Orbit, 2014; 33(6): 428–432 ! Informa Healthcare USA, Inc. ISSN: 0167-6830 print / 1744-5108 online DOI: 10.3109/01676830.2014.949793
ORIGINAL ARTICLE
Optical Coherence Tomography Imaging of the Proximal Lacrimal System James R. Wawrzynski1, Julie Smith1, Anant Sharma1, and George M. Saleh2,3 Bedford Hospital NHS Trust, South Wing, Kempston Road, Bedford, United Kingdom, 2NIHR Biomedical Research Centre at Moorfields Eye Hospital, London, United Kingdom, and 3UCL Institute of Ophthalmology, Moorfields Eye Hospital, London, United Kingdom Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
1
ABSTRACT Introduction: There are currently no routinely used imaging modalities for the proximal lacrimal system. Optical Coherence Tomography (OCT) is a safe and non-invasive method of high resolution cross-sectional imaging of tissue microstructures using infra-red radiation. In this study we investigate whether OCT may be used to image the punctum and proximal canaliculus. Methods: A cohort of healthy subjects with normal ocular anatomy and no symptoms of epiphora were prospectively invited to enrol. Spectral OCT images of the lower punctae were captured with a Topcon 3D Optical Coherence Tomography 2000 machine. Measurements were made of the maximal punctal diameter, canalicular diameter and canalicular depth. Our data for depth of the vertical canaliculus was compared to the widely quoted figure of 2 mm using a two-tailed t-test to check for a statistically significant difference at p50.05. Results: Thirty-six punctae of 18 subjects were scanned. The punctum was recognisable on the OCT image in all cases. The mean depth, width and cross- sectional area of the visualised canaliculi were 0.753 mm (SD 0.216), 0.110 mm (SD 0.067) and 9.49 10 3 mm2, respectively. The mean width of the punctum was 0.247 mm (SD 0.078). Discussion: We have demonstrated the first in-vivo high resolution images of normal punctal and vertical canalicular anatomy using spectral OCT. There is currently no other practical way to accurately image punctal and proximal canalicular morphology in vivo. OCT is a convenient and readily available tool in most eye clinics with resolution ideally suited for imaging of the punctum and proximal canaliculus. Keywords: Epiphora, In Vivo, lacrimal, OCT, punctum
INTRODUCTION
is also relevant to the design of punctal plugs and the assessment of their function. However there are currently no routinely used imaging modalities or objective quantitative assessment systems for the proximal lacrimal system. Optical Coherence Tomography (OCT) is a safe and non-invasive method of high resolution crosssectional imaging for tissue microstructures using infrared radiation. This technology was first described by Huang et al.2 in 1991; it has a resolution of 1–20 mm and can penetrate approximately 1–2 mm into the tissue.3 In this study we investigated the
The human lacrimal drainage system comprises an upper and lower punctum situated towards the medial end of both sets of eyelids. The lower punctum connects to a 2 mm section of descending vertical canaliculus before turning medially for 8 mm and eventually joining with the superior canaliculus then into the lacrimal sac.1 Punctal anatomy is clinically relevant in the management of epiphora because punctal stenosis is one of the many causes of this condition. Punctal anatomy
Received 29 May 2014; Revised 14 July 2014; Accepted 27 July 2014; Published online 12 September 2014 Correspondence: Dr. George Saleh, Consultant Ophthalmic and Oculoplastic Surgeon, Faculty Investigator at the NIHR Biomedical Research Centre at Moorfields Eye Hospital and the UCL Institute of Ophthalmology, CTC and NIHR BRC, 162 City Road, Moorfields Eye Hospital, London EC1V 2PD. E-mail: [email protected]
428
OCT Imaging of the Proximal Lacrimal System 429 feasibility of OCT imaging as applied to the punctum and proximal canaliculus.
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
MATERIALS AND METHODS A Topcon 3D Optical Coherence Tomography 2000 machine (Itabashi-ku, Tokyo, Japan) was used to create spectral OCT images of the left and right lower punctae of enrolled subjects. This technique was first proposed and demonstrated by one of the authors (AS). Inclusion criteria included healthy subjects who had no symptoms of epiphora and no background of ocular or oculoplastic pathology. The subjects were all members of staff at our eye clinic. Investigations were performed in accordance with the ethical standards defined by the Declarations of Helsinki. Full Institutional Review Board approval was awarded for this study. The medial lower lid was gently everted with care taken not to distort the anatomy to expose the punctum to the OCT scanner. Thus the vertical canaliculus was brought into the axial plane. Cross sectional and three-dimensional images were obtained using the anterior segment setting of the OCT machine. A total surface area of 6 mm 6 mm
was scanned using infra-red light of wavelength 840 nm. The scan speed was 50,000 images per second. This image was generated from 128 horizontal sections, each 47 mm apart (B scans). Each horizontal section was itself made up of 512 points (A scans). Vertical resolution was 47 mm, horizontal resolution was 20 mm and longitudinal resolution was 5 mm. A corresponding photograph was also produced to guide navigation of the OCT images (see Figure 1). OCT imaging was repeated three times in each patient. In each case all axial OCT sections were inspected by the operator and the section with the widest and deepest punctum and canaliculus was chosen. Measurements were made of the maximal punctal diameter, canalicular diameter and canalicular depth using the OCT scanner’s software version 7.11. The two-dimensional images were subsequently combined to render three-dimensional images (see Figure 2). The mean two-dimensional cross-sectional surface area and three-dimensional volume of the canaliculi was calculated assuming the canaliculus to be roughly cylindrical. Our data for depth of the vertical canaliculus was compared to the widely quoted value of 2 mm using a two-tailed t-test to check for statistically significant similarity or difference at p50.05.
FIGURE 1. Above; lower punctum and canaliculus of the right eye of subject 2. This is an example of a subject with a wide punctum and a long section of visualised vertical canaliculus. Below; lower punctum and canaliculus of the right eye of subject 9. This is an example of a subject with a narrow punctum but a long section of visualised vertical canaliculus. !
2014 Informa Healthcare USA, Inc.
430 J. R. Wawrzynski et al.
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
TABLE 1. Dimensions of the proximal lacrimal system of all 18 subjects.
FIGURE 2. Three-dimensional OCT scan rendition of the lower punctum of the left eye of subject 1, seen from above and posteriorly.
RESULTS Thirty-six punctae of 18 asymptomatic subjects were scanned. Results are seen in Table 1. The punctum was recognisable on the OCT image in all cases. The depth of the visualised canaliculus varied between 0.392 mm and 1.242 mm with a mean of 0.753 mm and a standard deviation of 0.216 mm. A two-tailed t-test revealed that our mean was statistically different to the 2-mm mean widely reported in the literature (p50.05).1,4,5 The width of the punctum varied between 0.104 mm and 0.401 mm with a mean of 0.247 mm and a standard deviation of 0.078 mm. The width of the canaliculus varied between zero and 0.226 mm with a mean of 0.110 mm and a standard deviation of 0.067 mm. The mean canalicular cross-sectional area was 9.49 10 3 mm2 and the mean volume of canaliculus that we could visualise was 7.15 10 3 mm3. There was no statistically significant correlation between punctal diameter and vertical canalicular length (Pearson product-moment correlation coefficient 0.23, p = 0.20). The distribution of vertical canalicular lengths followed a normal distribution (Kolmogorov-Smirnov test p40.05).
DISCUSSION We have demonstrated the first in-vivo, high resolution, images of normal punctal and vertical canalicular anatomy using spectral OCT. There is currently no other practical way to accurately image punctal and proximal canalicular morphology in vivo. OCT is a practical and readily available tool in most eye clinics. Its resolution is ideally suited to imaging of the punctum and proximal canaliculus. Ultrasound
Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject
1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18
Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left
Canalicular length/mm
Peak width of proximal lacrimal system/mm
970 1022 978 867 731 590 913 1109 1242 1150 709 643 735 771 771 769 990 898 979 460 392 558 572 777 528 539 472 691 393 1050 647 647 752 628 589 585
237 334 347 126 234 175 329 139 337 401 173 334 172 240 140 207 163 245 194 171 238 327 215 309 104 131 289 379 272 342 232 216 242 310 272 313
imaging of the proximal lacrimal system has been suggested in the past;6 however, it produced poorer images than OCT because of its much lower resolution. Ultrasound also differs from OCT in that the probe must touch the eyelid since air is a poor conductor of ultrasound waves. This may be uncomfortable for patients. By contrast, electromagnetic radiation travels readily through air allowing OCT images to be generated without touching the eye. In this feasibility study we have developed a standard protocol for a trained operator to generate two- and three-dimensional high-resolution OCT images of the lower punctum and canaliculus. The imaging sequence was completed in seconds. Our results show a mean canalicular depth of 0.753 mm, which is shorter than the frequently quoted value of 2 mm. The explanation for this is likely to be in part related to the poor penetrance of the infrared light through skin as compared to its excellent penetrance through the cornea. This is due to scattering of light caused by the random arrangement of Orbit
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
OCT Imaging of the Proximal Lacrimal System 431 collagen fibres in the skin as opposed to the orthogonal arrangement found in the cornea.1,7 Punctal OCT therefore relies on the scanner’s infra-red beam traveling directly through the canaliculus rather than through the surrounding skin. As a result, alignment of the punctum and canaliculus with the axis of the scanner’s infra-red beam is essential. This is consistent with our finding that the walls of the canaliculus come together as a ‘‘V shape’’ in nearly all cases. It is further evidenced by our finding that altering the axis of the scanner in relation to the eyelid can have a significant impact on the length of visualised canaliculus and the steepness of the ‘‘V shape.’’ It is therefore advisable to take the longest of three canalicular measurements as the true length. However even the longest canaliculus that we imaged (1.2 mm) was still much shorter than 2 mm; therefore, some further explanation is required: Once optimal alignment is achieved, it is unlikely that difficulty receiving a signal from deep inside the vertical canaliculus further contributes to the short mean canalicular depth because the distribution of canalicular lengths were found to follow a normal distribution rather than having a sharp cut off. In addition, there was no correlation between punctal diameter and canalicular length therefore it is unlikely that the narrow aperture of the punctum is limiting the ability of the OCT machine to image inside the canaliculus. The data may call into question the theory that the canaliculi are pulled open when the eyelids open,5 or whether the widely quoted figure of 2 mm is accurate;1,4,5 There is a paucity of cadaveric anatomical studies detailing variation in the length of the inferior vertical canaliculus. One cadaveric histological study does favour a length of 1 mm rather than 2 mm.8 It is also possible that in some cases the vertical canaliculus either turns or collapses after about 1 mm. With the advent of more sensitive imaging modalities such as OCT, more accurate data may be acquired. We had a small sample size because this was a feasibility study; as a further normative pool of data is acquired a clearer picture is likely to emerge. As the walls of the canaliculus often appear to come together in a ‘‘V shape,’’ it is difficult to decide at which point to measure the diameter of the canaliculus. As discussed above, this effect is likely to be due to the direction of the OCT cross sections running at a slightly different angle to the long axis of the canaliculus. Therefore we assumed the widest diameter seen just distal to the punctum to be the true width of the canaliculus. Future studies will image a greater number of asymptomatic patients to establish the normal anatomy and normal anatomical variants in more detail. Currently, assessment of punctal stenosis is based mainly on a subjective examination under the slit lamp. In 2003 Kashkouli et al.9 introduced a grading !
2014 Informa Healthcare USA, Inc.
system for punctal stenosis based on appearance under the slit lamp. However, such examination is restricted to external viewing of the punctum and remains partially subjective. No clear association was found between grade of stenosis and either symptoms or the effectiveness of punctoplasty. Probing with a syringe may be similarly unreliable since it may cause dilatation of the punctum/ canaliculus thus not giving an accurate representation of the patient’s normal anatomy. In clinical practice a subjective simple external examination of the punctum under the slit lamp in combination with syringing and tear film analysis is often used to decide on the need for surgery. There are no routinely used imaging modalities for the proximal lacrimal system: Development of an objective system for imaging the punctum is warranted. Further planned work will investigate the applicability of this method to clinical decision making in symptomatic patients. Shahid et al.10 recently highlighted two challenges in the treatment of patients with punctal stenosis. Firstly, 36% of their patients did not have resolution of symptoms after surgery, even though three quarters of these patients had anatomical success. Secondly, 9% of patients did not achieve anatomical patency after surgery. The first of these challenges could be addressed initially by undertaking a comparison between OCT versus current methods of pre-operative assessment of the punctum. Punctal OCT may also be a more reliable method of assessing anatomical success postoperatively. The second challenge could be addressed by using OCT to investigate the morphology of punctal stenosis in a wide variety of pre-operative patients. A comparison of their post-operative results may elucidate the applicability of OCT to patient selection for punctoplasty. These data may also reveal whether there is a role for OCT in the tailoring of surgical technique to the individual (one-snip, twosnip, three-snip, stenting, balloon dilation or posterior ampullectomy). In conclusion, we have shown that OCT may be used to create high resolution images of the lacrimal punctum and canaliculus. Further work is required to establish its clinical applicability on a wider scale.
ACKNOWLEDGEMENTS The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. The research was supported and part funded by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology.
432 J. R. Wawrzynski et al.
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
REFERENCES
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
1. Snell RS, Lemp MA. Clinical Anatomy of the Eye. London: Blackwell Science; 1998. 2. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991;254(5035):1178–1181. 3. Vakoc BJ, Fukumura D, Jain RK, Bouma BE. Cancer imaging by optical coherence tomography: preclinical progress and clinical potential. Nat Rev Cancer 2012; 12(5):363–368. 4. Sultanov M. X-ray anatomy of lacrimal canaliculi. Vestnik oftalmologii 1995;111(2):28–30.
5. Herranz RM, Herran RMC, eds. Ocular Surface: anatomy and Physiology, Disorders and Therapeutic Care. Boca Raton, FL: CRC Press, 2012. 6. Hurwitz JJ, Pavlin CJ, Hassan A. Proximal canalicular imaging utilizing ultrasound biomicroscopy A: normal canaliculi. Orbit 1998;17(1):S27–S30. 7. Keene DR, Engvall E, Glanville RW. ‘‘Ultrastructure of type VI collagen in human skin and cartilage suggests an anchoring function for this filamentous network’’. J Cell Biol 1988;107(5):1995–2006. 8. Hwang K, Kim DJ, Hwang SH. Anatomy of lower lacrimal canaliculus relative to epicanthoplasty. Journal of Craniofacial Surgery 2005;16(6):949–952. 9. Kashkouli MB, Beigi B, Murthy R, Astbury N. Acquired external punctal stenosis: etiology and associated findings. Amer J Ophthalmol 2003;136(6):1079–1084. 10. Shahid H, Sandhu A, Keenan T, Pearson A. Factors affecting outcome of punctoplasty surgery: a review of 205 cases. Br J Ophthalmol 2008;92(12): 1689–1692.
Orbit
ORIGINAL ARTICLE
Optical Coherence Tomography Imaging of the Proximal Lacrimal System James R. Wawrzynski1, Julie Smith1, Anant Sharma1, and George M. Saleh2,3 Bedford Hospital NHS Trust, South Wing, Kempston Road, Bedford, United Kingdom, 2NIHR Biomedical Research Centre at Moorfields Eye Hospital, London, United Kingdom, and 3UCL Institute of Ophthalmology, Moorfields Eye Hospital, London, United Kingdom Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
1
ABSTRACT Introduction: There are currently no routinely used imaging modalities for the proximal lacrimal system. Optical Coherence Tomography (OCT) is a safe and non-invasive method of high resolution cross-sectional imaging of tissue microstructures using infra-red radiation. In this study we investigate whether OCT may be used to image the punctum and proximal canaliculus. Methods: A cohort of healthy subjects with normal ocular anatomy and no symptoms of epiphora were prospectively invited to enrol. Spectral OCT images of the lower punctae were captured with a Topcon 3D Optical Coherence Tomography 2000 machine. Measurements were made of the maximal punctal diameter, canalicular diameter and canalicular depth. Our data for depth of the vertical canaliculus was compared to the widely quoted figure of 2 mm using a two-tailed t-test to check for a statistically significant difference at p50.05. Results: Thirty-six punctae of 18 subjects were scanned. The punctum was recognisable on the OCT image in all cases. The mean depth, width and cross- sectional area of the visualised canaliculi were 0.753 mm (SD 0.216), 0.110 mm (SD 0.067) and 9.49 10 3 mm2, respectively. The mean width of the punctum was 0.247 mm (SD 0.078). Discussion: We have demonstrated the first in-vivo high resolution images of normal punctal and vertical canalicular anatomy using spectral OCT. There is currently no other practical way to accurately image punctal and proximal canalicular morphology in vivo. OCT is a convenient and readily available tool in most eye clinics with resolution ideally suited for imaging of the punctum and proximal canaliculus. Keywords: Epiphora, In Vivo, lacrimal, OCT, punctum
INTRODUCTION
is also relevant to the design of punctal plugs and the assessment of their function. However there are currently no routinely used imaging modalities or objective quantitative assessment systems for the proximal lacrimal system. Optical Coherence Tomography (OCT) is a safe and non-invasive method of high resolution crosssectional imaging for tissue microstructures using infrared radiation. This technology was first described by Huang et al.2 in 1991; it has a resolution of 1–20 mm and can penetrate approximately 1–2 mm into the tissue.3 In this study we investigated the
The human lacrimal drainage system comprises an upper and lower punctum situated towards the medial end of both sets of eyelids. The lower punctum connects to a 2 mm section of descending vertical canaliculus before turning medially for 8 mm and eventually joining with the superior canaliculus then into the lacrimal sac.1 Punctal anatomy is clinically relevant in the management of epiphora because punctal stenosis is one of the many causes of this condition. Punctal anatomy
Received 29 May 2014; Revised 14 July 2014; Accepted 27 July 2014; Published online 12 September 2014 Correspondence: Dr. George Saleh, Consultant Ophthalmic and Oculoplastic Surgeon, Faculty Investigator at the NIHR Biomedical Research Centre at Moorfields Eye Hospital and the UCL Institute of Ophthalmology, CTC and NIHR BRC, 162 City Road, Moorfields Eye Hospital, London EC1V 2PD. E-mail: [email protected]
428
OCT Imaging of the Proximal Lacrimal System 429 feasibility of OCT imaging as applied to the punctum and proximal canaliculus.
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
MATERIALS AND METHODS A Topcon 3D Optical Coherence Tomography 2000 machine (Itabashi-ku, Tokyo, Japan) was used to create spectral OCT images of the left and right lower punctae of enrolled subjects. This technique was first proposed and demonstrated by one of the authors (AS). Inclusion criteria included healthy subjects who had no symptoms of epiphora and no background of ocular or oculoplastic pathology. The subjects were all members of staff at our eye clinic. Investigations were performed in accordance with the ethical standards defined by the Declarations of Helsinki. Full Institutional Review Board approval was awarded for this study. The medial lower lid was gently everted with care taken not to distort the anatomy to expose the punctum to the OCT scanner. Thus the vertical canaliculus was brought into the axial plane. Cross sectional and three-dimensional images were obtained using the anterior segment setting of the OCT machine. A total surface area of 6 mm 6 mm
was scanned using infra-red light of wavelength 840 nm. The scan speed was 50,000 images per second. This image was generated from 128 horizontal sections, each 47 mm apart (B scans). Each horizontal section was itself made up of 512 points (A scans). Vertical resolution was 47 mm, horizontal resolution was 20 mm and longitudinal resolution was 5 mm. A corresponding photograph was also produced to guide navigation of the OCT images (see Figure 1). OCT imaging was repeated three times in each patient. In each case all axial OCT sections were inspected by the operator and the section with the widest and deepest punctum and canaliculus was chosen. Measurements were made of the maximal punctal diameter, canalicular diameter and canalicular depth using the OCT scanner’s software version 7.11. The two-dimensional images were subsequently combined to render three-dimensional images (see Figure 2). The mean two-dimensional cross-sectional surface area and three-dimensional volume of the canaliculi was calculated assuming the canaliculus to be roughly cylindrical. Our data for depth of the vertical canaliculus was compared to the widely quoted value of 2 mm using a two-tailed t-test to check for statistically significant similarity or difference at p50.05.
FIGURE 1. Above; lower punctum and canaliculus of the right eye of subject 2. This is an example of a subject with a wide punctum and a long section of visualised vertical canaliculus. Below; lower punctum and canaliculus of the right eye of subject 9. This is an example of a subject with a narrow punctum but a long section of visualised vertical canaliculus. !
2014 Informa Healthcare USA, Inc.
430 J. R. Wawrzynski et al.
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
TABLE 1. Dimensions of the proximal lacrimal system of all 18 subjects.
FIGURE 2. Three-dimensional OCT scan rendition of the lower punctum of the left eye of subject 1, seen from above and posteriorly.
RESULTS Thirty-six punctae of 18 asymptomatic subjects were scanned. Results are seen in Table 1. The punctum was recognisable on the OCT image in all cases. The depth of the visualised canaliculus varied between 0.392 mm and 1.242 mm with a mean of 0.753 mm and a standard deviation of 0.216 mm. A two-tailed t-test revealed that our mean was statistically different to the 2-mm mean widely reported in the literature (p50.05).1,4,5 The width of the punctum varied between 0.104 mm and 0.401 mm with a mean of 0.247 mm and a standard deviation of 0.078 mm. The width of the canaliculus varied between zero and 0.226 mm with a mean of 0.110 mm and a standard deviation of 0.067 mm. The mean canalicular cross-sectional area was 9.49 10 3 mm2 and the mean volume of canaliculus that we could visualise was 7.15 10 3 mm3. There was no statistically significant correlation between punctal diameter and vertical canalicular length (Pearson product-moment correlation coefficient 0.23, p = 0.20). The distribution of vertical canalicular lengths followed a normal distribution (Kolmogorov-Smirnov test p40.05).
DISCUSSION We have demonstrated the first in-vivo, high resolution, images of normal punctal and vertical canalicular anatomy using spectral OCT. There is currently no other practical way to accurately image punctal and proximal canalicular morphology in vivo. OCT is a practical and readily available tool in most eye clinics. Its resolution is ideally suited to imaging of the punctum and proximal canaliculus. Ultrasound
Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject Subject
1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12 12 13 13 14 14 15 15 16 16 17 17 18 18
Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left Right Left
Canalicular length/mm
Peak width of proximal lacrimal system/mm
970 1022 978 867 731 590 913 1109 1242 1150 709 643 735 771 771 769 990 898 979 460 392 558 572 777 528 539 472 691 393 1050 647 647 752 628 589 585
237 334 347 126 234 175 329 139 337 401 173 334 172 240 140 207 163 245 194 171 238 327 215 309 104 131 289 379 272 342 232 216 242 310 272 313
imaging of the proximal lacrimal system has been suggested in the past;6 however, it produced poorer images than OCT because of its much lower resolution. Ultrasound also differs from OCT in that the probe must touch the eyelid since air is a poor conductor of ultrasound waves. This may be uncomfortable for patients. By contrast, electromagnetic radiation travels readily through air allowing OCT images to be generated without touching the eye. In this feasibility study we have developed a standard protocol for a trained operator to generate two- and three-dimensional high-resolution OCT images of the lower punctum and canaliculus. The imaging sequence was completed in seconds. Our results show a mean canalicular depth of 0.753 mm, which is shorter than the frequently quoted value of 2 mm. The explanation for this is likely to be in part related to the poor penetrance of the infrared light through skin as compared to its excellent penetrance through the cornea. This is due to scattering of light caused by the random arrangement of Orbit
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
OCT Imaging of the Proximal Lacrimal System 431 collagen fibres in the skin as opposed to the orthogonal arrangement found in the cornea.1,7 Punctal OCT therefore relies on the scanner’s infra-red beam traveling directly through the canaliculus rather than through the surrounding skin. As a result, alignment of the punctum and canaliculus with the axis of the scanner’s infra-red beam is essential. This is consistent with our finding that the walls of the canaliculus come together as a ‘‘V shape’’ in nearly all cases. It is further evidenced by our finding that altering the axis of the scanner in relation to the eyelid can have a significant impact on the length of visualised canaliculus and the steepness of the ‘‘V shape.’’ It is therefore advisable to take the longest of three canalicular measurements as the true length. However even the longest canaliculus that we imaged (1.2 mm) was still much shorter than 2 mm; therefore, some further explanation is required: Once optimal alignment is achieved, it is unlikely that difficulty receiving a signal from deep inside the vertical canaliculus further contributes to the short mean canalicular depth because the distribution of canalicular lengths were found to follow a normal distribution rather than having a sharp cut off. In addition, there was no correlation between punctal diameter and canalicular length therefore it is unlikely that the narrow aperture of the punctum is limiting the ability of the OCT machine to image inside the canaliculus. The data may call into question the theory that the canaliculi are pulled open when the eyelids open,5 or whether the widely quoted figure of 2 mm is accurate;1,4,5 There is a paucity of cadaveric anatomical studies detailing variation in the length of the inferior vertical canaliculus. One cadaveric histological study does favour a length of 1 mm rather than 2 mm.8 It is also possible that in some cases the vertical canaliculus either turns or collapses after about 1 mm. With the advent of more sensitive imaging modalities such as OCT, more accurate data may be acquired. We had a small sample size because this was a feasibility study; as a further normative pool of data is acquired a clearer picture is likely to emerge. As the walls of the canaliculus often appear to come together in a ‘‘V shape,’’ it is difficult to decide at which point to measure the diameter of the canaliculus. As discussed above, this effect is likely to be due to the direction of the OCT cross sections running at a slightly different angle to the long axis of the canaliculus. Therefore we assumed the widest diameter seen just distal to the punctum to be the true width of the canaliculus. Future studies will image a greater number of asymptomatic patients to establish the normal anatomy and normal anatomical variants in more detail. Currently, assessment of punctal stenosis is based mainly on a subjective examination under the slit lamp. In 2003 Kashkouli et al.9 introduced a grading !
2014 Informa Healthcare USA, Inc.
system for punctal stenosis based on appearance under the slit lamp. However, such examination is restricted to external viewing of the punctum and remains partially subjective. No clear association was found between grade of stenosis and either symptoms or the effectiveness of punctoplasty. Probing with a syringe may be similarly unreliable since it may cause dilatation of the punctum/ canaliculus thus not giving an accurate representation of the patient’s normal anatomy. In clinical practice a subjective simple external examination of the punctum under the slit lamp in combination with syringing and tear film analysis is often used to decide on the need for surgery. There are no routinely used imaging modalities for the proximal lacrimal system: Development of an objective system for imaging the punctum is warranted. Further planned work will investigate the applicability of this method to clinical decision making in symptomatic patients. Shahid et al.10 recently highlighted two challenges in the treatment of patients with punctal stenosis. Firstly, 36% of their patients did not have resolution of symptoms after surgery, even though three quarters of these patients had anatomical success. Secondly, 9% of patients did not achieve anatomical patency after surgery. The first of these challenges could be addressed initially by undertaking a comparison between OCT versus current methods of pre-operative assessment of the punctum. Punctal OCT may also be a more reliable method of assessing anatomical success postoperatively. The second challenge could be addressed by using OCT to investigate the morphology of punctal stenosis in a wide variety of pre-operative patients. A comparison of their post-operative results may elucidate the applicability of OCT to patient selection for punctoplasty. These data may also reveal whether there is a role for OCT in the tailoring of surgical technique to the individual (one-snip, twosnip, three-snip, stenting, balloon dilation or posterior ampullectomy). In conclusion, we have shown that OCT may be used to create high resolution images of the lacrimal punctum and canaliculus. Further work is required to establish its clinical applicability on a wider scale.
ACKNOWLEDGEMENTS The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. The research was supported and part funded by the National Institute for Health Research (NIHR) Biomedical Research Centre based at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology.
432 J. R. Wawrzynski et al.
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
REFERENCES
Orbit Downloaded from informahealthcare.com by Nyu Medical Center on 05/27/15 For personal use only.
1. Snell RS, Lemp MA. Clinical Anatomy of the Eye. London: Blackwell Science; 1998. 2. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991;254(5035):1178–1181. 3. Vakoc BJ, Fukumura D, Jain RK, Bouma BE. Cancer imaging by optical coherence tomography: preclinical progress and clinical potential. Nat Rev Cancer 2012; 12(5):363–368. 4. Sultanov M. X-ray anatomy of lacrimal canaliculi. Vestnik oftalmologii 1995;111(2):28–30.
5. Herranz RM, Herran RMC, eds. Ocular Surface: anatomy and Physiology, Disorders and Therapeutic Care. Boca Raton, FL: CRC Press, 2012. 6. Hurwitz JJ, Pavlin CJ, Hassan A. Proximal canalicular imaging utilizing ultrasound biomicroscopy A: normal canaliculi. Orbit 1998;17(1):S27–S30. 7. Keene DR, Engvall E, Glanville RW. ‘‘Ultrastructure of type VI collagen in human skin and cartilage suggests an anchoring function for this filamentous network’’. J Cell Biol 1988;107(5):1995–2006. 8. Hwang K, Kim DJ, Hwang SH. Anatomy of lower lacrimal canaliculus relative to epicanthoplasty. Journal of Craniofacial Surgery 2005;16(6):949–952. 9. Kashkouli MB, Beigi B, Murthy R, Astbury N. Acquired external punctal stenosis: etiology and associated findings. Amer J Ophthalmol 2003;136(6):1079–1084. 10. Shahid H, Sandhu A, Keenan T, Pearson A. Factors affecting outcome of punctoplasty surgery: a review of 205 cases. Br J Ophthalmol 2008;92(12): 1689–1692.
Orbit
