REFRACTIVE ERRORS and its management (2).pptx

Refractive errors including
myopia
Hypermetropia
Astigmatism including regular and irregular
Presbyopia
And its management and basics of correction

1. REFRACTIVE ERRORS Presented by: Dr. Shagun Gaur JR Ophthalmology

2. Introduction Emmetropia : It is state of refraction wherein parallel rays of light coming from infinity are focused at the sensitive layers of retina with accommodation being at rest. Ametropia : State of refraction wherein parallel rays of light coming from infinity with accommodation being at rest are focused either in front or behind the retina in one or both meridia. It includes: Myopia Hypermetropia Astigmatism

3. Myopia Refractive error in which parallel rays of light coming from infinity are focussed in front of the retina when accommodation is at rest .

4. Optics of myopia Optical system of a myopic eye is too powerful for its axial length. Far point of the myopic eye is a finite distance in front of the eye. Therefore , a near object situated at a far point is focused without any accommodation. Nodal point in myopic eye is further away from retina. Therefore image formed is larger as compared to emmetropic eye.

5. Etiology of myopia 1. Axial myopia- Results from increase in anteroposterior diameter of eyeball. It is the commonest form. 2. Curvatural myopia - Due to increased curvature of cornea , lens or both. 3. Positional myopia- Produced by anterior placement of crystalline lens in the eye. 4. Index myopia - Increase in refractive index of crystalline lens associated with nuclear sclerosis.

6. Myopic fundus

7. Complications of myopia Retinal detachment Complicated cataract Vitreous haemorrhage Choroidal hemorrhage

8. Atropine based protocol for myopia management .

9. https://www.researchgate.net/publication/336394787_Clinical_Management_and_Control_of_Myopia_in_Children

10. Hypermetropia Refractive state of the eye wherein parallel rays of light coming from infinity are focused behind the retina with accommodation being at rest.

11. Etiological types Axial Curvatural Index Positional Absence of crystalline lens Consecutive Commonest form Due to axial shortening of eyeball 1 mm shortening 3D of hypermetropia Curvature of cornea, lens or both is flatter Reducing the refractive power. 1mm increase in radius of curvature results in 6 diopters of hypermetropia Due to decrease in refractive index of lens in old age due to cortical sclerosis Also in diabetics under treatment Due to posteriorly placed lens Leads to aphakia : high hypermetropia. Overcorrected myopia Underpowered IOL implantation

12. Components of hypermetropia Total hypermetropia Manifest Latent Facultative Absolute Corrected by inherent tone of ciliary muscle . Not corrected by ciliary tone. Corrected by patient accommodative effort. Can’t be corrected by patient accommodative effort.

13. Variation of hypermetropia with age At birth : +2 to +3D hypermetropia which gradually reduces. 5-7 yrs : emmetropic and remains so till 50 yrs After 50 yrs : again 2 to 3 D Of hypermetropia occurs due to changes in crystalline lens. ( senile hypermetropia)

14. Fundus in hypermetropia Complications : Recurrent styes or blepharitis or chalazion . Accomodative convergent squint Amblyopia Predisposition for primary narrow angle glaucoma.

15. Surgical correction LASIK PRK(Photorefractive Keratectomy) Phakic IOLs RLE(Refractive Lens Exchange )

16. Astigmatism Type of refractive error wherein the refraction varies in different meridian. Irregular Regular

17. Regular Astigmatism Etiology : risk factors Family history of astigmatism Preterm/LBW Advancing age Corneal scarring/thinning Severe allergies Diabetes Preexisting refractive errors Lenticular Corneal Retinal Due to abnormalities of curvature of cornea. Curvatural Positional Index Due to oblique placement of macula

18. Types of Regular Astigmatism

19. Oblique astigmatism : Two principal meridian are not horizontal and vertical though these are at right angle to each other. Bi-oblique astigmatism : Two principal meridian are not at right angle to each other.

20. 2020–2021 BCSC Basic and Clinical Science Course™ Visit

21. Optics of Regular Astigmatism Sturm’s conoid : Configuration of rays refracted through the astigmatic surface and the distance between the two focal lines is known as the focal interval of sturm .

22. Clinical features Blurring of vision Asthenopic symptoms – difficulty in focusing, dull ache in eyes, headache Keeping the reading material close to the eyes Tilting of head Squinting i.e. half closure of lids Burning and itching Retinoscopy and AR - different power in two meridians Keratometry - different corneal curvature in two meridians in corneal astigmatism Astigmatic fan test Jackson’s cross cylinder test Investigations

23. Treatment Optical treatment : Cylindrical lens Spherical hard contact lenses may correct upto 2-3D of regular astigmatism. For higher degree toric contact lenses are needed

24. Irregular astigmatism I rregular change of refractive power in two meridians. Etiological- Curvatural: keratoconus, corneal scar Index: variable refractive index in different part of lens ( in cataract). Symptoms : Defective vision Distortion of objects Polyopia Signs: I rregular pupillary reflex on retinoscopy Keratoconus on slit lamp examination Distorted circles on Placido’s disc Irregular corneal curvature on photokeratoscopy and corneal topography

25. Treatment Optical: Contact lens which replace the anterior surface of cornea Laser: Phototherapeutic keratectomy with excimer laser Surgery: It is done in extensive corneal scarring Penetrating keratoplasty or Deep anterior lamellar keratoplasty

26. Presbyopia It is physiological insufficiency of accommodation due to reduced amplitude leading to progressive fall in near vision. It occurs between 40-45 years of age. Why ? Mainly due to sclerosis of crystalline lens and changes in its capsule. Or may be ciliary muscle itself became less efficient with advancing age (after 40 yrs )

27. Infancy - 14D of accomodation 45 years - fallen down to 4D 60 years - only 1 D remains

28. Amplitude of accommodation Difference between the dioptric power needed to focus at the near point and far point. E.g. at the age of 10 years AA= 100/7 - 100/ infinity = 14D

29. Hypermetropia - patient must accommodate more to achieve near vision. E.g. 3D hypermetropia- 3D of accommodation needed to see things clearly at infinity. So to see clearly at 25 cm 7 D of accommodation is needed. Myopia - 3D of myopia has far point at 33 cm. Thus to focus at 25 cm only 1D of accommodation is used.

30. Calculation of presbyopic correction : First determine NPA e.g. 33 cms Calculate Amplitude of accommodation = 100/33 = 3D Keep 1/3rd of this in reserve for comfortable near vision. At 25 cm -4D of accommodation is needed. Thus he requires 2 D of presbyopic correction.

31. Age based correction In practice the refractionist learns by experience to anticipate the approximate presbyopic correction from patients age. In ametropia the presbyopic correction is added to the patient’s distant correction and must be adjusted for different working distances. 45-50 years +1.00D addition 50-55 years +1.50D addition 55-60 years +2.00D addition Over 60 years +2.50D addition

32. Basic principles of presbyopic corrections Always find out refractive error for distance and first correct it. Find out presbyopic correction needed for each eye separately and add it to distant correction. Near point should be fixed by taking due consideration of profession of the patient Additional correction for the intermediate distance may be required.

33. Modes of prescribing presbyopic aid : spectacle correction Single vision reading glasses.( suited for those with no distant errors) Bifocal glasses Trifocal glasses Progressive glasses

34. Split bifocal Segment shapes for fused bifocal Cemented bifocal Solid bifocal Fused bifocal

35. Lens procedure used : Clear lens exchange Refractive lens exchange Presbyopic lens exchange