Treatment Methods for Presbyopia

Presbyopia is a disorder, where the lens of the eye loses its capacity to focus. This incapacity makes it hard to see items up close. Some scholars have suggested that presbyopia means "age of sight." Presbyopia is not similar to farsightedness because it involves the loss of accommodation and ability for the eye to correct to enhance clarity at various distances. In this context, the young eye requires to change its interval or shape to focus on close objects. The capability of the lens to change shape gives the lens elasticity, which when lost results to presbyopia. When people grow old, they tend to lose this elasticity, and this explains why the eye gradually loses its capacity to focus on close objects (Bennett, 2008).

How Presbyopia Occurs

Presbyopia happens when the cornea and lens refract light so that the light appears behind the retina

People realize they have this condition when they are about 45 years of age when they realize they need to hold reading materials far way, which helps them focus on the material. It is imperative to note that presbyopia is a natural part of the aging process. Therefore, the state can affect any individual as they grow old. On the other hand, the healthcare field has witnessed advancements; however, there has been no cure, yet for presbyopia. Nevertheless, it is possible to correct the condition with glasses or contact lenses. In some instances, health care providers recommend the addition of bifocals to existing lenses to correct the disorder (Menassa et al., 2012).

When the person suffering uses bifocal lenses, it is important to strengthen the bifocal prescription as the case worsens. At around the age of 65, individuals' eyes will have lost the elasticity required to focus close up. This, however, does not mean that it will be impossible for them to read. Using the right prescription, the individual can read comfortably. Even so, an individual might need to hold reading materials far way, or require large print and substantial light, which will make it possible to read. People who do not require glasses for distant vision may require half glasses, or reading glasses, which would make it easy for them to read (Thornton, 1997).

On the other hand, near-sighted people may be capable of reading without their glasses. Contact lenses make it is possible to correct one eye for near, and the other for far vision. This is "mono-vision," and it eradicates the need for bifocals or reading glasses; however, it can influence depth views. It is sometimes possible to produce mono-vision through laser vision correction. In addition, there are bifocal lenses that can correct both conditions. Currently, there are surgical procedures, which can help in correcting the condition (Adnan, 2013). This is recommended for people who do not want to wear glasses. In the medical field, most of the ailments have prevention approaches. In the case of presbyopia, there is no proven prevention.

Correcting Refractive Errors

Refractive errors are the commonest eye problems, and astigmatism supplements refractive error problems. Refractive error means that light does not focus in the correct spot on the eye, which then results to blurred vision. This comes in the form of nearsightedness (myopia), and (hyperopia) farsightedness. Myopia means that one can see close things, but once things are at a distance, it becomes a challenge. On the other hand, hyperopia means that one can see objects, which are at a distance, but when objects are near it becomes a challenge. Correcting the refractive errors follows several approaches. For instance, there are simple reading spectacles, progressive lenses, bifocal lenses or bifocal contact lenses. Correction of refractive error becomes easy when there is no great distance to cover. In such a case, there is addition of a plus-powered reading segment of the mask glass (Bennett, 2008).

Image 2: Refractive errors

Refractive error is not a disease, but it is a condition, which alters the ability of the eye to focus on near, or far objects. It is common through myopia, and hyperopia. A refractive error occurs when the retina is not able to focus light appropriately.

Myopia

It is the condition when the eye is too long, and the light is focused in front of the retina. An individual views close objects as clear, but views distant objects as unclear. This is because the eye has substantial optical power, and contact lenses, surgery or minus glasses help in correcting the situation.

(Adnan et al., 2013)

Hyperopia: it is the condition where the eye is too short and focusing of the right occurs behind the retina. In this case, the eye has less optical power.

(Adnan et al., 2013)

Astigmatism: It is the condition where the eye loses the capability of focusing the light evenly, ad equally. Although the condition can occur on its own, prior studies, have suggests that myopia and hyperopia are contributing factors.

(Adnan et al., 2013)

Refractive Power of the Eye

Cornea Changes

As people grow old, the corneal changes alter the refraction power of the eye. In the elderly, this is usually an alteration "with the rule" (Salvi, Akhtar and Currie, 2006) astigmatism to "against the rule" astigmatism. In the case of "with the rule," the vertical meridian of the cornea becomes steeper in comparison to the horizontal meridian. Therefore, the result is increased refractive power of the eye in the vertical axis, but a person finds it a challenge resolving objects the other meridian. In the other case, "against the rule "the horizontal meridian becomes steeper when one compares it to the vertical meridian. Therefore, the result becomes high refractive power along the horizontal axis, but the person has difficulties when focusing objects from a vertical view. In this regards, the cornea also experiences reduction of corneal luster, sensitivity and subsequent increase in corneal fragility, which influences the refractive power of the eye (Salvi, Akhtar and Currie, 2006).

Crystalline and lens changes

In the aging process, the lens absorbs more blue light, selectively. This happens because of the accrual of yellow stains in the lens region. The reduction in transmitting blue light amounts to a relative blindness, but this condition is common in renowned painters, especially those that use the blue paintings. On the other hand, the renowned symptoms of aging are the hardening of the lens because of biochemical and photochemical alterations. Patients undergo nuclear sclerosis prior formation of frank cataract. This also influences the refractive power of the eye because it is a contributor to presbyopia.

Retina

Notably, vision worsens with age and almost every measure of visual function shows loss of performance. Therefore, with increase in age there is decreased visual acuity, reduced sensitivity of visual region, reduced contrast sensitivity, and increased dark adaptation threshold. Reduced visual capability is a combination of ageing of neuronal elements of the visual system, alterations in the ocular media and pupillary miosis (Salvi, Akhtar and Currie, 2006). On the other hand, retinal pigment epithelium, which is crucial for the integrity of rods and cones, shows with aging increased pleomorphic activity, reduced cells in the posterior pole, reduced content of melanin, increased content of lipofuscin and reduced volume of cytoplasm.

Vitreous aging

Similar to other tissues, the vitreous also goes through a permanent aging process. It does this through changes in the collagen fibrils, and hyaluronic acid. In addition, with the aging process, the vitreous gel condenses, fibrils structure if the vitreous enhances, mobility of the fibrils structure increases, and there is formation of empty optical spaces, which all influence the refractive power of the eye. As there is increase of vitreous liquefaction, the resulting empty optical spaces for large cavities further result to the shrinking of the vitreous body from the retina. This further causes the detachment of posterior vitreous, which can result to the tear of the retina. As there is strong vitreoretinal adhesion in the peripheral retina, it is possible for the retina to tear during acute detachment. In the case of a curtain-like shadow in the region of vision, this means that there has been acute detachment and hence will need surgical intervention (Salvi, Akhtar and Currie, 2006).

Laser Refractive Eye Surgery

There have been many cases of refractive errors, which have seen to the development of surgical interventions in an effort to correct the errors. Commonly, the distribution of refractive errors is around the emmetropia, and evidence suggests that there are more cases in the hyperopic group in comparison to the myopic group. In the same context, many refractive surgical procedures aim at myopia (Brahma and McGhee, 2000). Although myopic people represent the minority, uptake of refractive surgery is high in the group. This explains that people with the condition tend to be quick when seeking medication. The laser technology is popular in many healthcare facilities.

The lasers utilize the ultraviolet light at a wavelength of 193 nanometers. On the other hand, there is still a controversy in the sense that people perceive it as new; therefore, it lacks full testing to reveal its capability in the correction of refractive errors (Brahma and McGhee, 2000). It works through absorption of the first tissue, or fluid, which the laser interacts, resulting to fragmentation of tissue into small molecules ejected from the surface of the tissue. In turn, they give rise to clapping sound of the laser treatment. Being a non-thermal laser, there is minimal collateral damage to the surrounding tissue. Each of the pulse tends to remove a quarter of the affected tissue (Charles et al., 2007).

Eximer Laser in Presbyopia Correction

The laser utilizes ultraviolet rays to correct presbyopia. It uses a combination of noble gas such as argon, krypton or xenon, and another reactive gas, such as chlorine. When there is electrical stimulation, and high pressure there is creation of exciplex, which in turn produces laser light in the ultraviolet range. In the case of surgical interventions, the laser has proven effective owing to the association of reactive and noble gases. Therefore, the eye absorbs the laser light, owing to the fact that the light does not have the capacity to cut. Then, the light disrupts the affected molecules from the surface of the eye. Owing to this capability, the laser can remove fine layers of surface material and still leave the remaining of the material in the same state. The excimer is able to re-shape the cornea, and correct myopia, hyperopia when necessary (Holzer et al., 2003).

Typical beam of the excimer laser

Wavelength Characteristics

Characteristic

Excimer Laser

Photon Energy

Diode pumped ND:YAG

Wavelength

1.17 eV

2.33 eV

3.53 eV

4.02 eV

4-66 eV

5.00 eV

6.42 eV

7.90 eV

Energy per Pulse

10 -1000 mJ

0.1-3 mJ

Repetition Rate

10-4000 Hz

1 kHz - 100 kHz

Power Range

1 -300 W

5 -60 W

Pulse Length, FWHM

10 ... 35 ns

15 -100 ns

Beam Quality

Large cross section, mutimode

TEM00

M2 < 1.2

Spatial Coherence

Low

High

Max. Energy Density

200 J/cm2

... 2500 J/cm2

Max. Peak Power Density

1000 MW/cm2

... 200 GW/cm2

Excimer Laser Procedure

The Excimer remains the most advanced technology in correcting hyperopia refractive errors. The laser has the capacity to gently reshape the cornea and remove the errors. The method is painless, but it requires local anesthetic eye drops. It removes 0.25 microns of tissue in a single pulse. In addition, it has a unique element, in that it can remove thin layers of the cornea, and still not affect the underlying layers (McGhee et al., 2002). An individual seeking correction through this procedure goes through vaporization of the cornea during the laser light disruption of molecular bonds. The procedure does not involve production of shock waves, or heat.

The procedure is available in any surgical facility and performed as an outpatient procedure. The procedure takes only ten minutes for each eye, which explains its wide usage. During the course of the procedure, the eyelids remain open using an eyelid speculum, which helps in preventing involuntary blinking. At last, it reshapes the corneal curvature. In shortsightedness, it flattens the cornea, in astigmatism, the procedure helps in achieving the asymmetrical curvature, and it steepens the curvature in correction of hyperopia. The laser objectively focuses the light rays on the retina to achieve the presbyopia correction (Shortt et al., 2006).

Procedure

The procedure, in reference to prior studies, is safe, reliable and painless. In addition, when compared to the traditional ways, such as glasses or contact glasses, this procedure is more effective. This technique aims at changing the manner, in which the retina bends light. Therefore, it interferes and helps in focusing of light on the retina to improve the mode of seeing. In the procedure, a microkeratome cuts a thin flap on the cornea's surface. Patients, prior to the procedure, are under anesthesia (Menassa et al., 2012), which helps in eliminating pain. The physician lifts the flap, and the excimer laser reshapes the corneas curvature, and improves the condition. Afterwards, the expert closes the flap and covers it with a protective lens.

Advantages of Eximer Laser

The excimer uses a new technology, whereby there is combination of noble gases and reactive gases. The reason behind this is that it can cut in tissues, without damaging the underlying tissues. In so doing, the intervention enhances healing, and quick recovery, with less pain. In the past, surgeons used scalpels to try reshaping the cornea, but with the laser technology, the procedure has become safe. In addition, the procedure takes less time, which further allows the patients to heal quickly (Shortt et al., 2006).

Other Procedures

Notably, there are many procedures, which attempt to correct the presbyopia condition. Some of them are non-invasive, whereas others are invasive. In addition, the procedures fall under any of the many categories, which include surface procedures, flap and laser procedures, and the corneal incision procedures. Among all the mentioned procedures, there is still need for research in the area to ascertain the most effective procedure in correction of presbyopia. This is because the procedures pose substantial risk. Laser technologies are the newest procedures, and they have shown effectiveness in correcting the condition. Some of them include laser thermal keratoplasty (LTK), Laser Assisted Sub-Epithelium Keratomileusis (LASEK) among many others.