Keep an eye out

Soon after the invention of the telescope in the 17th century, the advantages of mounting two of these instruments side-by-side were explored, leading to the development of binoculars. Binoculars are two mirror-symmetrical or identical telescopes that are mounted next to each other, aligned, and pointed in the same direction, allowing the user to view distant objects with both eyes. Unlike a monocular telescope, binoculars present the viewer with a three-dimensional image.1 Today, binoculars are used by many bird watchers, hunters, theatergoers, spectators at sporting events, and military personnel, as well as other hobbyists and professionals.

Binocular vision is a key attribute of human physiology and enables people to more adequately view their surroundings. Binocular single vision is a state of simultaneous vision that results from the fusion of two slightly dissimilar images from each eye. This form of vision requires a clear visual axis, sensory fusion through retinal correspondence, and motor fusion through proper alignment of the eyes. Binocular vision provides multiple advantages, such as a larger field of vision, compensation for blind spots, and stereopsis. Stereopsis refers to the ability to merge two horizontally disparate images simultaneously, which results in three-dimensional perception of an image and, thus, depth perception.2

Effects of enucleation

When a patient suffers a unilateral enucleation, their field of vision becomes compromised and they lose stereopsis. According to previous studies, monocular vision in contrast to binocular vision results in approximately 10 percent to 20 percent loss of peripheral vision.3 This decreased visual field, in combination with the lack of stereopsis, can interfere with hand-eye coordination and many activities of daily living such as driving, crossing the street, and navigating stairs. Furthermore, loss of binocular vision can affect patients’ ability to work, especially if they are in a field that involves visual tasks within three feet of the subject—such as surgery.3 Another primary concern with unilateral enucleation is the protection of the contralateral eye, which typically results in the recommendation that the patient wear polycarbonate lenses to protect the “good eye” from trauma.4

Despite the loss of stereopsis, patients with monocular vision can still use other cues to determine depth perception and visual orientation, such as apparent size of objects, shading, and motion parallax. Motion parallax occurs when movement of the head causes nearby objects to move in the opposite direction and distant objects to move in the same direction as the head when using an intermediate distance fixation point.2 In addition, an earlier study that analyzed surveys of patients with acquired monocular vision indicated that patients generally achieve a new baseline level of function within a year. However, this study also demonstrated that 91 percent of these patients receive no formal training to assist with adaptation, suggesting that there is yet a possible benefit of a formal training program for patients with unilateral enucleation.4

 

Figure 1. Hospital discharge status

Figure 1. Hospital discharge status

Findings

To examine the occurrence of injuries that resulted in a traumatic enucleation of the eye in the National Trauma Data Bank® (NTDB®) research dataset for 2014, medical records were searched using the International Classification of Diseases, Ninth Revision, Clinical Modification diagnoses codes. Specifically searched were records that contained the diagnosis code 871.3 (avulsion, displacement, enucleation, or evisceration of the eye). A total of 230 records were found; 176 records contained a discharge status, including 109 patients discharged to home, 18 to acute care/rehab, and 17 sent to skilled nursing facilities; 32 died. (See Figure 1). Of these patients, 72.6 percent were male, an average of 41.5-years old, had an average hospital length of stay of 9.5 days, an intensive care unit length of stay of 8.1 days, an average injury severity score of 18.4, and were on the ventilator for an average of 6.5 days. The top two mechanisms that accounted for two-thirds of the injuries were firearms (36.6 percent) and motor vehicles (28.9 percent). (See Figure 2).

Figure 2. Mechanism of injury

Figure 2. Mechanism of injury

Watch for hazards

Traumatic globe enucleation is the most severe form of ocular trauma that instantly results in monocular vision. To simulate the effect, imagine looking through a pair of binoculars and then closing one eye. The resulting image is flat with reduced peripheral vision. These severe injuries can happen at home, in the workplace, or anywhere in between. Prevention is the best treatment, so keep an eye out and try to avoid potential ocular hazards.

Throughout the year, we will be highlighting NTDB data through brief monthly reports in the Bulletin. The NTDB Annual Report 2015 is available as a PDF file for download. In addition, information is available on our website about how to obtain NTDB data for more detailed study. To submit your trauma center’s data, contact Melanie L. Neal, Manager, NTDB, at mneal@facs.org.

Acknowledgment

Statistical support for this article was provided by Chrystal Caden-Price, Data Analyst, NTDB.

 


References

  1. Binoculars. New World Encyclopedia. Available at: www.newworldencyclopedia.org/entry/Binoculars. Accessed January 3, 2015.
  2. Bhola R. Binocular vision. EyeRounds.org. Available at: http://eyerounds.org/tutorials/Bhola-BinocularVision.htm. Accessed January 2, 2016.
  3. Politzer T. Implications of acquired monocular vision (loss of one eye). NORA.cc. Available at: https://nora.cc/for-patients-mainmenu-34/loss-of-one-eye-mainmenu-70.html. Accessed January 2, 2016.
  4. Coday MP, Warner MA, Jahrling MA, Rubin PA. Acquired monocular vision: Functional consequences from the patient’s perspective. Ophthal Plast Reconstr Surg. 2002;18(1):56-63.

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