The eye is shaped as a slightly irregular, hollow sphere that receives light and translates it into images. Light first passes through the cornea, the clear, front “window” of the eye. The cornea’s refractive power bends (refracts) the light rays that move freely through the pupil, the opening in the center of the iris through which light enters the eye. The iris (the colored part of the eye) works like the shutter of a camera, by opening and closing. It has the ability to control the diameter and size of the pupil, thus controlling the amount of light entering the eye. After passing through the iris, the light rays pass through the natural crystalline lens. This clear, flexible structure operates like a camera lens, shortening and lengthening its width . Light rays pass through a dense, transparent gel-like substance, called the vitreous, that fills the globe of the eyeball and helps the eye maintain its spherical shape. In a normal eye, the light rays come to a sharp focusing point on the retina. The retina functions much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses, then sending them to the optic nerve.
The movements of the eyes are controlled by six pairs of muscles located on the outer part of each eye. Under normal circumstances, where both eyes look towards the same direction, one pair of muscles contracts while another relaxes. These pairs of muscles function separately with the intention to keep the eyes in parallel positions and to allow them to move towards all directions.
When the eyes coordinate successfully
For properly functional vision, both eyes must focus on the same element simultaneously. Each eye perceives the same object from a slightly different angle, thus sending two different images to the brain, which are then combined into one unique, three-dimensional image. In a process called convergence, each eyes sees an object from slightly different angles and the brain compares and processes the two sets of information to form a single, three-dimensional image. When both eyes see clearly and the brain processes a single image effectively, it is called stereopsis.
Strabismus – Diplopia – Amblyopia
Strabismus occurs when one eye looks directly towards an object while the other eye looks to a different direction, inwards or outwards. One clear image and one blurry image are both sent to the brain from each eye respectively. These images cannot be combined into one (diplopia) and the brain chooses to ignore the image received from the weaker eye. Thus, the greatest portion of eyesight is through one eye, leaving the weak one to be used much less (amblyopia).
The eyes function fully from the age of six months old, while the brain function that perceives and processes visual stimuli grows until the age of six to seven years old.
Diagnosing visual impairment
Stereoscopic vision can be defined as the visual ability to distinguish depth; good stereoscopic vision implies that both eyes cooperate and function properly making it unlikely for strabismus or amblyopia to develop. In general, the stereoscopic vision exam is the way to diagnose and treat any visual impairment in children.
What is strabismus and how is it caused?
Strabismus describes the condition in which the eyes do not function parallel to each other, meaning that one eye may be misaligned inwards, outwards, upwards or downwards. It usually occurs due to muscle instability.
Some traits that children share during their early development can be perceived as strabismus. For instance, a flat nose during the first months of the life of a child can give the impression that the eyes are pointed inwards. This is called pseudostabismus and it is up to a pediatrician or an ophthalmologist to diagnose it.
Strabismus is usually caused by instability of the eye muscles and bad cooperation of both eyes when perceiving visual stimuli. Family history on strabismus should be taken in considaration as well, since hereditary factors affect this condition.
How often does strabismus occur?
It is quite common for newborn babies to have misaligned eyes during the first weeks of their lives because the muscles are not yet in sync. If this condition persists, the baby should be examined. Strabismus may appear at infant age or later on during childhood or even adult years and it may be constantly noticeable or only when the person is tired, ill or focusing on objects in close proximity.
How is strabismus diagnosed?
Strabismus can be successfully diagnosed from the moment a child is born. As soon as the parents detect signs of strabismus, they should contact a doctor. Waiting until the child first goes to school can deem treating strabismus less effective. Medical history usually provides the necessary signs for the appearance of strabismus.
Ophthalmological exams for strabismus
Cover test: to determine the presence, type, and magnitude of ocular misalignment (strabismus). Two distinct methods can be used for the test. First, the single cover test to identify strabismus or pseudostrabismus. Second, the alternate cover test where the examiner occludes one eye and then the other, switching the occluder back and forth to occlude the eyes without allowing the patient to fuse in between occlusions. The patient is instructed to remain fixated to a specific object. If the non-covered eye moves to see the object then the patient suffers from strabismus.
Lang Stereo Test, Bagolini striated glasses test and red green glasses: These provide information regarding the quality of stereoscopic vision (normal and abnormal retina response).
Visual acuity and gaze test: This exam is essential for the interpretation of the cover test and the stereoscopic vision exam. The parents should perform these exams to their child to fully assess their visual function.
Since the 1960s it has been widely known that prompt and accurate diagnosis of any visual problem at a young age can lead to effective treatment and provide the patient with well-functioning eyes for the rest of its life.
The false belief that strabismus is self-treated as the child grows older comes from the fact that many newborns have pseudostrabismus, which deteriorates as they grow and as their nose becomes shaped. Unless treated on time, strabismus may not only cause visual deterioration but it may also lead to permanent loss of vision.
However, each case is unique and calls for a different treatment. In the best case, that will just include eye drops and exercises. If the situation calls for a more radical treatment, a combination of eye patch with or without glasses and in some cases surgery will be applied. It should be noted that parental support is crucial to strabismus treatment.
Glasses are sometimes prescribed to stabilize the gaze
How is strabismus treated with glasses?
For a farsighted child with strabismus, glasses are administered to omit the need for later adjustment. The glasses take over the gaze from the muscles and the eyes gradually come in alignment.
For a shortsighted child, glasses can mitigate sight as well as increase the possibilities of overcoming amblyopia and achieve fusion.
If my child wears glasses will they need an eye patch or an operation?
In some cases, glasses can resolve the problem by aligning the eyes; surgery may still be necessary to achieve full treatment. If the child suffers from amblyopia, both an eye patch and glasses will be prescribed and used.
Why will my child need to wear glasses recurrently if it can see well without them?
In the case of farsightedness, glasses are prescribed to align the eyes and not improve the vision, making it necessary for the child to wear them at all times.
When can my child stop wearing glasses?
The eyes grow with age and they become longer in shape and less farsighted. A child with farsightedness will gradually need weaker lenses usually until the beginning of adolescence. A child with shortsightedness glasses will keep on using them as a focus aid for far objects.
Strabismus operation is a safe and simple procedure, frequently combined with the use of glasses and a patch on the strong eye to fix the muscle coordination. During the operation the tension of the outer muscles is adjusted on one or both eyes to align the eyes. However, if a child of relatively old age undergoes this operation, the eyes may become aligned but fusion cannot be achieved.
What happens to my child during the operation?
The operation takes place in a hospital or ambulatory surgery unit. Blood and urine tests will be performed and there will be a meeting with the ophthalmologist. The anesthesiologist will also be present to give you information regarding the anesthesia that will be used. A sedative will be administered to the child pre-operatively to induce hypersomnia. The anesthesiologist will make sure that the child is asleep throughout the surgery. Postoperatively, there may be a little or no pain and the anesthesia might cause a nausea feeling. Discharge from the hospital will take place on the same day and one or both eyes might be covered with a surgical patch for a short period of time.
When will my child be discharged?
Your child will be discharged possibly on the day of the surgery. The doctor may administer an ointment or eye drops for a few days postoperatively. For approximately two weeks postoperatively, there will be redness in the parts of the eyes where the muscles were adjusted. Within one or two days, the child will be able to return to its everyday routine. Make sure you follow the instructions administered by the doctor.
Will there be more than one operation?
In most cases one surgical procedure is enough to treat strabismus. However, the possibility of a follow up surgery is always present as the adjustment percentage differs from child to child.
Why can’t my child only do the operation without the need to wear glasses afterwards?
The purpose of the operation is to adjust the percentage of the strabismus that cannot be fixed with the use of glasses. Please note that as your child grows older the need for farsight glasses will deteriorate – even maybe to a point that they aren’t necessary anymore. Also, if surgery is performed without the simultaneous use of glasses at a young age, then during adolescence the eyes might start to point at the opposite direction.
Will there be a need for glasses or an eye patch postoperatively?
If the child wore glasses before the surgery, then chances are that it will still need them postoperatively. The aim of the operation is to align the eyes as much as possible as one part of treatment. There is a need for glasses postoperatively and sometimes an eye patch for amblyopia will also be necessary.
Eye exercises – Orthoptics
Orthoptics intent to assist the eyes in moving together and support the image fusion. Consequently, these exercises are beneficial during postoperative recovery or when the eyes of the patient are almost but not completely aligned.
Orthoptics are also used preoperatively to evaluate the child’s fusion ability and prepare the eyes for postoperative fusion.
These exercises are performed under observationfrom an optometrist or an ophthalmologist specialized in orthoptics.
Dr. Kanellopoulos, in cooperation with doctors specialized in pediatric ophthalmology in the USA, has invented a series of eye exercises that may be performed on a computer at home. This is a very advantageous and successful method since children interact with it like a game. Therefore, the usage percentage has gone up and better results are observed in children.
As parents, you can support your child in maintaining good vision by beginning therapy as soon as possible and by following the ophthalmologist’s instructions.
- Vision protection: The chances that your child will have a good vision are better if you seek treatment at an early stage and if you make sure that the eye patch stays in place and the glasses are worn daily.
- Align the eyes: In most cases, surgery will align the eyes of your child. Even in cases when the issue was detected at a later stage, surgery restores the vision of the weak eye.
- Coordinate the function of the eyes: Fusion may be achieved with primary detection and immediate treatment. Unfortunately, that is not always possible for children that were born with strabismus or that had the condition long before treatment. In these cases the eyes may be treated in order to improve the appearance but visual problems will still persist. No matter how well the therapy is performed, perfect image fusion will never be achieved. That does not deprive a child of having a normal life, meaning the ability to play sports or have a successful career.