Optical Material Recycling Practices: A Look at Portuguese Optical Centers

Abstract

Purpose: This study aims to investigate the disposal practices of optical materials in Portuguese Optical Centers. Methods: This study, conducted in the Portuguese Optical Centers across 18 districts and 308 municipalities, divided the country into 4 regions for analysis. Utilizing Google Forms^®, a survey targeting Optical Center managers and related professionals was disseminated via email from February to May 2023, comprising 30 questions across 6 sections, including optical and contact lenses, maintenance solutions, eyeglass frames, and recycling participation. Data analysis employed IBM SPSS^® Statistics v.27, using non-parametric tests for variable distribution. Ethical standards and privacy policies were strictly observed throughout the research process. Results: Findings indicated that there were significant differences in the final treatment of organic and mineral lenses. Organic lenses were placed in the yellow recycling bin (22.2%), while mineral lenses were placed in the green recycling bin (37.9%). In the case of contact lenses, regardless of the type (RGP, scleral lenses, conventional hydrogels, and silicone hydrogel lenses), the majority (>50%) were disposed of in general trash. Regarding eyeglass frames, there were no significant differences between mass and metal frames, mostly being discard in general waste (~30.0%). Conclusion: Approximately half of the surveyed Portuguese Optical Centers were not actively involved in recycling. This represents a missed opportunity for optometrists to play a role in enhancing recycling rates through patient education.

1. Introduction

Climate change has emerged as the foremost long-term threat to global health in the 21st century [1]. While significant strides have been achieved across various sectors, the world continues to witness a persistent rise in global greenhouse gas (GHG) emissions, especially carbon dioxide (CO₂) [2,3].

One major contributor to these GHG emissions is the production and improper disposal of plastics. This is due to the energy-intensive nature of plastic manufacturing, which adds to CO₂ emissions [4]. Furthermore, when plastic waste is either incinerated or left to decompose in landfills, it releases GHG into the atmosphere, further intensifying the climate crisis [5]. In addition to these environmental challenges, plastics pose another serious problem. They have an extremely slow decomposition rate, sometimes taking centuries to break down naturally in the environment [4,6]. During this lengthy process, plastics can fragment into smaller microplastics, infiltrating ecosystems, causing harm to wildlife, and even entering the food chain, thereby affecting human health [7,8,9,10]. As a result, there is a growing global concern about the rising levels of plastic waste generation and disposal [4], and the subsequent adverse effects it brings about [11].

However, plastics have become indispensable in the field of ophthalmology, playing a crucial role in various aspects of eye care, such as lens, contact lenses (CL), and frames. This versatile and durable material has revolutionized the industry [12], offering numerous benefits while also presenting certain challenges, such as waste disposal. Within the optometry sector, a significant amount of waste is generated due to lens disposal, cutting (tiny plastic scraps are generated, and CR-39 plastic is composed of monomers and does not degrade easily), and polishing (after one month, the effluent is emptied into a 20 L plastic container), which negatively impacts the environment [13]. Hence, eye care professionals and lens manufacturers are concerned about the potential environmental impact of lens waste, disposal, and wastewater from ophthalmic spectacle lens production [10,14], particularly within the context of global climate change [15]. This concern is further heightened by data showing that between 2010 and 2011, ophthalmology in the northwest of England represented a carbon footprint of 1175 million tons of CO_2e [16]. Similarly, in optometry in the United Kingdom (UK) in 2020, the total annual carbon footprint amounted to 135,573 kgCO_2e [17].

In 2021 in Wales (UK), a survey was carried out among optometrists about their opinions about climate change and how it could be improved in optics. Thus, 87% of respondents stated that “Climate change is an important problem and measures must be taken to mitigate it” and 85% stated that “Climate change due to carbon emissions from human activity is an urgent problem”. On the other hand, there were two questions that elicited the most diverse responses and the most “disagree” responses. These statements were “Your employees are taking steps to be sustainable” and “Health systems in Wales are taking sufficient steps to be sustainable”. For the first statement about employees, 29% agreed, 31% were neutral, and 40% disagreed. For the second statement concerning health systems overall, 10% agreed, 36% were neutral, and 54% disagreed [17]. As a matter of fact, healthcare services are responsible for 4% of GHG emissions in the UK [18]. These emissions are comparatively lower than in other nations. For example, healthcare services are responsible for 7% of the GHG emissions in Australia [3], 10% in the United States of America (USA) [19], and 5% in both Canada [20] and Japan [21]. This suggests that healthcare-related emissions make up approximately 4.4% to 5.0% of the overall global emissions, positioning it as the fifth most significant source of carbon emissions [22,23]. The primary source of annual GHG emissions is travel, accounting for a substantial 69% (equivalent to 93,726 kg CO_2e) [11].

Regarding contact lens users, Rolsky et al. [24,25] discovered that 19% of over 400 surveyed CL users dispose of their lenses in the toilet or sink. Annually, this equates to an estimated 2.5 billion CL, weighing about 20 tons, entering wastewater treatment plants in the USA. More recently, a study [26] found that Americans flush up to 2.9 billion daily disposable CL down the drain each year, either by discarding them in the toilet or washing them down the sink. These adverse environmental effects can be mitigated through reuse, waste reduction, recovery, and recycling [27]. Thus, to address this issue, several optical companies in the USA, the UK, and the European Union (EU) have instituted initiatives and/or programs for both ophthalmic and CL recycling [28,29,30].

As a matter of fact, lens recycling in the EU is gaining attention and becoming increasingly important in the context of promoting a circular economy and reducing waste. Although there is no specific EU legislation that specifically targets lens recycling, it can fall under broader waste management and recycling regulations implemented by the EU member states. One example is directives and regulations that address waste management and recycling practices, including electronic waste and packaging waste, which may encompass certain types of optical devices and materials. Under the circular economy concept, countries are implementing funding programs and policies [31,32] as an alternative to the prevailing linear economic model [33]. It should also be noted that there are efforts to establish and promote lens recycling programs, although specifics may vary across EU member states. The following are some key points regarding lens recycling in the EU:

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Producer responsibility: The EU’s Waste Electrical and Electronic Equipment (WEEE) Directive [34] places the responsibility on producers to manage the proper disposal and recycling of electronic and electrical equipment, including certain types of optical devices. This directive encourages manufacturers and distributors to take responsibility for the environmental impact of their products, including lenses.

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Collection points and programs: In various EU countries, collection points and programs for lens recycling are being established. These may be available at optical retailers, eye care clinics, or recycling centers. Some programs facilitate the collection and recycling of both eyeglass frames and lenses.

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Partnership with optical industry: Collaborations between recycling organizations, waste management companies, and the optical industry are being fostered to facilitate lens recycling. Partnerships aim to streamline collection, sorting, and recycling processes, ensuring that used lenses are properly managed and recycled.

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Plastic waste management: Lenses, particularly CL, are often made of plastic materials that pose challenges for recycling. The EU is actively working toward addressing plastic waste and increasing the recycling rates of plastic products, including lenses, through initiatives such as the EU Plastics Strategy [35] and the Circular Economy Action Plan [32].

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Awareness and education: Efforts are being made to raise awareness among consumers, eye care professionals, and optical industry stakeholders about the importance of lens recycling. Education campaigns highlight the environmental benefits of proper lens disposal and recycling, encouraging individuals to participate in recycling programs and make informed choices.

As for the final destination of lens frames, also known as eyeglass frames, it can vary depending on their condition and material composition, as follows:

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Reuse and resale: If the lens frames are in good condition, they can be cleaned, repaired if necessary, and then sold or donated for reuse. Many eyewear retailers or specialized eyewear resellers offer programs where customers can trade in or donate their old frames for others to use.

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Recycling: Eyeglass frames made of materials such as metal, plastic, or acetate can often be recycled. In recycling facilities, frames may undergo processes such as shredding or melting to convert them into raw materials for manufacturing new products. Some eyewear manufacturers or optical retailers provide collection points or recycling programs specifically for eyeglass frames.

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Upcycling and repurposing: Eyeglass frames that are no longer functional or in demand for resale can be creatively repurposed or upcycled. They can be transformed into jewelry, decorative items, or even used in art projects.

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Landfill or incineration: Unfortunately, if lens frames are not suitable for reuse, recycling, or upcycling, they may end up in landfills or be incinerated. However, efforts should be made to minimize the disposal of eyewear frames in these ways, as they contribute to waste generation and environmental impact.

While lens and eyeglass frames’ recycling holds significant value, its adoption remains relatively recent in various regions. Therefore, there is currently a lack of information on how optometrists help recycle all the waste materials they receive and/or generate in their optical centers. Hence, the primary goal of this study is to clarify the ultimate destiny of materials used in Optical Centers in Portugal. This will enable the analysis of whether Portuguese Optical Centers have implemented recycling practices and/or programs for optical materials.

2. Materials and Methods

2.1. Study Area

This study was conducted in Portugal, an EU member since January 1986, specifically within Optical Centers. In 2023, there were 2190 Optical Centers operating in Portugal [36], distributed throughout the country.

For the purpose of this study, we focused on the Portugal administrative division—18 districts (Figure 1) and 308 municipalities. Moreover, for the purposes of statistical treatment, it was decided to divide Portugal into four regions: North, Central, South, and Lisbon and Tagus Valley (Figure 1).

2.2. Methods

A survey was created using Google Forms^®, addressed to those responsible for Portuguese Optical Centers. It was distributed via email to Optical Centers’ managers, Optical Companies (Wells, Grandvision, and Opticalia), the Optical Sustainability Support Association, and the Higher Institute of Education and Sciences of Lisbon (ISEC Lisboa) graduates. The survey remained accessible from February to May 2023.

The survey comprised 30 questions, with 14 of them (46.7%) being closed-ended type, and was structured into 6 distinct sections (Appendix A):

(1)

Optical Center characterization,

(2)

Ophthalmic lenses (mineral lenses, organic lenses, and polycarbonate lenses),

(3)

Contact lenses (rigid gas-permeable (RGP), scleral lenses, conventional hydrogels, and silicone hydrogel lenses),

(4)

Maintenance solutions (grouped or separate disposal),

(5)

Eyeglass frames (metal or plastic),

(6)

Participation in recycling campaigns.

Within each of these sections, questions were posed regarding the quantity and disposal methods of various materials.

Hypotheses

To audit the recycling practices of Portuguese Optical Centers, the following hypotheses were formulated:

Null Hypothesis (H₀).

There is no significant difference in the recycling practices among different types of optical materials (e.g., ophthalmic lenses, contact lenses, and eyeglass frames) in Portuguese Optical Centers.

Alternative Hypothesis (H₁).

There is a significant difference in the recycling practices among different types of optical materials (e.g., ophthalmic lenses, contact lenses, and eyeglass frames) in Portuguese Optical Centers.

2.3. Recycling Practices in Optical Centers

The optical centers surveyed in this study utilized a variety of recycling methods to manage their waste. These methods can be broadly categorized as follows:

• Single-Stream Recycling Collection: Half of the optical centers (50.75%) employed single-stream recycling, where all recyclable materials are collected together in a single bin. This method simplifies the recycling process for the centers, but it requires sorting at a recycling facility, which can increase contamination rates.
• Multi-Stream Recycling Collection: Other centers (29.85%) used multi-stream recycling, where different types of recyclable materials (e.g., paper, plastics, and metals) are separated into distinct bins. This method reduces contamination and improves the quality of recycled materials but requires more effort from the staff to sort the materials at the source.
• Mixed-Waste Collection: A small portion of the optical centers (19.40%) still used mixed-waste collection, where all waste, including recyclables, is collected together. This method often results in lower recycling rates, as it relies on external facilities to sort the recyclables from the general waste stream, which is less efficient and can lead to higher contamination levels.

The choice of recycling method varied depending on the specific policies and resources of each optical center.

2.4. Statistical Analysis

The results of the questionnaires were analyzed using IBM SPSS^® Statistics v.27. To assess the normal distribution of the variables, the Kolmogorov–Smirnov test was applied with a significance level of 0.1. Considering the non-parametric nature of the data, the Kruskal–Wallis or Mann–Whitney U Test was used for quantitative variables, while the Chi-square test was utilized for qualitative variables. Additionally, one-way ANOVA tests were performed to evaluate differences between centers for each factor, with further analysis using the Bonferroni post hoc test to identify specific differences between groups. The reliability of the questionnaire was verified with Cronbach’s alpha, yielding a value of 0.71, indicating acceptable internal consistency. Quantitative data were reported using the median (Me) and interquartile range (IQR). All ethical considerations pertinent to the study were strictly followed. Furthermore, the survey was conducted anonymously, adhering fully to the Privacy and Personal Data Protection Policy, as stipulated by Regulation (EU) No. 2016/679 of the European Parliament and the Council of 27 April [37].

3. Results and Discussion

3.1. Optical Center Locations and Year of Opening

The sample under analysis in this study was made up of 134 optical centers, representing 6.1% of the total optical centers in Portugal. Of the 134 optical centers sampled, 28.2% have been operating for up to 9 years, 33.6% have been operating for between 10 and 25 years, and 38.2% have been operating for over 25 years.

Concerning the geographical distribution of the participating opticians in this study, four distinct regions were defined based on the “District” variable: the North Region, the Central Region, the South Region, and the Lisbon and Tagus Valley Region. Notably, the majority of opticians were situated in the Lisbon and Tagus Valley Region, comprising 49.2% of the total, followed by the North Region at 20.0% and the Central Region at 18.5% (Figure 1). The South Region, on the other hand, boasted the lowest number of optical stores, at 12.3% (Figure 1). It is worth noting that there was a similar distribution of optical stores based on their year of opening (as determined by a Chi-square test with a p-value of 0.885).

To elucidate the disposal practices in greater depth, a descriptive analysis was performed, examining the quantities of discarded optical materials in relation to the years of operation of the centers (

Table 1. Median number and IQR of optical materials by location of the Portuguese Optical Centers.

Type of Optical Material	0–9 Years	10–25 Years	More than 25 Years
Glass lenses	0 [2.0]	1 [4.5]	0 [3.0]
Organic and polycarbonate lenses	10 [16.0]	8 [28.0]	10 [27.0]
RGP lenses	0 [0.0]	0 [0.0]	0 [0.0]
Hydrogel lenses	1 [8.0]	0.5 [6.0]	0 [5.5]
Packaging with maintenance solutions for lenses	2 [5.0]	1 [4.0]	2 [5.0]
Metal frames	2 [3.0]	3 [3.3]	2 [4.5]
Plastic frames	2 [4.0]	2.5 [4.3]	3 [4.0]

) and their geographical locations (

Table 2. Median number and IQR deviation of optical materials by location of the Portuguese Optical Centers.

Type of Optical Material	North	Central	Lisbon and Tagus Valley	South
Glass lenses	0 [1.5]	2 [10.0]	0 [3.0]	0 [3.0]
Organic and polycarbonate lenses	6 [37.0]	16 [58.0]	10 [17.0]	5 [28.0]
RGP lenses	0 [0.0]	0 [0.0]	0 [0.7]	0 [0.3]
Hydrogel lenses	2 [6.0]	2 [6.0]	0 [8.0]	0 [2.0]
Packaging with maintenance solutions for lenses	0 [3.0]	2 [5.0]	2 [5.0]	2 [4.0]
Metal frames	2 [3.0]	2 [5.0]	3 [4.0]	2 [3.0]
Plastic frames	2 [4.0]	3 [5.0]	3 [5.0]	2 [3.0]

).

3.2. Lens Disposal Treatment

Of the total response of the optics, 2.37 ± 4.95 (Me = 0; IQR = 3) mineral lenses and 35.43 ± 109.81 (Me = 10; IQR = 27) organic lenses were discarded. There were significant differences (p < 0.001) in the final treatment of organic and mineral lenses. Organic lenses were mostly placed in general waste (36.1%), returned to the manufacturer (32.9%), or placed in a yellow recycling bin (22.2%; Figure 2). Mineral lenses were placed in the green recycling bin (37.9%), in general waste (34.8%), or returned to the manufacturer (13.8%; Figure 2). Only around 5.0% of optical centers claimed to provide lenses a second use and less than 1.0% delivered them to VALORMED (Portuguese Packaging and Medicine Waste Management Company; Figure 2).

Studies have examined waste generation within the ophthalmic sector, particularly in the context of cataract [38] and glaucoma [39] surgeries. Organic ophthalmic lenses are typically manufactured from methacrylate or polycarbonate derivatives [40]. While there is currently no published research confirming the environmental impacts of discarding these lenses, ongoing studies are investigating the potential use of biodegradable materials in ophthalmic lenses. If successful, this approach could help alleviate the negative consequences of solid plastic waste. Patent literature outlines promising developments in the creation of biodegradable lens materials derived from renewable sources, such as corn isosorbide [41,42].

As for CL, regardless of the type (RGP, scleral lenses, conventional hydrogels, and silicone hydrogel lenses), they were mostly (>50%; Figure 3) thrown in the general trash. A small percentage (~9 to 16%) were placed in the yellow recycling bin or returned to the manufacturer (Figure 3). Of the total response of the optics, 1.17 ± 5.85 (Me = 0; IQR = 0) RGP/scleral lenses and 4.54 ± 8.25 (Me = 0; IQR = 6) conventional hydrogel/silicone lenses were discarded.

In alignment with the findings of this study, in the study by Rolky et al. [24] it was observed that approximately 38% of CL users exhibited a high likelihood of discarding their used CL in the sink or toilet. Another cause for concern is the fact that 10.5% of optometrists were very inclined to recommend this practice, while 12.2% were unlikely to provide any guidance on CL removal to their patients [24,25]. The relatively small size (average diameter of 14 mm) and weight (roughly ~20 mg) of CL result in limited plastic waste generation. Nevertheless, an estimated 20 tons of plastic finds its way into USA wastewater systems annually due to the improper disposal of CL [24,25].

The CL industry is continuously evolving, exploring advanced techniques and innovations to enhance vision and comfort, thereby improving the overall experience for wearers [43]. Despite these advancements, current CL packaging lacks clear disposal recommendations. Consequently, it is of utmost importance that optometrists advise their patients against disposing of CL in sinks or toilets. Optometrists and their staff should reinforce these instructions during every patient visit and at the time of CL purchase. Similarly, they must ensure the proper disposal of unwanted trial CL, because these lenses have the potential to fragment, contributing to the escalation of microplastic pollution.

However, there is a scarcity of research on the environmental implications of ophthalmic lenses (OL) and CL [15,25,44]. A considerable amount of research has concentrated on hydrogel materials, which attracted attention due to pioneering work on CL materials by scientists in the early 1960s. Hydrogels are identified as three-dimensional (3D) polymeric networks that can retain water [45]. These materials have found applications in a variety of fields, such as drug delivery systems, tissue scaffolding, water purification in polluted environments, water retention in arid areas [45], and the controlled release of fertilizers and pesticides [46]. CL do not naturally biodegrade, and when they are disposed of and become dehydrated, soft CL can turn brittle and break into microplastic-sized particles, which may lead to soil and water contamination [7,25]. However, aligning with the principles of the circular economy model, the recycling of CL is worth considering. There have been efforts to recycle hydrogels utilized in other applications, such as 3D-printed hydrogel materials or injectable hydrogels for tissue regeneration, which can biodegrade after fulfilling their intended purpose [47,48].

In 2019, global reports on trends in eyewear fittings revealed that 89% of new fittings or refits involved the incorporation of soft CL [49]. According to findings by Pillay et al. [50], 96.3% of CL users indicated their preference for soft CL, with the 30-day CL replacement modality being the most commonly recommended choice by optometrists (96%). As a result, 75.8% of CL users adopted this replacement modality. South Africa showed a higher adoption rate for the monthly replacement modality, ranging from 64% to 82%, as opposed to the international average of 39% in 2019 [50]. This difference may be due to the cost-conscious nature of the South African market, where daily and biweekly disposable CL options are typically seen as more expensive.

3.3. Eyeglass Frames’ Disposal Treatment

Regarding the final treatment of the frames, there were no significant differences (p > 0.1) between mass and metal frames. Most optical centers discarded the frames in general waste, returned them to the manufacturer, and/or provided them a second use (Figure 4). Of the total response of the optics, 5.09 ± 11.85 (Me = 2; IQR = 4) metal frames and 5.02 ± 11.31 (Me = 2; IQR = 5) plastic frames were discarded.

It should be noted that metal frames were still delivered to VALORMED (4.7%) and/or used for parts (6.3%; Figure 4).

Eyeglass frames can be made from a variety of materials, including metals, such as titanium, stainless steel, and various metal alloys, as well as plastics, such as cellulose acetate, cellulose propionate, polyamide, and polycarbonate. Unfortunately, once discarded, these materials generally have poor degradation capabilities, remaining as solid waste in the environment for an indefinite period [44]. Additionally, some frame materials may contain heavy metals, such as lead and chromium, which can leach into and contaminate the surrounding environment [44]. Notably, recent advancements in eyeglass frame materials have introduced bioacetate and hexetate, marketed as biodegradable and eco-friendly options [9]. However, it is essential to acknowledge that these materials currently have a relatively modest market presence and are still emerging in the eyewear industry.

Studies have indicated that 71% of people who wear eyeglasses change their frames within a 1- to 2-year period, with approximately one-third of them opting to discard their old eyeglasses [36]. Similarly, Pillay et al.’s study [50] revealed that over half of optometrists reported selling more than 10 new frames per week, and 61.1% of individuals who wear eyeglasses showed a high likelihood of purchasing a new frame. When acquiring a new frame, more than half were very inclined to retain their old eyeglasses, while approximately 18% were strongly inclined to dispose of them. In a previous study, 31% of respondents indicated that they discarded their frames [44]. According to anecdotal reports from optometrists, it seems that some individuals who wear eyeglasses like to keep a “backup” or extra pair in case their primary glasses are damaged or lost.

This behavior raises the possibility of significant volumes of eyeglass frames and OL waste ending up in landfills through solid waste disposal.

3.4. Maintenance Solutions’ Disposal Treatment

In the case of packaging for CL maintenance solutions, as they are plastic containers, the majority were discarded in the yellow recycling bin (44.3%; Figure 5). Still, some packaging was placed in general waste (17.2%) or returned to the manufacturer (23.0%; Figure 5).

On the other hand, the disposal of maintenance solutions presents several options (Figure 6): 48.7% were placed in the pipe or sewer, 26.9% did not dispose the solutions, and 21.0% were returned to the manufacturer.

Regarding the joint disposal of the packaging and the maintenance solution, 52.6% of optical centers stated that they do not dispose of them together, 25.9% returned them to the manufacturer, and 15.5% placed them in the general waste (Figure 7).

Presently, there is a lack of studies examining maintenance solutions. However, compared with other optical maintenance products, it has been found in the study by Pillay et al. [50] that 89.5% of eyeglass wearers disposed of lens-cleaning spray bottles designed for recycling in regular trash bins. In turn, only two participants mentioned refilling these bottles with the assistance of their optometrists. This practice presents a valuable opportunity to reduce plastic waste, and it is a strategy that more optometrists should consider. Such an approach aligns with the principles of hierarchical waste management, focusing on avoidance, reduction, and reuse of waste [51]. Furthermore, around 49.0% of people disposed of their glasses’ cases, while 40.5% opted to reuse or repurpose them [52]. These cases usually have a limited lifespan and are often thrown away when they become damaged. Eyeglass cases are made from various materials, such as tissue, acetates, and polyurethanes, some of which are recyclable. Likewise, the packaging for CL maintenance solutions should be made using biodegradable or compostable materials. This approach aims to encourage soil rejuvenation after disposal and mitigate the environmental impact of overburdened landfills.

3.5. One-Way ANOVA

To further investigate the differences in disposal practices among optical centers, a one-way ANOVA was conducted considering two main factors: years of operation of the center (

Table 3. Years of operation of the Portuguese Optical Centers.

Type of Optical Material	ANOVA Test (F-Statistic Value)	ANOVA Test (p-Value)
Glass lenses	0.837	0.436
Organic and polycarbonate lenses	0.344	0.709
RGP lenses	1.347	0.264
Hydrogel lenses	0.191	0.826
Packaging with maintenance solutions for lenses	0.037	0.964
Metal frames	1.35	0.263
Plastic frames	0.98	0.378

) and the geographical location of the center (

Table 4. Location of the Portuguese Optical Centers.

Type of Optical Material	ANOVA Test (F-Statistic Value)	ANOVA Test (p-Value)
Glass lenses	0.884	0.452
Organic and polycarbonate lenses	3.15	0.028
RGP lenses	0.675	0.569
Hydrogel lenses	1.227	0.303
Packaging with maintenance solutions for lenses	0.147	0.931
Metal frames	1.321	0.271
Plastic frames	1.591	0.195

).

The ANOVA test addressed whether newer optical centers discarded a significantly different amount of optical material compared to older centers. The p-values obtained (0.263 < p < 0.964) indicated that there were no significant differences in the average amount of optical material discarded between centers based on their years of operation.

The ANOVA test examined whether the average amount of optical material discarded varied significantly across the four regions considered in this study. The p-values indicated significant differences only for the disposal of organic and polycarbonate lenses (p = 0.028). Further analysis using the Bonferroni test identified that the regions contributing to these differences were the North and the Lisbon and Tagus Valley Regions (p = 0.019). Specifically, the North Region discarded an average of 98 lenses per month, compared to 15 lenses per month in the Lisbon and Tagus Valley Region.

3.6. Limitations and Strengths

This study has several limitations that need to be considered when interpreting the results. The sample represented only 6.1% of the total Optical Centers in Portugal, which may not fully capture the diversity of recycling practices across the entire country. However, the sample was strategically selected to cover all four major regions of Portugal, providing a comprehensive geographic representation. The data relied on self-reported practices from survey respondents, which could introduce bias or inaccuracies. Despite this, self-reporting is a widely used method in survey-based research and provides valuable insights directly from industry professionals. The study did not account for regional differences in recycling infrastructures that might affect the recycling practices of optical centers. However, by including a diverse range of centers from different regions, the study offered a broad overview of national practices and highlighted potential areas for intervention. The study was cross-sectional, providing a snapshot of current practices but not capturing changes over time. Future research should aim to include longitudinal data to observe trends and changes in recycling practices. Nevertheless, the current study established a crucial baseline for future comparisons and longitudinal studies. The strengths of this study include comprehensive geographic coverage, ensuring that the findings reflect a national perspective. By using a survey methodology, the study gathered direct insights from professionals actively involved in the industry, providing practical and relevant information on recycling practices. The study not only identified the current practices but also highlighted the main challenges and proposed actionable solutions to improve recycling practices in the optical industry. This study contributes to the growing body of research on sustainability practices within specific industries, offering valuable data that can inform both policy and practice in the optical sector. By acknowledging these limitations and strengths, the study provides a balanced and thorough understanding of the current state of recycling practices in Portuguese optical centers and lays the groundwork for future research and improvements.

4. Recommendations

The findings of this study emphasized the importance of optometrists proactively advising their patients on suitable disposal practices for ophthalmic products and containers. It is recommended that all products provided to patients should be accompanied by guidance on recycling and clear instructions for proper disposal. For that, manufacturers, possessing knowledge about the composition of lenses and frames, should communicate with optometrists to provide guidance on the optimal methods for disposing of these materials. However, the challenge lies in the variability of lens materials, with different substrates, inorganic coatings, and tints, making them incompatible for recycling. It is not feasible to visually categorize and separate lenses based on their material composition, and there are no discernible markings on fitted lenses to indicate whether they are made of materials such as CR-39^®, polyurethane, or polycarbonate. Organic lenses are categorized into thermoplastic (such as polyurethane and polycarbonate) and thermo-hardened (such as CR-39^®) materials. Recycling is feasible only for thermoplastic lenses, and even then, it depends on the specific treatments they undergo. Hence, it is crucial for manufacturers to specify the recyclability of the lens. To facilitate identification and sorting for recycling at the end of their life, it is suggested that manufacturers engrave a code on the periphery of the lens, such as the engravings on progressive addition lenses. The code might resemble the classification of different types of plastics, made according to the Resin Identification Coding System, created in 1988 by the Plastics Industry Society in the USA.

Sustainability in the optic industry involves implementing practices and policies that aim to minimize the environmental and social impact of the industry while promoting awareness and responsibility in the production and consumption of eyewear and related products. Key areas of sustainability in the optic industry include:

• Sustainable Materials: Opting for sustainable materials in the manufacturing of eyewear is crucial. This includes using recycled materials, such as recycled plastics and metals, instead of virgin sources. Additionally, sourcing renewable materials, such as certified wood or cellulose acetate, from sustainable sources can reduce the environmental impact of production.
• Responsible Production: The optic industry should commit to responsible production practices by reducing water consumption, energy use, and natural resource consumption during the manufacturing process. This can be achieved through process improvements, the use of more efficient technologies, and implementing conservation measures.
• Durable Design and Circular Fashion: Promoting durable design in eyewear, focused on product quality and longevity, is essential to reduce premature disposal and waste. Additionally, adopting circular business models, such as buy-back and eyewear frame recycling programs, encourages reuse and minimizes the environmental impact.
• Sustainable Packaging: Reducing the use of unnecessary packaging and utilizing recyclable or compostable packaging materials are important to minimize waste and the environmental impact. Eyewear packaging made from recycled or biodegradable materials helps reduce the product’s carbon footprint.
• Social Responsibility: In addition to environmental practices, sustainability in the optic industry also involves considering social aspects. This includes adopting ethical business practices, respecting workers’ rights, ensuring fair wages, and promoting safe and healthy working conditions throughout the supply chain.
• Education and Awareness: Promoting awareness about the importance of sustainability in the optic industry is crucial. This can be carried out through educational campaigns, transparent product labeling, and sharing information about sustainable practices adopted by the company.

By integrating these sustainability practices in the optic industry, it is possible to reduce the environmental impact, promote social responsibility, and provide consumers with more sustainable and conscious options. These actions are essential for building a more sustainable optic industry aligned with the principles of a circular economy. Moreover, enacting specific legislation focused on lens recycling, where manufacturers are accountable for indicating recyclability, may encourage optical centers to take a more proactive stance in promoting lens sustainability and reducing their carbon footprint.

5. Conclusions

The results obtained here revealed that 40.8% of surveyed Portuguese Optical Centers still do not carry out any type of recycling of optical materials. In contrast, the other 59.2% engaged in various recycling practices, with the most common being placing lenses in the yellow recycling bin. However, a lack of awareness regarding the chemical composition of lenses and frames often results in improper disposal of these materials. Approximately half of the surveyed optometrists were not actively involved in recycling, representing a missed opportunity for optometrists to enhance recycling rates through patient education.

The major findings of this study highlighted the need for better awareness and proactive behavior among optometrists regarding recycling practices. The challenges identified included the variability of lens materials, lack of discernible markings for material composition, and insufficient communication between manufacturers and optometrists regarding the recyclability of lenses, making it difficult to properly dispose of lenses and frames in an environmentally friendly manner.

Proposed solutions included engraving codes on the periphery of lenses to indicate material composition, similar to the Resin Identification Coding System, and ensuring manufacturers provide clear instructions on the recyclability of their products. By integrating these sustainability practices, the optic industry can reduce its environmental impact, promote social responsibility, and provide consumers with more sustainable options. Enacting specific legislation focused on lens recycling could further encourage Optical Centers to promote lens sustainability and reduce their carbon footprint.