Refractive Errors of eye


Refractive  Errors
Refractive error is the most common visual problem
This defect prevents light rays from converging into a single focus on the retina


Refraction of light occurs when light passes from one medium to another of different refractive index (ie. density)
Refractive Components of the Eye: Cornea, Aqueous humor, Lens, Vitreous humor


MYOPIA (Near Sightedness)

·         Causes light rays to be focused in front of the retina
·         Myopia may occur because of excessive light refraction by the cornea or lens or because of an abnormally long eye.
·         There is inability to accommodate for objects at a distance
HYPEROPIA (farsighted)    

·         Causes the light rays to focus behind the retina & requires the patient to use accommodation to focus the light rays on the retina for near & far objects.
·         This type of refractive error occurs when the cornea or lens does not have adequate focusing power or when the eyeball is too short.



·         Is caused by an irregular corneal curvature
·         This irregularity causes the incoming light rays to be bent unequally.
·         Consequently, the light rays do not come to a single point of focus on the retina.        Occur in conjunction with any of the other refractive errors.



·         Is the loss of accommodation associated with age.
·         This condition generally appears at about age 45yrs.
·         As the eye ages, lens becomes larger, firmer & less elastic
·         These changes, which progress with aging, decrease the eye's accommodating ability
·         There is an inability to accommodate for near objects


·         Is defined as the absence of the lens.
·         The lens may be absent congenitally or it may be removed during cataract surgery or a perforating wound or ulcer.
·         The absence of the lens results in a significant refractive error
·         Without the focusing ability of the lens, images are projected behind the retina.

a. Nonsurgical Corrections
l. Corrective glasses
·         Myopia- minus corrective glasses (concave) 
·         Hyperopia-plus corrective lens (convex)
·         Presbyopia -plus corrective lens (convex)/ Reading glasses
·         Presbyopia+myopia or astigmatism- combined glasses with bifocal or trifocal lower glasses OR 'no-line' bifocal (multifocal)
·         Aphakia- plus corrective lens (convex) which are very thick, heavy and unattractive.
2.Contact lenses
·         Provide better vision than glasses
·         Made from various plastic and silicone substances
·         The person must remove contact lenses immediately, if any of the following problems occur..
o   l. Redness
o   2. Sensitivity
o   3. Vision problems
o   4. Pain

Types of contact glasses
 Rigid Lenses:
1.       Standard Rigid Lenses
·         Rigid plastic; smaller than cornea.
·         Long lasting, least expensive to purchase; corrects all types of pass through the cornea refractive errors.
·         Daily wear.    
·         Requires separate care solution

2.       Gas Permeable rigid lenses
·         Similar, but plastic allows oxygen to pass through the cornea
·         Long lasting, more comfortable;  flexible wearing schedule.
·         More expensive and requires separate care solution
 Soft Lenses:
·         Standard
·         High water content
·         Toric
·         Disposable
·         Daily disposable
Corneal molding, also called as orthokeratology, is the sue of specially designed, rigid, gas permeable contact lenses to alter the shape of the cornea.

These are designed to eliminate or reduce the need for eyeglasses or contact lenses and correct refractive errors by changing the focus of the eye.
Surgical management include
·         Laser surgery
·         Intraocular lens (IOL) implantation
·         Thermal procedures

l. Laser assisted in situ keratomileusis (lasik)
·         For patients with low to moderately high amounts of myopia, hyperopia, and astigmatism.                
·         Using a laser or surgical blade to create a thin flap in the cornea.
·         Using new technology called 'wave-front' the laser is then programmed to use a map of the patient's cornea to sculpt the cornea and correct the refractive error.
·         The flap is then repositioned and adheres on its own without sutures in a few minutes.
·         placed in front of the natural lens.

2.         Thermal procedures
·         Laser thermal keratoplasty (LTK)  
·         Conductive keratoplasty (CK)
·         For patients with hyperopia or presbyopia
·         Using laser or high radio frequency, heat is applied to the peripheral area of the cornea to tighten it like a belt and make the central cornea steeper.
·         Only the less dominant eye is treated

3.         Photorefractive keratectomy (PRK)
·         Indicated for low to moderate amounts of errors.
·         Good option for a patient with insufficient corneal thickness for LASIK flap.
·         Only the epithelium is removed and the laser sculpts the cornea to correct the refractive error

·         Intra corneal ring segments (ICRs) are 2 semi-circular pieces of plastic that are implanted between the layers of the cornea to treat mild myopia
·         Refractive intraocular lens (refractive IOL) for patients with high degree of myopia or hyperopia. Involves removal patients natural lens and implantation of IOL
·         Phakic intraocular lenses (phakic IOLs) for patients with high degree of myopia or hyperopia. IOL is placed in front of the natural lens.

4.         Thermal procedures
·         Laser thermal keratoplasty (LTK)
·         Conductive keratoplasty (CK)
For patients with hyperopia or presbyopia
Using laser or high radio frequency, heat is applied to the peripheral area of the cornea to tighten it like a belt and make the central cornea steeper.
Only the less dominant eye is treated



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item Refractive Errors of eye
Refractive Errors of eye
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