Myopia
Introduction
The structure of your eye is to blame. When your eyeball is too long or the cornea -- the protective outer layer of your eye -- is too curved, the light that enters your eye won’t focus correctly. Images focus in front of the retina, the light-sensitive part of your eye, instead of directly on the retina. This causes blurred vision. Doctors call this a refractive error.
High myopia: It’s a more serious form of the condition, where the eyeball grows more than it is supposed to and becomes very long front to back. Besides making it hard to see things at a distance, it can also raise your chance of having other conditions like a detached retina, cataracts, and glaucoma.
Degenerative myopia: Also called pathological or malignant myopia, it is a rare type you usually inherit from your parents. Your eyeball gets longer very quickly and causes severe myopia, usually by the teenage or early adult years. This type of myopia can get worse far into adulthood. Besides making it hard to see things at a distance, you may have a higher chance of having a detached retina, abnormal blood vessel growth in the eye (choroid neovascularization), and glaucoma.
Symptoms
Chances are the only symptom is that more distant objects are blurred. You may also notice:
Headaches
Squinting
Eye strain
Eye fatigue when you try to see objects more than a few Feet away
Children with myopia often have trouble reading the blackboard at school.
Diagnosis and Treatment
An eye exam can show you if you’re myopic. Glasses, contacts, or refractive surgery can usually correct the problem.
When you have myopia, your prescription for glasses or contact lenses will be a negative number. The more negative the number, the stronger your lenses will be. For example, -3.00 is stronger than -2.50.
Your prescription helps the eye focus light on your retina. That clears up your vision.
Eye surgery can improve your vision so much you may no longer need to wear glasses or contacts. The most common procedures for myopia are:
Photorefractive keratectomy: Also called PRK, this surgery uses a laser to sculpt the middle layer of your cornea. That flattens the cornea’s curve and lets light rays focus closer to or on your retina.
LASIK: This is the most common surgery for myopia. The surgeon uses a laser or another tool to create a thin flap on the top layer of your cornea. They sculpt the cornea with another laser and move the flap back into place.
EVO Implantable Collamer Lens (ICL): Using a microscopic incision, a contact lens made of a soft, polmeric materialis implanted into your eye between you natural lens and your iris. It helps refract light on the retina, producing clearer vision.
In the case of high myopia, special contacts or atropine eyedrops have been found to be effective in slowing the progression. In some cases, your doctor may suggest cataract or clear lens replacement surgery.
Does It Get Better Over Time?
Myopia runs in families and will probably start in childhood. Multifocal lens (glasses or contacts) and eye drops such as atropine, pirenzepine gel, or cyclopentolate can help slow the progression. Your eyes usually stops changing after your teenage years, but not always. The incidents of myopia have been rising at an alarming rate in recent years. If you notice changes in your vision, get your eyes checked. See your eye doctor every year.
Optics of Myopia
Before discussing Optics of Myopia we should ratify parishioner phrase in Myopia. Briefly, the uncorrected myopia or nearsighted person. Usually can see up close better than far away. Hence, the term “nearsighted” make sense.
Derived from two Greek root words from myein “to shut” – ops “eye”.
Myopia is the refractive state of the eye in which with normal tonic accommodation, the parallel rays of light are brought to a focus on a point in front of the retinal plane when the eye is at rest.
In myopia the eyeball is usually deformed ; the deformation occurs at the posterior part of the globe only ,the anterior part is normal. The eyeball is usually large and looks prominent. When adducted the equator can be seen.
Refractive Error Definition
A refractive error is a very common eye disorder . It exists when the rays of light do not focus on the retina means the eye cannot clearly focus the images from the outside world .
The eye’s optical system is to powerful over converging light in front of the retina . ( Myopia/Nearsighted)
The result of refractive errors is blurred vision, double vision , haziness or eye strain . which is sometimes so severe that it causes visual impairment .
Optics of Myopia: In myopes a near object may be focused without any effort of accommodation if it is situated at the punctum remotum . The image on the retina of an object at infinity is made up of circles of diffusion formed by divergent beam.
In view of the absence of sharp focus the distant objects appear blurred. The nodal point in myopes is farther away from the retina and the image formed is larger in size which partly compensates for the blur due to absence of sharp focus .
Accommodation is of little value to myopes, as any exercise of accommodation would only accentuate his visual problem . It would neither increase his vision nor reduce his myopia . In higher errors of refraction the amplitude of accommodation is small.
The patient has no incentive to improve it and convergence does not get an accommodative influence . All these factors result in fatigue of accommodation and eye strain. Due to dissociation of convergence and accommodation exophoria commonly occurs and this may ultimately break into exotropia.
The eye of simple myopia is large and prominent. The Anterior chamber is deeper than normal and the pupil reacts sluggishly to light. The macula is slightly nearer to the disc than in a normal eye .
The visual axis gets so altered that in some cases the angle alpha becomes slightly negative which gives an impression of a convergent squint . In myopia more commonly one sees a divergent strabismus.
Optical System
The optical system is too powerful for it’s axial length , over converging light in front of the retina ( myopia / nearsighted).
Image of Distant Object
Image of distant object on retina is made up of circle of diffusion formed by divergent beam since the parallel rays of light coming from the infinity are focused in front of the retina.
Far Point of the Myopic Eye : Far point is finite point in front of eye . The far point of myopic eye is 70 cm.
Nodal Point : Nodal point is further away from retina . The nodal point of human eye is located 17 mm in front of the retina.
Accommodation : Accommodation in uncorrected myopes is not developed normally , they may suffer from convergence insufficiency , exophoria and early presbyopia as they grow.
Image Formation: In myopia image formed in front of eye which is corrected by placing the negative lenses .
Optical Treatment : Include prescription of appropriate concave lens minimum acceptance providing maximum vision should be prescribed .
Never Overcorrected myopia
Guidelines For Correcting Low Degree Of Myopia Upto-6D :
Children younger than 8yrs should be fully corrected and instructed to use their glasses constantly.
Adult younger than 30 years :
Usually accept their full correction .
Older than 30 years :
Not able to tolerate a full correction with which the patient feels comfortable .
Prescribe less than full correction with which the patient feels comfortable.
