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Myopia

MagazineOctober 1998 (Vol. 9 Issue 7)Myopia

Laser eye surgery, the so called miracle solution to myopia, has many hidden dangers, including the possibility that it may make your eyesight worse

Laser eye surgery, the so called miracle solution to myopia, has many hidden dangers, including the possibility that it may make your eyesight worse.

The advertisements are persuasive. "Do away with glasses forever"; "revolutionary treatment permanently corrects short sightedness"; "experience the life enhancing effect".

To the casual observer, laser surgery has all the hallmarks of a miracle (albeit an expensive one at lb2000 plus). But, the technique is still in its infancy and, as research reveals, often fails to live up to the glossy promises.

Vision is measured in dioptres, with normal vision rated at zero and moderate myopia classified as up to 6 dioptres. In myopia, the eyeball is too long to focus, or refract, incoming light perfectly onto the retina (this is known as a refractive error). Laser surgery aims to correct the problem by shaving away a fraction of the cornea in order to change the shape of the eye which allows the eye to focus better.

There are two types of laser treatment for short sightedness: photoreactive keratectomy (PRK), in which the laser energy is applied to the surface of the cornea; and the newer laser in situ keratomileusis (LASIK). With LASIK, a thin flap of corneal tissue is partially cut and folded back; the laser is then applied to the tissue below. Doctors believe that when the laser is applied to the deeper corneal tissue instead of the surface, vision recovery is much quicker and results are more permanent, though this has yet to be proved conclusively.

The existing research on laser surgery is fairly unsatisfactory. It consists of small trials with handfuls of people. Many researchers, such as those at Cedars-Sinai Medical Centre in Los Angeles, remain cautious: "Only when large numbers of patients undergo the procedure will we be able to determine [its] safety and efficacy" (Refract Corneal Surg, 1992; 8: 269-73). In London, doctors at Moorfield Eye Hospital have drawn similar conclusions: ". . . longer follow up will be required to establish when refractive outcome can be expected to stabilise and whether there are late consequences (Eye, 1993; 7: 617-24).

What has been demonstrated is that laser surgery works best with those who have a mild to moderate level of myopia. In highly myopic eyes, PRK can cause corneal scarring, visual loss and a considerable degree of regression-myopia which becomes progressively worse again (Am J Opthalmol, 195; 119: 263-74). LASIK appears to be a better choice for those with severe myopia (J Refract Surg, 1996; 12: 575-84; J Refract Surg, 1998; 14: 19-25), although it is unlikely to be completely effective in correcting astigmatism (J Refract Surg, 1997; 13: 511-20). LASIK also carries its own specific risks. It requires an extra surgical step cutting the flap on the cornea so there are potentially more complications, such as the flap of tissue being cut improperly or not fitting back into place.

While LASIK treatment also seems to result in less excessively hazy vision one of the primary complications of PRK (Klin Monatsbl Augenheilkd, 1991; 199: 153-9) as well as less post surgical pain (J Refract Surg, 1997; 13: S425-6), it is a newer, less well researched procedure, not as widely available, and many doctors are simply not trained in its use.

With LASIK, post surgical complications are not rare. In one study, 6.52 per cent of eyes developed regular astigmatism, 4.43 per cent were left with tissue deposits (scarring) on the eye and 6.54 per cent developed small epithelial cysts (J Refract Surg, 1997; 110: 521-7).

In one study of 10 patients (14 eyes) with moderate to high myopia, LASIK patients experienced reduced contrast sensitivity for up to one month after surgery. This gradually corrected itself over the next two months (J Cataract Refract Surg, 1998; 24: 183-9).

Poor results

Although many doctors play down the adverse effects, research shows that not all patients feel happy with the results. In one study, around 10 per cent of patients felt very disappointed. Those with extreme myopia fared worse than those with a moderate condition, and most complained of glare and distortion in the early months after surgery (Br J Opthalmol, 1995; 79: 881-7). In another, an estimated 10-20 per cent of patients experienced regression and so requested repeat surgery, often misleadingly referred to as an "enhancement procedure" (Opthalmol, 1998; 105: 131-41). To combat this problem, the authors inexplicably offer this solution: perform a deliberate over correction of around 50 per cent, involving a deeper cut into the eye. But, over correction, whether deliberate or accidental, is a huge risk since it can leave you far sighted instead of near sighted. Once this happens, all you can do is return to your glasses. Laser surgery cannot correct farsightedness, whatever the cause.

Although one US study argued that PRK is a promising procedure, only two thirds of patients had any significant improvement, and a little more than half achieved a change within one dioptre of attempted correction (Arch Opthalmol, 1991; 109: 1525-30). Another study recognised that laser surgery has "significant potential for adverse results", but brushed this aside by saying that at least these complications are less severe than those associated with conventional eye surgery (Cornea, 1996; 15: 557-65).

In the longest follow up to date, 83 participants were followed for six years after PRK laser surgery (Opthalmol, 1998; 110: 273-81). Each of the patients experienced a refractive undercorrection, the magnitude of which was related to the size of the attempted correction (in other words, the more the surgeon tried to do for them, the greater the margin of error). So, 91 per cent of those whose myopia was mild (-2 dioptres) experienced a correction of to within about one dioptre of the intended correction. But this figure dropped dramatically in the group with moderate myopia (-7 dioptres), where only 19 per cent achieved a correction within about one dioptre of the intended correction.

The authors noted that corneal haze and night halos were the most common side effects. While the haze appeared to clear up over the first year, night halos remained a problem throughout the study period.

Another common adverse effect of laser surgery is what are called "central islands". These are undercorrected zones in the centre of the treated cornea, which are occasionally the reason for double vision, halos and reduced visual acuity. In one study of 62 eyes (33 patients), the incidence of central islands was 72.6 per cent (Klin Monatsbl Augenheilkd, 1996; 208: 423-7). These are more common in attempted correction of -3 dioptres or more. When central islands are "steep", ie, more pronounced, the suggested solution is to have the eye shaved again at a later date (J Refract Surg, 1996; 12: 715-20).

Finally, laser surgery will not stop the eye's ageing. Indeed, as people age and the lens loses its ability to change shape and focus, many become farsighted. This may mean that even with laser surgery, by your mid 40s or 50s you may be back to wearing glasses again this time to improve your far sightedness.

Taking a deeper look

Delaying the ageing process and preventing disease in the eye requires greater attention to nutrition, exercise (see box, p 2) and protection from harmful environmental influences.

Practitioners are beginning to come around to the idea that visual disturbances are symptoms in the first stage of the progressive, but preventable, degeneration of the eye. For them, diseases such as cataracts and glaucoma are simply extreme forms of a common process. This theory gains some credence from the fact that people with myopia are known to be at a greater risk of developing eye diseases such as age related macular degeneration (AMD), glaucoma and cataracts. In one study, intraocular pressure (most commonly associated with glaucoma) was associated with the development of myopia. The progression of myopia in 49 children aged 9 to 12 years was studied over a period of two years. What they discovered was that the rate of myopia in those children with high intraocular pressure (IOP) was nearly double that of those with a lower IOP (Doc Opthalmol, 1992; 102: 249-55).

Although almost every child can recall being told that carrots are good for your eyes, nutrition to improve eyesight is not a subject which has received much serious consideration in the medical journals. Vitamin A (found in, among other things, carrots) is undoubtedly vital for healthy eyes. Carotene is metabolised in the intestinal mucosa into retinol, which is then transported to the liver where the vitamin is stored in the form of retinyl palmitate. Thus, in diseases which affect the liver, reduced vision and even blindness are common.

When diet is studied, it is usually in relation to serious conditions such as macular degeneration (J Am Optom Assoc, 1996; 67: 30-49) and cataracts (Crit Rev Food Sci Nutr, 1995; 35: 111-29), rather than refractive errors such as myopia. More recently, the damage which free radicals can do to the eye has received attention. Inflammation of the eye can occur when toxins such as free radicals build up in the body and on the eye (Nutrition, 1996; 12: 274-7). Preventative measures in the form of taking antioxidants have been extensively shown to help prevent visual deterioration (Am Epidemiol, 1996; 6: 60-6; Am Ann N Y Acad Sci, 1980; 570: 372-82; Acta Opthalmol, 1993; 71; 214-8).

One study did look specifically at the association between diet and myopia. The nutritional profiles of 24 children who developed myopia between the ages of seven and 10 years were compared with the nutritional data of 68 10 year old subjects with perfect eyesight (Optom Vis Sci, 1996, 73: 638-43). The results showed that those children who developed myopia had a generally lower intake of many essential nutrients than did those children whose vision remained good. Specifically, there were statistically significant differences in energy intake, protein, fat, vitamins B1, B2 and C, phosphorous, cholesterol and iron in the diet.

This demonstrates the importance of the role of metabolism in eye health. If the blood pH (acid-alkaline balance) becomes acidic, muscle tone increases, turning the eyes inward, while an alkaline pH will interfere with normal muscle tone, leaving eyes posturing outward and generally fatigued. Blindness and cataracts are linked to diabetes, and reduced night vision is often linked to impaired liver function. Gastro intestinal disorders, such as candida overgrowth and parasites, can also contribute to poor vision because they interfere with the normal assimilation of essential proteins, vitamins and nutrients.

Educational eye strain

The role of the environment is also important. Other reviews have concluded that the increasing prevalence of myopia among children and young people is related to the stress, physiological and psychological, placed on them by the educational system. Long hours of close work force the eye to strain unnaturally when focusing on objects farther away (Tidsskr Nor Laegeforen, 1991; 73: 3635-7; Gig Sanit, 1996; 24: 19-22). One Japanese study found that there was also a strong relationship between failing eyesight and the sitting posture of young students during study. It concluded that myopia is strongly associated with shortness of viewing distance and increased neck flexion (Nippon, Ganka Gakkai Zasshi, 1997; 101: 393-9). This data is of course relevant for adults who work or study in similarly unfavourable conditions.

What has received less research attention is the subject of electromagnetic fields (EMFs) and eye damage. Ann Silk is a retired optician and member of the Royal Society of Medicine. For the last 10 years she has made a special study of the effects of EMFs on eye function, and she has recently published her findings in a two part series in the Journal of Electromagnetic Hazard and Therapy (1998, 8: 10-11 and 9: 8-9).

Ms Silk confirms through her research that EMFs can cause eye damage both directly and indirectly. For instance, low level microwaves, such as those found in everyday communications equipment, have been shown to cause direct damage to the retina, iris and macula. She also reports that dopamine loss, which can be triggered by external electrical fields, can lead to blurred vision. Dopamine is a hormone essential for the development and maintenance of the health of the eye.

According to conventional wisdom, reduced night vision comes with age, or with wearing certain types of corrective lenses. "Reduced night vision, or night myopia, can have a nutritional cause, usually a zinc deficiency. But it can also be caused by sitting in a magnetic field all day," says Ms Silk.

Research into indirect damage has proved more challenging to obtain. But researchers in Tokyo have recently investigated the growth of both E coli and Bacillus subtilis in a stronger than normal magnetic field. Their findings indicated that not only was cell growth greater, but also the death rate of bacterial cells was inhibited. Research at UCLA in California has also shown that fungi proliferate in electromagnetic fields.

The polymers used in the manufacture of contact lenses can also be affected by the emissions from VDUs. Ongoing studies quoted by Ms Silk have shown that they can develop minute holes which can irritate and affect the health of the eye.

Now is the time to watch, as many of those who have had laser eye surgery in the last 10 years approach the point when long term adverse effects may begin to reveal themselves.

Perhaps the point is to address the underlying causes of eye problems, such as nutrition, before leaping to cover up the symptoms.

!APat Thomas


How many vitamins for healthy living?

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