refractive errors.sha.pptx

8/13/2019 Refractive Errors.sha.pptx

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Raisa Janet Ariestha ( I 111 09 041)Refractive Errors


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Refraction is defined as the ratio of the

refractive power of the lens and cornea (therefractive media) to the axial length of theglobe


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Ametropia(refractive error):

There is a mismatchbetween the axiallength of the eyeand the refractive

power of the lensand cornea

Emmetropia(normal sight) : The

ratio of the axiallength of the eye tothe refractivepower of the

cornea and lens isbalanced.


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Refers to the ability to adjust the strength of the lens bychanging its shape, which in turn is regulated by theciliary muscle.

Accommodation involves the lens, zonule fibers, andciliary muscle.

Accommodation


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When the ciliary muscleis relaxed, the ligaments (bands oftissue) attached to the lens pull the lens flat and therefore

less curved and weakly refractive. Contracting the ciliary muscle reduces the tension in the

ligaments, so that the lens assumes a more curved shapebecause of its elasticity.

The greater curvature allows the lens to increase itsstrength, resulting in greater bending of the light rays.

Accommodation

Therefore, in far vision, the ciliarymuscle is relaxed and the lens is

flat, but during near vision, themuscle contracts and allows thelens to become more convex.


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Myopia(Shortsightedness)

Hyperopia(Farsightedness)

Astigmatism

Presbyopia

Refractive Anomalies


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A discrepancy between the refractivepower and axial length of the eye suchthat parallel incident light rays converge at

a focal point anterior to the retina Etiology: not clear. Familial patterns of

increased incidence suggest the influenceof genetic factors

Causes

excessive long globe (axial myopia) : morecommon

excessive refractive power (refractive myopia)

Myopia(Shortsightedness)


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Forms:- Stasioner Myopia/school age myopia

persistent when adult- Progressif Myopiaprogressif although in

adult, because increase eye ball length- Malignant Myopiaprogressif, can make

retinal ablasion and blindness Symptom :- Blurred distance vision

- Squint in an attempt to improve uncorrectedvisual acuity when gazing into the distance

- Space between palpebra is decreased- Headache

Myopia


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Myopia


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Correction of myopia

Myopia


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In hyperopia, there is a discrepancybetween the refractive power and axiallength of the eye such that parallel

incident light rays converge at a focalpoint posterior to the retina

Classification :

- an excessively short globe with normal

refractive power (axial hyperopia)- or, less frequently, to insufficient refractivepower in a normal-length globe (refractivehyperopia)

Hyperopia (Farsightedness)


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Symptoms:

- In young patients, accommodation cancompensate for slight to moderate

hyperopia.

- Asthenopic symptoms such as eye pain orheadache, burning sensation in the eyes,blepharoconjunctivitis, blurred vision, andrapid fatigue.

Hyperopia (Farsightedness)


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Hyperopia


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Correction ofhyperopia

Hyperopia


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The disorder is characterized by a curvatureanomaly of the refractive media such that parallelincident light rays do not converge at a point butare drawn apart to form a line.

Refractive media is not spherical

refractdifferently along one meridian than alongmeridian perpendicular to it 2 focal points (punctiform object is represent as2 sharply definedlines)

Astigmatism


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Classification :1. External astigmatism: astigmatism of the anterior surface

of the cornea.2. Internal astigmatism: the sum of the astigmatic

components of the other media. Astigmatism can also be classified according to the location

of the meridian of greater refraction:1. With-the-rule astigmatism (most common form): The

meridian with the greater refractive power is vertical, i.e.,between 70 and 110 degrees.

2. Against-the-rule astigmatism: The meridian with thegreater refractive power is horizontal, i.e., between 160and 20 degrees.

3. Oblique astigmatism: The meridian with the greaterrefractive power is oblique, i.e., between 20 and 70degrees or between 110 and 160 degrees.

Astigmatism


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Symptoms: Patients with astigmatism seeeverything distorted; asthenopic symptomssuch as a burning sensation in the eyes orheadache.

Regular astigmatism involving only twomeridians approximately perpendicular toeach other.

Irregularastigmatism the curvature and the

refractive power of the refractive media arecompletely irregular. There are multiple focalpoints, which produces a completely blurredimage on the retina

Astigmatism


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Treatment of regular astigmatism: Thepurpose of the correction is to bring thefocal lines of two main meridianstogether at one focal point. This requires alens that refracts in only one plane.Cylinder lenses are required for thisapplication.

Treatment of irregular astigmatism: This

form cannot be corrected with eyeglasses.External astigmatism may be managedwith a rigid contact lens, keratoplasty, orsurgical correction of the refractive error.

Astigmatism


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Presbyopia is an age-related visual impairment

Physiologic loss of accommodation in advancing age- Deposit of insoluble proteins in lens in advancing ageelasticity of lens progressively decreasedecreaseaccommodation

- Decrease cilliary muscle contraction Symptoms : Blurred vision, inability to see fine details ,

delays in focusing at near or distance, oculardiscomfort, headache, asthenopia, squinting, fatigue ordrowsiness from near work

Presbyopia


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The lens of eyeglass that use of patient

presbyopi depend on them age;

+ 1.0 D40 th of age+ 1.5 D 45 th of age

+ 2.0 D 50 th of age

+ 2.5 D

55 th of age+ 3.0 D60 th of age

Presbyopia


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Thankyou

refractive errors.sha.pptx

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