Pre-operative evaluation of senile cataract

Farhana AdninB.Optom,4th batch,Institute of Community Ophthalmology,University of Chittagong

Astigmatism correction

Definition ???When parallel rays of light come from infinity and create multiple focal point with accommodation at rest is called astigmatism.

For exampleThe image may be focused on the retina in the horizontal (sagittal )plane,but not on the retina in the vertical plane Most Astigmatic cornea have two curves,one is steeper and another oner a flatter curve

OPTICSA.CompoundHyp.AstigB.Simple Hyp.C D E Mixed AstigF.SimpleMyop.AG.CompoundMyop.A

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ClassificationBased on focus of the principal meridian-1. Simple astigmatism: Simple hyperopic astigmatism Simple myopic astigmatism

2.Compound astigmatism:Compound hyperopic astigmatismCompound myopic astigmatism

3.Mixed astigmatism

Cont

ContinueBased on axis of the principal meridians-1.Regular astigmatism:With the rule astigmatismAgainst the rule astigmatismOblique astigmatism2. Irregular astigmatism

Based on severity-Mild astigmatism : 3.00 D

Regular AstigmatismWhen horizontal and vertical meridians are at right angle to each other.With the rule astigmatism :The two principal meridian are at perpendicular to each other but vertical meridian is more curved than horizontal meridian.Range-60 to 120 degree

ContAgainst the rule astigmatism : In which the horizontal meridian is more curved than the vertical meridian.Range : 0 to 30 degree, 150 to 180 degree.

Oblique astigmatism : Where the two principal meridian are not the horizontal or vertical but these are perpendicular to one other.Range : 30 to 60 degree, 120 to 150 degreeFor example : If one axis in 45 and another axis in 135 degree

Regular astigmatismEtiology1.Corneal - abnormalities of curvature [common]

2. Lenticular- rare. It may be:Curvatural - abnormalities of curvature of lens as seen in lenticonus. Positional - tilting or oblique placement of lens , subluxation. iii. Index astigmatism variable refractive index in different meridian. 3. Retinal - oblique placement of macula [rare]

Cont..Eye strainDiscomfortHeadacheDry eyeSensitivity to lightBlurred vision Frequent blinking

Head tiltHalf closer of the lidOval or tilt optic discDifferent power in different meridianSymptomsSigns

Cont..Investigations:RetinoscopyKeratometry AutorefractometerAstigmatic fan testJackson cross cylinderStenopaeic slit

contManagement:

Spherocylindrical spectaclesContact lens --Soft contact lens -- Toric -Soft lenses -Rigid gas permeable lenses Refractive surgery

Refractive surgeriesAstigmatic Keratotomy-upto 4-6DPhoto Astigmatic refractive Keratectomy [PARK]- upto 3DLASIK surgery-upto 5-10D

Irregular AstigmatismDefective visionDistortion of objectsPolyopia Irregular pupillary reflexCorneal irregularityIrregular corneal curvature

SymptomsSigns

Etiology : Corneal Scars Keratoconus Flap complicationsMarginal degenration , Lenticular Cataract maturation

Investigations:Placido's disc test reveals distorted circles Corneal topographyPenta cam

Treatment :1.Optical treatment : RGP contact lenses Hybrid contact lenses Scleral lenses Piggyback lens2.Corneal Cross-Linking With Riboflavin and Ultraviolet Irradiation3.Penetrating Keratoplasty [PKP]4.Deep Anterior Lamellar Keratoplasty [DALK] etc.

Physiological astigmatism

Diameter of cornea in vertical axis is 11.5mm and in horizontal meridian is 12mm.This means horizontal meridian is flatter than vertical.Because diameter is inversely proportional to curvature. Occur as lid press on anterior corneal surface.Make vertical meridian steeperOnly small astigmatic errorUsually 0.12DNo treatment required

Total astigmatism

Corneal astigmatism: When the cornea has unequal curvature or dioptric power on the anterior surface.

Internal astigmatism: It occurs due to posterior surface of cornea & tilting of crystalline lens.

Total astigmatism: The sum of corneal & internal astigmatism.

Residual astigmatism:

The amount of astigmatism that still remains after correction of a refractive error.

In the case of correction of corneal astigmatism using rigid contact lens ,lenticular residual astigmatism is exposed.

Surgical induced astigmatismUsually following cataract surgery Induced by incission or suture

If without suture ---

Against the rule astigmatism (superior limbal incission)With the rule astigmatism (temporal limbal incission)

If with suture ----(Opposite )

With the rule astigmatism (superior limbal incission)Against the rule astigmatism (temporal limbal incission)

ContManagement:After 1 month of surgery spectacles prescribed.

Others-Selective removal of sutures: If more than 2-3 D WTR astigmatism present then after 2 month , suture with the steepest curve must be removed.Relaxing incisions combined with compression (upto 10D etc

Case studyMR-910951Name: Abdul BarekAge- 20 yGender- MaleC/O- Dimness of vision B/EVAR-6/60 |PH 6/9VAL-3/60 |PH 6/9

Objective refraction-OD)-2.50D/-8.50DC @40degOS)-9.00D/-12.00DC@170deg

Subjective refraction-OD)-2.00D/-6.00DC@40....6/18OS)-8.00D/-8.00DC@170...6/24

No glass prescribedPatient was given RGP contact lensOD)-5.00/6.00/9.00...6/9OS)-5.oo/7.15/9.20....6/9

When to prescribe...?1.Symptomatic patient:~rarely