13.10.10 refractive disorder

REFRACTION DISORDER

PURNAMANITA SYAWAL

BKMM MAKASSAR

REFRACTION

• Process to measure a patient’s refractive error

• Determine optical correction needed to focus light rays from distant & near objects onto retina

• Provide the patient with clear & comfortable vision

REFRACTIVE MEDIA

1. KORNEA

- Contribute ±2/3 of refracting power

of the eye → 43 D

2. THE LENS

- Contribute 1/3 of refractive power of

the eye → 20 D

- Total convergence power of the eye

58,7 D (not 43 ± 20 D) due to the distance between the cornea & the lens (deep of anterior chamber) that substract → 4 D ( ±63 – 4 D = 58,7 D)

REFRACTIVE MEDIA, cont..

3. THE PUPIL

- Reduce amount of light

enters the eye

- Decrease aberrations

- Increases the depth

of focus when costricting

REFRACTIVE STATES OF THE EYE

• Emmetropia

• Ammetropia

1. Myopia

2. Hyperopia

3. Astigmatism

EMMETROPIA• Emmetropia (normal vision) Eye focusing power perfectly

matched to globe length

• Image focused precisely on retina

• Normal vision confers focal length of infinity

AMMETROPIA

Ammetropia Refractive apparatus (cornea and lens) is

Axial length is

Axial myopia Normal Too long

Refractive myopia Too strong Normal

Axial hyperopia Normal Too short

Refractive hyperopia Too weak Normal

Mismatch between the optical power & length of the eye

Etiology :

MYOPIA (Nearsighness)

• Focused image in front of the retina

CAUSE OF MYOPIA

1. Causes Autosomal dominant inheritance

– Mild Myopia (-0.5 to -2.0 D) by age 5 to 8 years

– Moderate Myopia (-2.0 to -5.0 D) by age 8-14

– Severe Myopia (<-6.0 D) by age 20 to 28 years

2. Environmental Cause (Prolonged reading, close work)

– Mild Myopia (-0.5 to -2.0 D) by age 8-14 years

– Moderate Myopia (-2.0 to -5.0 D) by age 20-28

CAUSE OF MYOPIA cont..

1. Structural or axial myopia Antero-⇒posterior (AP) diameter longer than normal (N)

2. Curvature myopia AP diameter is ⇒normal, but corneal curvature steeper than N

3. Increased index of refraction

4. Anterior displacement of the lens

SYMPTOMS OF MYOPIA• Blurred vision for distance

• Squint (due to blepharospasm- like action to act as a pinhole)

• Headache

• Myopic school → usually detected at 9-10 yo, increase till mid-teens (stable at ≤ S-5,00D)

• Progressive myopia, increase up to -4 D/year,may reach up to -10 D or – 20 D → predispose to retinal detachment & primary open angle glaucoma

HYPEROPIA

• Hyperopia (Farsightedness) Normal in infants (+0.50 to +2.50 Diopters) – Vision normalizes by age 5 to 8 years old

• Light rays focus behind cornea– Cornea too flat or lens too weak for globe– Near objects not seen clearly

• Correction: Convex lenses (convergent, plus power)

CAUSE OF HYPEROPIA

1. Structural or axial hyperopia → AP

diameter shorter than N

2. Curvature hyperopia

3. Index of refraction hyperopia

• LATENT HYPEROPIA : part of the refractive error completely corrected by accomodation, only be measured by cycloplegic refraction & not manifest refraction

• MANIFEST OR ABSOLUTE HYPEROPIA : part of hyperopia not corrected by accomodation

• FACULTATIF HYPEROPIA = MANIFEST HYPEROPIA – ABSOLUTE HYPEROPIA

HYPEROPIAEx : Patient 25 yo, visual acuity 6/20

- Correction with S + 2,00 D → 6/6

- Correction with S + 2,50 D → 6/6

- Correction with cycloplegik S +5,00 D→ 6/6

So, this patient have :

- Absolute hyperopia S +2,00 D

- Manifest hyperopia S + 2,50 D

- Facultatif hyperopia = S +2,50 – S+2,00 = S+0,5D

- Latent hyperopia S +5,00 D – S +2,50 D =

S +2,50 D

SYMPTOMS OF HYPEROPIA

• Blurred vision for distance

• Frontal headache prolonged use of near ⇒vision

• Asthenopia : fatigue, burning eye sensasion & periorbital pain when fixing at an object for prolonged periods of time

• Light sensitivity

• Decreased in near visual acuity at a younger age than in emmetropic eyes

ASTIGMATISM• Astigmatism – Non-spherical

corneal surface– Parts of surface

(meridians) are

steeper than others– Objects blurry at any

distance – The curvature of the optical systrm varies in

different meridians thus refracting the incident ligth differently in those meridians

ASTIGMATISM• With the rule astigmatism : the vertical meridians is

steeper

• Againts the rule : the horizontal meridians is steeper

• Regular astigmatism : Principles meridians are 90 ⁰apart

• Irregular astigmatism : Principles meridians are not 90 apart, can’t be completely corrected by ⁰spectacles,

but with contact lens

REGULAR ASTIGMATISM

SIMPLE ASTIGMATISM

Lens correction C +Lens correction C -

REGULAR ASTIGMATISM

COMPOUND ASTIGMATISM

Lens correction S (-) C (-) Lens correction S (+) C (+)

REGULAR ASTIGMATISM

MIXED ASTIGMATISM

Lens correction S (-) C (+)

S (+) C (-)

SYMPTOMS OF ASTIGMATISM

• Blurred vision for far and near• Squint (for pinhole effect)• Asthenopic symptoms• Frontal headaches• Tilting of the head

TRANSPOSITION OF SPHEROCYLINDRICAL NOTATION

Ex : - 0,75 + 0,50 x 180 -0,25 -0,50 x 90

Ex :

TRANSPOSITION OF SPHEROCYLINDRICAL NOTATION

New sphere = old sphere + old cylinder

New cylinder = old cylinder, but with opposite sign

New axis = old axis changed by 90⁰

MANAGEMENT REFRACTIVE ERROR

1. Management: Refractive Error Correction

Non-Surgical Options (Myopia : concave

lens, hyperopia : convex lens, Astigmatism :

cylinder lens)

- Eye Glasses

- Contact Lenses

2. Refractive surgery

- Laser In Situ Keratomileusis (LASIK)

- Intrastromal corneal ring (ICR)

- Phakic Intraocular Lenses

AMBLYOPIA

• Decreased visual acuity of one eye (uncorrectable with lenses) in the absence of :

- Organic eye disease insufficient enough to

explain the level of vision

- Caused by visual deprivation due to any cause

(congenital or acquired ) during the critical

period of development (up to age 8-9 yo) that

prevents the establisment of normal vision in

the involved eye

CAUSES OF AMBLYOPIA

• Strabismus (most common cause)• Anisometropia• High hyperopia• Opacities : corneal scars, cataract• Optic nerve disease• Retinal disease

LOW VISION

LOW VISION (WHO)

CAUSE OF LOW VISION• Children : Optic atrophy, Congenital, cataract,

Congenital idiopathic nystagmus, Congenital abnormalities of the brain & nerv system

• Early adult life : Stargard’s disease, Retinitis pigmentosa

• Working years: Diabetic retinopathy (>>), Myopia,Uveitis,

Corneal dystrophies, Degenerative condition (cataract & macular disease)

• Retirement : Cataract, AMD, Glaucoma, Retinal detachment

SYMPTOMS OF LOW VISION

• Difficulty in : - reading

- recognize people’s face

- task → fine detailed vision

• Color vision deficits• Contrast sensitivity variably affected• Mobility not affected

LOW VISION AID

• OPTICAL DEVICES :

- Microscopic glassess

- Hand magnifiers

- Stand magnifiers

- Telescope

- Closed-circuit Television

(CCTV)

LOW VISION AID

• NON OPTICAL DEVICES

- Typoscope

- Standing reading book

- Writing frame

- Sunglassess lens

- Large print

- Contrast

ACCOMODATION

• Accomodation mechanism the eye ⇒changes refractive power by altering the shape of its crystalline lens

• The posterior focal point is moved forward in the eye during accommodation so far point moves closer to the eye

ACCOMODATION

• It is the process by the eye changes its refractive power to focus on near objects. It results from increased curvature of lens due to contraction of the ciliary muscle. The stimulus to accomodation is a blurred retinal image.

PRESBYOPIA

• It’s physiologic disease in the amplitude of accommodation associated with aging

• There is less bulging of the lens with accommodation due to a change in the crystalline lens that result in decrease in the elasticity of the lens fiber or hardening of the lens

SYMPTOMS OF PRESBYOPIA

• Larger reading distance required• Inability to focus on close work• Excessive illumination required for close

work

TREATMENT OF PRESBYOPIA

• Add positive lenses correction according to age

- 40 yo : S + 1,00 D

- 45 yo : S + 1,50 D

- 50 yo : S + 2,00 D

- 55 yo : S + 2,50 D

- 60 yo : S + 3,00 D

- > 60 yo : S + 3,00 D