OPTIC

EYES

The eye is one of the most complex parts of the body. The different parts of the eye allow the body to take in light and perceive objects around us in the proper color, detail and depth. This allows people to make more informed decisions about their environment. If a portion of the eye becomes damaged, you may not be able to see effectively, or lose your vision all together. Eyes are one of the five senses which is the only means of optical natural living things. Optical instrument is not God's gift to the less sophisticated tools of modern optics. The lens in our eye is the fastest lens when focusing an object to make it look obvious. There is no one tool that could rival any speed created an object. 

 

There are several physical and chemical elements that make up the eye. The eye is also heavily involved with the nervous system, which allows the brain to take in information from the eyes and make the appropriate decisions on how to act upon this information. The nerves must be kept in prime condition or the brain may start to receive false images, or you will not take in enough information to get an accurate perception of your environment.

Eye Parts	Description and Functions
Cornea	The cornea is the outer covering of the eye. This dome-shaped layer protects your eye from elements that could cause damage to the inner parts of the eye. There are several layers of the cornea, creating a tough layer that provides additional protection. These layers regenerate very quickly, helping the eye to eliminate damage more easily. The cornea also allows the eye to properly focus on light more effectively. Those who are having trouble focusing their eyes properly can have their corneas surgically reshaped to eliminate this problem.
Sclera	The sclera is commonly referred to as the "whites" of the eye. This is a smooth, white layer on the outside, but the inside is brown and contains grooves that help the tendons of the eye attach properly. The sclera provides structure and safety for the inner workings of the eye, but is also flexible so that the eye can move to seek out objects as necessary.
Pupil	The pupil appears as a black dot in the middle of the eye. This black area is actually a hole that takes in light so the eye can focus on the objects in front of it.
Iris	The iris is the area of the eye that contains the pigment which gives the eye its color. This area surrounds the pupil, and uses the dilator pupillae muscles to widen or close the pupil. This allows the eye to take in more or less light depending on how bright it is around you. If it is too bright, the iris will shrink the pupil so that they eye can focus more effectively.
Conjunctiva Glands	These are layers of mucus which help keep the outside of the eye moist. If the eye dries out it can become itchy and painful. It can also become more susceptible to damage or infection. If the conjunctiva glands become infected the patient will develop "pink eye."
Lacrimal Glands	These glands are located on the outer corner of each eye. They produce tears which help moisten the eye when it becomes dry, and flush out particles which irritate the eye. As tears flush out potentially dangerous irritants, it becomes easier to focus properly.
Lens	The lens sits directly behind the pupil. This is a clear layer that focuses the light the pupil takes in. It is held in place by the ciliary muscles, which allow the lens to change shape depending on the amount of light that hits it so it can be properly focused.
Retina	The light focuses by the lens will be transmitted onto the retina. This is made of rods and cones arranged in layers, which will transmit light into chemicals and electrical pulses. The retina is located in the back of the eye, and is connected to the optic nerves that will transmit the images the eye sees to the brain so they can be interpreted. The back of the retina, known as the macula, will help interpret the details of the object the eye is working to interpret. The center of the macula, known as the fova will increase the detail of these images to a perceivable point.
Ciliary Body	Ciliary body is a ring-shaped tissue which holds and controls the movement of the eye lens, and thus, it helps to control the shape of the lens.
Choroid	The choroid lies between the retina and the sclera, which provides blood supply to the eye. Just like any other portion of the body, the blood supply gives nutrition to the various parts of the eye.
Vitreous Humor	The vitreous humor is the gel located in the back of the eye which helps it hold its shape. This gel takes in nutrients from the ciliary body, aqueous humor and the retinal vessels so the eye can remain healthy. When debris finds its way into the vitreous humor, it causes the eye to perceive "floaters," or spots that move across the vision area that cannot be attributed to objects in the environment.
Aqueous Humor	The aqueous humor is a watery substance that fills the eye. It is split into two chambers. The anterior chamber is located in front of the iris, and the posterior chamber is directly behind it. These layers allow the eye to maintain its shape. This liquid is drained through the Schlemm canal so that any buildup in the eye can be removed. If the patient's aqueous humor is not draining properly, they can develop glaucoma.

  

The Image Formation in eyes

Our eyes can see when there are objects that reflect light entering the eye. The light is then refracted by the lens of the eye so that the image formed on the retina. The image formed by the lens of the eye is real inverted and scaled. The shadow is then transmitted to the brain by the optic nerve so that we can see and respond. Here's an illustration of the formation of the optical instrument . 

Accommodation power   

The distance between the lens of the eye is the retina remains will never change unless permanent damage. To see objects lying fickle, convex eyepiece should be changed. By changing the curvature of the lens is to change the distance of the lens focus. When the eyes see objects that are far away, the eye muscles are relaxed and the lens of the eye becomes more flat (thinning). Conversely, when the eyes see objects that are very close, in a state of contraction of the eye muscles and eye lenses become more convex (thicken). Thickening and thinning is intended that the eye shadow can fall right in retina so it can be seen clearly. Well, the ability to thicken and the depletion of the eye lens is called the power of accommodation of the eye.

PP and PR

Optical devices have a restricted range of eye see objects. We know there is much point his name near the eye and the eye point. Eyes Far point (punctum remotum) is the furthest point of the eye that can still be seen with the eye in a state of berakomodasi. Near the eye point (punctum proximum) is the closest point of the eye that can still be seen clearly by eye in a state of maximum accommodation. Normally a point distant normal adults is not infinite and the closest point is 25 cm. If a point distant or near the point of no longer seseuai with normal size then the sign of optical instruments naturally we experienced eye defects. There is a picture that show the PP and PR in different eyes.

 

Disorders of the Eye

Refractive errors of the eye are seen in 20 percent of children and have been found to run in families. The most common refractive errors are astigmatism, hyperopia (farsightedness) and myopia (nearsightedness).

11.  Hyperopia

Hyperopia is a condition in which an image of a distant object becomes focused behind the retina; making objects up close appear out of focus. The characteristics of patients with nearsightedness is he cannot see clearly objects that are located close eye though was maximum accommodation. The cause is not the eye lens can become convex properly so that the rays from close objects will cast a shadow in the back of the retina. People with nearsightedness can be helped by using glasses (optical instrument) or positive convex lens. The power of the lens that can be used depending on the patient hyperopia point near the patient. In order to view objects at a normal reading distance (25 cm), then the patient must use a farsighted eyeglass lenses that produce shadows in front of the lens at a distance equal to a point near the patient

12. Myopia

      Myopia is a condition in which, opposite of hyperopia, an image of a distant object becomes focused in front of the retina, making distant objects appear out of focus. Myopia is the most common refractive error seen in children and can be corrected with eye glasses or contact lenses. A person who has a disability eye nearsighted cannot see distant objects clearly. This eye defect caused the eye lens cannot be flattened well so that parallel rays coming from objects falling in front of the retina. Point the patient is far less than infinity. People with nearsightedness (myopia) can be helped by using glasses with concave lenses or negative. The amount of lens power (diopters) used very nearsighted patients far point depend on the patients. In order to see objects at a distance of infinity as normal eye, nearsighted patients should use a concave lens which produces a shadow in front of the lens at a distance equal to the far point the patient. So the distance of virtual shadow is formed s’ = point away patients

 3. Astigmatism 

 Astigmatism is a condition in which an abnormal curvature of the cornea can cause two focal points to fall in two different locations, making objects up close and at a distance appear blurry. People with astigmatism are not able to see the lines and vertical horizontal together. The reason is the shape of the cornea is not spherical but rather curved in one area than in other areas. Astigmatism suffers can be helped with optical instrument such as silindris lens. Only an eye care professional can accurately detect, diagnose and treat astigmatism. That's why it's so important to test children who may not know they're having a vision problem, and why routine comprehensive eye care exams are vital to maintaining healthy vision and healthy sight. Astigmatism treatments help the eyes focus images correctly on the retina at near, middle and far distances. This can be accomplished through prescription eyeglasses, contact lenses or in some instances, through the use of surgery that reshapes the cornea of the eye. Each astigmatism treatment option has benefits and drawbacks that should be discussed completely with an eye care professional.

 

14. Presbyopia

In Presbyopia, a person’s eye progressively diminishes in its ability to focus on near objects with age. The exact mechanism that causes this “loss” in focusing ability is not completely proven. However, most researchers believe that the crystaline lens inside the eye loses its flexibility with age as an early cataract begins to form. It is a defect of the eye in which sufferers have not been able to see well objects at a great distance and very close. Patients have much less than infinite point and near point greater than 25 cm. This loss in flexibility directly causes a loss in person’s ability to focus. Similar to grey hair, presbyopia is a symptom that everyone experiences as they age. The first symptoms are usually noticed by 38 years of age and present to us as headaches.

Treatment for presbyopia has advanced significantly in recent years with many options now available to our patients. Some of the following options you may find helpful as follows.

1.      Reading Glasses

Over the counter reading glasses are sold to many people in drug stores, and in dollar stores. They are an effective form of treatment for people who see well in the distance. Of course, these do not work for near sighted individuals, and only work well for far sighted individuals who have small degrees of far sightedness.

2.      Contact Lenses

This is a very effective form of treatment that can be tried during a contact lens examination

3.      Bifocal Glasses

This works very well for most people. The top portions of the glasses are for seeing in the distance and the bottom portions of the lenses are for seeing up close. The two main types of bifocal glasses are glasses with and without a line. A progressive addition lens does not have a line. Lots of people prefer the “no line” or progressive lens because it is cosmetically pleasing. However, we prefer the lined bifocal because it is easier for a patient to adapt too. During the routine eye examination, a prescription is always given to the patient, and bifocal glasses are an excellent option for glasses.