aphakia and pseudophakia

APHAKIA AND PSEUDOPHAKIA

PRESENTER- DR. SHWETA

MODERATOR- DR. ANUBHA MITTAL

DEFINITION

Absence of crystalline lens.

Lens is absent from the pupillary line and does not take part in refraction.

CAUSES

Congenital absence of lens. Surgical aphakia. Aphakia due to absorption of lens matter. Traumatic extrusion of lens. Posterior dislocation of lens.

OPTICS OF APHAKIA

CHANGES IN CARDINAL DATA OF EYE Eye becomes highly hypermetropic. Total power of eye +44 D. Anterior focal point becomes 23.2 mm in front of cornea. The posterior focal point is about 31mm behind the cornea. The two principal points are almost at the anterior surface of cornea. Nodal points are located about 7.75 mm behind the anterior surface of

cornea.

ACCOMODATION IN APHAKIA

Total loss of accommodation. Glasses for near and distance are required.

BINOCULAR VISION Aniseikonia of 5% is compatible with binocular vision In aphakia aneisokonia is detrimental to development of normal

binocular vision

CLINICAL FEATURES Defective vision for near and far.

SIGNS Limbal scar Anterior chamber is deeper Iridodonesis Pupil – jet black Purkinje’s image test- 2 images Fundus examination- hypermetropic small disc Retinoscopy- high hypermetropia

TREATMENT By convex lens.

MODALITIES FOR CORRECTING APHAKIA Spectacles Contact lens IOL Refractive corneal surgery

BY SPECTACLES Most common +10 D is used Cylindrical lens required in surgically induced aphakia Additionally +3 to +4 D for near vision

ADVANTAGES Cheap Easy and safe method

DISADVANTAGES[1] IMAGE MAGNIFICATION Image size depends on axial length and keratometry reading

1D of convex power leads to about 3 % magnification of image, thus 10 D = 30%

Difference of image size between the two eyes of about 7 % is tolerable

beside that give rise to diplopia i.e., two images of one object are seen one small (from normal eye) and other larger (from aphakic eye).

Objects appear larger they appear falsely closer than reality, and this leads to physical in-coordination.

Not useful in unilateral aphakics

[2] ROVING RING SCOTOMA

Edge of a convex lens acts as a prism

Higher the power of the convex lens the greater is the prism angle (alpha). Light falling on the prism bends towards its base by an angle alpha/2 .

Aphakic spectacles, the angle alpha being large, the light falling at the edge of the lens bends towards the center of the lens (base of prism)

And does not reach the pupil and is, therefore, not seen.

Resulting in an area of the visual field which is not visible to the patient, or scotoma.

And because the edge of the lens is present all around the lens like a ring, so it gives rise to a ring shaped scotoma.

Position of this scotoma is not fixed in the visual field because the eye keeps moving (or roving) in relation to the aphakic spectacle.

JACK-IN-THE-BOX-PHENOMENON

[3] PIN CUSHION AFFECT

Magnification of image is more at the periphery of the lens due to prismEffect, objects appear stretched out (large, nearer, elongated in radial direction) at the corners like a pin-cushion.

Moving objects appear to be faster

Straight lines become curves

4) RESTRICTED VISUAL FIELD Both monocular and binocular vision is restricted 50° all around

5) COLOUR VISION PT may complain of colored hue Due to absence of natural filter of crystalline lens

6) COSMETIC BLEMISH Eyes appear larger Seen more in young aphakics

7)THICK AND HEAVY GLASSES

CONTACT LENS

ADVANTAGES

Less magnification of image No chromatic aberrations No prismatic affect Wider field of vision Cosmetically acceptable Better for uniocular aphakics

DISADVANTAGES

More cost Cumbersome to wear-both for young and old age Corneal complications may be associated

INTRAOCULAR LENS IMPLANTATION

Secondary IOLs- PCIOL IRIS CLAW LENS

SFIOL

REFRACTIVE CORNEAL SURGERY[1] KERATOPHAKIA

A lenticule prepared from donor cornea is placed between the lamellae of the patient’s cornea

[2] EPIKERATOPHAKIA

A lenticule prepared from donor cornea is stitched over the surface of patient’s cornea after removing the epithelium

PSEUDOPHAKIA Condition of aphakia when corrected with implantation of IOL is called

as pseudophakia.

Also called Artiphakia

CALCULATION OF IOL POWER

Most common method is SRK I (Sanders Retzlaff and Kraff) by regression formula

P = A-0.9k-2.5L

P = power of IOLA = constantL = axial length of eyeball

SRK IIBased on axial length, A constant is modified as

If L is <20 mm - A +3

20-20.99 mm - A+2

21-21.99 mm - A+1

22-24.50 mm - A

>24.50 mm - A-1.5

MODIFIED SRK-IIA constant is modified as-

If L is <20 mm - A +1.5

20-21 mm - A +1.0

21-22 mm – A + 0.5

22-24.5 mm- A

24.5-26 mm – A -1.0

>26 mm - A -1.5

SRK/T – Retinal thickness is also measured.

more accurate for long eyes i.e. >26mm.

Holladay- used in eye with AL 24.5 – 26mm.

Hoffer q – best for short eyes i.e AL <19mm.

REFRACTIVE STATUS OF PSEUDOPHAKIC EYE Emmetropia Consecutive myopia Consecutive hypermetropia Astigmatism

EMMETROPIA It is produced when the power of the IOL

implanted is exact. It is the most ideal situation. Such patients require plus glasses for near vision

CONSECUTIVE MYOPIA

occurs when IOL implanted overcorrects the refraction of eye.

Such patients require glasses to correct myopia for distance vision.

May or may not require glasses for near vision.

CONSECUTIVE HYPERMETROPIA

occurs when underpower IOL is implanted

such patients require plus glasses for distance vision and additional +2 to +3 D for near vision.

ASTIGMATISM

Varying degree of surgery- induced astigmatism is also present

SIGNS OF PSEUDOPHAKIA Surgical limbal / corneal scar Anterior chamber is deep Mild iridodonesis Purkinje image test – 4 images Pupil is blackish with shining reflex

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