Observation of Posterior Precortical Vitreous Pocket Using Swept-Source Optical Coherence Tomography

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1 Anatomy and Pathology Observation of Posterior Precortical Vitreous Pocket Using Swept-Source Optical Coherence Tomography Hirotaka Itakura, Shoji Kishi, Danjie Li, and Hideo Akiyama Department of Ophthalmology, Gunma University, School of Medicine, Maebashi, Japan Correspondence: Hirotaka Itakura, Department of Ophthalmology, Gunma University, School of Medicine, Showa-machi, Maebashi, Gunma, , Japan; Submitted: January 29, 2013 Accepted: April 5, 2013 Citation: Itakura H, Kishi S, Li D, Akiyama H. Observation of posterior precortical vitreous pocket using swept-source optical coherence tomography. Invest Ophthalmol Vis Sci. 2013;54: DOI: / iovs PURPOSE. To observe posterior precortical vitreous pockets (PPVPs) using swept-source optical coherence tomography (SS-OCT). METHODS. We performed SS-OCT in both eyes of 58 volunteers (36 men, 22 women) using 12- mm horizontal vertical scans through the macula and optic disc. To minimize age-related changes (liquefaction or posterior vitreous detachment), all subjects were a mean of 26.2 years (range, years). The refractive errors ranged from 9.5 diopters (D) to þ3.0 D. To estimate the PPVP size, we measured the height between the fovea and the anterior border of the PPVP and the maximal width in the 12-mm horizontal scan through the fovea and disc. RESULTS. SS-OCT visualized the PPVPs as boat-shaped lacunae in the macular area bilaterally in all subjects (maximal width, lm; mean width, ; central height, lm; mean height, in the right eyes, with no significant difference in the left eyes). There was a significant correlation between the PPVP height and myopic refractive error. The posterior wall of the PPVP was a thin vitreous cortex, thinnest at the fovea. The septum was between the nasal border of the pocket and Cloquet s canal, which extended forward and tilted superiorly in all cases. A channel connected Cloquet s canal and the PPVPs bilaterally in 54 (93.1%) of 58 cases. CONCLUSIONS. SS-OCT clarified the boat-shaped PPVP structure in vivo. Although the central height increased with the myopic refractive error, the width was unchanged. A channel connecting Cloquet s canal and PPVP suggested the route of aqueous humor into the PPVP. Keywords: posterior precortical vitreous pocket, swept-source optical coherence tomography, vitreous humor, Cloquet s canal, channel A posterior precortical vitreous pocket (PPVP) is a liquefied lacuna anterior to the macular area that is physiologically present in the vitreous of adults. 1 A PPVP first was reported in autopsy eyes, in which the vitreous gel was stained with fluorescein. The presence of PPVPs has been confirmed during triamcinolone-assisted vitrectomy 2 and by spectral-domain optical coherence tomography (SD-OCT). 3 5 The anterior border of a PPVP is vitreous gel and the posterior border is comprised of a thin layer of the vitreous cortex attached to the retina. A septum is present between the nasal border of the PPVP and Cloquet s canal. 5 The peculiar structure of the premacular vitreous cortex plays a key role in the development of various vitreomacular disorders, such as macular holes and idiopathic premacular fibrosis. 6,7 However, the physiologic function of PPVPs is unknown. Worst described the bursa premacularis, which he observed by injecting India ink into the vitreous in postmortem eyes. 8,9 In his original report, the bursa was anterior to the detached convex-shaped vitreous cortex that forms the subbursal space. Based on the concept of the bursa premacularis, the vitreous cortex is anatomically detached from the retina in the macular area. Worst described two channels that connect the bursa and Cloquet s canal. 9 He speculated that inflammation of the anterior chamber after cataract surgery may affect development of cystoid macular edema through the channels. Swept-source OCT (SS-OCT) is a new generation of OCT that provides higher penetration into the choroid and sclera. SS- OCT enables clear visualization of the vitreous and the choroid. Using SS-OCT, we examined the morphologic features of PPVPs in normal subjects. METHODS We performed SS-OCT (DRI OCT-1 Atlantis; Topcon, Tokyo, Japan) consecutively in both eyes of 58 healthy volunteers (36 men, 22 women) while they were sitting. This OCT system has an A-scan repetition rate of 100,000 Hz, and its light source operates in the 1-lm wavelength region. The light source is a wavelength-tunable laser centered at 1050 nm with a 100-nm tuning range; the axial resolution is 8 lm, the lateral resolution 20 lm, and the imaging depth 2.3 mm in tissue. The ocular fundus was scanned in six horizontal 12-mm scans that included the entire extent of the PPVPs, the centers of which were aligned at the plane through the optic disc and fovea, and two vertical 12-mm scans through the fovea and optic disc. The subject ages ranged from 22 to 40 years (average, years). No eyes had an ocular disease. Subjects over 40 years of age were excluded to minimize age-related changes in the vitreous such as liquefaction or posterior vitreous detachment. 10 The refractive powers were measured using a commercial topographer (Autoref-Topographer RT-6000; Tomey Corporation, Nagoya, Japan) and ranged from 9.5 diopters (D) to þ3.0 Copyright 2013 The Association for Research in Vision and Ophthalmology, Inc. j ISSN:

Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3103 FIGURE 1. Measurement of the PPVP in the right eye of a 25-year-old woman.

2 Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3103 FIGURE 1. Measurement of the PPVP in the right eye of a 25-year-old woman. To enhance the vitreous structure, the brightness and contrast were increased, the levels of which exceeded the brightness and contrast of the retinal image. The height of the PPVP is defined as the distance between the fovea and the anterior border (h) and the width (w) is the maximal diameter in the 12-mm horizontal scan through the fovea and the disc. T, temporal; N, nasal. D (average, D) in the right eyes and from 9.5 D to þ3.0 D (average, D) in the left eyes. During the OCT examination, we placed the scanner head backwards for anterior focusing, which allowed us to capture the anterior extent of the PPVP in the B-scan images. After obtaining the SS-OCT images, we adjusted the contrast to visualize the gel, liquefied pocket, and the cortex. To estimate the size of the PPVPs, we measured the height between the fovea and the anterior border of the PPVP, according to our previous report, 11 and the maximal width in the 12-mm horizontal scan through the fovea and the disc (Fig. 1). All values are expressed as the mean 6 standard error of the mean with the range. The differences between groups were analyzed using the Mann-Whitney U test or Wilcoxon signedrank test. The correlations between groups were analyzed using Pearson s correlation coefficient test. P values less than 0.05 were considered significant. The study was conducted according to the tenets of the Declaration of Helsinki. The institutional review board ethics committee approved the study. All individuals provided informed consent after having received a detailed explanation of the purpose of the study. RESULTS SS-OCT visualized the PPVPs clearly in both eyes of all participants. The anterior border of the PPVP was delineated by the vitreous gel, and the posterior border was a thin layer of vitreous cortex attached to the retina (Figs. 2, 3). A septum was between Cloquet s canal and the nasal border of the PPVP. The configuration of the PPVP was almost symmetrical in both eyes of each subject (Figs. 2, 3). In the vertical scans, the height of the pocket was lower inferiorly than superiorly in all subjects (Fig. 2B). Cloquet s canal extended forward and tilted superiorly in all cases (Fig. 3B). In 54 (93.1%) of 58 cases, the channel connecting Cloquet s canal and the PPVP was seen at the anterior septal edge in both eyes (Figs. 2A, 3A). The connecting channel was detected in 100 (86.2%) of the 116 eyes in the horizontal scan through the fovea. Although the channel was not identified in the other 16 (13.8%) eyes in the horizontal scans through the fovea, the channel was seen in the horizontal scans above the fovea in seven (6.0%) eyes (Fig. 3A) and below the fovea in one (0.9%) eye. The channel was not detected in any scan in both eyes of four (6.9%) cases (Fig. 4). The refractive errors were significantly (P < 0.01) more myopic in 54 cases with a bilateral connecting channel (right eye, D; left eye, D) than in four cases without a bilateral connecting channel (Fig. 5; right eye, D; left eye, D). The mean height of the PPVP at the fovea was lm (range, ) in the right eyes and lm (range, ) in the left eyes. There was no difference between the right and left eyes. There was a significant correlation between the height and the refractive error in the right eyes (Fig. 5; r ¼ 0.43, P < 0.001) and the left eyes (r ¼ 0.29, P < 0.05). The greater the degree of myopia, the higher the height of the PPVP (Fig. 6). The mean width of the PPVP through the fovea was lm (range, ) in the right eye and lm (range, ) in the left eye. There was no significant difference between the width and refractive error in both eyes. DISCUSSION PPVPs first were observed in autopsy eyes in which the gel was stained with fluorescein. 1 Triamcinolone-assisted vitrectomy allowed intraoperative visualization of the PPVP. 2 Time-domain OCT depicted the vitreous cortex when it was slightly detached from the retina; however, the imaging failed to show the inner structure of the vitreous. Noise-reduced SD-OCT visualized the PPVP in most eyes. However, because of the low sensitivity of the vitreous and limited scan length, SD-OCT occasionally failed to visualize the entire PPVP. 5 In the current study, SS-OCT with a 12-mm scan length visualized for the first time the entire structure of the PPVP.

$The refractive error was 3.5 D in the right eye and 4.5 D in the left eye. (A) A horizontal scan through the fovea and the optic disc showed a boat-shaped PPVP and connecting channel (arrows).$

3 Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3104 FIGURE 2. Symmetrical posterior PPVPs were seen in both eyes of a 24-year-old woman. The refractive error was 3.5 D in the right eye and 4.5 D in the left eye. (A) A horizontal scan through the fovea and the optic disc showed a boat-shaped PPVP and connecting channel (arrows). (B) A vertical scan through the fovea showed that the anterior border of the PPVP was higher superiorly than inferiorly (arrows) in both eyes. The dotted lines in the fundus photographs indicated the scan direction and length. c, Cloquet s canal; p, PPVP; S, superior; I, inferior. Because of high penetration and high speed, SS-OCT was superior to SD-OCT for depicting the choroid and the vitreous compared. If the vitreous was enhanced by increasing the brightness and contrast in the OCT images, the vitreous structure always was observed if it was present, although the quality of the retinal images decreased due to excessive brightness and contrast. The PPVPs appeared as boat-shaped vitreous lacunae in the macular area, and the posterior wall of the PPVPs was a thin vitreous cortex attached to the retina. Worst described the bursa premacularis as a pear-shaped sack with its own outer membrane. 9 The bursa premacularis is situated on the convexly elevated posterior vitreous membrane (Pars patelliformis membranae vitrealis), which forms subbursal premac-

4 Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3105 FIGURE 3. The findings in a 39-year-old man. (A) A connecting channel (arrow) was seen above the fovea (a) although it was not seen thorough the fovea (b) in the horizontal scans of the right eye. (B) The cross-sectional views of Cloquet s canal in the vertical scan. Cloquet s canal extended forward and was tilted superiorly. The dotted lines in the fundus photographs indicated the scan direction and length. ular space. The PPVP is probably the same space as the bursa premacularis described by Worst, except there are no membranes, just a layer of premacular cortical vitreous that are adherent to the macula in young adulthood. While the posterior wall of PPVP is a thin vitreous cortex itself, the anterior border is vitreous gel. The mean height of the PPVPs was lm (range, ) and the mean maximal width was lm (range, ) in the right

$Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3106 FIGURE 4. The case of the right eye of a 26-year-old woman with 0.25 D of refractive error.$

5 Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3106 FIGURE 4. The case of the right eye of a 26-year-old woman with 0.25 D of refractive error. No connecting channel was seen in the septum between Cloquet s canal and the nasal border of the PPVP. The PPVP was small with a thick septum (arrow) and the anterior potion of the septum had a lamellar structure. eyes. The PPVPs were symmetrical in both eyes of each individual; thus, the size of the PPVPs did not differ in the left eyes. The height of the PPVPs increased along with the myopic refractive error (Fig. 5). Using SD-OCT, we examined the size of PPVPs without highly myopic eyes and reported that the mean height was mm at the fovea and the horizontal diameter was a mean of mm. 5 The dimensions of PPVPs in the current study were slightly larger than our previous report because this study contained high myopia probably. In the vertical scans, the superior portion of the PPVP always enlarged when the participants were sitting (Fig. 2B), as we reported previously. 11 Gravity may affect the shape of the PPVPs. FIGURE 5. There was a significant correlation (r ¼ 0.43, P < 0.001) correlation between the refractive errors and the height of the PPVP in the right eyes of the 58 participants. The greater the degree of myopia, the higher the height of the PPVP. A connecting channel was seen in 54 eyes (solid circles) and not in four eyes (open circles). A noteworthy finding in the current study was a connecting channel between the nasal side of the PPVPs and the temporal side of Cloquet s canal in 93.1% of cases, the presence of which suggested that the PPVPs are not isolated lacunae. If Cloquet s canal extended to the posterior chamber behind the lens (Berger s space), aqueous humor may drain into the PPVPs via the connecting channels. We described the role of PPVPs in vitreoretinal interface diseases, such as macular holes and idiopathic premacular fibrosis. 6,7 The connecting channel may have a pathophysiologic role in PPVPs. No connecting channel was seen in either eye of four subjects, in whom the refractive errors were emmetropia (two cases); hyperopia (one case); and low myopia (one case; Fig. 5). These cases had small PPVPs with thick septums between the PPVPs and Cloquet s canal, and the anterior edge of the septum had a lamellar structure (Fig. 4). It is unclear whether the connecting channel collapsed in these cases as a result of the overlying vitreous gel. Worst described two channels between the bursa and Cloquet s canal. 9 One channel was a superior branching channel that arose from the roof of the bursa and merged into Cloquet s canal. However, using SS-OCT, we could not observe the orifice of the superior branching channel in the roof of the PPVP. Because the imaging depth of SS-OCT is 2.3 mm in tissue, we could not explore the anterior extent of the superior branching channels. Another the lower branching channel was connected to the bottom of the bursa and the Martegiani s space in Cloquet s canal. The connecting channel in the current study appeared to coincident with the lower branching channel described by Worst. 9 In conclusion, SS-OCT showed the detailed structure of PPVPs in vivo. The configuration of the PPVP is boat-shaped. Although its central height increased with increasing myopia, its width was unchanged. A channel connected Cloquet s canal and the PPVPs, which suggested the route of aqueous humor into the PPVPs.

Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3107 FIGURE 6. The case of the right eye of a 23-year-old man with 7.0 D of myopia. The height of the PPVP was 1.

6 Posterior Precortical Vitreous Pocket Observation IOVS j May 2013 j Vol. 54 j No. 5 j 3107 FIGURE 6. The case of the right eye of a 23-year-old man with 7.0 D of myopia. The height of the PPVP was lm and the width was lm in the 12-mm horizontal scan through the fovea and disc. The PPVP tended to be higher in myopic eyes. The dotted line in the fundus photography indicated the scan direction and length. Acknowledgments The authors alone are responsible for the content and writing of the paper. Disclosure: H. Itakura, None; S. Kishi, None; D. Li, None; H. Akiyama, None References 1. Kishi S, Shimizu K. Posterior precortical vitreous pocket. Arch Ophthalmol. 1990;108: Fine HF, Spaide RF. Visualization of the posterior precortical vitreous pocket in vivo with triamcinolone. Arch Ophthalmol. 2006;124: Johnson MW. Perifoveal vitreous detachment and its macular complications. Trans Am Ophthalmol Soc. 2005;103: Mojana F, Kozak I, Oster SF, et al. Observations by spectraldomain optical coherence tomography combined with simultaneous scanning laser ophthalmoscopy: imaging of the vitreous. Am J Ophthalmol. 2010;149: Itakura H, Kishi S. Aging changes of vitreomacular interface. Retina. 2011;31: Kishi S, Hagimura N, Shimizu K. The role of the premacular liquefied pocket and premacular vitreous cortex in idiopathic macular hole development. Am J Ophthalmol. 1996;122: Kishi S, Shimizu K. Oval defect in detached posterior hyaloid membrane in idiopathic preretinal macular fibrosis. Am J Ophthalmol. 1994;118: Worst J. Cisternal systems of the fully developed vitreous body in the young adult. Trans Ophthalmol Soc U K. 1977;97: Worst J. Extracapsular surgery in lens implantation (Binkhorst lecture). Part IV. Some anatomical and pathophysiological implications. J Am Intraocul Implant Soc. 1978;4: Uchino E, Uemura A, Ohba N. Initial stages of posterior vitreous detachment in healthy eyes of older persons evaluated by optical coherence tomography. Arch Ophthalmol. 2001;119: Itakura H, Kishi S. Alterations of posterior precortical vitreous pockets with positional changes [published online ahead of print March 19, 2013]. Retina. doi: /iae. 0b013e31827d262a.

Case Report Is Optical Coherence Tomography a Useful Tool to Objectively Detect Actual Posterior Vitreous Adhesion Status?

Case Reports in Ophthalmological Medicine Volume 2016, Article ID 3953147, 5 pages http://dx.doi.org/10.1155/2016/3953147 Case Report Is Optical Coherence Tomography a Useful Tool to Objectively Detect