|Year : 2021 | Volume
| Issue : 1 | Page : 52-55
Iris thickness and volume be measured using iris base instead of scleral spur as reference in anterior optical coherence tomography scan
Alka Mahale, Rajiv Khandekar, Yasir Zia
Department of Research, King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia
|Date of Submission||08-Jun-2020|
|Date of Decision||10-Dec-2020|
|Date of Acceptance||05-Jan-2021|
|Date of Web Publication||09-Sep-2021|
Dr. Rajiv Khandekar
Department of Research, King Khaled Eye Specialist Hospital, Riyadh 7191, 11462
Source of Support: None, Conflict of Interest: None
PURPOSE: To compare the iris parameters (iris thickness [IT] and volume) measured at different locations on iris determined using iris base (IB) and scleral spur (SS) in healthy Saudi eyes and factors affecting the differences.
METHODS: Healthy eyes of Saudi persons were evaluated using anterior segment optical coherence tomography (AS-OCT). The IT was measured using Image J software and OCT scans in the horizontal axis in light on and light off condition. First IB was used as reference, and then, SS was used as reference for these measurements.
RESULTS: One hundred healthy eye's AS-OCT scan was studied. The IT at the temporal side of the horizontal axis at 750 μ away from IB with lights on was 0.526 ± 0.08 μ, whereas it was 0.52 ± 0.08 μ from SS. The difference was significantly more in IB than SS method (P = 0.005). This difference if IT in SS and IB method was not affected by gender (Mann–Whitney P = 0.3), type of refractive error (K W P = 0.7), and level of illumination (K W P = 0.7).
CONCLUSION: IT and IV measured using IB provided reliable data but overestimates compared to SS method. In the absence of SS visibility, IB could be alternative to assess iris parameters.
Keywords: Anterior optical coherence tomography, iris thickness, iris volume, scleral spur
|How to cite this article:|
Mahale A, Khandekar R, Zia Y. Iris thickness and volume be measured using iris base instead of scleral spur as reference in anterior optical coherence tomography scan. Saudi J Ophthalmol 2021;35:52-5
|How to cite this URL:|
Mahale A, Khandekar R, Zia Y. Iris thickness and volume be measured using iris base instead of scleral spur as reference in anterior optical coherence tomography scan. Saudi J Ophthalmol [serial online] 2021 [cited 2023 Mar 28];35:52-5. Available from: https://www.saudijophthalmol.org/text.asp?2021/35/1/52/325788
| Introduction|| |
Anterior segment optical coherence tomography (AS-OCT) is a diagnostic tool superior to previously available ultrasound and direct visualization using the magnification by slit-lamp bio-microscopy. Its added benefit in high-resolution images and “no contact” to the eye of patient has increased its usage, especially in children and for eyes with trauma. Children aged <12 years of age had undergone anterior OCT examination for the diagnosis and management decisions. For iris parameter evaluation by AS-OCT, scleral spur (SS) is normally used as reference point. However, in some instances, lack of clear visibility of SS could hamper the use of AS-OCT in anterior segment biometry. Walton et al. noted that in cohort of children with late diagnosis of congenital glaucoma, only 47% of cases had visible SS, but 80% had clearly visible ciliary body (CB) on gonioscopy. A number of conditions that are related to corneal scarring and haziness could mimic congenital glaucoma and visibility of SS by gonioscopy could be difficult. In such conditions, imaging technique could enable the clinician to diagnose and manage cases properly. Children who AS-OCT using 1310 nanometer wavelength light have improved visibility of CB structures involved at the angle of anterior chambers. In such circumstances, base of CB as reference to fixate the location on iris surface to measure iris thickness (IT) could be an option.
Anterior OCT has been found to be a useful tool to study the changes in the anatomy of CB during accommodation and effect of medications such as pilocarpin., However, to the best of our knowledge, it is not used as marker as a substitute of SS to measure IT and iris volume in health eyes.
We compared IT of healthy Saudi eyes measured by AS-OCT using both the SS and base of CB as index to identify the location on iris surface.
| Methods|| |
This was the part of the institutional research and ethics board approved research project (1365-P). The details of ethical issues, population, and details of study participants are given in our previous publication.
Demographic data such as age and gender were collected form the electronic health records.
Cornea/anterior segment (CAS) OCT (three-dimensional CAS-OCT SS-1000, Tomey Corp., Tokyo, Japan) was used to scan the eye. Right eye (OD) and left eye (OS) scanning was performed first with the room light on (LON) (70–100 Lux) and then with the room light off (LOFF) (<5 lux) for 5 min. All AS-OCT images were acquired by an ophthalmic technician specifically trained in using this equipment.
The scan in the horizontal 0°–180° meridian for each of the four settings (OD/OS/LON/LOFF) was obtained and checked manually for its quality by investigators. A successful scan was defined as one that included the complete cornea, angle, iris, and lens without artifacts. SS on the nasal and temporal aspects was marked in each eye by the ophthalmologist. The SS anatomically represents the junction between the inner wall of the trabecular meshwork and the sclera is marked by a prominent inner extension (inward protrusion) of the sclera with a change in curvature of its inner surface.
IT was measured at 500 μm (D1) and 750 μm (D2) from the SS. For measurement from the SS, the points of intersection at the anterior surface of the iris were identified. These landmarks were defined as the point at the anterior iris surface on a line perpendicular to the trabecular meshwork of 500 μm and 750 μm, respectively, from the SS. The Casia software automatically marks these points once the SS and angle recess has been defined by the observer.
For measurement using the iris base (IB) method, we used the most anterior end of CB projecting into the angle of the anterior chamber and a line is drawn perpendicular to iris plane that separate CB from iris (identifying the IB). From IB, a line is drawn parallel to iris plane following the curvature of iris up to 500 μm. At this place, we made a perpendicular line from iris epithelium side to endothelium side and IT is measured at this point (D1). The line parallel to iris was further continued up to 750 μm. Here again, a perpendicular line was drawn, and IT was measured at 750 μm point (D2) [Figure 1].
|Figure 1: Anterior segment optical coherence tomography showing schematic points for measuring iris thickness by using ciliary body as reference|
Click here to view
The image was saved and transferred to Image J 1.51k, a Java-based image processing program developed at the National Institutes of Health and the Laboratory for optical and computational instrumentation (LOCI, University of Wisconsin, USA) for measurement of IT.
The data were collected using spreadsheet of Microsoft XL®. After consistency checks, it was transferred into spread sheet of Statistical Package for the Social Sciences (SPSS 25) (IBM, Chicago, USA). For the continuous outcome variables such as IT and IV, we estimated mean and standard deviations. To compare outcomes in subgroups of SS and IB, we calculated difference of mean, its 95% confidence interval and two-sided P values. P < 0.05 was considered statistically significant. While comparing the difference in of IT in IB and SS method in subgroups, we used nonparametric method and presented two sided P values using Mann–Whitney (MW) P value for gender and Kruskal Wallis P value for RE.
| Results|| |
We studied 100 eyes of 100 Saudi Adults. Their mean age was 41.7 ± 14.5 years. Male were 56 and 50 were ODs. Their refractive status suggested that 35 were emmetropic, 33 had mild grade of myopia, 17 with moderate myopia, and 11 with high myopia.
The IT parameters in temporal and nasal side of horizontal axis at 500 μm and 750 μm away from (1) SB and (2) SS in lights on and light off condition is given in [Table 1]. Apart from 500 μm away in lights off in both nasal and temporal location, IB method gave significantly higher values as compared to SS method.
|Table 1: Iris thickness parameters using scleral spur and It is base method as reference|
Click here to view
The difference in IT at 750 μm temporal in light on and off in IB and SS method was not significantly different among male and female participates (MW P = 0.32).
The difference in IT at 750 μm temporal in light on and off in IB and SS method was not significantly different by refractive status of eye (Kruskal Wallis P = 0.67).
The difference in IT at 750 μm temporal in light on and off in IB and SS method was not significantly different in persons age (Kruskal Wallis P = 0.72).
| Discussion|| |
Our study revealed that using the base of CB is feasible to measure IT and volume but gave consistently higher values compared to those measured using SS. These differences noted in SS and IB method were not influenced by gender, illumination, and location on either side of pupil on the horizontal axis.
Location of CB in the eye varies with ethnicity of the population. Chinese person's eye has thinner CB and more anteriorly located ciliary processes compared to the American Caucasians. These anatomical differences could make the eye more vulnerable to have narrow angle and angle closure glaucoma. To the best of our knowledge, information about anatomical details of CB position among Arabs is not described. With similar proportion of angle closure and open angle glaucoma in a community-based survey in Oman, one can conclude that structures of angle of anterior chamber in the Arab population seem to differ from those of Oriental and Far East Asian population. Thus, nomogram of AS OCT for the Arab population using CB method need to be generated and compared to the eyes with glaucoma instead of concluding from the data of other countries.
Neuyen et al. used swept-source (SS) and noted that in eyes of patients with angle closure glaucoma, the choroidal thickness was thicker than normal healthy Caucasians. Choroid and iris are mesodermal structure and likely to have similar changes in the pathological conditions. The changes in the anterior segment in eyes with glaucoma are more prominent and routinely easily measurable. In conditions where visibility is marred due to corneal conditions, one can study iris changes by anterior OCT. If SS is not clearly visible in images, one can use base of CB to study iris, but further research is needed in pathological conditions to compare our findings among healthy eyes of the Arab population.
In normal eyes, one can use base of CB as reference to evaluate IT and iris volume with similar reliability as done by using SS to note distances on iris surface. However, one should note that IB method gives consistently higher values than SS method.
We thank Ches Souru and Sejo Verghese of research department to support data entry, data management.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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