3D Printed Galilean Telescope for Low-Vision Patients^†

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this work, the authors present a 3D printed Galilean telescope for low vision patients. They perform an extensive set of tests to validate the performance of the telescope against an off-the-shelf telescope using widely used N-BK7 lenses from a major optics supplier.

Overall, the article is well written and easy to follow. However, I have some comments and specific issues I would like to bring to their attention:

1. There was no mention of the durability of the resin. No mechanical tests were performed. Resin is significantly more susceptible to scratching compared to N-BK7 and may not be practical for everyday use. Routine handling or cleaning could substantially deteriorate the performance of the telescope.
2. Resin, even after polishing, can exhibit significantly higher scattering compared to conventional N-BK7. The only optical test performed on the sample lenses was a resolution analysis/MTF cut-off type of test, which cannot quantify scattering. I would suggest either performing scattering tests in vitro (using, for example, PSF or other techniques to quantify straylight in vitro), or citing the relevant literature.
3. For the Zemax modeling presented, it appears that the only parameters changing are the refractive index and the Abbe number. Is this correct? Please specify which parameters were modified in the modeling.
4. Please explain why one should prefer 3D printed over conventional optics. The article lacks an extensive discussion of the pros and cons of using 3D printed lenses. There are some generic points brought up about 3D printed optics in the manuscript, but there needs to be a concrete discussion. One weak point I observe is that significant post-processing is required to achieve acceptable quality optics, which essentially undermines the argument of cheap and easily produced optics. Overall, I would prefer a slightly different article structure. I think it would be beneficial to include a discussion section where the findings are discussed extensively, presenting the advantages as well as the limitations of the 3D printed telescope.
5. One limitation of the article is the validation on a single patient. I believe that if the authors want to present clinically significant results (visual acuity comparison, etc.) and draw performance conclusions from them, they will need to include many more subjects. Alternatively, they can present this single patient only to demonstrate clinical feasibility, but this needs to be clearly stated in the manuscript.
6. Albeit minor, I think that since this system will be handled by the patient, to mention whether it is toxic free and safe for handling.

Author Response

Comments 1: There was no mention of the durability of the resin. No mechanical tests were performed. Resin is significantly more susceptible to scratching compared to N-BK7 and may not be practical for everyday use. Routine handling or cleaning could substantially deteriorate the performance of the telescope.

Response 1:

We thank the Reviewer for this observation. The durability and mechanical properties used in our analysis were obtained from the manufacturer's specifications, as presented in Section 2.2 (Table 2). Additionally, our proposal was conceived as a provisional solution intended to support patients temporarily, while they secure the resources needed to obtain specialized equipment. This clarification has been added to the manuscript in Section 5 (362-366), also a few lines to clarify that durability and scratch of the resin comparted to glass, were added (373-375).

https://formlabs.com/3d-printers/resin/tech-specs/#data-sheets

https://support.formlabs.com/s/article/Resin-Care?language=en_US

Comments 2: Resin, even after polishing, can exhibit significantly higher scattering compared to conventional N-BK7. The only optical test performed on the sample lenses was a resolution analysis/MTF cut-off type of test, which cannot quantify scattering. I would suggest either performing scattering tests in vitro (using, for example, PSF or other techniques to quantify straylight in vitro), or citing the relevant literature.

Response 2:

We thank the Reviewer for this valuable observation. As was mentioned in Section 3.2 of the manuscript, “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…” These parameters are particularly relevant for low vision patients, as they directly impact what patients can see.

We fully agree with the Reviewer that light scattering is an important parameter in the characterization of optical systems. However, in this particular proof-of-concept study, scattering was not considered a limiting factor for the intended application. The contrast sensitivity test is an indirect indicator of the material’s scattering level. Although the scattering is not quantitatively measured, the results of this test suggest that it does not significantly affect the patient. The benefit of magnification outweighs any potential negative effect caused by scattering. Nonetheless, we recognize its relevance and will take this into account in future work, where a more comprehensive optical characterization, including scattering measurements, is planned.

Comments 3: For the Zemax modeling presented, it appears that the only parameters changing are the refractive index and the Abbe number. Is this correct? Please specify which parameters were modified in the modeling.

Response 3:

The Reviewer is correct: the optical model was modified by adjusting the refractive index and the Abbe number, which resulted in a change in the focal lengths of the lenses. Consequently, the distance between the lenses had to be adjusted in order to achieve an afocal system. We added a paragraph to the manuscript to clarify this point in Section 2.1 (lines 131-133).

 

Comments 4: Please explain why one should prefer 3D printed over conventional optics. The article lacks an extensive discussion of the pros and cons of using 3D printed lenses. There are some generic points brought up about 3D printed optics in the manuscript, but there needs to be a concrete discussion. One weak point I observe is that significant post-processing is required to achieve acceptable quality optics, which essentially undermines the argument of cheap and easily produced optics. Overall, I would prefer a slightly different article structure. I think it would be beneficial to include a discussion section where the findings are discussed extensively, presenting the advantages as well as the limitations of the 3D printed telescope.

Response 4:

We agree with and thank the Reviewer for this comment. We have added a Discussion section to the manuscript to address the findings, as well as the limitations, advantages and disadvantages of the work. This content is included in Section 5, lines 325–384.

We also agree that the time and cost associated with traditional polishing methods are high. Nevertheless, the final cost of our complete telescope remains lower than that of a commercial device. Currently, we are developing a new surface finishing technique for 3D-printed lenses that does not require traditional polishing, and the results obtained so far are very promising. We have achieved a completely transparent surface in just five minutes. These findings will be presented in a future publication.

Comments 5: One limitation of the article is the validation on a single patient. I believe that if the authors want to present clinically significant results (visual acuity comparison, etc.) and draw performance conclusions from them, they will need to include many more subjects. Alternatively, they can present this single patient only to demonstrate clinical feasibility, but this needs to be clearly stated in the manuscript.

Response 5:

We agree with the Reviewer. We have clarified in the manuscript that a proof-of-concept test was carried out in a patient as part of the validation process. This information has been added to the Abstract, Section 1 (line 93), Section 4 (line 287), and Section 5 (line 328) of the manuscript.

Comments 6: Albeit minor, I think that since this system will be handled by the patient, to mention whether it is toxic free and safe for handling.

Response 6:

We appreciate all comments, whether minor or major, as they help us improve our work. According to FormLabs, its standard resins are designed to be as safe as or safer to handle than common household chemicals or adhesives. When assessing potential acute health effects from inhalation or ingestion, no significant effects or critical hazards are known.

https://support.formlabs.com/s/article/Resin-Care?language=en_US

 

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents a novel and highly impactful approach to fabricating Galilean telescopes using 3D printing (Stereolithography) for low vision patients. The work is well-motivated, methodologically sound, and demonstrates promising clinical results. It also addresses a real-world problem and shows measurable improvement. However, there are several areas where the manuscript could be improved in terms of clarity, structure, and scientific depth.

• The sample size is unclear on patients. Paper shows data from one patient only, which is acceptable. But, need to mention "proof-of-concept" in the summary. 
• 3D printing is well explained. It is recommended to add a few sentences to compare the cost of traditional method vs 3D printing. 
• Clear Resin V4.0 is chosen for fabrication. It is unclear why this choice was made over other available options. 
• Stereolithography, specifically 2-photon polymerization based methods have shown great control and finish for nm scale 3D prints as well. It would be good to add some text about use of 2PP methods in future for enhancing this even more. Few work to be visited:
  
  • Ovsianikov, A., Farsari, M., & Chichkov, B. N. (2011). Photonic and biomedical applications of the Two-photon polymerization technique. In Stereolithography: Materials, Processes and Applications (pp. 257-297). Boston, MA: Springer US.
  • Singhal, A., Dalmiya, A., Lynch, P. T., & Paprotny, I. (2023). 2-photon polymerized IP-DIP 3D photonic crystals for Mid IR spectroscopic applications. IEEE Photonics Technology Letters, 35(8), 410-413.
  • Thompson, Jessica R., et al. "Two-photon polymerized poly (caprolactone) retinal cell delivery scaffolds and their systemic and retinal biocompatibility." Acta biomaterialia 94 (2019): 204-218.
• Can choosing a different material improve chromatic aberration? and also improve device performance? 
• Please add 1-2 sentences for future work in section 5. Conclusions.

Comments on the Quality of English Language

Manuscript has some grammatical errors. Recommend another revision.

Author Response

Comments 1: The sample size is unclear on patients. Paper shows data from one patient only, which is acceptable. But, need to mention "proof-of-concept" in the summary. 

Response 1:

We agree with the Reviewer. We have clarified in the manuscript that a proof-of-concept test was carried out in a patient as part of the validation process. This information has been added to the Abstract, Section 1 (line 93), Section 4 (line 287), and Section 5 (line 328) of the manuscript.

Comments 2: 3D printing is well explained. It is recommended to add a few sentences to compare the cost of traditional method vs 3D printing. 

Response 2:

We thank the Reviewer’s comment. We added these sentences to Section 5, lines 325-384.

Comments 3: Clear Resin V4.0 is chosen for fabrication. It is unclear why this choice was made over other available options. 

Response 3:

We thank this observation. The resin used in this study was selected based on FormLabs’ official recommendations for printing transparent components, as indicated on their website. According to the manufacturer, this material is specifically formulated to produce clear parts suitable for optical applications, which made it a suitable choice for the proof-of-concept stage of our work.

https://formlabs.com/blog/creating-camera-lenses-with-stereolithography/?srsltid=AfmBOoq1WPkeBUMUb_bGdW_gAyWOjpc0tdbes8AuTTB0nmfpIIjlSKqW

Comments 4: Stereolithography, specifically 2-photon polymerization based methods have shown great control and finish for nm scale 3D prints as well. It would be good to add some text about use of 2PP methods in future for enhancing this even more. Few work to be visited:

• Ovsianikov, A., Farsari, M., & Chichkov, B. N. (2011). Photonic and biomedical applications of the Two-photon polymerization technique. In Stereolithography: Materials, Processes and Applications (pp. 257-297). Boston, MA: Springer US.
• Singhal, A., Dalmiya, A., Lynch, P. T., & Paprotny, I. (2023). 2-photon polymerized IP-DIP 3D photonic crystals for Mid IR spectroscopic applications. IEEE Photonics Technology Letters, 35(8), 410-413.
• Thompson, Jessica R., et al. "Two-photon polymerized poly (caprolactone) retinal cell delivery scaffolds and their systemic and retinal biocompatibility." Acta biomaterialia 94 (2019): 204-218.

Response 4:

We thank the Reviewer for this insightful suggestion. We agree that 2-photon polymerization (2PP) represents a highly promising technique for achieving nanometric resolution and exceptional surface quality in 3D-printed optics. We have added a brief discussion on the potential application of 2PP for future enhancement of our approach in Section 5 (lines 375-379), along with citations to relevant studies recommended by the Reviewer.

Comments 5: Can choosing a different material improve chromatic aberration? and also improve device performance? 

Response 5:

We agree with the Reviewer. By selecting a different material—whether a resin or a glass—that lets us fabricate a Flint lens and a Crown lens, we could reduce chromatic aberration. Nevertheless, because this is not the primary aim of the present work, the search for new materials will be undertaken at a later stage.

Comments 6: Please add 1-2 sentences for future work in section 5. Conclusions.

Response 6:

We thank this comment. We have added future work to Section 5, lines 368-384.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed all of my concerns and comments.