeculectomyTrabeculectomy

Astigmatism noticed after Astigmatism noticed after trabeculectomy is due to the partial trabeculectomy is due to the partial thickness scleral flap created and thickness scleral flap created and sutured.sutured.

‘‘with the rule’with the rule’ astigmatism. astigmatism. Small incision trabeculectomies are Small incision trabeculectomies are

beneficial.beneficial.

Calculation of post Calculation of post operative astigmatismoperative astigmatism

Intra operative keratometry.Intra operative keratometry.

Vector analysisVector analysis

Vector has magnitude and direction.Vector has magnitude and direction.

Astigmatism also has cylindrical Astigmatism also has cylindrical power (magnitude) and axis power (magnitude) and axis (direction).(direction).

The component powers of 2 cylinders are The component powers of 2 cylinders are taken as vectors and these vectors are taken as vectors and these vectors are directed at angles twice the actual angle directed at angles twice the actual angle of orientation before the eye.of orientation before the eye.

K1 = pre operative corneal astigmatismK1 = pre operative corneal astigmatism K3 = post operative corneal astigmatismK3 = post operative corneal astigmatism K2 = surgically induced astigmatism.K2 = surgically induced astigmatism.

K3K3

K1K1

K2 K2

K3K3

K1K1

K2 K2

Law of sines and cosinesLaw of sines and cosines

Amplitude of K2 = Found using the Amplitude of K2 = Found using the law of cosines.law of cosines.

Angle = Found using the law of Angle = Found using the law of sines.sines.

K2 K2 22= K1= K122+ K3+ K322 – 2K1K3 cos k2 – 2K1K3 cos k2

K1 K2 K3K1 K2 K3

----------- = ---------- = ---------------------- = ---------- = -----------

Sin k1 Sin k2 Sin Sin k1 Sin k2 Sin k3k3

Example:Example: K1= 3.00× 25°K1= 3.00× 25° K3= 1.50× 100°K3= 1.50× 100°

Find K2.Find K2.

K3K3

K1K1

K2 K2

K3K3

K1K1

K2 K2

K2K222 = 3.00 = 3.00 22 + 1.50 + 1.50 22 – 2(3.00) (1.50) – 2(3.00) (1.50) (cos 150°)(cos 150°)

= 11.25 - 9 cos 150° ( cos = 11.25 - 9 cos 150° ( cos 150°= - 0.866)150°= - 0.866)

= 11.25 + 7.794= 11.25 + 7.794

= 19.044= 19.044

K2 = 4.36.K2 = 4.36.

K3 K2K3 K2 ------ = --------------- = --------- Sin k3 Sin k2Sin k3 Sin k2

Sin k3 = K3 Sin k2Sin k3 = K3 Sin k2 ------------------------------ K2K2K3 = Arcsine 1.50 sin 150K3 = Arcsine 1.50 sin 15000

-------------------------------------- 4.364.36 = 9.9= 9.900

Keratometry,Keratometry, Photokeratoscopy,Photokeratoscopy, slit lamp examination,slit lamp examination, manifest refractionmanifest refraction

aid in identification of tight aid in identification of tight sutures.sutures.

Management Management

Conservative Conservative Intervention Intervention

Conservative Conservative

Spectacle correction.Spectacle correction.

Contact lenses.Contact lenses.

Surgical Surgical

Selective cutting of sutures.Selective cutting of sutures. Selective tightening or loosening of Selective tightening or loosening of

continuous sutures.continuous sutures. Limbal relaxing incisions.Limbal relaxing incisions. Coupling: astigmatic keratotomy.Coupling: astigmatic keratotomy. LASIK can be performed safely LASIK can be performed safely

following cataract surgery after 6 following cataract surgery after 6 weeks weeks

Selective cutting of Selective cutting of sutures sutures

It was found that in a case of post op It was found that in a case of post op astigmatism of +6D at 60astigmatism of +6D at 600 0 cutting cutting the suture at 60the suture at 600 0 reduced the reduced the astigmatism to + 2 D.astigmatism to + 2 D.

Selective tightening or Selective tightening or looseningloosening

This is done in continuous sutures. This is done in continuous sutures.

Limbal relaxing incisionsLimbal relaxing incisions

LRI guideLRI guide

A radial incision produces flattening in A radial incision produces flattening in the axis of the incision and flattening 90 the axis of the incision and flattening 90 degrees away.degrees away.

Arcuate incisions produce flattening Arcuate incisions produce flattening of the axis of the incision and steepening of the axis of the incision and steepening 90 degrees away.90 degrees away.

Short arcuate incisions which are Short arcuate incisions which are less than 15 degrees arc produce the less than 15 degrees arc produce the most steepening 90 degrees from the most steepening 90 degrees from the incision.incision.

Post keratoplasty Post keratoplasty astigmatism astigmatism

Selective suture removal.Selective suture removal. Before any surgical intervention in Before any surgical intervention in

post keratoplasty patients, all post keratoplasty patients, all sutures have to be removed and sutures have to be removed and stability of refraction is assessed for stability of refraction is assessed for atleast 1 month.atleast 1 month.

Relaxing incisionsRelaxing incisions

Wedge resectionsWedge resections

Astigmatic keratotomy.Astigmatic keratotomy.

All incisions are performed at graft All incisions are performed at graft host interface so that host tissues host interface so that host tissues are not disturbed in case of need for are not disturbed in case of need for regraft later on.regraft later on.

““Prevention is better Prevention is better than curethan cure””

Thank You