3D Printed Galilean Telescope for Low Vision Patients

1. Introduction

According to the World Health Organization (WHO), at least, 2.200 million people have one vision impairment (VI), of whom 1.000 million could have been prevented. Besides this, most eye conditions are higher in low- and middle-income countries, furthermore in underserved populations [1,2,3]. As reported by the WHO and the International Classification of Diseases ICD-11 [4], visual impairment occurs when an eye condition as age-related macular degeneration, cataract, corneal opacity, diabetic retinopathy, glaucoma, refractive error or trachoma, affects the visual system and one or more of its vision functions as visual acuity (VA), color vision, stereopsis/binocular vision (depth perception), contrast sensitivity, and/or vision in the peripheral visual fields [5,6,7,8]. The diagnosis of VI is realized through a non-invasive and simple measurement of the VA. The test consists of discerning two high contrast points in space by using an optometric chart placed in a fixed position (6 meters or 20 feet) [1,9,10].

Commonly, visual impairment is classified in two different groups measuring the visual acuity in the better eye, the first group is distance VI which could have the levels of: a) mild, VA ≥20/40 and ≤20/70, b) moderate, VA ≥20/70 and ≤20/200, c) severe, VA ≥20/200 and ≤20/400, d) blindness, ≥20/200 and ≤20/1200 or counts fingers (CF) at 1 meter, e) blindness, ≥20/1200 and light perception, and f) blindness, no light perception. The second group is near VI with VA ≥ N6 or M 0.8 at 40 cm [1,11]. Following the data reported by the Pan American Health Organization (PAHO), in the first group, 217 million people have distance VI from moderate to severe, which, based on the European Council of Optometry and Optics (ECOO), is defined or diagnosed as low vision (LV) [1,11]. Low vision cannot be corrected by ordinary glasses, surgery, or medication, which limits daily activities such as reading, writing, recognition of faces and facial expressions, safe walking and movement, among many others [12,13,14]. However, LV patients can improve their quality of life by using optical devices like telescopes and specific visual aids, which boost their functionality and enable them to maintain a certain degree of independence.

On the other hand, the versatility of 3D printing to fabricate custom pieces with high precision, low costs, and reduced times allows adapting this technology to the needs of each user. Hence, it is not surprising that 3D printing has experienced rapid growth in scientific, technological, and medical fields. For instance, in medical applications, orthopedic and cranial implants [15], surgical instruments [16], and external prostheses [17] are some areas where additive tech has been implemented. The low manufacturing costs compared to traditional fabrication methods and the ability to generate accurate anatomical models for surgical planning and medical training are some of its advantages. Also, 3D printing enables the use of a wide variety of biomedical materials [18,19], including biocompatible polymers [20], ceramics, and metals [15], ensuring compatibility with the human body and reducing rejection risks. In Ophthalmology, 3D printing has also had a significant impact where it has facilitated the creation of indirect ophthalmoscopes [21], intraocular lenses [22], and specialized optical devices [23], allowing the exploration of new materials and optical geometries that optimize the efficiency of visual aids and offering innovative solutions to improve the quality of life of people with visual impairment. These, and the earlier mentioned, precise and rapid manufacturing of lenses and optical devices, are just some of many reasons why 3D printing has emerged as a promising tool in Optics applied to visual rehabilitation. Therefore, we propose a 3D printed Galilean telescope (GT) for low vision patients, accessible to both the vulnerable and nonvulnerable sectors of the population that can contribute to the Sustainable Development Goals (SGDs-3), for achieving universal coverture of health, with the advantages of fabrication times, costs, and weight are considerably reduced. Also, we want to demonstrate that 3D printing lenses can be used directly in medical instrumentation and not just as prototypes, besides contributing to new strategies in the design and accessible optical device manufacturing. In previous work [24,25,26,27,28], we showed that optical lenses, including spherical, aspherical, and freeform designs, can be easily and rapidly fabricated using additive technology. Hence, in this paper, we report the fabrication of a complete Galilean telescope—including both the lenses and the tube—using the commercial FormLabs Form 3 3D printer with high-resolution stereolithography (SLA) technology and Clear resin V4.0 from the same company. Its optical performance was evaluated by comparing the 3D-printed GT to a BK-7 glass GT assembled from the LSB04 Thorlabs lens kit. To test its clinical functionality, the device was evaluated by a patient with low vision as part of a proof-of-concept study. The patient demonstrated a significant improvement in vision—from 10/80 to 10/32 in visual acuity, and from 6 to 18 cpd in contrast sensitivity. The work is organized as follows: a brief introduction about low vision and the importance that 3D printing has reached in recent years, is presented in Section 1; optical and mechanical parameters used for the lenses and the telescope's tube fabrication, are described in Section 2; instrument’s optical functionality is shown in Section 3; instrument’s clinical tests are shown in Section 4; finally, in Section 5, conclusions and final comments are presented.

2. Galilean Telescope Fabrication

The tube and lenses of the Galilean telescope were entirely 3D printed using the FormLabs Form 3 commercial 3D printer, which employs high-resolution stereolithography (SLA) technology and Clear Resin V4.0 from the same company [29,30,31]. To evaluate the optical quality and dimensional accuracy of the fabricated components, geometric parameters such as radii of curvature, diameters, and surface figure were carefully measured. Additionally, since the roughness of 3D-printed surfaces may influence light scattering and thus affect the final image quality, it was also assessed during the functionality tests, particularly on these printed elements. The following sections describe the optical and mechanical parameters used, as well as the fabrication process.

2.1. Lens Selection

The Galilean telescope with a power of magnification of 2X is the most common, simple, and recommended visual aid for low vision patients [32,33,34]. It is for this reason that, in this work, we follow its design for the fabrication of the telescope. Also, Galilean telescopes are compact and lightweight systems that are easy to assemble in glasses, allowing LV patients to improve their distance vision through practical and non-voluminous devices. Moreover, GT's low-power optics provide a large visual field, compared to bigger magnification telescopes, facilitating orientation and the patient’s safe walking and movement. The power of magnification of 2X was obtained by using two BK-7 glass lenses, taken from the LSB04 Thorlabs lens kit, the LA1509-A planoconvex lens, and the LC1715-A planoconcave lens. The optical parameters of the lenses are summarized in Table 1, and the corresponding optical design is shown in Figure 1a).

Figure 1 presents the spot diagrams corresponding to different field angles for both the glass and resin Galilean telescopes. As expected, chromatic aberration is present in both designs due to the use of singlet lenses, with a more noticeable dispersion observed in the resin telescope. This increase in chromatic aberration is attributed to the lower Abbe number and refractive index variations of the 3D-printed resin material. Despite the presence of chromatic aberration, its impact on the visual performance of low vision patients is negligible, as the color fringes remain below the threshold of perceptibility for the intended application. It is important to note that changes in the refractive index in the optical model lead to variations in the focal length of both lenses, requiring adjustments to their separation to achieve an afocal system. Therefore, both telescope designs remain viable for clinical use.

To ensure faithful reproduction of the required optical specifications in the 3D-printed lenses, the optical parameters of Table 1 were input into AutoCAD to obtain the lenses' render, Figure 2a). The CAD models were then sent to the 3D printer to initiate the printing process. This involved preparing the files in the printer’s software, setting the appropriate parameters such as a layer thickness of 25 microns and a print orientation angle of 30 degrees, and ensuring the printer was calibrated for optimal accuracy. Once these steps were completed, the 3D printer fabricated the components layer by layer according to the digital designs.

When the printing of the 3D lenses is finished, they are post-processed. First, they are exhaustively washed in the Form Wash to remove all the traces of unsolidified resin. Then, they pass a final curing process in the Form Cure to maximize their strength and stability [26], Figure 2b). Finally, the lenses are polished by the conventional method in specialized optical polishing machines, Figure 2c). Polishing process enhances the optical surface quality, significantly reduces light dispersion, and optimizes lens transmittance. This process, performed at the INAOE’s Optical Workshop, is described next.

2.2. Optical Fabrication

The lenses were polished using a Strasbaugh® 6DA-DC4 polishing machine. To perform the grinding process, the lens is mounted on the machine's overarm with a glass tool positioned below it on the rotating axis, Figure 3a). The inverted configuration helps maintain symmetric material removal, considering the resin density, Table 2.

The resin parameters are critical for understanding the polishing process, ensuring low irregularity, and achieving high surface quality. A surface finish roughness of approximately 15 microns was achieved for the grinding stage. The next stage was the polishing process, which is critical due to the challenges of polishing soft materials such as the resin. This stage was also performed in the Strasbaugh® 6DA-DC4 polishing machine; a polishing pad to make a balance between density and solvent resistance, ensuring compatibility with the resin, was used. The pad was the POLITEX™ polyurethane pad from Pureon; the polishing compound was Kontax 602 from Universal Photonics, a high-purity alumina formulation specifically designed for plastic materials. Figure 3b) shows the results for the resin lenses after polishing.

When the polishing process is ended, a completely reflecting, transparent, and smooth surface is observed, Figure 3c). The irregularity measurements of the lens surfaces were performed using a Zygo Mark II interferometer. The 3D-printed lenses were tested using two reference surfaces: a flat for the two flat surfaces, and a sphere for the concave and convex surfaces; both reference surfaces with a precision of PV = λ/20 ≈ 32 nm (λ = 632.8 nm). The measured irregularity for the spherical surfaces was 4.45λ peak-to-valley (PV) and 0.81λ root mean square (RMS) for the eyepiece, and 4.53λ PV and 0.76λ RMS for the objective. For the flat surfaces, the measured irregularity was 6.83λ PV and 1.17λ RMS for the eyepiece, and 8.23λ PV and 1.52λ RMS for the objective lens.

The radius of curvature was measured with the same interferometer in linear mode, along with a digital scale from Easson™, attached to a precision linear rail, used to displace the lens and to determine the distance between the vertex and the center of curvature position. The radii of curvature for the spherical surfaces were -25.83 mm and 51.9 mm for the eyepiece and objective lenses, respectively. Additionally, the diameters and thickness of the 3D printed lenses were measured using a Mitutoyo digital caliper. The diameter and thickness for the eyepiece were 25.42 mm and 2.05 mm, and 3.10 mm and 25.43 mm for the objective, respectively. Next, roughness measurements are described.

3.3. Roughness

A Linnik interferometer [35,36], with two Edmund Optics lenses of 25 mm fixed focal length and a numerical aperture of 0.0306, placed in both arms of the interferometer, was used to measure the surface roughness from the resin lenses, Figure 4.

Figure 5a) shows one of the interferograms obtained with the Linnik interferometer for the roughness measurements, and Figure 5b) shows one roughness profile of the surfaces under test. It's worth mentioning that this measurement was realized over a length lₘ of 21.21 μm, corresponding to the size of the spot generated by the 25 mm fixed focal length lens used in the Linnik interferometer.

The roughness average (Ra) for the 3D printed lens with surface finish polished with the traditional method was of 1.569 nm ±0.35 nm. The peak-to-valley (PV) measurement was 14.237 nm ±3.41 nm. Note that these values align with the roughness characteristic of printed surfaces [37]. Next, the design and mechanical parameters of the telescopes’ tubes are described.

2.4. Tube Design

For assembling the two Galilean telescopes (the 3D printed, and the BK-7 glass), customized tubes were also designed in AutoCAD [38]. The tubes were created to provide adequate support for the lenses during the user’s handling. The principal function of the tubes was to optimize, and to provide a better user experience of the patients, Figure 6.

The ergonomics of the telescope was a special parameter considered during the design of the tubes. Thus, the tubes were designed with texturized surfaces to enhance adherence which is a very useful characteristic to visual impaired people. The tubes design´s texture facilitates holding and handling of the telescope, reducing the risk of slipping and allowing a more intuitive use, Figure 7. The tube has a 70.5 mm maximal length stretched and 53.5 mm minimal length compressed. The design incorporates a threaded adjustment mechanism that allows easy-to-use focusing with a 17 mm range. Furthermore, the adjustment has a linear travel of one millimeter per turn, providing precise and gradual control, so users can adapt the focus to their specific visual needs. This feature is practical and highly beneficial for patients with low vision because it allows them to optimize their visual experience without requiring sudden movements or complex adjustments.

To eliminate spurious light that could affect the telescope's performance, a black paint coating was applied to it, Figure 7. The paint coating minimizes unwanted internal reflections, enhances contrast and image quality, and contributes to the care and material’s durability, ensuring the telescope’s appropriate performance within different use conditions. Following, the instrument functionality tests are presented.

3. Instrument Optical Functionality

To evaluate the 3D printed GT functionality, its optical performance was compared to a BK-7 glass GT. As was earlier mentioned, the optical parameters of the 3D printed GT were defined from the design obtained to the BK-7 glass GT assembled from the LSB04 Thorlabs lens kit, with the LA1509-A planoconvex lens, and the LC1715-A planoconcave lens, see Table 1. The characterization of the instrument included optical resolution tests, angular magnification and field of view. Next, the results for evaluating the viability of using 3D printed lenses in visual aids' applications for low vision patients are shown.

3.1. Optical Resolution

The telescopes’ optical resolution analysis was realized using the standard USAF 1951 resolution target, and an Edmund Optics OE-18112 camera, with 18.1 megapixels. The distance between the camera and the target was adjusted to ensure that the target filled the entire field of view of the camera. The experimental setup configuration allows a precise optical performance evaluation by measuring the instruments’ ability to resolve fine details in the resolution target.

Observe that, for the glass lenses telescope, the maximum resolution achieved was 4.49 lp/mm, as the bars of group 2, element 2, were perceptible (see Figure 8a). Compared to the resin lenses telescope which reached a maximum resolution of 4.00 lp/mm, with the bars of group 2, element 1, being discernible (see Figure 8b). Note that differences in optical resolution between the analyzed telescopes are relatively small which leads to obtaining very similar images. The two instruments showed the capability to discern fine details, which is essential for low vision patients. As can be seen, the two models have a very similar optical performance, which indicates that, regardless of the lens used, telescopes effectively enhance object visibility and assist patients to improve their quality of life. Note that the differences in the values obtained for the instrument resolution are not significant enough to affect what the patient distinguishes, allowing the two telescopes to be considered a viable option for adapting optical aids. Next, the optical parameters of the telescopes are presented, focusing on key aspects such as angular magnification and field of view that determine the system’s visual performance.

3.2. Optical Parameters

The optical performance of the Galilean telescopes was evaluated in terms of angular magnification and field of view, two critical parameters in visual aid systems (see Table 3). The angular magnification was determined using Zemax, based on the focal lengths of the objective and eyepiece lenses calculated from the measured curvature radii (see section 2.2). The nominal magnification for both telescopes is shown in Table 3. The field of view was estimated by measuring the angular extent of the scene visible through the telescope, as described in references [38,39], which is inherently limited in Galilean designs due to the negative eyepieces. Despite this limitation, the resulting field of view was sufficient for practical use in mobility and reading tasks, making the system suitable for patients with low vision.

Following this, the clinical functionality of the instruments is described in detail, including the evaluation of their effectiveness in improving visual performance in patients with low vision. This section discusses the outcomes of clinical tests and measurable improvements in visual acuity and contrast sensitivity achieved with the use of telescopes.

4. Instruments Clinical Functionality

The development of accessible optical devices for low vision patients, especially those of vulnerable sectors, is a real need which must be attended. On this matter, this work seeks to contribute to new strategies in the design and manufacture of these instruments which are useful for this sector of the population. In this section, we describe the tests conducted as part of a proof-of-concept study to evaluate and adapt the 3D printed Galilean telescope for a 75-year-old female patient, who provided informed consent and was diagnosed with myopia magna, pseudophakia, ocular infarction with hemorrhage, retinal thinning, retinal detachment in the right eye, and central scotoma in the same eye. The instruments used in this study were specifically adapted to enhance the patient's visual acuity and contrast sensitivity, two key factors that must be corrected to improve vision functions for individuals with visual impairments. The complete patient data is shown in Table 4.

After applying the best correction with spectacles in both eyes, visual acuity was evaluated with ophthalmic lenses using the LEA numbers, which is specifically designed for patients diagnosed with low vision (Figure 9). According to the International Classification of Diseases (ICD-11), the patient was classified with moderate low vision. These results indicate that the patient can see at 10 feet (3 meters) what a person with normal vision could see at 100 feet (30 meters), Table 4. The LV patient reported an improvement of one line of visual acuity when using the ophthalmic filter.

Optical aids must be adapted after applying the best correction to the eye with the best visual acuity. In this case, the 3D printed Galilean telescope was adapted to the left eye. Before visual acuity measurements were taken, the patient is provided with detailed instructions for manipulating the telescopes. Additionally, the device could be used until the patient felt comfortable and was able to correctly focus on the optotypes in the LEA numbers. For the two BK-7 glass lenses, the patient gained a visual acuity of 10/40, while for the 3D printed GT, patients’ visual acuity improved to 10/32. The two instruments enhanced the patient’s visual acuity: the glass-lens telescope showed an improvement of 4 lines, while the resin-lens telescope achieved 5 lines of improvement in visual acuity. Before adapting the telescopes, the patient's contrast sensitivity was measured using the FACT (Functional Acuity Contrast Test); a 6 cpd value for the left eye (LE) was obtained, indicating an inadequate functional vision, which limited her daily activities, Table 5. Contrast sensitivity is crucial for daily life, as it relates to facial recognition, navigating stairs, and, in general, the recognition of distances and objects. The contrast sensitivity in the left eye significantly improved after adapting the Galilean telescopes for the patient. The resin-lens and the BK-7 glass-lens achieved a value of 18 cpd, Table 5.

As can be seen, the patient showed significant improvements after telescopes adapting, achieving visual acuity and sensitivity contrast values within the normal range, demonstrating the clinical functionality of the instruments.

5. Discussion

The development of a 3D-printed Galilean telescope for low vision patients represents a significant innovation in the field of accessible optical aids. This work serves as proof of concept, demonstrating the fabrication method, clinical functionality, and ergonomic feasibility of designing low-cost solutions for visual rehabilitation using additive manufacturing technologies. Unlike existing commercial devices, which often require specialized manufacturing processes and involve high costs [40,41,42,43], this proposal focuses on equitable access to technology, making it accessible to both vulnerable and non-vulnerable populations. A cost comparison between commercial BK7 glass lenses and 3D-printed lenses shows that the commercial lenses (objective and eyepiece) cost approximately $50.00 (USD), while the 3D-printed lenses (objective and eyepiece) cost $27.00 (USD), representing a cost saving of approximately 46%. It is important to note that the commercial lenses’ cost reflects large-scale manufacturing by a supplier, whereas our 3D printing lenses cost corresponds to the production of two pieces. Therefore, if produced at scale, the cost of 3D-printed lenses could be reduced even further, reinforcing their potential for low-cost, accessible optical solutions.

From the optical functionality analysis, the 3D-printed GT achieved a resolution of 4.0 lp/mm, which enables the identification of fine details, an essential feature for visually impaired individuals [44]. This performance level reinforces the validity of the proposed approach.

Clinically, substantial improvements were observed in visual acuity (from 10/80 to 10/32) and contrast sensitivity (from 6 cpd to 18 cpd), translating into real functional gains for the patient. These results are consistent with previous studies demonstrating the efficacy of telescopices as optical aids in low vision populations [44], with the difference that this is an affordable and customizable 3D-printed system.

Beyond optical and clinical performance, this proof of concept also integrates ergonomic considerations into the design. Patients reported that the shape of the telescope's tube facilitated grip, reduced the risk of slipping, and allowed for intuitive use. This user-centered design approach, particularly important for individuals with sensory impairments, marks a significant improvement. Moreover, a comparison of the lens weights demonstrated that the two BK7 glass lenses weighed 28.684g, whereas the two resin lenses weighed 21.9g, resulting in a 26.82% reduction in lens relative weight. This reduction contributes to a lighter overall device, further enhancing comfort and usability for the patient.

This initiative also directly contributes to the achievement of the Sustainable Development Goal 3 (Good Health and Well-being) by providing a functional and affordable visual rehabilitation tool with the potential for local production and distribution, even in resource-limited settings. These kinds of solutions are key to advancing universal health coverage, as they combine technological innovation with health equity. We seek to further develop this proposal so that, in the future, these prototypes can be donated to low-income individuals to help improve their quality of life, either temporarily, while they secure the resources to obtain specialized equipment, or even permanently, as a viable long-term alternative.

Despite all its advantages, this proof of concept has certain limitations. The small clinical sample size prevents immediate generalization of the results. Broader comparative validation with mid- and high-end commercial devices is needed, along with long-term durability and performance testing. Further research into advanced optical materials and optimization of multi-component 3D printing designs could provide valuable future directions. These developments may lead to improved durability and greater resistance to scratches and surface defects in resin-based optics, making them more comparable to traditional glass components. Also, recent advances in 2-photon polymerization (2PP) have demonstrated outstanding surface quality and submicron resolution in 3D-printed optical components. Although currently limited by cost and fabrication volume, the integration of 2PP could significantly improve the surface accuracy and optical performance of future designs [45,46,47].

On the other hand, we are currently working on developing a novel surface finishing technique to eliminate the need for conventional polishing. This future advancement aims to further reduce manufacturing costs and simplify the overall production process, ultimately enabling more efficient and accessible production of high-quality optical components.

6. Conclusions

A 3D printed Galilean telescope for low vision patients, lightweight, economical and easy, precise and rapid manufacturing, fabricated using additive technology, was presented. The optical performance of the 3D printed GT showed the power to discern fine details, with a value of 4.0 lp/mm in optical resolution. Clinical functionality tests showed that when the 3D printed GT was adapted to the LV patient, visual acuity increased by up to 4 lines on the LEA numbers, from 10/80 to 10/32. The 3D GT telescope also enhanced patient’s contrast sensitivity, improving it from 6 cpd to 18 cpd. The patient showed significant improvements after the telescopes adapting, achieving visual acuity and sensitivity contrast values within the normal range, demonstrating the clinical functionality of the instruments in the proof of concept.