This document discusses refraction and myopia. It begins with an introduction to the optics of the human eye and refractive errors. It then focuses on myopia, defining it as a refractive error where the eyeball is too long or the refractive power of the eye is too strong. It describes the types of myopia, including juvenile onset and pathological axial myopia. Signs, symptoms, complications, and treatment approaches for myopia are summarized, including correction methods like glasses and surgery. The document emphasizes the importance of monitoring for degenerative changes in high myopia.

1. Refraction 1
Prof K N Jha, MS
Email: kirtinath.jha@gmail.com

2. Learning Aims
• To understand the Optics of the human eye
• Introduction to Refractive Errors
• Myopia: definition, etiology, clinical features,
diagnosis, complications, and treatment

3. Optics of the human eye
• Human eye is a complex optical system.
• It consists of cornea , aqueous humor,
crystalline lens, and the vitreous humor.
• This arrangements permits to make the eye
compact and small.

4. Main refracting surfaces
• Air-cornea interface
• Aqueous-lens interface
• Lens-vitreous humor interface

5. Reduced schematic eye
• Schema= a diagrammatic representation.
• In the reduced schematic eye the whole eye is
regarded as single ideal refracting element , an
ideal spherical refracting surface separating two
media of different refractive indices with one
optical centre( the nodal point , N).

6. Reduced schematic eye

7. Dimensions of the reduced eye
• Distance from anterior corneal surface to the
nodal point: 5.6 mm
• Distance from nodal point to the fovea: 17
mm
• Length of the eye 5.6 + 17 mm= 22.6 mm.

8. Refractive status of the eye
• Emmetropia
• Ametropia
• Refractive status ( static refraction) of the eye:
emmetropia , myopia, hypermetropia, astigmatism.
• Anisometropia: difference between the spherical
equivalents between the two eye.

9. Ametropia : Classification
• Axial
• Refractive: curvature, index

10. Emmetropic eye

11. Myopic eye

12. Hypermetropic eye

13. Far Point

14. Ametropia and Axial Length of the Eye

15. Pupil size and Visual acuity

16. Refraction and subjective correction of
refractive errors
• Objective refraction
Retinoscopy without cycloplegia
Cycloplegic refraction
Use of autorefractometer
Keratometry
• Subjective verification of refraction

17. Retinoscopy
Subjective verification

18. MYOPIA

19. Myopic eye

20. Prevalence
• Prevalence increases steadily with age.
• Some ethnic groups have higher prevalence at
all ages.

21. Myopia
Congenital myopia
Developmental myopia
- Juvenile onset myopia
- Adult onset myopia
• Simple myopia
• Pathological axial
myopia

22. Juvenile-onset myopia
• It is myopia with onset between 7-16 years of age, that occurs
due primarily to growth in axial length.
• Risk factors: Esophoria, against-the-rule astigmatism,
premature birth , family history, and intense near work.
• Earlier onset of myopia shows greater progression.
• In ¾ of teen myopia stabilize at about 15-16 years.
• In the rest , progression continues into the 20s and 30s.

23. Adult-onset myopia
• Begins at about 20 years of age
• Extensive near work is a risk factor for
development of myopia.

24. Etiologic factors
• Genetic: Some severe forms of myopia suggest
dominant , recessive, and even sex-linked
inheritance pattern.
• Environmental: near work, higher educational
achievements, nutritional factors.

25. Simple myopia
• Occurs as a variant in the frequency curve in the axial
length and the curvature.
• Abnormal axial length is the most important factor.
• Fundi : No degenerative changes.
• Myopia do not usually exceed -5 to -6 D.
• Does not progress beyond adolescence.

26. Pathological axial myopia
• It is degenerative and progressive.
• Refractive changes appear in childhood, usually
between 5-10 years of age.
• Increases steadily up to 25 years of age and beyond.
• Myopia may amount to 15-25 D or more.
• Degenerative changes in the fundus appear late in life.

27. Pathological axial myopia
• Strongly hereditary.
• Commoner in male than female.
• Racial predilection in Jews and Japanese.
• Other etiological factors : endocrine and
nutritional factors, debility or illness.

28. Pathological axial myopia
Changes in the eye ball
- Elongation of the eye ball, particularly
involving the posterior pole.
- Posterior staphyloma may form.

29. Symptoms of myopia
• Indistinct distance vision.
• Eye strain due to convergence accommodation
dissociation and exophoria.
• Floaters, and occasionally flashes of light.

30. Signs
• Eyes may appear prominent.
• Anterior chamber deeper than normal.
• Pupils are larger.
• Apparent divergent squint.

31. Fundus changes in Myopia
• Optic disc and the posterior pole: myopic crescent , Central
choroidal atrophy, Foster Fuchs spot, lacquer cracks.
• Peripheral retinal degeneration
- Cystoid degeneration
- Lattice degeneration
- Formation of retinal holes and detachment
• Vitreous degeneration

34. Prognosis
• Moderate myopia ( -5 to - 6D): prognosis is
good.
• High myopia: Prognosis depends on the
-corrected visual acuity
-fundus changes

35. Prevention of complications
• Examination of the fundus periphery with
indirect ophthalmoscope.
• Prophylactic treatment of retinal tear/ and
holes likely to lead to retinal detachment.
• Avoidance of contact sport in patient with
degenerative myopia.

37. Management of Myopia
• In children:
- Cycloplegic refraction
- Full correction ( spherical and cylindrical)
- Frequent refraction ( every 6-12 months)
and periodic changes of glasses.
- contact lens for older children with high
refractive errors .

38. Correction of Myopia

39. Surgery for Myopia
• Corneal surgery: RK, LASIK
• Clear Lens extraction
• Phakic intraocular lens implantation

41. Points to Remember
• Schematic eye
• Refractive status of the eye
• Myopia: Definition, clinical features,
complications, diagnosis, and treatment