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emmetropia

-eye that lacks visual defects.-image that is formed on persons retina is clear and precise.-a persons eye is free of refractive error.

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Accommodation of eye

-process by which the vertebrate eye changes optical powerto maintain a clear image (focus) on an object as its distancechanges.-acts like a reflex, but can also be consciously controlled.

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Refractive errors ametropia

- a condition of the eye in which images fail to come to aproper focus on the retina, due to a discrepancy betweenthe size and refractive powers of the eye.

-Myopia

-Hyperopia-Astigmatism-Presbyopia

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myopia

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Definition

-Nearsightedness

-is when light entering the eye is focused incorrectly, makingdistant objects appear blurred.

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Clinical classification

Clinical classification

Simple myopiaNocturnal myopiaPseudomyopia

Degenerative myopia Induced myopia

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Simple myopia

-eye that is too long for its optical power,

-optically too powerful for its axial length.-More common than other type-Generally less than 6 Diopters

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Pseudomyopia

-increase in ocular refractive power due to overstimulation of

the eye's accommodative mechanism or ciliary spasm-

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Degenerative myopia

- high degree of myopia associated with degenerative

changes in the posterior segment of eye-degenerative changes can result in abnormal visual function,such as a decrease in best corrected visual acuity orchanges in visual fields.

-Sequelae- retinal detachment- glaucoma

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Induced myopia

-result of exposure to various pharmaceutical agents,

variation in blood sugar levels, nuclear sclerosis of thecrystalline lens,-often temporary and reversible.

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Possible etiology

Type of myopia Etiologies

Simple myopia InheritanceSignificant amount of near workUnknown

Nocturnal myopia Significant levels of dark focus ofaccommodation

Pseudomyopia Accommodative disorderHigh exophoriaCholinergic agonist agent

Degenerative myopia InheritanceRetinopathy of prematurityInterruption of light passing through

ocular media

Induced myopia Age related nuclear cataractExposure to sulphonamidesSignificant variability in blood sugar

level

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Screening and examination

retinoscope

snellen chart retinoscope.

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Management

Type of myopia Management

Simple -prescription for spectacle-high exophoria fulltime wear of the full refractive correction formyopia is warranted- esophoria at near - plus lens addition for near may beappropriate.

-Myopic Astigmatism - prescription when the amount ofstigmatism is 0.50 D or greater

Nocturnal -prescription for minus lenses for use only at night-myopia under normal illumination - prescription for a second

pair of glasses for night time

Pseuomyopia -goal of treatment- relax the patients accommodation.-full minus lens power- not be prescribed for long-term use- treatment - Vision therapy, Instillation of a cycloplegic agent,Near point plus lens addition, Instruction in visual hygiene.

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Degenerative -include appropriate treatment for retinal complications.-Patients should be educated about the symptoms of retinaldetachment.- prescription for spectacle-

Inducedmyopia

Treat the causative agent

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Refractive surgery

- Radial keratotomy (RK)- Photorefractive keratectomy (PRK)- Laser-assisted In-situ Keratomileusis (LASIK)