Aphakia and its correction
Definition The lens is absent from the pupillary area Congenital absence Dislocation into the vitreous Extruded outside the eye Surgically removed Absorption of the lens matter
Effects of Aphakia Changes in the cardinal data of the eye Image formation in the aphakic eye Visual acuity in aphakia Accommodation in aphakia Binocular vision in aphakia
Changes in the cardinal data of the eye Eye is highly hypermetropic Power is reduced to 44D (60D) Anterior focal point is 23.2 mm in front of cornea (17.2mm)Posterior focal point is 31mm behind cornea (24.4mm)
Changes in the cardinal data of the eye Principal points are at the anterior surface of cornea ( 1.5mm behind) Nodal points are 7.75 mm behind anterior surface of cornea (7.2mm)
Image formation in the aphakic eye Image size in aphakia corrected with spectacles is 30% magnified Image size in aphakia corrected with contact lens is magnified by 4.5 to 5%
Visual acuity in aphakia Visual acuity of spectacle corrected eye is recorded better than actual visual acuity in terms of visual angles
Accommodation in aphakia Total loss of accommodation Bifocal or progressive spectacles Multifocal IOLs
Binocular vision in aphakia Monocular aphakia corrected with spectacles will result in aniseikonia Can be corrected with IOL or Contact lens
Clinical features Associated abnormalities Operative scar at limbus Deep AC Iridodonesis Jet black pupil Absent Purkinje images (3,4) Associated abnormalities High hyperopia Fundus exam -small disc
Correction of aphakia Spectacle Contact lens Intra-ocular lens Refractive corneal surgery
Total power Total dioptric power = +58 D Cornea= +42 D Lens= +16 D Refractive state = Emmetropia 11/17/2018
Total power Total dioptric power = +42 D Cornea= +42 D Lens= +0 D Refractive state = High Hypermetropia 11/17/2018
Total power A high power (thick) convex lens is required to correct vision 11/17/2018
Spectacle correction +10 D lens with correction of associated astigmatism ( usually ATR ) Add + 3 D for near vision ( Total +13D ) Advantages Cheap Easy safe
Spectacle correction Many disadvantages Heavy glasses Poor cosmetic appearance
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Spectacle correction Many disadvantages Magnification of 30% - unilateral aphakia, assess distance
Magnification Spectacle magnification= Corrected image size Uncorrected image size Anterior focal distance in ametropia Anterior focal distance in emmetropia 23.2 = 1.36 = 30 % magnification 17.05 11/17/2018
False depth False depth perception 11/17/2018
False depth False depth perception 11/17/2018
False depth False depth perception 11/17/2018
False depth False depth perception 11/17/2018
False depth False depth perception 11/17/2018
False depth False depth perception 11/17/2018
False depth False depth perception 11/17/2018
Spectacle correction Many disadvantages Restricted field of vision Roving ring scotoma
Ophthalmology is easy 11/17/2018
thalmology is 11/17/2018
Ophthalmology is easy Ring scotoma- 11/17/2018
? almology . Ring scotoma- 11/17/2018
Ophthalmology is easy 11/17/2018
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Ring scotoma- 11/17/2018
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Roving Ring scotoma- 11/17/2018
Jack in the box- 11/17/2018
Spectacle correction Spherical aberrations – pincushion defect
Aphakic glasses Pin cushion effect 11/17/2018
Spectacle correction Spherical aberrations – pincushion defect Coloured vision Separate glasses for near
Total power Total dioptric power = +58 D Cornea= +42 D Lens= +16 D Refractive state = Emmetropia 11/17/2018
Total power Total dioptric power = +42 D Cornea= +42 D Lens= +0 D Refractive state = High Hypermetropia 11/17/2018
Total power CONTACT LENS 11/17/2018
Contact lenses +13 D contact lens For near vision – spectacle correction is needed ( Add +3D ) Advantages- Less magnification Less prismatic distortions Better field of vision Better cosmetically Better for uniocular aphakia Disadvantages- Requires good maintenance Cost cumbersome
Intra-ocular lens Lens is placed inside the eye Positions and power ACIOL- +17D Iris fixated- +18D PCIOL- +20 D Advantages Good optics Permanent Disadvantages- Surgical procedure - complications
Intra Ocular Lens Parts Optic Haptic Material PMMA Silicone Hydrogel
Refractive Corneal Surgery Keratophakia Epikeratophakia Hyperopic Lasik - Can correct small amounts of hyperopia up to 4 D