The use of bifocal and progressive addition lenses amongst presbyopes

Bifocal lens are lenses that features two distinctive powers which is the distance and near segment. Progressive additional lenses (PAL) are corrective lenses used in eyeglasses to correct presbyopia and other disorder of accommodation. They are characterized by a gradient of increasing lens power added to the wearer’s correction for the other refractive error. The addition value prescribed depends on the level of presbyopia of the patient and is closely related to age and to a lesser extent existing prescription.

Until the early 1980s almost all multifocal were segmented bifocal and trifocals lenses since that time, there has been steady growth in the usage of progressive addition lenses (PAL) and approximately 50% of the multifocal currently dispensed in the united state are of progressive design. There are significant optical differences between and within the segmented and progressive multifocal lenses that affect the vision that is providing to the patient.

In terms of comparison PAL lens give clarity in all fields of vision, distance, intermediate and near vision, but if the bifocal is not properly measured in terms of segment height, it can create image jump. Progressive addition lenses requires utmost care and skills from the optician while bifocal can be easily fitted.

The first fused bifocal was invented in 1908 by John L. Borsch, a Philadelphia ophthalmologist and 22mm round bifocal segment. Throughout the history of multifocal lens development, there has been an effort to device a lens with an invisible segment; in 1955 Irving rips of younger optics created the first seamless or invisible bifocal, a precursor to all progressive lenses.

The first PAL design was patented by Owen Aves in 1907. However, few advanced occurred until 1959 when the varilux was developed by Bernard Maitenaz in France. It was not until 1962 that ominifocal became the first PAL available in the united state, followed by the varilux II in 1973 since that time numerous PALs have been introduced to market.

Many theories abound through the invention of bifocal and also varilux lenses, Benjamin Franklin in 1784 is generally credited with the invention of bifocal lenses. Bruneni (1994) optical laboratory association wrote that there has been a steady growth in usage of progressive addition lenses (PAL) and approximately 50% of PALs currently dispensed in the United States are of progressive design. He also wrote that result shows, reveals the inability of authors to read or write, were it not for the recent invention of glasses.

According to Bomile (2012), presbyopia, although normal and inevitable, is the first unmistakable, irreversible sign for many patients that they are getting older. So, when working with presbyopic patients it’s even more important than usual to consider the psychological and emotional implication of the recommendations, because presbyopia is a very big deal.  Not only does it greatly increase their complexity of choices in vision care.

The aging population increasingly demands excellent near vision for viewing computers and other digital devices at the same time. They have higher expectations than ever for elipse, distance, intermediate and near vision as well as spectacle independence than for presbyopic patient, the key part of the process of accepting presbyopia is the patient understanding that a single pair of glass simply will not meet all of their needs, for patient with a distance prescription, the lined bifocal or progressive addition lenses (PALs) for everyday use is based on a combination of life style and desire.

Stark and Obrecht (1987) states that with new digitally surfaced (PALs) most patient rapidly adopt to them, but patient whose primary concern is to have the very widest width of reading area may be better suited to lined bifocal. Traditional (PALs) are not design to optimize intermediate vision, so office workers should be educated on the benefits of near variable focused or computer (PALs). Many patient choose to use bifocal lenses because of easy adaptation and easily affordable for the patient in terms of price.

Sullivan (1989) states that since the introduction of PALs to the united market. PALs have steady increased their share of the multifocal market. Boorish and Hitzeman (1983) states that several studies have shown a large percentage of patients prefer PALs compared to bifocal lenses. PALs provide continuous change of power from distance through intermediate to near power that provides the wearer with a seamless visual space and eliminates the unusable area of visual space caused by the top line of a bifocal segment.

A deterring feature of PALs is that the design necessary results in unwanted astigmatism in the periphery of the lens, usually located in the lower diagonals relative to lens centre. PALs have both cosmetic and vision advantages compared to segmented multifocal. The cosmetics benefit results from the seamless design and are apparent. The vision advantage results from elimination of the bisecting region of unusable vision associated with the top of the bifocal segment, resulting in continuous visual space from distance through intermediate to near. The vision advantages with PALS compared to bifocal is supported by a study that showed patient preference for PAL compared to a blended bifocal by Fowler (1989) both of which are seamless.

The strong preference for PALS to bifocal is further supported by another study by Sheedy (2004) in which 265 habitual bifocal wearers were fitted with PALS. 72% of these patients preferred the pals, because progressive lenses have no image jump and no area of intermediate blur, many wearers describe their vision with progressive lenses as more natural than with bifocals. The width and areas of the three viewing zones (distance, intermediate and near) and the magnitude unwanted astigmatism have been recorded by Ellerbrok (1942). He said that even the largest intermediate and near error-free zones are smaller than those required to view a typical computer screen or standard paper respectively and also smaller than the normal amount of ocular rotation used to view non central target.

This means that the progressive additional lenses wearer must learn to move their head more and their eye less in viewing non central objects and tolerate some blur of typical non central foveally fixation objects. However, one must consider the purpose and reason for using such eye wear. The overall visual comfort ability for the individual should come first.

Conclusion

In comparison, bifocal lenses can be easily fitted but PAL require utmost care and skills from the optician; bifocal lenses are easily adaptable but a progressive addition lens is not easily adaptable once a PAL pupillary distance measurement is not properly measured, that means the lens is automatically destroyed that is why the fitting of PALs requires utmost care. As upcoming dispensing opticians, from our practical experiences we have been able to gather  that the comfortability of a patient’s eye defect is in our hands, so in fitting of lenses we should be extra careful so as not to endanger the patient. As a result of the findings, it was observedthat:

  • There were no observables changes between the use of bifocal to PAL.
  • There were more respondents using bifocal lenses than PALs.
  • There is a difference between the factors influencing the use of bifocal and PAL.

 Recommendations

Based on the findings of the study, the following are thereby recommended:

  1. Enlightenment programmes: Sufficient and adequate enlightenment programmes should be carried out by both opticians and optometrists to educate the presyopes on the use of bifocal and PAL.
  2. Provision of PAL lenses: The production of PAL should be considered in terms of cost by the manufacturer.
  3. In the course of taking case history, adequate history of patient is taken to avoid patient discomfort from the use of lenses.

 References

Benjamin, F. (1784) inventor of bifocal Boorish IM, Hitzeman SA: comparism of the acceptance of progressive addition multifocal with blended bifocals JAM Optom ASSOL 44, 45, 19 83.

Bomile, W. (2012) psychological and emotional implication of the recommendation Boroyan HJ, Cho MH fuller BC, et at: line multifocal wearers prefer progressive addition lenses AM J Optom ASSOC 66, 296, 1995.

Boorish and Hitzeman (1983) Annalysis of a progressive addition lens population.

Sheedy, J. & Campbell, C (2005). Progressive powered lenses the minkutz theorem, Optom Sci 82 (10): 9,6 – 22.

Sheedy, J., Hardy, R.F. & Hayes, J.R. (2006) progressive addition lenses measurements and ratings” Optometry 77 (37):23 – 39.

Sheedy (2004) Annalysis of a progressive addition lens population.

Smonet, P., Papinean, Y. & Laprint, R. (1986). Peripheral power variations in progressive addition lenses. AM J. Optom Physiol Opt 63: 873, 1986.

Stark, L. & Obrecht, G. (1987). new digitally surfaces P.A L

Sullivan (1989) introduction of PALs to the united market.

Sullivan, C.M. & Fowler, C.W. (1987). Analysis of a progressive addition lens population. Ophthalmic Physiol Opt 9:163, 1987

Uemura, T., Arai, Y. & Shimazakii, C. (1980). Eye-head coordination during lateral gaze in normal subjects Acta otolaryngology 90:191.

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