SPECIFIC MECHANISMS OF VISUAL
LOSS: GENERAL CONSIDERATIONS
Literature Reports
Because of the infrequent occurrence of this complication, few
clinical studies have been conducted, and most incidents in the literature are contained
within case reports. No prospective studies of perioperative visual loss have been
performed. Accurate incidence data are sparse, nor is it known what percentage of
complications are actually reported. Recently, the ASA established a Postoperative
Visual Loss Registry,[49]
in which cases of visual
loss are submitted anonymously to a central location (ASA Closed Claims Study at
the University of Washington). The website for the Registry is http://depts.washington.edu/asaccp/eye/index.shtml.
In April 2003, the project was nearing its goal of collecting 100 cases. When completed,
the registry will be the largest single collection of cases of postoperative visual
loss and should provide a relatively comprehensive description of the characteristics
of these patients. The drawback of this project is the lack of a comparison group
as a control and thus an inability to establish causative factors.
Case reports have the disadvantage of many different sources of
reporting bias. For example, because many reports have described hypotension and
anemia as "risk factors," there may be a tendency to continue to publish reports
ascribing visual loss to these factors to the exclusion of others. Nonetheless,
case reports over a lengthy period and a few retrospective studies and published
surveys largely provide much of the current knowledge base on postoperative visual
loss. The current chapter will provide an update of the data compiled from all the
published case reports.
Case reports were obtained by performing a MEDLINE search.[50]
The search criteria included ION, retinal vascular occlusion, cortical blindness,
and anesthesia and surgery. Only English language publications were included. Patient
information could not be obtained from publications containing only aggregate data.
In many instances, specific data such as blood pressure, hematocrit, and fluids
administered are missing. Case reports were divided into retinal ischemia, ION,
and cortical blindness. The differential diagnosis, including symptoms and commonly
used diagnostic tests, will be discussed first. In the next section, the specific
mechanisms responsible for retinal and ON injury will be explained in detail.
