This document provides an overview of common errors of refraction, including emmetropia, ametropia, hypermetropia, myopia, and astigmatism. It defines each condition and discusses their etiology, classification, signs and symptoms, investigations, and management approaches. For each error of refraction, the document describes optical and surgical treatment options as well as important considerations for treatment in children versus adults. Overall, the document serves as a comprehensive guide to understanding and managing different types of refractive errors.

1. ERRORS OF REFRACTION
Dr Saurabh Kushwaha
Resident Ophthalmology

2. SCOPE
 Emmetropia
 Ametropia
 Hypermetropia
 Myopia
 Astigmatism

3. EMMETROPIA
 State of refraction where parallel rays of
light coming from infinity are focused at the
sensitive layer of retina with accommodation
being at rest

4. NORMAL VARIATION WITH AGE
 At birth
• Eyeball is relatively short
• +2 to +3D hyperopia which gradually reduces
 By the age of 5 -7 years
• Eye is emmetropic till the age of 50 years
• In 50% of the population emmetropia is not
reached and some degree of hypermetropia
persists
• On the other hand, the mark maybe overshot,
and the eye may become myopic

5.  After 50 years of age
• Tendency to develop hypermetropia again
• It due to 2 factors, both associated with lens
• Outer cortical fibers have lesser
curvature, decreasing the converging
power
• Refractive index of cortex increases and
lens becomes homogenous decreasing
the converging power
 After 65 years of age, all of the hypermetropia
becomes absolute due to loss of accommodation

6. AMETROPIA
 State of refraction where parallel rays of light
coming from infinity are focused either in front or
behind the sensitive layer of retina in one or
both meridian
 Components of ametropia
• Corneal power
• Anterior chamber depth
• Crystalline lens power
• Axial length

7. PREVALENCE OF AMETROPIA
 Stenstrom’s study from Uppsala, Sweden
• Low myopia (≤ 2D) : 29%
• Moderate myopia (2-6D) : 7%
• High myopia (>6D) : 2.5%
• Emmetropia & hypermetropia up to 2D: 61%
• High hypermetropia : 0.5%

8. HYPERMETROPIA
 State of refraction where parallel rays of
light coming from infinity are focused behind
the retina with accommodation being at rest

9. CLASSIFICATION
 Aetiological types
 Clinical types
 Classification by extent of error

10. AETIOLOGICAL TYPES
 Axial hypermetropia
 Curvatural hypermetropia
 Index hypermetropia
 Positional hypermetropia
 Absence of crystalline lens
 Consecutive hypermetropia

11. CLINICAL TYPES
 Simple hypermetropia
• Axial hypermetropia
• Curvatural hypermetropia
 Pathological hypermetropia
• Congenital hypermetropia
• Acquired hypermetropia
 Functional hypermetropia

12. CLASSIFICATION ON EXTENT
OF ERROR
 Low - refractive error of +2D or less
 Moderate - refractive error of +2.25 to +5.0D
 High - refractive error of +5.25D or more

13. COMPONENTS
 Total hypermetropia
 Latent hypermetropia
 Manifest hypermetropia
• Facultative hypermetropia
• Absolute hypermetropia
Total hypermetropia = Latent + Manifest (Facultative + Absolute)

14. SYMPTOMS
 Asymptomatic (<1D) in young patients is corrected
by mild accommodative effort
 Aesthenopic symptoms (1-2D), patients develops
aesthenopic symptoms due to sustained
accommodative efforts
 Defective vision (2-4D) with aesthenopic symptoms
 Defective vision (>4D ) only

15. SIGNS
 Reduced visual acuity
 Size of the eyeball may be normal or may
appear small as a whole. A scan may reveal short
anteroposterior length of the eyeball
 Cornea may be slightly smaller than normal,
may be cornea plana
 Anterior chamber is comparatively shallow since
the eyeball is small and the size of lens varies very
little and angle is narrow (predisposition to narrow
angle glaucoma)

16. FUNDUS EXAMINATION
 Optic disc may appear small and hyperaemic
with ill-defined margins and may mimic papillitis
 The vascular reflex may be accentuated and
the vessels may show undue tortuosity and
abnormal branching
 Foveal reflex may be situated at greater
distance from disc margin.
 The retina as a whole may shine due to
greater brilliance of light reflection (shot silk
appearance)

17. COMPLICATIONS
 Recurrent styes, blepharitis or chalazion
 Accommodative convergent squint
 Amblyopia
 Anisometropic
 Strabismus
 Uncorrected bilateral high hypermetropia
 Predisposition to develop primary narrow
angle glaucoma

18. MANAGEMENT
 Optical treatment
 Surgical treatment
 Visual hygiene

19. OPTICAL TREATMENT
 Basic principle is to prescribe convex lenses, so
that the light rays are brought to focus on the retina
 Total amount of hypermetropia should always be
discovered under complete cycloplegia
 Total manifest refractive error when small (≤1D),
correction is given only if the patient is
symptomatic
 Spherical correction given should be comfortably
acceptable to the patient.

20. CORRECTION IN CHILDREN
 Children < 4 years usually accept full cycloplegic measurement
 Once child reaches the school age, consider reducing the plus
power by about 1/3, but the child should not accommodate more
than 2.5D continually for distance
 Child may not accept the power prescribed. So, always first
under correct that the child accepts comfortably. Gradually
increase the correction at 6 months interval.
 If there is associated exophoria, hypermetropia is corrected by
1-2D
 In presence of accommodative convergent squint, full correction
should be given in the first sitting
 It is important to remember that hypermetropia may diminish
with the growth of the child, so refraction should be carried out
every 6 months

21. CORRECTION IN ADULTS
 Manifest hypermetropia is corrected
 Absolute + Facultative
 Maximum power with clear vision should be
prescribed which the patient is comfortable with

22. SURGICAL CORRECTION
 Conductive keratoplasty/corneal refractive
therapy
 Laser thermal keratoplasty
 Photorefractive Keratectomy
 Hyperopic LASIK
 Phakic IOLs
 Refractive lens exchange

23. VISUAL HYGIENE
 While reading or doing intensive near work,
take a break about every 30 mins
 Maintain proper reading distance
 Sufficient illumination
 Limit on time spent watching TV, videogames
 Sit 5 – 6 feet away from TV

24. MYOPIA
 State of refraction where parallel rays of light
entering the eye are focused in front of retina
with accommodation being at rest

25. CLASSIFICATION
 Aetiological types
 Clinical types

26. AETIOLOGICAL TYPES
 Axial myopia
 Curvatural myopia
 Index myopia
 Positional myopia
 Myopia due to excess accommodation

27. CLINICAL TYPES
 Congenital myopia
 Simple or developmental myopia
 Degenerative or pathological myopia
 Acquired myopia

28. CONGENITAL MYOPIA
 Common in premature babies or with birth
defects
 Stationary (8-10D)
 Associated with
• Increase in axial length
• Esotropia
• Other congenital anomalies of eye
 Early and full correction under cycloplegia
 Poor prognosis in unilateral cases with
severe myopia and anisometropia

29. SIMPLE MYOPIA
 Physiological/ school myopia
 Commonest type
 Results due to normal biological variations in
development of eye
 Age of onset is 7-10 yrs
 Moderate severity of <5D, never exceeds 8D

30. DEGENERATIVE MYOPIA
 Progressive in nature
 Related to heredity, general growth process
 Heredity linked growth of retina
 Factors affecting general growth process
 Age of onset is early adult life
 Severe >6D

31. SYMPTOMS
 Distant blurred vision
 Half shutting of eyes
 Asthenopic symptoms
 Muscae volitantes
 Night blindness
 Divergent squint

32. SIGNS
 Prominent eyeballs
 Large cornea
 Anterior chamber is deep
 Large & sluggishly reacting pupil

33. FUNDUS EXAMINATION
 Optic disc : appears large and pale & at its temporal edge,
myopic crescent.

34.  Sub retinal neovascularization
 Sub retinal hemorrhage

35.  Posterior staphyloma
Foster – Fuchs's spots

36. COMPLICATIONS
 Macular hemorrhage
 Retinal tears, detachment
 Vitreous hemorrhage
 Choroidal hemorrhage
 Complicated cataract
 Nuclear sclerosis
 Primary open angle glaucoma

37. MANAGEMENT
 Optical treatment
 Surgical treatment

38. OPTICAL TREATMENT
 Basic principle is to prescribe concave lenses, so
that the light rays are brought to focus on the retina
 Minimum acceptance providing maximum vision
 HIGH MYOPIA - undercorrection is done to avoid
• near vision problem
• minification of images
 Contact lenses are better

39.  LOW MYOPIA(<6D):Young children, glasses required only if
• Isometropia
<2years ≥ -4.0D
2-3years ≥ -3.0D
• Anisometropia:
≥ -2.5D
• Give full correction under cycloplegia
• Avoid overcorrection
 LOW MYOPIA(<6D): Adults
• <30years-full correction
• >30years-less than full correction with which patient is
comfortable for near vision

40. SURGICAL CORRECTION
 Radial keratotomy
 Lamellar corneal refractive procedures
 Laser based procedures
• PRK, LASIK, LASEK, C-LASIK, E-LASIK
 Miscellaneous corneal refractive procedures
• Orthokeratology
• Intracorneal contact leses
• Intra stromal corneal ring segments
• Gel injectable adjustable keratoplasty
 Intraocular refractive procedures
• Phakic refractive lenses
• Refractive lens exchange

41. ASTIGMATISM
 State of refraction where parallel rays of
light from a point source fail to meet in a focal
point, but form focal lines, resulting in a blurred
and imperfect image
 Types
•Regular astigmatism
•Irregular astigmatism

42. REGULAR ASTIGMATISM
 Refractive power changes uniformly from
one meridian to another principal meridian
 Depending upon axis and angle between
the two principal meridian
• With-the-rule astigmatism
• Against-the-rule astigmatism
• Oblique astigmatism
• Bi-oblique astigmatism

43. TYPES
 Simple astigmatism
• Simple hyperopic astigmatism
• Simple myopic astigmatism
 Compound astigmatism
• Compound hyperopic astigmatism
• Compound myopic astigmatism
 Mixed astigmatism

44. ETIOLOGY
 Corneal astigmatism - curvatural [common]
 Lenticular is rare. It may be:
• Curvatural - lenticonus
• Positional - tilting or oblique placement
of lens, subluxation
 Retinal - oblique placement of macula [rare]

45. SYMPTOMS
 Blurring of vision
 Asthenopic symptoms
 Tilting of head
 Squint

46. INVESTIGATIONS
 Retinoscopy
 Keratometry
 Computerized corneal tomography
 Astigmatic fan test
 Jackson cross cylinder

47. MANAGEMENT
 Optical treatment
• Spectacles
• Contact lenses
 Surgical treatment
 Small astigmatism- treatment is required only
• In presence of asthenopic symptoms
• Decreased vision
 High astigmatism- full correction
• Better to avoid new astigmatic correction in adults
because of intolerable distraction
• Bi-oblique, mixed, high astigmatism are better
treated by contact lenses

48. IRREGULAR ASTIGMATISM
 Irregular change of refractive power in
different meridia

49. ETIOLOGY
 Corneal irregular astigmatism
• Scars
• Keratoconus
• flap complications
• marginal degenration
 Lenticular irregular astigmatism
• Cataract maturation
 Retinal irregular astigmatism
• scarring of macula
• tumours of retina
• choroid

50. SYMPTOMS
 Defective vision
 Distortion of objects
 Polyopia

51. INVESTIGATIONS
 Placido's disc test reveals distorted circles
 Computerized corneal topography

52. MANAGEMENT
 Optical treatment
• Contact lenses
• Scleral lenses
• Piggyback lens
 Surgical treatment
• Penetrating keratoplasty

53. THANK YOU