Refractive errors: Types, Symptoms and Treatment

Refractive errors are eye conditions that causes the eyesight problems to the patient. The Patient will be suffering from the symptoms like blurry vision and Headache. These errors are mainly due to the alteration in the shape of the eyeball, cornea or the lens. Based on this there are different types of the Refractive errors.

Myopia

• It is also called short-sightedness and the refractive power in the eye is more than required.
• This disease affects the distance vision of the patient and the patient can see objects that are near, but it will be difficult for the patient to see the objects that are further away.
• The light rays focus in front of the retina and this defect is corrected by using a concave lens. The concave lens will direct the light on the retina.
• It is always indicated with a negative sign which tells us how much decrease is required to correct it.

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Types of Myopia 

• Axial Myopia- the axial length of the eye is more.
• Curvature Myopia- there is an increase in the curvature of the cornea.
• Index Myopia- The refractive index of the lens is higher than the average value.
• Positional Myopia- it is due to the anterior lens dislocation.

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Symptoms

• Patients will not be able to see far objects clearly, there will be a blurry vision for far objects in myopic patients.
• Headache
• Eyes Strain
• Tiredness when seeing far away
• Poor performance of young children in school
• The patient with myopia has long eyes, a thin sclera, and a deep anterior chamber.
• Ciliary muscle atrophy
• Retinal changes can be observed.

Complications of Myopia

• Cataracts
• Glaucoma
• Retinal detachment

Diagnosis

Standard eye exams are done to diagnose myopia.

Treatment

• Spectacles and contact lenses with the correct power can be used to treat the disorder.
• Surgeries are also helpful to correct the refractive power of the eye.
•  LASIK is a laser-assisted in situ keratomileus procedure that is the most common surgery for correction of near-sightedness.

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Myopia treatment

Hypermetropia 

• It is also called Farsightedness.
• The refractive power of the eye is less than required.
• The light rays focus behind the retina.
• It is corrected with a convex lens which will direct the light rays on the retina
• It is indicated with a positive sign to show how much increase is required to correct it.

  Hypermetropia 

Types of Hypermetropia

• Axial Hypermetropia- Lesser axial length
• Curvature Hypermetropia- Lesser curvature of the lens
• Index Hypermetropia- index decreases due to old age
• Positional Hypermetropia- posterior dislocation of the lens

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Total Hypermetropia

• It is of two types: latent and manifest hypermetropia
• Latent hypermetropia is due to ciliary body tears and Manifest hypermetropia can either be due to facultative (can be overcome by an accommodation) or absolute (cannot be overcome by accommodation).

Symptoms Of Hypermetropia

• Headache
• Blurred vision
• Far vision affected 
• Small-sized eyeball
• Weakness in ciliary muscle
• Tiredness in the eyes
• Watering of eyes

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Examination

• On examination, the eye is small with a flatter cornea and a shallow anterior chamber.
• A shiny retina that is a shot silk retina will be observed.
• Convergence squint can be seen because of excessive accommodation.

Treatment

• Spectacles or contact lens
• Refractory surgeries like Lasik
• High-degree hypermetropia is corrected with intraocular lens implantation

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Astigmatism

• Astigmatism occurs when there is a difference in refractive power between the 2 principal axes.
• There are multiple focal points and two different image forms.
• Astigmatism occurs when the corneal lens is curved more steeply in one direction than the other. 

Types of Astigmatism

• Simple Hypermetropic
• Simple Myopic
• Compound Hypermetropic
• Compound Myopic
• Mixed Astigmatism

Types On the basis of the position of the axes

• Oblique Astigmatism- if the two axes are perpendicular to each other but are not at 90° and 180° in the eye.
• Bi-oblique Astigmatism- if the angle is less than 90°. 

Types based on power

• Regular Astigmatism- when the power is constant over a single axis, it is regular astigmatism.
• Irregular Astigmatism- if there is variation in a single axis.

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Symptoms Of Astigmatism

• The patient will complain of blurred vision and eyestrain.
• Headaches
• Difficulty with night vision
• Squinting
• Distorted vision

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Treatment

• Cylindrical spectacles with the correct power can be used to correct this disorder.
• Severe cases are treated with intraocular lens implantation.
• Refractive surgery can be used.

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Aniseikonia

• There will be a difference in the image size of the two eyes.
• The physiological difference between image sizes is 5% and this helps in-depth perception but here an image difference of more than 5% leads to this disease.
• The Isekonia glasses are used to treat it.

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