Aphakia

Aphakia

1. APHAKIA DR.ANKITA MAHAPATRA

2. introduction Aphakia means absence of crystalline lens from the eye. Optically Aphakia means absence of lens from pupillary area and it does not takes part in refraction Absence of crystalline lens from patellar fossa

3. Causes :

4. Optics of aphakia CHANGES IN CARDINAL DATA OF EYE IMAGE FORMATION IN APHAKIC EYE VISUAL ACUITY IN APHAKIA ACCOMODATION IN APHAKIA BINOCULAR VISION AND APHAKIA

5. CHANGES IN CARDINAL DATA Eye becomes highly HM Power reduces from +60 to +44D Anterior focal point becomes 23.2 mm in front of cornea Posterior focal 31 mm behind the cornea Two principle points are almost on anterior surface of cornea Nodal points are nearer to each other and 7.75mm behind cornea

6. Average image magnification reported by different methods of aphakia correction Spectacle : 33% Contact lens : 10% ACIOL : 2-5% PCIOL : 0 %( about) IMAGE FORMATION IN APHAKIC EYE

7. Large image falsifies the VA recorded on the Snellen’s chart VA recorded theoretically better than the actual VA in terms of visual angle A vision of 6/9 with corrected aphakic eye should be equivalent to 6/12 of an emmetropic eye because of high magnification of spectacle (33%) VISUAL ACUITY IN APHAKIA

8. Due to absence or loss of lens from its position accommodation become zero ACCOMODATION IN APHAKIA :

9. Presence of aniseikonia is detrimental to the development of BSV ( < 5% aniseikonia ) In uniocular aphakic child , the major hindrance to development of BSV is aniseikonia of 30% due to anisometropia, develop suppression amblyopia. Unilateral aphakic if corrected with spectacle , usually develop annoying diplopia As soon as possible operation of another eye in bilateral cataract. IOLS claim to offer no barrier to fusion since the image size of the pseudophakic eye is same as that of phakic emmetropic eye. BINOCULAR SINGLE VISISON AND APHAKIA

10. OPTICAL DEFECT IN APHAKIA Acquired high hypermetropia Against the rule astigmatism Absence of accommodation Change in colour vision

11. CLINICAL FEATURES SYMPTOMS : Marked defective vision for far and near. Erythropsia and cynopsia i.e., seeing red and blue Images due to excessive entry of ultraviolet and infrared rays in the absence of crystalline lens.

12. Limbal scar - Surgical Aphakia . Anterior chamber deeper than normal. Iridodonesis . Jet black pupil. Purkinje image test: 3rd and 4th images are absent. Fundus examination: small hypermetropic disc. Retinoscopy shows high HM SIGNS :

13. TREATMENT

14. SPECTACLE Optical principle is to correct the error by convex lens of appropriate power.

15. Predicting the power of an aphakic lens Laurance suggested the power of spectacle lens F ap h ak i c = + 11.00 D + (1/2 ) F p r e - ap h ak i c Retzlaff and karff described formula of predicting aphakic refraction F ap h ak i a = 80.4 – 1.65 L - 0.7 K Where ,L = axial length of eye , K = preoprative keratometry finding in diopters

16. Increased retinal image size Decreased field of view Presence of ring scotoma, Jack-in-the-box-phenomenon Spherical aberrations Motion of object in field of view Cosmetic blemishes Increased ocular rotations Cumbersome to use Problem of near vision DISADVANTAGES

17. If correcting lens is placed at anterior focal point of the eye, size of retinal image directly proportional to the anterior focal length and inversely proportional to the refracting power of the eye. Retinal image size ( aphakia /emmetropia) (23.23/17.05) = (58.64/43.05) = 1.36 Or increased in retinal image size of 36% In unilateral aphakia corrected with spectacles BSV impossible due to high magnification 1. INCREASED RETINAL IMAGE SIZE

18. In B/L aphakia greatly increased image size means that aphakic patients must adapt to new size - distance relationship Familiar object not only appear to be much larger , they also appear to be much closer Initially , patient is visually uncoordinated, he/she Pours water on the table instead of glass until eventually after Some months of trial and error , a new coordination of Hand and eye develops.

19. Sometimes aphakic patients achieve central visual acuity that exceeds the best VA obtained before surgery due to magnification of retinal image size. Inc r e a sed m a gni f i c a tion m a y pe r mit the p r es c r i bi n g of weaker reading addition.

20. 2. DECREASED FIELD OF VIEW 50 degree all around Both monocular and binocular vision restricted

21. Based on prismatic effect of strong plus lens causes angular gap in object space completely around the lens which is know as ring scotoma 3.RING SCOTOMA center to the ring scotoma wearer has corrected vision Ring scotoma of about 15 degree extending from 50-65 degree from central fixation

22. Ring scotoma moves in opposite direction of the eye movement ( roving eye scotoma ) Ring scotoma creates different problems especially from 2 - 10 feet , which is generally in ordinary room Factors effect on size and position of ring scotoma Lens power Vertex distance Lens size Pupil size Lens thickness Base curve Except vertex distance and pupil size all other show direct relation with size of ring scotoma

23. Object seems to jump in and out of field of view as it moves out of and into the ring scotoma Simply sudden disappearance and sharp reappearance of the object in visual space with ring scotoma JACK-IN-THE-BOX-PHENOMENON :

24. Magnification of image is more at the periphery of the lens due to prism effect 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.PIN CUSHION DISTORTION

25. 5 . MOTION OF OBJECT IN FIELD OF VIEW In high plus error , when the eyes are steady and head moved to wards an object then marked reversed motion (against motion) of the field of view is experienced This is due to prismatic effect ( base in ) in the direction of head movement This motion often referred to as swim swim can be avoided by moving the eyes from one fixation point to another while the head stationary but this may produce distortion Best procedure is to turn head slowly so that head and eye moves slowly

26. Angle of eye turning in changing fixation from one object point to another increases in comparison to emmetropic. 7. INCREASED OCULAR ROTATION

27. 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 FB sensation Corneal complications may be associated

28. It is treatment of choice who are unsuitable for IOL implantation or who have experienced a failed IOL implants Common in unilateral aphakia Contact lens provide less image magnification (about 5-7%) which make possibility of BSV in uniocular aphakia

29. 6-10 weeks post surgical to permit healing/ settling of power Find any contraindication for CL fit Spectacle Refraction Measurement of Ocular dimension Keratometry Pupil size, shape, position Eyelids integrity C L fitting Over refraction (astigmatism / near addition) BSV After care GENERAL PROCEDURE

30. RGP lenses : cases with high corneal astigmatism and corneal distortion Hydrogel lenses : cases with low astigmatism or failed RG P lens wearers Silicone elastomer : cases with low astigmatism and pediatric aphakic patients Scleral lenses : patients with significant corneal distortion Tinted lenses :to attenuate bright light and offer some UV protection CONTACT LENS OPTIONS IN APHAKIA

31. ADVANTAGES Little image magnification No spherical and prismatic aberration Minimum or no aniseikonia Normal peripheral field Cosmetically well accepted DISADVANTAGES Risks and complications may be more Infections Dislocation of IOL ( child rubbing eye) Posterior capsular opacities It needs specially qualified surgeons and sophisticated instrument. The cost is more IOL

32. IOL IOL implantation in cataract ,has good outcome IOL implantation in children provides the benefit of reducing dependency on compliance in comparison with other external optical devices. Disadvantages are technical difficulties of implanting an IOL in eyes of children, selecting an appropriate IOL power, and the risk of PCO. Both IOLs and aphakic contact lenses may provide similar visual acuity (VA) after surgery for unilateral cataract in the presence of good compliance In unilateral cases, primary implantation is indicated as soon as the patient is fit for anesthesia, ideally between 2 and 3 months of age.

33. AGE (YRs) RESIDUAL REFRACTION 2-4 +5D 4-5 +4D 5-6 +3D 6-7 +2D 7-8 +1.5D 8-10 +1D 10-14 +0.5D >14 PLANO IOL POWER CONSIDERATION FOR MYOPIC SHIFT

34. 1. PARENTAL COUNSELLING : Post op care Treatment of amblyopia Frequent follow ups for changing refraction Chances of PCO, glaucoma, squint and management 2. SITE OF IOL IMPLANTATION : Capsular support a. adequate – in the bag b. compromised – Capsular tension ring or sulcus fixation 3. PEDIATRIC CAPSULORHEXIS : Hard to perform due to high capsule elasticity and tension

35. 4 . SECONDARY IOL IMPLANTATION : If adequate peripheral capsular support is present, the IOL is placed into the reopened capsular bag or in the ciliary sulcus. Most commonly used IOL for secondary implantation is the three piece AcrySof Intraocular Lenses. Anterior chamber IOLs and scleral or iris-fixated posterior chamber IOLs are used in children when other viable options are lacking.

36. Refractive corneal surgery is under trial for correction of aphakia . It includes 1.KERATOPHAKIA : Lenticule prepared from donor cornea is placed between the lamella of patient’s cornea. REFRACTIVE CORNEAL PROCEDURE

37. 2.EPIKERATOPHAKIA : A lenticule prepared from donor cornea is stitched over the surface of patient’s cornea after removing epithelium. 3.LASIK

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