Correction of ametropia

Correction of Ametropia is very basic topic in Optometry background. Hope the SlideShare may help you. This PPT will help Bachelor students (B.optoms).

1. Presenter :AMRIT JHA SUBJECT CODE: MO101 Correction of Ametropia ©A Jha

2. What is ametropia ? Ametropia (a condition of ref. error) is defined as a state of refraction wherein the parallel rays of light coming from infinity (with accommodation at rest) are focused either in front or behind the retina, in one or both the meridian . Ametropia includes the following : - Hypermetropia - Myopia - Astigmatism ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

3. HYPERMETROPIA Light is focused behind retina, i.e. posterior focal point is behind the retina. Also known as long or far sightedness. AETIOLOGICAL TYPE :- Axial hypermetropia : 1mm axial length of eye shortening cause 3D hypermetropia . Curvatural hypermetropia : When the curvature of the cornea or lens is flatter than normal. An increase of 1mm in its radius of curvature produces a hypermetropia of 6D. Index hypermetropia : It occurs due to change in refractive index of lens or cornea. It may also occur in diabetic under treatment. Positional hypermetropia : Due to posteriorly placed lens. (Congenital or trauma) Absence of crystalline lens: Congenital or acquired. Leads to aphakia which is condition of high hypermetropia . ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

4. Continuation… CLINICAL TYPE :- Simple hypermetropia : It’s commonest form and is due to normal biological variation in size and shape of eyeball. It could be axial or curvatural . Pathological hypermetropia : (a) Congenital : Seen in conditions like; Microphthalmos , Microcornea , Congenital aphakia etc. (b) Acquired : It includes senile( curvatural or index), positional, aphakia , consecutive, retrobulbar orbital tumer types of hypermetropia . Functional hypermetropia : It results from paralysis of accommodation as seen in patients with 3 rd nerve paralysis and internal ophthalmoplegia . ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

5. Components of Hypermetropia : Total Hypermetropia : After complete cycloplegia with atropine. Latent Hypermetropia : Amount of hypermetropia that is corrected by tone of ciliary muscle. Manifest Hypermetropia : Remaining amount of Hypermetropia which is not corrected by tone of ciliary muscle. Facultative Hypermetropia : Amount that can be corrected by patient’s accommodative effort. Absolute Hypermetropia : Residual amount of manifest hypermetropia . ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

6. Continuation… For example, If the patient having vision 6/9 improves with +0.50 DSph to 6/6, by fogging method, patient reads 6/6 with +2.0 DSph and after a cycloplegic refraction patient reads 6/6 with +3.5DSph. Find, MH, AH, FH, LH, and TH ??? AH = +0.5 DS MH = +2.0 DS (By fogging method) and TH = +3.5 DS (By cycloplegia ) Soln ; MH = AH+FH or, FH = MH – AH = +2.0 DS - +0.5 DS = + 1.50 DS TH = MH +LH or, LH = TH-MH = 3.5 DS – 2.0DS = +1.50 DS So, final correction by Donder’s formula Rx = MH+1/3 LH = +2+1/3X1.5= +2+0.5 = +2.5DS ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

7. Clinical Pictures SYMPTOMS SIGNS 1. Asymptomatic . If less than 1 D of hyperopia . 1. Visual acuity varies with degree of power and amount of accommodation. 2. Asthenopic symptoms like; tiredness of eyes, frontal headache, watering etc. 2. Size of eyeball may appear small as a whole or normal. 3.Defective vision with asthenopic symptoms, if having 2-4 D of hyperopia . 3. Anterior chamber shallow and the angle is narrow. 4. Defective vision only. When the amount of hyperopia is more than 4 D. 4. Fundus examination may reveal pseudopapillitis & foveal reflects at greater distance from disc margin (+ ve angle kappa). 5. The effect of aging on Vision. Occurrence of progressive loss of accommodative power with ageing. 5. Shot silk appearance of retina and abnormal branching of retinal vessels. 6. Intermittent sudden blurring of vision and crossed-eye sensation. 6. A-scan biometry may reveal a short anteroposterior length of the eyeball. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

8. Treatment of hypermetropia There are mainly 3 options and they are; Spectacle correction with convex lens. Contact lens. Surgical treatment. 1. Spectacle correction with convex lens:- It is most common and easy method of correcting hypermetropia . There are few fundamental rules for prescribing glasses and they are as follows:- a. General rule: Total amount of hypermetropia should always be discovered by performing cycloplegic refraction. Correction is given only when patient is symptomatic in case of less than 1D. b. For adults: Manifest correction must be given. Correction for infinity must be done rather than for six meter examination room. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

9. Continuation… b. For adults manifest hypermetropia correction this formula must be followed; ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

10. Continuation… c. For children: ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

11. Continuation… 2. Correction with contact lenses:- Advantage of CL over spectacles for Hypermetropia or, Aphakia ; Contact lenses (CL) are indicated in unilateral hypermetropia (anisometropia) mostly. CL are cosmetically better. CL provides increased, wider and field of view Less magnification of image. Elimination of aberration & prismatic effect of thick glass. 3. Surgical treatment:- Surgical treatments for hypermetropia includes; (a) Corneal refractive therapy. (b) Laser thermal keratoplasy . (c) Hyperopic LASIK or PRK (d) Phakic IOLs. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

12. APHAKIA Aphakia is one of causative factor for producing high degree of Hypermetropia . Aphakia literally means absence of crystalline lens from the pupillary area and do not take part in refraction. CAUSE :- Congenital absence of lens. Surgical aphakia Traumatic extrusion Posterior dislocation. CLINICAL FEATURES:- The only symptom in aphakia is marked defective vision for distance as well as for near. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

13. Continuation… Signs of aphakia :- Limbal scar in surgical aphakia . Anterior chamber is deeper than normal. Iridodonesis of iris can be seen Pupil is jet black in colour . Only two purkinje’s image is seen. On slitlamp examination, absence of lens from pateller fosa is seen. Fundus eamination shows hypermetropic small disc. Retinoscopy reveals high hypermetropia . ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

14. Correction of aphakia . Modalities for correcting aphakia includes; Spectacles Contact lens IOLs Refractive corneal surgery. 1. Spectacle Correction:- It is cheap, easy and safe method of correcting aphakia . However, presently, it’s not common mode of correction due to it’s disadvantages. Disadvantages of spectacle correction in aphakia :- (a) Image magnification (b) Spherical aberrations. (c) Prismatic aberration (d) Restricted field of vision. (e) Coloured vision. (f) Cosmetic blemish. (g) Cumbersome to use. (h) Problem for near vision. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

15. Continuation… 2. Contact lenses :- Same as discussed in side 11( Hypermetropia ). 3. IOLs Implantation:- IOL implantaion is the best available method of correction of aphakia . Therefore, it is the commonest modality being employed nowadays. 4. Refractive Corneal Surgery:- Refractive surgery is under trial for correction of aphakia . It includes; a. Keratophakia b. Epikeratophakia c. Hyperopic LASIK ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

16. MYOPIA Parallel rays of light coming from infinity are focused in front of the retina with acc. at rest Also known as short or near sightedness. AETIOLOGICAL TYPE :- Axial myopia : 1mm axial length of eye lengthening cause 3D myopia. Curvatural myopia : When the curvature of the cornea, lens or both are steeper than normal radius of curvature produces a myopia of 6D. Index myopia : It occurs due to change increse in refractive index of lens due to nuclear sclerosis. Positional myopia: Due to anteriorly placed lens. (Congenital or trauma) Myopia due to excessive accommodation: occurs in patient with spasm of accommodation. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

17. Continuation… CLINICAL TYPE :- Congenital myopia : 1. It is usually associated with an increase in axial length and overall globe size. 2. Present since birth. It is usually diagnosed by age of 2-3 years of child. 3. High degree (8-10D) of error and mostly remains constant. 4. Most of time it’s unilateral as anisometropia. 5. Associations are like; Premature baby, Marfan syndrome, congenital convergent squint , microphthalmos , aniridia , megalocornea , congenital separation of retina. 6. Treatment: Full cycloplegic refractive error including any astigmatic correction. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

18. Continuation… Simple or developmental myopia : 1. It is commonest variety of myopia and also known as physiological myopia. 2. Usually, the onset occurs at school going age 8-12 years of child. So, also called school myopia. 3. Axial and curvatural type of simple myopia is considered with role of genitical , physiological variation and under-development of the eyeball. 4. Symptoms include; - Poor vision for distance, - Half shutting of the eyes, - Asthenopic symptoms like; development of convergence weakness, exophoria , suppression in one eye, ciliary spasm, eye strain. - Change in psychological outlook of myopic child. Becomes less active in outdoor activity. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

19. Continuation… 5 . Signs include; - Predominant eyeball. - Anterior chamber is slightly deeper than normal. - Pupils are somewhat large and bit sluggishly reacting. - Fundus is normal; rarely temporal myopic crescent may be seen. - Magnitude of error. In simple myopia usually the error does not exceed 6-8 D. Acquired myopia: Some of the causes of acquired myopia are; (1) Index myopia (2) Curvatural myopia (3) Positional myopia (4) Consecutive Myopia (5) Pseudomyopia (6) Space Myopia (7) Drug induced myopia Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system. ©A Jha

20. Continuation… Pathological or degenerative myopia : 1. It is also known as progressive myopia. As, the name indicates, is a rapidly progressive error which starts in childhood at 5-10 years of age and results in high myopia (7-6 D). 2. Degenerative changes in eyes occurs at very early adulthood of child. 3. Results due to rapid Axial growth of eyeball which is not normal biological developmental process. 4. It is linked with hereditary/ genetic factor and general growth process. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

21. Clinical Pictures SYMPTOMS SIGNS 1. Poor vision for distance. Defective vision 1. Prominent eye ball and large cornea. 2. Change in psychological outlook . 2.Magnitude of refractive error increases by about 4D yearly till age of 20 years. 3. Muscae volitantes and floating black opacities in front of the eye. 3. Myopic crescent, optic disc appears large & pale. 4. Progressive degenerative changes of retina, choroid , sclera and vitreous. 4. Foster- Fuch’s spot are seen at the macula & Cystoid degeneration at periphery. 5.Night Blindness due to chorioretinal degenerative changes. 5. Lattice degeneration and/or snail track lesion may be associated. 6. Squeezing and half shutting of eyes to create stenopic effect. 6. Posterior staphyloma due to ectasia of sclera at posterior. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

22. Treatment of Myopia There are mainly 3 options and they are; Spectacle correction with concave lens. Contact lens. Surgical treatment. 1. Spectacle correction with concave lens:- a . Basic rule of correcting myopia : Conversely to hypermetropia , the minimum acceptance providing maximum vision should be prescribed in myopia. b. Guidelines for correcting low degree of Myopia ( upto -6.00 D) : In children up to 3 years of age, guideline shown in Table 3.2. In children above 3 years of age, myopia should be fully corrected and instructed to use their glasses constantly. Never overcorrect myopia. In case of adult , younger than 30 years, if full correction over 3 D is not tolerated. Then under correction must be done for present. Full correction may be given in future. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

23. Continuation… 2. Correction with Contact lens: - It’s same as, advantage of contact lens over glasses discussed in hypermetropia . - Contact lens helps to get rid off peripheral distortion and minification produced by high myopic glass correction. - Some authors report that wearing hard CL also slow down progression of myopia. - Myope wearing a full contact lens correction needs more accommodation for near work as compared with a spectacle wearer. So, they develop presbyopia comparatively earlier. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

24. Continuation… 3. Correction by Surgical Treatment: It has become very popular nowadays. It should be performed after the error gets stabilized. Preferably after 18-20 years of age. Few of the refractive surgeries for myopia correction are as follows; (A) Keratorefractive procedure : 1. Incision procedure - Radial keratotomy. 2. Lamellar corneal refractive procedures – Epikeratoplasty , Smile technique etc. 3. Laser ablation corneal procedure – PRK, LASEK, LASIK etc. 4. Corneal implant. 5. Corneal tissue moulding – Orthokeratology . (B) Lens based refractive procedure : PRLs and RLE. (C) Combined refractive procedure : Bioptics and Trioptics . ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

25. Continuation… 4. Preventive measures : a. Therapeutic interventions : Atropine , even in low strength of 0.01% eye drops, instilled nightly are reported to slow down the progression of myopia. Pirenzepine 2% gel, applied twice a day, is also reported to slow down the myopia progression. b. Genetic counselling . c. Visual hygine and balanced diet. d. Low vision aids: These are indicated in patients of progressive myopia with advanced degenerative changes, where useful vision is not obtained with glasses and CLs. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

26. ASTIGMATISM Astigmatism is a refractive error in which the refraction varies in different meridian i.e., rays of light entering the eye cannot converge to a point focus but from focal lines. Aetiologically , astigmatism (Regular or Irregular ) can be defined as, 1. Corneal astigmatism : It is the result of abnormalities in curvature of cornea. It may be congenital or acquired (occurrence is often irregular). 2. Lenticular astigmatism : It is comparatively rare. a. Curvatural astigmatism : due to abnormal curvature of the lens. Eg : lenticonus . b. Positional astigmatism : due to oblique placement or congenital tilting of the lens. Eg : subluxation of the lens. c. Index astigmatism: due to varriable refractive index of lens in different meridian. Eg : diabetic patient developing nuclear sclerosis and/or cataract. d. Retinal astigmatism: due to oblique placement of macula. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

27. Regular Astigmatism. The astigmatism is regular when the refractive power changes uniformly from one meridian to another (i.e. there are two principle meridian). Types of Regular astigmatism:- 1. With-the-rule astigmatism: Two principal meridian are placed at right angle to one another, but the vertical meridian is more curved than horizontal. 2. Against-the-rule astigmatism: It refers to the astigmatic condition in which the horizontal meridian is more curved than the vertical meridian. 3. Oblique astigmatism: It refers to the astigmatism where the two principal meridian are not the horizontal and vertical, though these are at right angle to each other. 4. Bi-oblique astigmatism: In this type of regular astigmatism, the two principal meridia are not at right angle to each other. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

28. Refractive type of Regular astigmatism 1. Simple astigmatism :- A. Simple myopic - Light ray focused on retina In one meridian and in front of the retina in the another meridian. B. Simple hyperopic - Light ray focused on retina In one meridian and in behind of the retina in the another meridian. 2. Compound astigmatism :- C. Compound myopic - Light rays in both the meridian are focused in front of the retina. D. Compound hyperopic - Light rays in both the meridian are focused behind of the retina. 3. Mixed astigmatism :- Light ray focused behind retina In one meridian and in front of the retina in the another meridian. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

29. Treatment of Astigmatism Clinical Features : - Blurring of vision, Asthenopic symptoms, Tilting of head, Squinting and half closure of the eye, Burning and itching of eye, Reading material may be held close to eye etc. Treatment:- Optical correction : 1. The cylindrical lens may be prescribed in form of spectacles. 2. Hard CLs may correct up to 2-3 D of regular astigmatism. 3. Bi-oblique, mixed and Higher degree of astigmatism (regular or irregular) are better treated by Contact lens/ toric CL than by spectacle. Surgical treatment : It is indicated in extensive very high astigmatism or corneal scarring(when vision does not Improve with contact lens) and consists of penetrating keratoplasty , astigmatic LASIK etc. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.

30. ©A Jha Ref: Theory and practice of optics and refraction, A K Khurana & A text book on Optics and Refraction, Arbinda eye care system.