APHAKIA SLIDESHOW PRESENTATIONS PPT.pptx

APHAKIA PPT
POWERPOINT
SLIDESHARE
KNOWLEDGE
OPTOMETRIST
PROFESSIONAL EYE CARE
EYE KNOWLEDGE

1. APHAKIA Naoba Mutum F.Y. M.OPTOM

2. APHAKIA Aphakia literally means absence of crystalline lens from the eye. However, from the optical point of view it may be considered a condition in which the lens is absent from the pupillary area and does not take part in refraction. Aphakia produces a high degree of hypermetropia.

3. CAUSES OF APHAKIA Congenital absence of lens: May occur in a very rare condition. Surgical aphakia occurring after removal of lens is the commonest presentation. Aphakia due to absorption of lens matter is noticed rarely after trauma in children Traumatic extrusion of lens from the eye also constitutes a rare cause of aphakia. Posterior dislocation of lens in vitreous (traumatic or spontaneous) produces optical aphakia

4. OPTICS OF APHAKIC EYE Optics of aphakic eye can be discussed under the following topics : Changes in the cardinal data of the eye Image formation in aphakic eye Visual acuity in aphakia Accommodation in aphakia Binocular vision and aphakia

5. CHANGES IN CARDINAL DATA OF THE EYE Following optical changes occur after removal of crystalline lens Total power of the eye is reduced to about +44D from +60D. So, the eye becomes highly hypermetropic. 2. Anterior focal point becomes 23.2 mm in front of the cornea. 3. Posterior focal point is about 31 mm behind the cornea i.e. about 7 mm behind the eyeball. (The anteroposterior length of the eyeball is about 24 mm.) 4. Two principal points are almost at the anterior surface of cornea.

6. 5. Nodal points are very near to each other and are located about 7.75 mm behind the anterior surface of cornea. Fig 1. APHAKIC EYE

7. IMAGE FORMATION IN APHAKIA Fig 2 shows comprehensively the size of image formed in emmetropia, uncorrected aphakia, spectacle corrected aphakia, contact lens corrected aphakia and IOL corrected aphakia. Fig 2. Image formation and image magnification in aphakia A. Uncorrected aphakia, B. Spectacle corrected aphakia C. Contact lens corrected aphakia D. Aphakia corrected by a posterior chamber IOL.

8. Average image magnification reported by different methods of aphakia correction ( in a preoperative emmetropic eye ) is about: SPECTACLE : 33% CONTACT LENS : 10% ANTERIOR CHAMBER IOL : 2% - 5% and POSTERIOR CHAMBER IOL : O%

9. VISUAL ACUITY IN APHAKIA The Snellen’s visual acuity in spectacle corrected aphakia is falsified due to a large image size. The vision recorded is theoretically better than the actual visual acuity in terms of visual angles. The visual acuity of 6/9 in a spectacle corrected aphakic eye should be considered equivalent to 6/12 of an emmetropic eye .

10. ACCOMMODATION IN APHAKIA There occurs a total loss of accommodation due to absence of lens. Therefore either bifocal or two separate pairs of glasses – one for distant vision and another for near vision – are required. With such glasses patients do feel handicapped for intermediate distances, but they learn to adjust. Progressive or varifocal glasses perhaps provide better alternative.

11. BINOCULAR VISION AND APHAKIA The presence of aniseikonia is detrimental to the development of normal binocular functions. It has been reported that aniseikonia less than 5% is compatible with binocular vision. In monocular aphakic children the major hindrance to development of binocular vision is aniseikonia of 30% due to anisometropia. Such children usually develop suppression amblyopia. The neglected patients of this type develop deviation of the operated eye.

12. When spectacles are given for correction of aphakia in adult patients who have normal or useful vision in the other eye, binocular single vision is difficult or impossible. Such patients usually develop annoying diplopia. Thus, to attain binocularity in unilateral aphakia is a big problem. Even in bilateral aphakia, binocularity is not always present. Worth’s four-dot test many a time reveals suppression or diplopia in such cases. It is not advisable that a long period should lapse between the operations of the two eyes in bilateral cataracts. During this period as the eyes are dissociated, convergence becomes poor and stereopsis and even fusion may not be attained, if the interval is prolonged .

13. Fortunately use of IOLs has largely solved the problems associated with uniocular aphakia. The IOLs are claimed to offer no barrier to fusion since the image size of the pseudophakic eye is almost the same as that of the phakic emmetropic eye. Even in pseudophakic patients, binocularity is not attained in 100% of cases. In a study in unilateral pseudophakic (other eye emmetropic), all the three grades of binocular single vision were present in 90% of cases.

14. CLINICAL FEATURES: SYMPTOMS Marked defective vision for both distance and near Photophobia Eye strain and fatigue Erythropsia and cyanopsia [ seeing red and blue images due to excessive entry of UV and infrared rays ]

15. SIGNS Pupil is jet black in colour. Purkinje’s images shows only 2 images. Retinoscopy and AR reveals high hypermetropia. Anterior chamber is deeper than normal. Iridodonesis can be demonstrated. Fundus examination shows hypermetropic small disc. Limbal scar may be seen in surgical aphakia. naoba optom

16. TREATMENT Modalities for correcting aphakia include: • Spectacles • Contact lens • IOL and • Refractive corneal surgery

17. SPECTACLES Spectacle prescription had been the most commonly employed method of correcting aphakia in the past. However presently use of aphakic spectacles has been markedly decreased. Roughly, about +10D with cylindrical lenses for surgically induced astigmatism are required to correct aphakia in previously emmetropic patients. However exact power of glasses will differ in individual cases and should be estimated by refraction. An addition of +3 to +4 is required for near vision to compensate for loss of accommodation.

18. The problems of correcting aphakia with high-plus spectacle lenses include Magnification of approximately 20%–35% 2. Altered depth perception resulting from the magnification 3. Pincushion distortion; for example, doors appear to bow inward difficulty with hand–eye coordination 4. Ring scotoma generated by prismatic effects at the edge of the lens (causing the “jack-in the-box” phenomenon) extreme sensitivity of the lenses to minor misadjustment in vertex distance, pantoscopic tilt, and height .

19. Aphakic lens with magnification and pincushion distortion. (Courtesy of Tommy Korn, MD.)

20. 5. Since the image is magnified by 35%, so spectacles are not useful in unilateral aphakia (produce diplopia). 6. In addition, aphakic spectacles create cosmetic problems. The patient’s eyes appear magnified and, if viewed obliquely, may seem displaced because of prismatic effects. The high-power lenticular lens is itself unattractive, given its “fried-egg” appearance. For these reasons, intraocular lenses and aphakic contact lenses now account for nearly all aphakic corrections. Nevertheless, spectacle correction of aphakia is sometimes appropriate, as in bilateral infantile pediatric aphakia .

21. 7. Restricted field of view 8. Coloured vision The patient may complain of coloured hue in the vision. It occurs due to the absence of natural filter of a crystalline lens and due to the chromatic aberration. 9. Cosmetic blemish: Thick glasses are cosmetically embarrassing as the eyes also appear larger behind the glasses. This effect is more felt by young aphakics . 10. Cumbersome to use The glasses are very thick and heavy and so are cumbersome to use.

22. 11. Problem of near vision Thick bifocal glasses are especially difficult to adjust with. Patients may have to keep separate pair of glasses for near and distance vision Advantages of spectacle : It is a cheap, easy and safe method of correcting aphakia .

23. LENS DESIGN IN APHAKIA 1 . LENS MATERIALS The new aphakic spectacles should utilize the same details in lens design and lens materials as in the old glasses. Keeping the base curves as flat as possible will not only reduce the lens- induced magnification, but shorten the vertex distance, which further decreases the magnification. The desirable high plus lenses will be hyperaspheric , but they will bring some degradation of VA since the lens power diminishes towards the periphery.

24. 2. OPTICAL CENTRES Any misalignment between a lens OC and the eyes pupillary center will create a lens-induced prismatic effect. A 1mm displacement of the OC of a +10D lens will generate 1prism diopter of image shift. If the OC movement is outward, it will induce base-out effect, which will stimulate an eye movement inward (convergence) to maintain fusion, just as with exophoria, likewise moving the OC inward induces an esophoria.

25. 3. FRAME SIZE Recommend using as small a frame size as is cosmetically applicable, even though a large lens does reduce the impact of the ring scotoma. Adjustable nose pads will allow the lens to be positioned as close to the cornea as eyelash clearance will permit which helps decrease the magnification. In addition with the lens positioned closer to the eyes, the field of vision is increased and the peripheral image degradation resulting from the aspheric lens design is decreased.

26. 4. PANTASCOPIC TILT Normally the tilt of aphakic lenses should be kept at 5-7 from the vertical this is less tilted than the 10-15 standard for most glasses. And the OC of the distance lens lowered 0.5mm for every degree of tilt allowing the visua l axis of the eye to pass through the optical centre of the lens in the most frequently used ocular positions. CLINICAL POINT: Any increase in pantoscopic tilt adds astigmatic and spherical power via residual astigmatism to either a plus or minus lens, especially a high-powered one. Thus an undercorrected hyperope or myope will sometimes tilt his glasses excessively to obtain some additional corrective power.  

27. 5. BIFOCALS The most frequently used bifocal for the aphake is the 28mm D- segment. It is interesting that most aphakes will manage to deal with the intermediate distances satisfactorily with bifocals. They accomplish this feat partly from the magnification created by the lens image magnification factor, and partly from the eyes normal depth of focus, which is enhanced by a small pupil. Further, from a practical standpoint , most patients discover that they can improve their intermediate vision by sliding the glasses down their nose.

28. Increasing the vertex distance of plus lenses in this way increases effective plus power in the distance lens and provides the extra plus needed for intermediate distances – and for reading too. ** For example, if a +12 D lens is moved from 10 to 16 mm from the cornea and the object of regard is 1 meter away, the effective lens power becomes +12.75D. Attention to these design details by both the refractionist and optician will increase your patient satisfaction . **

29. CLINICAL POINT Even aphakes who are happy with contact need to have a pair of aphakic spectacles available for emergencies. In fact, they should practice using those glasses occasionally to get used to the inherent magnifications and distortions, to help prepare for those circumstances where they can’t use their contacts .

30. 2. CONTACT LENSES Advantages of contact lenses over spectacles include: Less magnification of image, Elimination of aberrations and prismatic effect of thick glasses Wider and better field of vision Cosmetically more acceptable and Better suited for uniocular aphakia

31. Disadvantages of contact lenses More cost Cumbersome to wear especially in old age and in childhood and Corneal complications may be associated .

32. Types of Contact Lenses for Aphakia There are several types of contact lenses that can be prescribed for aphakia. The choice depends on the age of the patient, the condition of the eye, and patient preference. A. Soft Contact Lenses D. Hybrid Contact lens B. RGP lenses E. Custom made lenses C. Scleral lenses

33. CONTACT LENSES FOR PEDIATRIC APHAKIA Congenital Aphakia : Children born without a natural lens, or who undergo early cataract surgery, often require contact lenses. Unlike adults, intraocular lenses (IOLs) may not be implanted in infants or young children because their eyes are still growing. Silicone Hydrogel Lenses : These are often chosen for children due to their comfort and oxygen permeability. Frequent Lens Changes : As children’s eyes grow, their refractive error changes. Contact lenses need to be regularly updated to accommodate growth.

34. There are several possible options for contact lens correction of pediatric aphakia. These include 1.S oft (hydrogel and silicone hydrogel) contact lenses, 2.S ilicone elastomer lenses, and 3.R igid contact lenses (corneal, corneo -scleral, mini-scleral, and scleral lenses).

35. SOFT CONTACT LENSES Soft contact lenses are relatively easy to fit to infantile aphakes , historically, this has probably been the primary factor leading to their common use in pediatric contact lens fitting. However, soft contact lenses are more commonly dislodged and ejected from infant eyes as compared to adult eyes due to factors such as excessive eye rubbing.  Toric soft contact lenses are rarely prescribed to pediatric aphakes due to the excessive lens thickness associated with their prescription.

36. Soft contact lenses do not mask corneal astigmatism, and The application and removal of soft contact lenses by parents can also be very difficult due to a combination of the very small palpebral aperture and the high-plus power of the lens. Silicone hydrogel contact lenses are definitely the preferred option of soft contact lenses for infantile aphakia, because—even in a high-plus power—these lenses will generally have an oxygen transmissibility that satisfies the Holden-Mertz criterion for no corneal edema during daily wear.

37. SILICONE ELASTOMER LENSES   Lens has a very high oxygen transmissibility due to the silicone elastomer material. Because of their increased modulus, those lenses are easier to apply and will usually result in better visual acuity compared to soft contact lenses. They are also more stable on the eye compared to soft or rigid contact lenses and are not as easily rubbed out or mislocated. Unfortunately, there are many problems associated with the use of silicone elastomer lenses.

38. GP CONTACT LENSES   The use of rigid lenses in pediatric contact lens fitting is becoming more widespread, as these contact lenses can be manufactured from highly oxygen-permeable materials that easily satisfy the Holden-Mertz criterion for both daily and overnight wear, even at the very-high-plus powers required by aphakic infants.  GP contact lenses can also be manufactured very accurately in virtually any custom parameters. Rigid contact lenses can correct any corneal astigmatism and offer far greater material stability compared to soft contact lenses, as they do not dehydrate on the eye. Potential contact lens complications with high-plus lenses—such as corneal vascularization and corneal edema—are less common with GP contact lenses.

39. Corneal GP contact lenses do have disadvantages. Initially, they are generally less comfortable compared to soft contact lenses. Due to the greater precision required with GP corneal lens fitting, these lenses will need to be modified more frequently as the eye grows. 17  As they do not mold completely to the shape of the cornea, rigid contact lenses are more prone to foreign bodies being trapped beneath them compared to soft contact lenses. Mechanical irritation and subsequent corneal abrasions can be a problem if infants do rub their eyes, and GPs are more easily ejected from the eyes compared to soft lenses. 18  It should be noted that mini-scleral and scleral contact lenses offer many advantages over corneal lenses including superior initial comfort, good stability on the eye, excellent vision, and less corneal abrasions (due to the fact that these lenses are fitted with corneal clearance and in a semi-sealed state). 19  Hence, these contact lenses should be strongly considered once aphakic children have reached early school age (i.e. > 6 years), as lens replacement will be less frequent at this age due to a significant reduction in the rate of growth of the eye, and application of these lenses will generally be easier due to a child being more cooperative.

40. Power and Design of Aphakic Contact Lenses High Plus Power : Aphakic lenses require high plus power (+10 to +20 diopters or more) to compensate for the loss of the natural lens. The specific power depends on the eye’s refractive needs after lens removal. Large Diameter : Aphakic lenses may need to be larger than regular contact lenses to ensure stability, especially in children or people with irregular corneas. UV Protection : Since aphakic eyes are more prone to light sensitivity and UV damage (as the natural lens provides UV filtering), many aphakic contact lenses come with UV-blocking properties.

41. Special Considerations for Pediatric Aphakia: Daily Wear Lenses : Infants and young children typically use daily wear lenses to reduce the risk of infection. Parental Involvement : Parents or caregivers are responsible for inserting, removing, and cleaning the lenses. Education on proper lens care is essential to prevent complications such as infections or corneal damage .

42. 3. INTRAOCULAR LENS IMPLANTATION Implantation is the best available method of correcting aphakia. Therefore it is the commonest modality being employed nowadays. Types of IOLs Used in Aphakia 1. Anterior Chamber IOLs (ACIOLs) : Placed in front of the iris, commonly used when the posterior capsule is damaged. 2. Posterior Chamber IOLs (PCIOLs) : Placed behind the iris in the capsule where the natural lens was, commonly used during cataract surgery. 3. Scleral-fixated IOLs : Used when both capsule and zonules are compromised. 4. Iris-claw IOLs : Attached to the iris, used in certain aphakic cases.

43. Benefits of IOLs in Aphakia Permanent vision correction without external aids (glasses/contact lenses) Improved quality of life Better peripheral vision and depth perception compared to glasses Lower risk of complications compared to long-term contact lens use

44. Pediatric Aphakia and IOLs Special considerations for infants and young children. Why IOL implantation is usually delayed in pediatric patients: Eye growth and development Risk of complications in growing eyes Temporary correction options (contact lenses or spectacles) until IOL implantation becomes feasible .

45. Recent Advances in IOL Technology Accommodating IOLs: Designed to restore some level of natural accommodation. Extended Depth of Focus (EDOF) IOLs: Provide a continuous range of focus.

46. 4 .REFRACTIVE CORNEAL SURGERY Refractive corneal surgery is under trial for the correction of aphakia. It includes the following: i . Keratophakia : In this procedure a lenticule prepared from the donor cornea is placed between the lamellae of the patient’s cornea. ii. Epikeratophakia : In this procedure a lenticule prepared from the donor cornea is stitched over the surface of the patient’s cornea after removing the epithelium. iii. Hyperopic LASIK.

47. Main complications of surgical aphakia include : Spectacle intolerance: Due to image  magnification  (up to 30%),  optical aberration , prismatic effect and roving ring scotoma, spectacles are not well tolerated by aphakic patients. Due to  unequal refractive power between the eyes, wearing spectacles with single-eye aphakia may cause  double vision. 2. Glaucoma: Secondary angle closure glaucoma may occur due to vitreous prolapse. 3. Retinal detachment. 4. Aphakic bullous keratopathy