Introduction
Visual correction is a crucial component of our daily lives. With a particular focus on presbyopia, a condition that affects individuals from the age of 40, progressive lenses have emerged as a prominent solution for those seeking precise vision at different focal distances. These multifocal lenses allow for a smooth and natural transition between visual focuses, significantly enhancing the user's visual experience.
In this blog, we will explore the various types of progressive lenses available, including recent innovations in custom progressive lenses, an emerging technology that is revolutionizing the field. Additionally, we will delve into the intricacies of the power surfaces of these lenses and the importance of proper adaptation for optimal vision. We will also discuss the potential of progressive lenses in myopia control, providing a comprehensive understanding of how these lenses can benefit both adults and children in managing their visual health.
Different Types of Progressive Lenses
The ophthalmic lens market offers a variety of progressive lenses designed to meet the specific visual needs of each user. These lenses can vary in terms of their power gradients and may offer additional features such as filters to reduce eye fatigue and anti-reflective technology for improved visual clarity.
Some of them are:
Bifocal lenses are among the most common types of progressive lenses. They provide two distinct focus zones: one for distance vision and another for near vision. This clear transition between the two focal distances allows users to switch quickly between them, which is beneficial for those who require clear visual correction at both distances. However, the visible dividing line may be aesthetically less pleasing for some users.
Trifocal lenses, on the other hand, incorporate a third intermediate focus zone that provides clear vision at intermediate distances, such as reading a book or working on a computer. Like bifocal lenses, trifocal lenses also have visible dividing lines.
Traditional progressive lenses are known for their smooth and gradual transition between different focal distances. Unlike bifocal and trifocal lenses, they do not have visible dividing lines, making them aesthetically attractive. These lenses offer uninterrupted vision, gradually adapting to different focal distances. In Mexico, there is a wide variety of progressive lenses available, varying in quality and brand.
Recently, we have seen the emergence of custom progressive lenses. These lenses leverage advanced technology to customize the focus zones and lens power based on the specific needs of each user, enhancing the visual experience and potentially reducing the required adaptation time.
Each type of progressive lens has its own advantages and disadvantages, and the choice of progressive lenses will depend on the individual needs and preferences of each user. As always, it is recommended to consult with an optical professional to receive personalized guidance and determine which type of progressive lenses is most suitable. With the constant advancement of technology, we can expect to see further improvements and customizations in the development of progressive lenses.
Power Surfaces of Progressive Lenses
Progressive lenses are a marvel of optical engineering, combining mathematical, physical, and optical principles to provide clear vision at different focal distances (De Lestrange-Anginieur, 2021). Their design is based on a power profile characterized by a complex mathematical surface that adapts to the varying heights or thicknesses of the lenses (Sheedy, 2004).
This surface, the result of high-tech computational precision and manufacturing, has a variable and smooth shape that allows for a gradual change in the optical power of the lens from top to bottom. This gradual power change along the lens surface provides the necessary visual correction to see clearly at different distances.
The Lensmaker's equation, an essential tool for understanding the design of progressive lenses, states that the power of a lens is proportional to the difference in refractive indices between the lens material and the surrounding medium, and inversely proportional to the lens focal length (Hecht, 2002). In simpler terms, this means that the power of a lens (its ability to bend light and therefore change focus) can be modified by changing the material from which the lens is made (changing its refractive index) or by changing its curvature (changing the focal length). The thin lens equation is a special case of the Lensmaker's equation. It applies when the lens thickness is small compared to the other dimensions of the lens and the distances from objects to the lens (Born & Wolf, 1999). Although progressive lenses are not always considered "thin lenses," these fundamental concepts still apply and provide a solid foundation for their design and understanding.
Recent advances in lens manufacturing technology have allowed for the creation of custom progressive lenses. Using computer-aided design (CAD) techniques and advanced mathematical principles such as differential and integral calculus, manufacturers can tailor the power surface of progressive lenses to the individual needs of each user, providing precise visual correction and greater comfort.
In conclusion, the science behind progressive lenses represents an intriguing convergence of mathematics, physics, and optics, capable of transforming the way we correct refractive errors and perceive the visual world. As we advance in design and manufacturing techniques, we can expect to see increasingly personalized and optimized progressive lenses, further enhancing the visual experience for users.
Adaptation of Progressive Lenses
Ensuring the proper adaptation of progressive lenses is crucial to achieve optimal and comfortable vision, which requires considering individual optical parameters, the user's daily activities, and specific characteristics of the ocular surface (Chu, 2010).
From an optical perspective, it is vital to measure various parameters to ensure proper adaptation of progressive lenses. These include the nasopupillary distance, vertex distance, pantoscopic angle, panoramic angle, and mounting height (Sheedy, 2004). These parameters can be influenced by emerging technologies, such as measurement applications that offer superior precision compared to traditional methods. In fact, we recently conducted a study comparing conventional measurements of these parameters with those obtained through an application we developed, and we found significant differences that highlight the importance of accuracy in these measurements to avoid potential adaptation issues.
Regarding the user's daily activities, it is essential to tailor progressive lenses to individual needs. For example, someone who works extensively on a computer or engages in a lot of reading will require a different focus than someone involved in intense physical activities. Furthermore, the rise of technology-centric jobs and activities raises the need to consider new variables, such as prolonged exposure to digital screens.
Lastly, the anatomical characteristics of the ocular surface also play a crucial role in the adaptation of progressive lenses. The curvature of the cornea, pupil size, and the position of the cornea and crystalline lens can significantly influence the fit of progressive lenses (Muñoz, 2007).
With the emergence of emerging technologies in the field of optics, such as custom progressive lenses, it becomes even more important to consider all these factors when adapting progressive lenses. These custom lenses, manufactured using advanced technology, are designed based on the user's specific optical parameters and optimized for their daily activities and ocular characteristics, providing even clearer and more comfortable vision.
The importance of a qualified optical professional to perform precise adaptation of progressive lenses is unquestionable. Proper fitting of progressive lenses requires a comprehensive approach that takes into account individual visual needs, daily activities, and unique ocular characteristics of each user to ensure clear and comfortable vision at all focal distances.
Control of Myopia with Progressive Lenses
Myopia, a common refractive condition commonly known as nearsightedness, has become a global challenge in eye health (Holden et al., 2016). There are various strategies for its control, and among them, progressive lenses have emerged as an option that has sparked multiple research studies.
Progressive lenses, with their multifocal design, can correct vision at different distances and have shown some efficacy in reducing the progression of myopia in certain cases (Aller & Wildsoet, 2013). However, their effectiveness can vary significantly among individuals and tends to be more moderate compared to more specialized interventions.
For example, the use of atropine eye drops, a medication that inhibits eye accommodation, has proven to be a highly effective method for myopia control in various clinical studies (Chua et al., 2012). However, this treatment may have side effects such as photophobia and diminished near vision, so its use should be closely monitored by a visual healthcare professional.
To optimize the use of progressive lenses in myopia control, further extensive and detailed studies are needed. This effort could include the development and evaluation of custom progressive lenses for children, considering their growth rate, lifestyle, and individual response to these lenses. Emerging technological advancements could allow even more precise customization of these lenses, potentially enhancing their efficacy in myopia control.
In conclusion, although progressive lenses can play a role in myopia control, it is crucial to understand that their effectiveness may vary, and other treatment options may be more suitable for some individuals. The best strategy will depend on each person's individual situation and should be discussed with a visual healthcare professional. With ongoing advances in lens technology and our understanding of myopia, we can expect a future with more personalized and effective treatment options.
Final remarks
The use of progressive lenses represents a significant innovation in presbyopia correction, providing individuals over the age of 40 with clear and comfortable vision at different focal distances (De Lestrange-Anginieur, 2021). These lenses offer a smooth transition between different visual focuses, contributing to a more natural and uninterrupted visual experience compared to bifocals and trifocals.
In the field of myopia control, progressive lenses show promising potential, especially for children who are more susceptible to myopia development. Although current results suggest that progressive lenses may not be as effective as other treatments such as atropine eye drops, further research and personalized solutions are needed to maximize their potential in this field (Aller & Wildsoet, 2013; Chua et al., 2012).
Furthermore, our recent research has highlighted the importance of precise measurements in the adaptation of progressive lenses. Individual optical parameters, unique ocular characteristics, and daily activities of the user must be carefully considered to achieve optimal fitting. While conventional measurements still prove useful, technological advancements such as digital applications provide opportunities to improve accuracy and user satisfaction in progressive lens adaptation (Sheedy, 2004).
In conclusion, proper use and professional monitoring of progressive lenses are essential to fully harness their benefits. With personalized adaptation and ongoing monitoring, these lenses can offer an effective solution to the visual challenges of modern life, helping individuals maintain healthy vision throughout their lives. As we move forward, it is exciting to envision the potential of emerging technologies such as custom progressive lenses, which could provide even further enhancements in visual correction and treatment of specific eye conditions.
Emiliano Terán
References
Aller, T. A., & Wildsoet, C. (2013). Bifocal soft contact lenses as a possible myopia control treatment: a case report involving identical twins. Clinical and Experimental Optometry, 96(4), 394-398. DOI: 10.1111/j.1444-0938.2007.00230.x
Atchison, D. A., & Smith, G. (2000). Optics of the Human Eye. Butterworth-Heinemann. link
Born, M., & Wolf, E. (1999). Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light. Cambridge University Press. link
Chua, W. H., et al. (2012). Atropine for the treatment of childhood myopia. Ophthalmology, 119(2), 347-354. DOI: 10.1016/j.ophtha.2011.07.031
De Lestrange-Anginieur, E., Kee, C.S. Optical performance of progressive addition lenses (PALs) with astigmatic prescription. Sci Rep11, 2984 (2021). https://doi.org/10.1038/s41598-021-82697-0
Hecht, E. (2002). Óptica. Madrid, España: Pearson Educación. link
Holden, B. A., et al. (2016). Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology, 123(5), 1036-1042. DOI: 10.1016/j.ophtha.2016.01.006.
Sheedy J, Hardy RF, Hayes JR. Progressive addition lenses--measurements and ratings. Optometry. 2006 Jan;77(1):23-39. DOI: 10.1016/j.optm.2005.10.019
Muñoz G, Albarrán-Diego C, Sakla HF. Validity of autorefraction after cataract surgery with multifocal ReZoom intraocular lens implantation. J Cataract Refract Surg. 2007 Sep;33(9):1573-8. doi: 10.1016/j.jcrs.2007.05.024. PMID: 17720072.
Comments