Prevalent misconceptions about acute retinal vascular occlusive disorders

Abstract

Acute retinal vascular occlusive disorders collectively constitute one of the major causes of blindness or seriously impaired vision, and yet there is marked controversy on their pathogeneses, clinical features and particularly their management. This is because the subject is plagued by multiple misconceptions. These include that: (i) various acute retinal vascular occlusions represent a single disease; (ii) estimation of visual acuity alone provides all the information necessary to evaluate visual function; (iii) retinal venous occlusions are a single clinical entity; (iv) retinal vein occlusion is essentially a disease of the elderly and is not seen in the young; (v) central retinal vein occlusion (CRVO) is one disease; (vi) fluorescein fundus angiography is the best test to differentiate ischemic from nonischemic CRVO; (vii) the site of occlusion in CRVO is invariably at the lamina cribrosa; (viii) clinical picture of CRVO is often due to compression or strangulation of the central retinal vein (CRV) in the lamina cribrosa and not its occlusion; (ix) an eye can develop both CRVO and central retinal artery occlusion (CRAO) simultaneously; (x) every eye with CRVO is at risk of developing neovascular glaucoma; (xi) lowering intraocular pressure (IOP) helps to improve retinal circulation in an eye with CRVO; (xii) every patient with retinal vein occlusion should have complete hematologic and coagulation evaluation; (xiii) the natural history of CRVO does not usually involve spontaneous visual improvement; (xiv) management of CRVO is similar to that of venous thrombosis anywhere else in the body, i.e. with aspirin and/or anti-coagulants; (xv) fibrinolytic agents can dissolve an organized thrombus in the CRV; (xvi) it is beneficial to lower blood pressure in patients with CRVO; (xvii) panretinal photocoagulation used in ischemic retinal venous occlusive disorders has no deleterious side-effects; (xviii) glaucoma or ocular hypertension can cause branch retinal vein occlusion; (xix) branch retinal vein occlusion can cause neovascular glaucoma; (xx) in eyes with CRAO, the artery is usually not completely occluded; (xxi) CRAO is always either embolic or thrombotic in origin; (xxii) amaurosis fugax is always due to retinal ischemia secondary to transient retinal arterial embolism; (xxiii) asymptomatic plaque(s) in retinal arteries do not require a detailed evaluation; (xxiv) retinal function can improve even when acute retinal ischemia due to CRAO has lasted for 20 h or more; (xxv) CRAO, like ischemic CRVO, can result in development of ocular neovascularization; (xxvi) panretinal photocoagulation is needed for “disc neovascularization” in CRAO; (xxvii) fibrinolytic agents are the treatment of choice in CRAO; (xxviii) there is no chance of an eye with retinal arterial occlusion having spontaneous visual improvement; (xxix) absence of any abnormality on Doppler evaluation of the carotid artery or echography of the heart always rules out those sites as the source of embolism; and (xxx) absence of an embolus in the retinal artery means the occlusion was not caused by an embolus. The major cause of all these misconceptions is the lack of a proper understanding of basic scientific facts related to the various diseases. The objective of this paper is to discuss these misconceptions, based on these scientific facts, to clarify the understanding of these blinding disorders, and to place their management on a rational, scientific basis.

Introduction

Acute retinal vascular occlusions are blinding disorders, and yet there is marked controversy on their pathogeneses, clinical features and particularly their management. This is because the subject is plagued by multiple misconceptions. During the past 40 years, I have been engaged in basic, experimental and clinical scientific research on various types of acute retinal vascular occlusion, as well as dealing with ophthalmologists and physicians managing patients with these disorders in many parts of the world. This experience has shown that one of the major causes of confusion and controversy concerning these diseases has been widespread misunderstanding about many of their fundamental aspects. Unfortunately, misconceptions, which have been passed from generation to generation of ophthalmologists have become conventional wisdom and often even considered “well-established facts”. When those “facts” are challenged, and even if new scientific information shows that they are no longer valid, the initial reaction is almost always skepticism or even ridicule.

It is not unusual to find that in many cases the clinical understanding of the diseases are generally based on the ingrained folklore or “gut feelings” which have been inherited over generations, viz. traditional believing and not on any solid scientifically basis. They often have originated in the pronouncements of leading clinicians or famous “Professors”. To justify what they believe or advocate, they usually fall back on what they call “Clinical Experience” (sometimes “my long years of clinical experience”), without giving any scientifically valid reason. Because of their high status in the profession or other reasons, people automatically take their statements as accurate. There is also the phenomenon of “bandwagon jumping”. If someone well-known proposes a theory or a mode of treatment, a number of his followers start to publicize that without paying any attention to its scientific merit. Once they are repeated again and again at conferences and other gatherings, people start to propagate those, and those statements gradually creep into the textbooks and journals. After a few repetitions and citations, they become accepted as “well-established facts” and take on a life of their own (Hayreh, 2000). Therefore, for some of the misconceptions it is impossible to track the origin and reasons of such “folklore”. In this connection, I am reminded of Langley (1899), who back in 1899 succinctly stated that: “Those who have occasion to enter into the depths of what is oddly, if generously, called the literature of a scientific subject, alone know the difficulty of emerging with an unsoured disposition. …Much that he is forced to read consists of a record of defective experiments, confused statements of results, wearisome description of detail, and unnecessary protracted discussion of unnecessary hypotheses.” All these considerations apply to several of the misconceptions discussed below in this manuscript.

The objective of this paper is to discuss, based on the current scientific knowledge, the many misconceptions and fallacies concerning various acute retinal vascular occlusions, with the intent to clarify the understanding of these blinding disorders and put their management on a rational, scientific basis.