A presenattion on errors of refraction (Hypermetropia, myopia and astigmatism)

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