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Editors Selection IGR 14-1
Basic Research - Conjunctiva: Distribution of lymphatic vessels in the monkey conjunctiva
Comment by Neeru Gupta on:
48740 Quantitative study of the topographic distribution of conjunctival lymphatic vessels in the monkey, Guo W; Zhu Y; Yu PK et al., Experimental Eye Research, 2012; 94: 90-97
Lymphatics, known to exist in normal human conjunctiva, are explored by Guo et al. in adult Rhesus monkey. In this topographic and depth distribution study of conjunctival lymphatic vessels, VEGFR3 and 5'N-ase markers are used as lymphatic endothelial cell markers. The demonstration of a clear central lumen and lack of basement membrane positive profiles would have been helpful, particularly for initial smaller lymphatics of the superficial network.
Using histoenzymatic 5'N-ase stain for quantification studies, the authors found no difference in density or drainage zone among superior, inferior, nasal and temporal quadrants. In this study, 2 dimensional technique were used to evaluate conjunctival lymphatics, and do not take into account variable thickness of conjunctiva from limbus to fornix or between quadrants. The definition of 'density' as the ratio of projected two-dimensional areas of lymphatics/conjunctiva, is problematic as lymphatics or drainage zone would also depend on conjunctival thickness. Application of known 3D vessel measurement techniques1,2 may have provided additional insights.
The study would have benefited from the use of more sensitive blood vessel endothelial markers to label blood vessels, and though the authors admit the limitations of alkaline phosphatase (ALPase) as a blood vessel marker, the ALPase-positive channels in this study were rather thin relative to lymphatics and may not have labelled larger arteries and venules. Further studies of parameters such as lymphatic length and branching, known to change in response to physiological conditions, injury and disease3-5 may provide useful baseline information.
The authors found that lymphatic diameter was larger in superior and nasal quadrants compared to other quadrants. A discussion of the functional and possible clinical relevance would have been interesting. The authors discuss the role of conjunctival lymphatics in glaucoma and aqueous humor drainage from the anterior chamber of the eye. In this context, a discussion of the possible connection between conjunctival lymphatics and known ciliary body lymphatics6 would have been of interest.
References
- Artacho-Perula E, Roldan-Villalobos R, Cruz-Orive LM. Application of the fractionators and vertical slices to estimate total capillary length in skeletal muscles. J Anat 1999; 195: 429-437.
- Gambino LS, Wreford NG, Bertram JF, Dockery P, Lederman F, Rogers PA. Angiogenesis occurs by vessel elongation in proliferative phase human endometrium. Hum Reprod 2002; 17: 1199-1206.
- Ikomi F, Kawai Y, Nakayama J, Ogiwara N, Sasaki K, Mizuno R, Ohhashi T. Critical roles of VEGF-D-VEGF receptor 3 in reconnection of the collecting lymph vessels in mice. Microcirculation 2008; 15: 591-603.
- Ushiki T, Abe K. Identification of arterial and venous segments of blood vessels using alkaline phosphatase staining of ink/gelatin injected tissues. Arch Histol Cytol 1998; 61:215-219.
- Volchek M, Girling JE, Lash GE, Cann L, Kumar B, Robson SC, Bulmer JN Rogers PA. Lymphatics in the human endometrium disappear during decidualization. Hum Reprod 2010; 25: 2455-2464.
- Yücel YH, Johnston MG, Ly T, Patel M, Drake B, Gümüş E, Fraenkl SA, Moore S, Tobbia D, Armstrong D, Horvath E, Gupta N. Identification of lymphatics in the ciliary body of the human eye: a novel 'uveolymphatic' outflow pathway. Exp Eye Res 2009; 89: 810-819.
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