Eyesight, Computers and Refractive Surgery

Problems caused by computers are the second most frequent reason for young healthy people to visit their ophthalmologist. What happens to people that use computers for long hours during the day is basically what is called “asthenopia”, that is difficulties in vision. The second problem is of course problems caused by repetitive movements of the fingers and of the muscles of the arm.

The consequences of computers on vision and the eyes are still under general observation, but any kind of permanent damage hasn't yet been verified.

More than 50% of computer users suffer from eye fatigue, headaches and blurry vision. These symptoms sometimes affect the person's general health, creating a sense of fatigue, which leads to decreased work performance.

There are also some indications that, in rare cases, people working long hours in front of a computer, face an increased risk for glaucoma.

How do computers affect our vision?

When we are viewing a computer screen, what happens is that we lose depth perception, i.e. stereopsis, and our focus is always on a single point. Also, our eye convergence (what happens when we're looking at something really close) is continuously hyperactive and the frequency of blinking is decreased. This is completely different from reading a printed page, since most computer monitors, especially those with a CRT, do not emit a single image, but an image that passes frame by frame and our brain connects it so we can see a continuous image; it is an image with diffused light and has very different contrast and clarity. After using a computer for many hours, what happens is that the cones, the cells we use to perceive colors, are always hyperactive and the image from the cones' hyperactivity stays in our brain, despite the change of image on the computer screen. This is called “after effect” or McCollough effect and sometimes color perception is reversed.

Things that worry us with computer use is if we are exposed to radiation and UV radiation and how much, and if this can potentially lead to cataract. It should be noted that there is proof that the radiation we receive, especially when it comes to UV radiation, is less than that of a fluorescent bulb, so there is no dangerous radiation for the eye and no proof that this can lead to cataract.

Ophthalmological symptoms caused by PC use

Headache during and after PC use
Pain between the eyes
Dry and/or irritated eyes
Blurry vision
Slow focus during screen use

After long hours of PC use there is difficulty in viewing distant objects

Occasional diplopia
Poor color perception

General physical symptoms caused by PC use

Pain in the neck and the shoulders
Back pain
Fatigue, maybe even pain, of the hands and wrists

Decreased work performance, frequent mistakes, fatigue

Ways to avoid such symptoms

The computer monitor should be on a lower level than the eyes.
The keyboard should be in such a position that the bottom of our arms and wrists is parallel to the ground.

The seat should be adjustable, so it can cater to the user's needs.

The thighs, like the arms, should be parallel to the ground.
Contrast and brightness of the screen should be adjusted to the desired setting, so that the user feels comfortable and doesn't tire his eyes.
The lighting in the room must be three times brighter than the monitor.

A screen filter should be used.
It is important to work on a big screen, so it isn't tiring to read or write a text.
Στην οθόνη δεν πρέπει να αντανακλά φώς από παράθυρο ή άλλη φωτεινή πηγή.

The screen shouldn't reflect light from a window or another light source.
It is necessary to clean your screen regularly.
Adjust the font size on your screen, choosing a setting which is comfortable, if the software gives you that choice.
Adjust brightness and contrast on your screen.
People who use computers all the time may experience some refractive anomalies, like slight myopia, slight astigmatism, slight hyperopia; if this is corrected with the use of glasses or contact lenses, it will help them use these devices easier.
Use of artificial tears may help with xerophthalmia that long hours in front of the PC might cause, due to the decrease in blinking speed and frequency; proper moisturizing of the atmosphere, in which the person works and uses the PC, may also help.

The most important thing of all is to have short and frequent breaks of 2-3 minutes every 15-20 minutes of work or 5 minutes for every 30 minutes or 10 minutes for every hour.

Myopia, hyperopia and astigmatism correction, which aims at improving vision and reduce or even eliminate dependence on glasses and contact lenses, has been possible for several years, with various surgical techniques and is an integral part of refractive surgery.
The strides that have been made in biomedical technologies, lasers and ophthalmology allow us today to correct these refractive anomalies and stop being dependent on glasses and contact lenses. The results are impressive. The procedure is done fast, painlessly and the patient leaves the clinic immediately and without bandages.

Refractive anomalies or ametropias are myopia, hyperopia and astigmatism: Myopia is the condition in which distant vision is affected when the axial length of the eye is big in comparison to the curvature and the refractive strength of the cornea. Light rays that enter the eye focus in front of the retina, which results in a blurry visual image, when the myopic person focuses on relatively distant objects. On the contrary, close objects, as a rule, remain clear. In hyperopia, it is close vision that is mainly affected, but distant vision can as well, because the axial length of the eye is small in relation to the curvature and the refractive strength of the cornea. The light rays focus behind the retina which results in an effort by the hyperopic person to continually adjust his vision, which, after some time, is no longer feasible. In astigmatism the cornea is not round but elliptical, light focuses on many points on the retina, which results in blurry close and distant vision. Astigmatism can coexist both with myopia and hyperopia.

The traditional way to treat refractive abnormalities is with glasses and contact lenses. For various reasons, many people do not wish to wear them either because they're tired of the long-term use, or for aesthetic and professional reasons or because they can't tolerate contact lenses (intolerance and allergy to contact lenses or, more usually, to the chemical cleaning fluids; giant papillary conjunctivitis). For these people there is an indication to undergo refractive surgery. In theory every person with a refractive abnormality can undergo such a corrective procedure: -Those who are over 18 years of age and their refraction has remained stable for the past year. -In general, all those who are interested in their appearance and want good quality of vision without dependence on glasses or contact lenses.

For the proper treatment of refractive abnormalities, thorough preoperative tests are needed. The most important tests, besides a general ophthalmological examination, refraction and keratometry, are corneal topography, pachymetry and the cell measurement of the corneal endothelial. Latest developments in topography devices allow as to examine in significant detail the condition of the anterior and the posterior surface of the cornea. Topography devices such as Pentacam, Orbscan and Wave-Front analyzers have helped enormously to enrich our knowledge on refraction and vision quality, as well as to understand the causes for cases with inexplicably poor vision. Those tests and measurements are of extreme importance, since the results of the procedure depend directly on the consistency and precision of these measurements. It is important to know that in order to have precise results, we should stop wearing contact lenses at least 7 days before the tests and the procedure.

The type of laser used for these procedures (excimer laser) functions by sculpting and giving shape to the corneal surface, so as to eliminate the refractive abnormality. The technique mostly used worldwide today is laser-assisted in situ keratomileusis (LASIK) which is a combination of microsurgery and laser. LASIK is appropriate for myopias from -1.00 up to -12.00 D, depending on the indications. Hyperopia and astigmatism have more restrictions (up to -6 D), but we can interfere to reduce the abnormality if it is larger. The surgeon creates a flap on the cornea and lifts it up like a cap. The laser acts under the surface and on the corneal layer, sculpting its surface without injuring it. The flap closes and the procedure ends. The procedure is done with eye drops and is completely painless. Laser application lasts less than 30 sec and the whole procedure lasts no more than 5 minutes. No protective lens or sutures are needed and there is no pain or discomfort postoperatively.

This way, immediate vision restoration can be achieved (within a few hours) and the patient leaves the clinic without bandages and without needing his glasses. An alternative technique is called photorefractive keratectomy (PRK). In PRK no flap is created; the corneal epithelial is simply removed and the laser is applied directly. At the end of the surgery, a therapeutic contact lens is worn until the epithelial is healed. This technique may be used if the thickness of the cornea does not allow us to perform a LASIK procedure. The corneal condition, the age of the patient, the degrees of the refractive fault, the result of the topography and the pachymetry are, generally, some of the factors that will affect the surgeon's strategy.
It is now generally accepted that the use of lasers has brought impressive results with its aim being to stop the dependence of patients on glasses and corrective lenses. Success is considered if 0 sph & cyl (+/- 0,50 D) is achieved and this can be done today with almost 99% success rate. Technology has made significant strides so that today we can consider this procedure completely successful, reliable and very safe. Additionally, it allows us to know preoperatively who are eligible candidates for the procedure, if we can move on with safety and inform the patients for the possible result. We can now say that this significant increase in the percentage of refractive surgeries is due to the rapid advances of Excimer Lasers, that allow us to correct with precision high degrees of myopia, hyperopia and astigmatism.

After the procedure, it is possible to alter the result (involution) either within the first six months or at any time in the future. This can happen if:

Healing process is very intense for a patient. In this case, it is possible for involution to be observed. This happens in the first 6 months and if it does, we can, after a certain amount of time has passed (and if the remaining thickness is sufficient and certainly in cases not related to corneal ectasia), repeat the laser procedure to correct whatever problem has remained without any additional fees.

Myopia in this particular person is progressive. This means that it can suddenly start increasing, at any time and any age. This would happen anyway, regardless of any laser procedure. The benefit for the person that has a laser eye surgery is that his myopia will start increasing again from 0 degrees or near zero. If, for example, someone had 5 degrees of myopia and, after the surgery, this has decreased to 0.5, then, if after a year his myopia increases by one degree than he will have 1.5 degrees (0.5 remaining plus 1 degree from the increase), while if he hadn't had the surgery his myopia would be 6 degrees (5 he had and 1 degree from the increase). If myopia, therefore, increases after the first 6 months from the surgery, then we are dealing with progressive myopia. In other words, the result is considered permanent if within 6 months from the surgery, no alteration is observed. Every change after this period can be considered genetic information and is treated accordingly.

To conclude, we should point out that radiation from the Excimer Laser does not pose any risks for the eye or the body, because all its energy is spent exclusively at the point of application and does not penetrate the tissues more deeply.

For more information you can visit our website www.eyeclinic.com.gr/en.

G. Chronopoulos, Ophthalmologist Surgeon

(published in tlife.gr)




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