VENNILA.C.R REFRACTION

Refractive Errors Refractive Errors Emmetropia Emmetropia Ametropia Ametropia

Emmetropia Emmetropia Emmetropia means no Refractive error Emmetropia means no Refractive error It is the ideal condition in which the incident parallel rays come to a perfect focus upon the light sensitive layer of the retina, When accommodation is at rest It is the ideal condition in which the incident parallel rays come to a perfect focus upon the light sensitive layer of the retina, When accommodation is at rest

Ametropia Ametropia Ametropia means Refractive error Eye Ametropia means Refractive error Eye It is the opposite condition, wherein the parallel rays of light are not focused exactly upon the retina, When the accommodation is at rest It is the opposite condition, wherein the parallel rays of light are not focused exactly upon the retina, When the accommodation is at rest

Ametropia Ametropia Myopia Myopia Hypermetropia Hypermetropia Astigmatism Astigmatism

Myopia Myopia Principal focus is formed in front of the retina Principal focus is formed in front of the retina

Causes Causes Axial Myopia Axial Myopia Curvature Myopia Curvature Myopia Index Myopia Index Myopia Abnormal position of the lens Abnormal position of the lens

Axial Myopia Axial myopia results from increase in anteroposterior length of the eye ball. Axial myopia results from increase in anteroposterior length of the eye ball. Normal Axial length- 23mm to 24mm Normal Axial length- 23mm to 24mm 1mm increase in AL – 3Ds of Myopia 1mm increase in AL – 3Ds of Myopia

Curvature Myopia Curvatural myopia occurs due to increased curvature of the cornea and Lens or both. Curvatural myopia occurs due to increased curvature of the cornea and Lens or both. Anterior surface of the cornea- 7.8mm Anterior surface of the cornea- 7.8mm Posterior surface of the cornea- 6.5mm Posterior surface of the cornea- 6.5mm 1mm increases in radius of curvature results in – 6 Ds of Myopia 1mm increases in radius of curvature results in – 6 Ds of Myopia

Index myopia Index myopia results from increase in the refractive index of crystalline lens. Index myopia results from increase in the refractive index of crystalline lens. Refractive index of normal Lens Refractive index of normal Lens

Abnormal position of the lens Positional myopia is produced by anterior displacement of crystalline lens in the eye. Positional myopia is produced by anterior displacement of crystalline lens in the eye. Accommodative Myopia:. Myopia due to excessive accommodation.

Types Types Congenital myopia Congenital myopia Simple Myopia (or) Developmental myopia Simple Myopia (or) Developmental myopia Pathological Myopia (or) Degenerative myopia Pathological Myopia (or) Degenerative myopia Acquired myopia Acquired myopia

Congenital myopia Congenital myopia is present since birth however, it is usually diagnosed by the age of 2 – 3 years. Congenital myopia is present since birth however, it is usually diagnosed by the age of 2 – 3 years.

Simple myopia Simple or developmental myopia is the commonest variety. It is considered as a physiological error not associated with any disease of the eye. Simple or developmental myopia is the commonest variety. It is considered as a physiological error not associated with any disease of the eye. Power limit less than 6D Power limit less than 6D

Aetiology Axial type of simple myopia Axial type of simple myopia Curvatural type of simple myopia Curvatural type of simple myopia

Pathological myopia Myopia associated with degenerative changes in the eye. Myopia associated with degenerative changes in the eye. Myopia more than 6D to25D or More than 25D Myopia more than 6D to25D or More than 25D

Aetiology Axial growth Axial growth (i) Heredity (ii) General growth process

Acquired myopia Some of the causes of acquired myopia * Index myopia * Curvatural myopia * Positional myopia * Consecutive myopia * Pseudo myopia * Space myopia * Night myopia (or) Twilight myopia * Drug induced myopia

Symptoms Poor vision for distance Poor vision for distance Asthenopic symptoms Asthenopic symptoms Exophoria Exophoria Muscae volitantes (pathological) Muscae volitantes (pathological) Night blindness (pathological) Night blindness (pathological)

Signs Large eye ball Large eye ball deep Anterior chamber deep Anterior chamber sluggish Pupil sluggish Pupil Large Disc Large Disc

Complications Complications Retinal tear – Vitreous haemorrhage Retinal tear – Vitreous haemorrhage Retinal detachment Retinal detachment Degeneration of the vitreous Degeneration of the vitreous Primary open angle Glaucoma Primary open angle Glaucoma Posterior cortical cataract Posterior cortical cataract Posterior staphyloma Posterior staphyloma

Treatment Treatment Optical Optical Spectacle Correction (Concave Lens) Contact lens Surgical SurgicalPRKKeratomileusisEpikeratophakia Redial Keratotomy

Optical Treatment Concave lens Concave lens Myopic with Exophoria give full correction. Myopic with Esophoria give under correction.

Hypermetropia Principal focus is formed behind the retina Hypermetropia Principal focus is formed behind the retina

Causes Causes Axial Hypermetropia Axial Hypermetropia Curvature Hypermetropia Curvature Hypermetropia Index Hypermetropia Index Hypermetropia Abnormal position of the lens Abnormal position of the lens

Axial Hypermetropia Axial hypermetropia is by far the commonest Axial hypermetropia is by far the commonest In fact, all the new- borns are almost invariably hypermetropic (approx,+2.50D) This is due to shortness of the globe, and is physiological. In fact, all the new- borns are almost invariably hypermetropic (approx,+2.50D) This is due to shortness of the globe, and is physiological. Normal axial length – 23mm to 24mm Normal axial length – 23mm to 24mm 1mm decrease in AL – 3Ds of hypermetropia 1mm decrease in AL – 3Ds of hypermetropia

Curvature Hypermetropia In which the curvature of cornea, Lens or both is flatter than the normal resulting in a decrease in the refractive power of the eye. In which the curvature of cornea, Lens or both is flatter than the normal resulting in a decrease in the refractive power of the eye. Anterior surface of the cornea- 7.8mm Anterior surface of the cornea- 7.8mm Posterior surface of the cornea- 6.5mm Posterior surface of the cornea- 6.5mm 1mm increase in radius of curvature results in – 6Ds of hypermetropia 1mm increase in radius of curvature results in – 6Ds of hypermetropia

Index Hypermetropia Index hypermetropia occurs due to change in refractive index of the lens in old age. It may also occur in diabetics under treatment. Index hypermetropia occurs due to change in refractive index of the lens in old age. It may also occur in diabetics under treatment. Refractive index of Normal Lens Refractive index of Normal Lens- 1.42

Classification Classification Total Hypermetropia may be divided into Total Hypermetropia may be divided into (a) Latent Hypermetropia (a) Latent Hypermetropia (b) Manifest Hypermetropia (b) Manifest Hypermetropia (i) Facultive Hypermetropia (i) Facultive Hypermetropia (ii)Absolute Hypermetropia (ii)Absolute Hypermetropia

Latent Hypermetropia LH which is corrected physiologically by the tone of ciliary muscle. As a rule latent hypermetropia amounts to only one dioptre. It can be revealed only after atropine cycloplegia. LH which is corrected physiologically by the tone of ciliary muscle. As a rule latent hypermetropia amounts to only one dioptre. It can be revealed only after atropine cycloplegia.

Manifest Hypermetropia MH is made up of two components Facultative hypermetropia is that part of hypermetropia which can be corrected by the effort of accommodation. Facultative hypermetropia is that part of hypermetropia which can be corrected by the effort of accommodation. Absolute hypermetropia which can not be overcome by the effort of accommodation. Absolute hypermetropia which can not be overcome by the effort of accommodation.

Clinical Types Simple hypermetropia Simple hypermetropia Pathological hypermetropia Pathological hypermetropia Functional hypermetropia Functional hypermetropia

Simple hypermetropia It results from normal biological variation in the development of the eye ball. It includes Axial and Curvatural HM. It may be hereditary. It results from normal biological variation in the development of the eye ball. It includes Axial and Curvatural HM. It may be hereditary.

Pathological hypermetropia PH results due to either congenital or acquired conditions of the eye ball which are out side the normal biological variations of the development. PH results due to either congenital or acquired conditions of the eye ball which are out side the normal biological variations of the development.

The Normal Age Variation The Normal Age Variation At birth:- 2D to 3 D Commonly Present At birth:- 2D to 3 D Commonly Present At the age of 5 Yrs- 90% of Children’s are Hypermetropic At the age of 5 Yrs- 90% of Children’s are Hypermetropic At Puberty:- Emmetropic At Puberty:- Emmetropic

Symptoms Symptoms Head ache Head ache Blurred vision particular near work Blurred vision particular near work Convergent squint Convergent squint Early onset of presbyopia Early onset of presbyopia Eye Strain Eye Strain

Complications Complications Eye appears to be small including cornea and anterior chamber becomes shallow Eye appears to be small including cornea and anterior chamber becomes shallow Extreme cases – Microphthalmos Extreme cases – Microphthalmos Retinal reflex – Shot silk-Retina Retinal reflex – Shot silk-Retina

Treatment Treatment Optical Optical Spectacle ( Convex Lens ) Contact lens Hypermetropic with Exophoria give under correction Hypermetropic with Esophoria give full correction Surgical SurgicalThermokeratoplasty

Astigmatism Astigmatism is that condition of Refraction where the point focus of light cannot be formed upon the Retina Astigmatism Astigmatism is that condition of Refraction where the point focus of light cannot be formed upon the Retina

Causes Causes Curvature Curvature Ex: Keratoconus, Lenticonus etc.. Ex: Keratoconus, Lenticonus etc.. Centering error Centering error Ex: Sub location of the lens Ex: Sub location of the lens Refractive index Refractive index Ex: Cataract Ex: Cataract Retinal Retinal Oblique placement of macula Oblique placement of macula

Types Types Regular Regular Irregular Irregular

Regular astigmatism Regular astigmatism Refractive types Refractive types Physiological types Physiological types

Refractive types Refractive types Simple astigmatism Simple astigmatism Compound astigmatism Compound astigmatism Mixed astigmatism Mixed astigmatism

Physiological types Physiological types With rule astigmatism With rule astigmatism Against rule astigmatism Against rule astigmatism Oblique astigmatism Oblique astigmatism Bioblique astigmatism Bioblique astigmatism

Symptoms Symptoms Head ache Head ache Blurring of vision Blurring of vision Eye tired Eye tired Eye ache Eye ache Head Tilt Head Tilt Half-closure of the lids (High astigmatism) Half-closure of the lids (High astigmatism) Blurring & Itching (Low astigmatism) Blurring & Itching (Low astigmatism)

Treatment Optical Treatment Optical Treatment * Cylindrical lens * Under correction * Contact lens (RGP, Toric) Refractive surgery Refractive surgery * Astigmatic Keratotomy * Astigmatic Keratotomy * PRK, LASIK

Study Reports Study Reports Percentage of astigmatism Percentage of astigmatism * D50% * D25% * D24% *>4.00D1% Percentage of Types Percentage of Types * with rule38% * Against rule30% * Oblique32%

Duo chrome test To test if the eye has been under corrected or over corrected or is properly corrected Duo chrome test To test if the eye has been under corrected or over corrected or is properly corrected

Astigmatic Fan To know the axis and power in Astigmatism Astigmatic Fan To know the axis and power in Astigmatism

Jackson cross cylinder To refine the axis and power of cylinder Jackson cross cylinder To refine the axis and power of cylinder

Presbyopia Presbyopia This is a physiological aging process, In which the near point gradually recedes beyond the normal reading or working distance This is a physiological aging process, In which the near point gradually recedes beyond the normal reading or working distance

Causes Causes Lens matrix is harder and less easily moulded Lens matrix is harder and less easily moulded Lens capsule is less elastic Lens capsule is less elastic Progressive increase in size of the lens Progressive increase in size of the lens Weakening of the ciliary muscle Weakening of the ciliary muscle

Symptoms Symptoms Patient holds the book at arms length Patient holds the book at arms length Patient prefers to read in bright light Patient prefers to read in bright light Eye strain Eye strain Head ache Head ache Eyes feels tired and ache Eyes feels tired and ache

Treatment Convex lens Treatment Convex lens Methods of prescription Methods of prescription * Occupation * Occupation * Working distance * Working distance * Age * Age Surgical Surgical * Anterior ciliary sclerotomy * Anterior ciliary sclerotomy * Laser thermal keratoplasty * Laser thermal keratoplasty * Small diameter corneal inlays * Small diameter corneal inlays

Aphakia Aphakia Aphakia means absence of the Crystalline lens from the Eye ball Aphakia means absence of the Crystalline lens from the Eye ball

Causes Causes Congenital Congenital Surgery Surgery Traumatic Traumatic

Optics of Aphakia Anterior focal distance – 23mm (N-15mm) Anterior focal distance – 23mm (N-15mm) Posterior focal distance- 31mm (N-24mm) Posterior focal distance- 31mm (N-24mm) The Nodel point of the eye is thus moved forward The Nodel point of the eye is thus moved forward Strong converging (convex) lens- +10D Strong converging (convex) lens- +10D

Signs Signs Anterior chamber – Deep Anterior chamber – Deep Iris Iris (i) Iridodonesis (or) Tremulousness (ii) Peripheral button-hole iridectomy mark Pupil - Jet black reflex Pupil - Jet black reflex Absence of the 3 rd and 4 th Purkinje images Absence of the 3 rd and 4 th Purkinje images Retinoscopy – reveals high hypermetropia and astigmatism Retinoscopy – reveals high hypermetropia and astigmatism Ophthalmoscopy – As in hypermetropic fundus with a small optic disc Ophthalmoscopy – As in hypermetropic fundus with a small optic disc

Disadvantages Disadvantages Image magnification of about 25-30% Image magnification of about 25-30% Spherical aberration, Peripheral and Pincushion Spherical aberration, Peripheral and Pincushion Roving ring scotoma (The scotoma extents Roving ring scotoma (The scotoma extents from 50°- 65° from central fixation) from 50°- 65° from central fixation) Jack in the box Jack in the box Restriction of the visual field Restriction of the visual field Coloured vision Coloured vision Inaccurate spectacle correction because of errorneous vertex distance Inaccurate spectacle correction because of errorneous vertex distance

Treatment Treatment Spectacle ( Convex lens ) Spectacle ( Convex lens ) Contact lens Contact lens Secondary IOL Secondary IOL Epikeratophakia Epikeratophakia Keratophakia Keratophakia

Aphakic formula P = X / D P = IOL power X = Refractive power

Pseudophakia Pseudophakia Pseudophakia means False lens Pseudophakia means False lens

Image magnification

Calculation of IOL power P = A-2.5*L -0.9K P = IOL Power A= Constant value 2.5= AC depth 2.5= AC depth L = Axial length in mm L = Axial length in mm 0.9= Corneal curvature 0.9= Corneal curvature K = Corneal diapters

Refractive stages of a Pseudophakic eye Refractive stages of a Pseudophakic eye Emmetropia Emmetropia Consecutive myopia Consecutive myopia Consecutive hypermetropia Consecutive hypermetropia

Advantages Advantages Image magnification is only 0- 2% Image magnification is only 0- 2% No spherical and prismatic aberrations No spherical and prismatic aberrations Minimum (or) No Anisokonia with rapid return of binocularity Minimum (or) No Anisokonia with rapid return of binocularity Normal Peripheral field of vision and eccentric vision Normal Peripheral field of vision and eccentric vision Freedom from handling of the optical devices Freedom from handling of the optical devices Cosmetically it is well accepted Cosmetically it is well accepted

Disadvantages Disadvantages Risks and complications may be more Risks and complications may be more Initially, the cost is more Initially, the cost is more PCO PCO CME CME IOL related complications IOL related complications

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