Major visual defect. When the optician spreads his hands, the refractive surgeon steps in

The visual defect scale is nothing more than its classification into low, medium and high (low, moderate and high). For defects that, on some continuum of the scale, can be corrected by laser procedures, the scales are as follows:

Short-sightedness:

• small – also called school, up to -3 D,
• average – between -3D and -6 D (according to some sources between -3D and -8D)
• large – above -6 D (according to some sources above – 8D)

Hyperopia:

• small – up to +2.5D
• average – +2.5D to +6.0D
• large – over +6.0D

Astigmatism:

• low – up to 1 cylindrical dioptres (usually does not require correction)
• medium – from 1 to 2 cylindrical diopters
• high – from 2 to 3 cylindrical diopters
• very high – more than 3 cylindrical diopters

However, before deciding on laser correction of vision defects, each of us goes through the same path: at the beginning are glasses, and a little further – contact lenses.

Eyeglasses and contact lenses in large and complicated visual defects

For small to medium defects, uncomplicated defects (and astigmatism likes to be complicated…) and defects that occur solo (rather than in pairs, e.g. myopia plus astigmatism) the selection of corrective eyeglass lenses is easy and the patient can even achieve almost 100 percent visual acuity in the best possible correction. What does this mean? It means that we will be able to see simply perfectly in eyeglasses well chosen for us by a specialist.

Unfortunately, in a situation in which the patient’s visual defect is at the end of the scale – or rather, in the spectrum that marks this end: pay attention to the fact that a high or very high visual defect starts “from”, “above” the given number of diopters/cylindrical diopters – and, in addition, we have to deal with varicose vision (in each eye a different defect, for example. in each eye a different defect, e.g. -10 and in the left -14 diopters) it is very difficult to select such glasses or contact lenses, after wearing which the patient, despite a high defect of vision, is able to see well and function without problems. This is a situation in which we go beyond the possibilities that modern optics gives us – this also applies to contact lenses.

Despite the possibility of preparing for the patient glasses that have index lenses (index is the refractive index of a material, that is, the speed of a wave at the boundary of two media – the boundary of air and the boundary of the lens material, the higher the index, the thinner and lighter the eyeglasses), with large visual defects even in glasses made by an optician with the greatest care and with the best materials, the eyeglass lenses will protrude beyond the frame, and the image seen through the glasses will not be clear and stable.

Contact lenses may be a better solution, but a very high visual defect will always be a significant handicap for the patient, and the resulting “vision compromise” will only be a choice of the lesser of two evils.

Can high and very high vision defects be corrected with laser procedures

Too high a visual defect – myopia above -10 diopters and farsightedness above +5 diopters – is a contraindication to laser correction. Similar problems with laser correction arise in the case of irregular astigmatism, which is difficult to treat. However, the possibility of laser surgery is always decided on an individual basis and after very detailed qualifying examinations.

However, this does not mean that a farsighted or nearsighted person with a severe visual defect has to settle for glasses or contact lenses.

If we cannot undergo laser correction of a high or very high vision defect due to too thin cornea, other anatomical conditions related to the structure of the eye or our health (absolute contraindication), we should turn to traditional surgical methods, such as implantation of intraocular toric single, bifocal or trifocal lenses, phakic lens docking or refractive lens replacement.

For example, phakic lens implantation is ideal for patients with myopia up to -20 diopters, hyperopia up to +10 diopters and astigmatism up to 6 diopters.

It is also possible to use combined methods. For example, the maximum vision defect is corrected with a phakic lens, and the remaining residual defect is compensated for with a contact lens or by using laser vision correction.