Investigation of the Lower Punctum Parameters: A Spectral Domain Anterior Segment Optical Coherence Tomography Study.

PURPOSE: To evaluate the dimensions of lower punctum in a sample of Iranian normal population using spectral domain anterior segment optical coherence tomography (OCT).
METHODS: In this cross-sectional study, 102 eyes of 102 healthy volunteers were enrolled. All participants underwent a detailed history and complete ophthalmic examination. Lower punctum metrics were measured using OCT (Spectralis, Heidelberg) with the anterior segment module. External punctal diameter was defined as the largest diameter at the surface of the punctum. Internal punctal diameter was measured at two different depths of 100 μm and 500 μm from the external surface. Measurements were repeated for 30% of data by another grader. The agreement was measured using intraclass correlation coefficient (ICC).
RESULTS: The mean age of the participants was 61.5 ± 7.9 years. The mean external punctal diameter was 425.6 ± 124.3 μm. The mean internal punctal diameter at 100 μm and 500 μm was 183 ± 97.5 μm and 77.7 ± 51.4 μm, respectively. The agreement between the graders was high in assessing all punctal characteristics (ICC >0.9 for all measurements).
CONCLUSION: The spectral domain OCT can be used for measuring lower punctum diameter with acceptable reproducibility. Copyright:

INTRODUCTION

The punctum is the only visible part of the tear drainage system. The upper and lower eyelid punctum are located at the apex of the lacrimal papillae on the upper and lower eyelid margins.1 Understanding the normal anatomy of the punctum is essential to treat a variety of diseases such as stenosis or improper dilatation of the punctum, which could lead to disruption of the tear flow.2 Furthermore, understanding the normal punctum anatomy could be helpful for more accurate design of punctal plugs.

Most of our knowledge about the normal anatomy of lacrimal drainage system has come from cadaver studies. However, numerous methods such as ultrasonography have been used for accurate measuring of the anatomical dimensions in in vivo condition.34 Recently, optical coherence tomography (OCT) has been introduced to assess the punctum and proximal part of canaliculus. Wawrzynski et al.5 showed that OCT could provide high-resolution images of the punctum and vertical canaliculus. However, normal values of these OCT measures have yet to be determined in different populations. The aim of this study was to evaluate the lower punctum features in Iranian normal population using OCT.

METHODS

In this cross-sectional study, healthy volunteers aged between 20 and 70 years were recruited. Most of them were companies of the outpatients referred to Khatam-Al-Anbia Eye Hospital, Mashhad, Iran. The study protocol was approved by the Ethics Committee of Mashhad University of Medical Sciences (Ethics code of IR.MUMS.fm.REC.1396.764). Written informed consent was obtained from all participants. The study protocol adhered to the Declaration of Helsinki.

All participants underwent a detailed history and complete ophthalmic examination. Lid margins were thoroughly examined. Slit-lamp biomicroscopy and evaluation of the ocular surface were performed as well. The subjects with epiphora, long-term use of ocular drops except for artificial tears, previous history of chemotherapy, lower eyelid anomalies, lesions or history of the lid and lacrimal drainage disease, or surgery were excluded. Patients with tear meniscus height >2 mm or tear break-up time test <5 s were also excluded. In each patient, only one eye was enrolled in the study.

All OCT images were obtained by one experienced operator on a separate day without any further manipulation for ophthalmic examination. Lower punctum metrics measurements were performed using OCT (Spectralis, Heidelberg Engineering, Heidelberg, Germany) set on the anterior segment module [Figure 1]. This system acquires 40,000 A-scans/second with a 7-μm axial resolution in tissue. All images were acquired using the scleral setting, a mode in which enhanced depth imaging can be performed. While the eyes were open and the lower eyelid margin was everted using a cotton swap without any pressure, the lower punctum was positioned to a plane perpendicular to the light source. The brightness was set to be 25%, and the angle of each cross-sectional scan was 15°. Images were obtained at a working distance of about 12 mm with 8 mm coverage of the lower eyelids. Automated real-time setting with an average between 2 and 20 frames was chosen. Three OCT images were obtained for each subject, and the highest quality scan was chosen subjectively.

Figure 1

Representative image of anterior segment optical coherence tomography of the inferior punctum

Measurements of lacrimal punctal anatomy, as visualized on OCT, were taken using Heidelberg Eye Explorer software (version 1.6.8) (Heidelberg Engineering, Heidelberg, Germany). The best and clearest one was chosen for measuring the lower punctum diameters. A skilled grader (A.S.) measured the dimensions. External punctal diameter was defined as the largest diameter at the surface of the punctum. Internal punctal diameter was measured at two different canalicular depths of 100 and 500 μm from the external punctum [Figure 1]. To evaluate the reproducibility, 30% of measurements were repeated by another experienced researcher (S.G.).

Statistical analysis was performed using SPSS windows program version 16 (SPSS Institute, Inc., Chicago, IL, USA). All experimental values are presented as mean ± standard deviation and median and interquartile range (IQR). Normal distribution was evaluated using Kolmogorov–Smirnov test. P < 0.05 was considered statistically significant. The comparison between men and women was done by independent t-test. Pearson's correlation coefficient was used to evaluate the linear relationship between variables. The agreement between observers was measured using intraclass correlation coefficient (ICC) with single measures, absolute agreement method.

RESULTS

One hundred and two eyes of 102 healthy volunteers were enrolled in the present study. The mean age of the participants was 61.5 ± 7.9 years (29–69 years), and 53 (52%) of them were male.

The mean external punctal diameter was 425.6 ± 124.3 μm (median, IQR: 403, 336.2–503.2 μm). Mean internal punctal diameter at 100 μm and 500 μm was 191.6 ± 101.7 μm (median, IQR: 155, 107.2–262) and 79.6 ± 61.4 μm (median, IQR: 61, 44–98.5), respectively. All values showed normal distributions in the study participants. There was a significant correlation between external punctal diameter and internal punctal diameter at 100 μm (r = 0.821; P < 0.0001) and 500 μm (r = 0.770; P = 0.006). There was no significant difference between men and women in all punctal measurements [Table 1]. There was no significant correlation between age and punctal measurements (P > 0.05).

Table 1

Punctal characteristics in the study population

Variables	Total (n=102)	Male (n=53)	Female (n=49)	P*
External punctal diameter
Mean±SD	425.6±124.3	434.5±134.5	416±112.9	0.455
Median	403	408	399
IQR	336.2-503.2	340-563	319-492
Internal punctal diameter at 100 mm
Mean±SD	183±97.5	191.6±101.7	173.8±92.8	0.360
Median	155	162	140
IQR	107.2-262	119-275	99-234
Internal punctal diameter at 500 mm
Mean±SD	77.7±51.4	79.6±61.4	75.7±38.4	0.709
Median	61	52	69
IQR	44-98.5	43-104	44-96

*Based on student’s t-test. SD: Standard deviation, IQR: Interquartile range

There was a good agreement between graders in measuring punctal diameters. ICC was 0.928 for external punctal diameter, 0.950 for internal punctal diameter at 100 μm, and 0.901 for internal punctal diameter at 500 μm.

DISCUSSION

In the present study, we used OCT to measure lower punctum dimensions in Iranian healthy subjects. The punctum could be recognized and measured on the OCT images in all subjects. There was a good agreement between observers in assessing the punctal dimensions.

Understanding the anatomy of the punctum and the vertical portion of the lacrimal canal plays an important role in the success of lacrimal system surgeries and can also help determine the etiology of epiphora, especially in patients with punctal stenosis and obstruction.6 Furthermore, the design, fitting, and insertion of the punctal plug are dependent on knowing the exact anatomy of this part.78 The use of lacrimal system imaging techniques can be helpful in the diagnosis of lacrimal canal disease. Because of the surface and prominent status of the lacrimal canal, imaging techniques commonly used for the evaluation of the lacrimal drainage system such as dacryocystography,9 ultrasound biomicroscopy,34 and magnetic resonance imaging may not accurately represent the size of the punctum.10

Anterior segment OCT is a noncontact imaging modality that uses infrared light at a wavelength of 840 nm to image the anterior segment structures of the eye.11 Wawrzynski et al.5 were the first to demonstrate its applicability for evaluation of the lower punctum diameter and vertical canaliculus. They evaluated 36 eyes and provide the OCT measurements of the width of the punctum, and the width, depth, and cross-sectional area of the visualized canaliculi using Topcon 3D OCT. Afterward, some other studies applied OCT in assessing the punctal features and provided the values for the variables, including inner punctal diameter at different depth, punctal depth, and intrapunctal tear meniscus depth.121314

In our study, the mean outer punctal diameter was 425.6 μm which is in the range of the reported values (215–645 μm) in previous studies. The inner punctal diameter in our study was 183 μm at 100 μm and 77.7 μm at 500 μm from the surface. The reported inner punctal diameter values (50–234 μm) showed even more variability in different investigations. However, this is mainly due to different definition of this dimension. Similar to Timlin et al.,12 we measured the inner punctal diameter at a fixed distance from surface which could facilitate to provide better comparison between studies.

OCT-based evaluation of lacrimal drainage system, however, has some limitations. First, the assessment of the upper punctum is challenging. The upper punctum is slightly rotated posteriorly, and it is difficult to rotate the opening.12 This could be remedied by designing newer devices that would direct the infrared at the right angle to the upper punctum. Second, the exact effect of everting the lower eyelid margin on punctum size is not clear. Third, the dimensions are currently measured manually, since no automatic software is available for punctal diameters. On the other hand, the ability to capture images quickly without the need for eye contact and the ability to three-dimensional reconstruct and visualize the surface of a puncture are undeniable benefits of OCT.

In conclusion, OCT is a useful technique for imaging the inferior punctum. Values measured by OCT have acceptable reproducibility and can be evaluated for this purpose.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.