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A Discussion of Central Retinal Vein Occlusion and Axial Length

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									      COMMENTARY



      A Discussion of Central Retinal Vein                                                             for its induction with more severe field
                                                                                                       loss. 10,11 The latter is a likely index of

      Occlusion and Axial Length                                                                       venous resistance along the hemi- and
                                                                                                       central retinal veins in the optic nerve head
                                                                                                       region, 12 the implication being that this
          William H Morgan                                                                             segment of retinal vein may narrow in glau-
          McCusker Glaucoma Centre, Lions Eye Institute, University of Western                         coma. Why this should occur is not clear.
          Australia, Nedlands, Australia                                                               However, we do know that the pressure
                                                                                                       gradient along the central retinal vein in the
      In this issue of Asian Journal of                64 years and the mean axial length was          lamina cribrosa region may be high,13,14 and
      OPHTHALMOLOGY, there are 2 fasci-                23.77 mm.1 A recent study examining the         with lamina thinning from glaucoma,15 will
      nating studies of the relationship between       relationship between age and axial length       rise further. This may lead to elevated shear
      retinal venous occlusion and axial length.       in American patients undergoing cataract        stress within the vein and result in endothe-
      The article by Mehdizadeh et al concluded        surgery demonstrated a longer axial length      lial cell proliferation and change,16 with re-
      that the axial length in branch and central      in younger patients, with a mean axial          sultant luminal narrowing. This is supported
      retinal vein occlusion (BRVO and CRVO)           length of 24.1 mm in the 60- to 70-year-        by histological evidence of endothelial cell
      was shorter than that in a control group.1       old patients. 5 Additionally, patients with     proliferation from patients with CRVO.17
      However, the work by Mirshahi et al was          any degree of myopia are more likely to         Histopathological studies of CRVO have usu-
      case-control in design and suggested that        undergo cataract surgery than those             ally examined eyes removed due to neo-
      the axial length in the CRVO group was no        with emmetropia or hyperopia.6 Hence, it        vascular glaucoma, and so one cannot be
      different from that in a control group.2 We      is possible that the inclusion of patients      certain what changes occurred leading up
      are thus placed in the interesting position      undergoing cataract surgery induced an          to the venous occlusion, at the time of the
      of making some sense of these differing          axial length bias, which may also account       occlusion, or as a neovascular sequela.
      conclusions.                                     for some of the axial length difference in           Sadly, our ability to treat CRVO and
           CRVO is a cause of devastating visual       the control groups from the 2 articles          BRVO is very weak. It is difficult to know
      loss with a 5-year incidence of 0.2% in the      (23.11 mm vs 23.77 mm).                         the place for direct optic disc surgery at
      older age group.3 The landmark study of              As both authors say, there is some          present.18 Laser anastomotic techniques
      risk factors for CRVO was a case-control         evidence of a relationship between refrac-      are currently being trialled and may prove
      study examining 258 patients with CRVO           tive error and CRVO, but this is also con-      useful for certain forms of CRVO.19 Unfortun-
      and 1142 carefully matched controls. 4           tentious and the results of studies are         ately, current laser photocoagulation
      The authors found controls who matched           inconsistent.4 If we suppose that a relation-   therapy for prevention of neovascular glau-
      the patients for point of entry into the         ship between axial length and CRVO does         coma often does not work.20 Further inves-
      specialty or general clinic, as well as rough-   exist, then we need to ask how this could       tigation of risk factors predictive of CRVO
      ly matching the age, race, and sex. The          be so. There is a relationship between          and BRVO is certainly warranted. The links
      major risk factors identified were elevated      optic disc size and axial length.7 However,     between CRVO, retinal vascular changes,
      intraocular pressure (IOP), glaucoma             there is no proven relationship between         and glaucoma, including the other vascu-
      history, and elevated blood pressure.            optic disc size and CRVO.8 There is a rela-     lar features of glaucoma such as optic disc
           The selection of controls for a case-       tionship between glaucoma, IOP, and             rim haemorrhages and venous collaterals,
      control study is never easy. Finding the         myopia, 9 which could explain some of           deserve more study.17
      controls can be more difficult than the pa-      any relationship between axial length and
      tients because one needs to select controls      CRVO.                                           References
      matched for characteristics that may be              Of all the putative factors possibly        1. Mehdizadeh M, Ghassemifar V, Ashraf H,
                                                                                                          Mehryar M. Relationship between retinal
      associated with the variable(s) under            implicated with CRVO, glaucoma and el-             vein occlusion and axial length of the eye.
      investigation. Mehdizadeh’s group used 18        evated IOP have the greatest odds ratio.4          Asian J Ophthalmol 2005;7:146-148.
      controls taken from a cataract assessment        Spontaneous venous pulsation is less            2. Mirshahi A, Moghimi S, Rajabi MT. Central
                                                                                                          retinal vein occlusion: role of axial length.
      clinic having measurements for intraocular       frequent in glaucoma, and a greater                Asian J Ophthalmol 2005;7:149-151.
      lens calculation. The mean age was               ophthalmo-dynametric force is required          3. Klein R, Klein BE, Moss SE, Meuer SM.


152   Volume 7, Number 4, 2005                                                                                   Asian Journal of OPHTHALMOLOGY
                                                                                                                                      COMMENTARY


      The epidemiology of retinal vein occlusion:              glaucoma suspects. Opthalmology 2004;               Soc 1981;79:371-422.
      the Beaver Dam Eye Study. Trans Am                       111:1489-1494.                                  18. Martinez-Jardon CS, Meza-de Regil A,
      Ophthalmol Soc 2000;98:133-141.                    12.   Morgan WH, Balaratnasingam C, Hazelton              Dalma-Weiszhausz J, et al. Radial optic
4.    The Eye Disease Case-Control Study Group.                ML, House PH, Cringle SJ, Yu DY. The                neurotomy for ischaemic central vein
      Risk factors for central retinal vein occlusion.         force required to induce hemivein pulsation         occlusion. Br J Ophthalmol 2005;89:
      Arch Ophthalmol 1996;111:545-554.                        is associated with the site of maximal field        558-561.
5.    Tuft SJ, Bunce C. Axial length and age at                loss in glaucoma. Invest Ophthalmol Vis                                        ,
                                                                                                               19. McAllister IL, Douglas JP Constable IJ, Yu
      cataract surgery. J Cataract Refract Surg                Sci 2005;46:1307-1312.                              DY. Laser-induced chorioretinal venous
      2004;30:1045-1048.                                 13.   Morgan WH, Yu DY, Alder VA, et al. The              anastomosis for nonischemic central retinal
6.                           ,
      Younan C, Mitchell P Cumming RG,                         correlation between cerebrospinal fluid             vein occlusion: evaluation of the complica-
      Rochtchina E, Wang JJ. Myopia and                        pressure and retrolaminar tissue pressure.          tions and their risk factors. Am J
      incident cataract and cataract surgery: The              Invest Ophthalmol Vis Sci 1998;39:                  Ophthalmol 1998;126:219-229.
      Blue Mountains Eye Study. Invest                         1419-1428.                                      20. Hayreh SS, Klugman MR, Podhajsky P       ,
      Ophthalmol Vis Sci 2002;43:3625-3632.              14.   Morgan WH, Yu DY, Cooper RL, Alder VA,              Servais GE, Perkins ES. Argon laser
7.    Rudnicka AR, Frost C, Owen CG, Edgar                     Cringle SJ, Constable IJ. Retinal artery and        panretinal photocoagulation in ischemic
      DF. Nonlinear behavior of certain optic                  vein pressures in the dog and their                 central retinal vein occlusion. A 10-year
      nerve head parameters and their determi-                 relationship to aortic, intraocular, and            prospective study. Graefes Arch Clin Exp
      nants in normal subjects. Ophthalmology                  cerebrospinal fluid pressure. Microvasc             Ophthalmol 1990;228:281-296.
      2001;108:2358-2368.                                      Res 1997;53:211-221.
8.    Mansour AM, Walsh JB, Henkind P Optic   .          15.   Jonas JB, Berenshtein E, Holbach L.
      disc size in central retinal vein occlusion.             Anatomic relationship between lamina            Address for Correspondence
      Ophthalmology 1990;97:165-166.                           cribrosa, intraocular space, and cerebro-       Dr William H Morgan
9.    Wong TT, Klein BEK, Klein R, et al. Refrac-              spinal fluid space. Invest Ophthalmol Vis
                                                                                                               McCusker Glaucoma Centre
      tive errors, intraocular pressure, and                   Sci 2003;44:5189-5195.
      glaucoma in a white population.                    16.   DePaola N, Gimbrone MA, Davies PF,              Lions Eye Institute
      Ophthalmology 2003;110:211-217.                          Dewey CF. Vascular endothelium responds         University of Western Australia
10.   Jonas JB. Central retinal artery and vein                to fluid shear stress gradients. Arterioscler
      collapse pressure in eyes with open angle                Thromb 1992;12:1254-1257.                       2 Verdun St
      glaucoma. Br J Ophthalmol 2003;87:                 17.   Green W, Chan CC, Hutchins GM, Terry            Nedlands, WA
      949-951.                                                 JM. Central retinal vein occlusion: a
11.   Morgan WH, Hazelton ML, Azar SL, et al.                  prospective histopathologic study of 29
                                                                                                               Australia, 6009
      Retinal venous pulsation in glaucoma and                 eyes in 28 cases. Trans Am Ophthalmol           E-mail: whmorgan@cyllene.uwa.edu.au




                                                                With Grateful Thanks
      The members of the Editorial Board of Asian Journal of OPHTHALMOLOGY wish to express their gratitude to the following
      individuals for their invaluable input as reviewers of articles submitted to the Journal in 2005.

      Dr Shantha Amrith                                        Dr Rajat Maheshwari                                 Dr Lennard Theane
      Dr Muna Bhende                                           Dr Michael Munoz                                    Dr Ravi Thomas
      Dr Helen V Danesh-Meyer                                  Dr Gerard Nah                                       Dr Wasee Tulvatana
      Dr Gus Gazzard                                           Dr Rajul Parikh                                     Dr Joseph Anthony J Tumbocon
      Dr Raf Ghabrial                                          Dr Vilavun Puangsricharern                          Dr Marissa Valbuena
      Dr Stuart Graham                                         Dr Jovina See                                       Dr. Sharadini Vyas
      Dr Santosh Honavar                                       Dr Santiago Antonio B Sibayan                       Dr Mark Walland
      Dr Alex P Hunyor                                         Dr Mandeep Singh                                    Dr Jenn Chyuan Wang
      Dr Patricia Khu                                          Dr James Smith                                      Dr Inez Wong
      Dr Sao Bing Lee                                          Dr Gangadhara Sundar                                Dr Mario Yatco
      Dr Edgar Leuenberger                                     Dr Anna Tan                                         Dr Leonard Yip
      Dr Kenneth Li                                            Dr Clement Tan
      Dr Seng Chee Loon                                        Dr Clement Tham



Asian Journal of OPHTHALMOLOGY                                                                                                    Volume 7, Number 4, 2005       153

								
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