Eyeshot: Ocular Injuries Caused by TASER Pistols

Michael A. Thiel; Claude Kaufmann


Eur Heart J. 2020;41(41):3984-398. 

The heart and eye are both pressurized multi-chamber organs that are interspersed with a complex system of electrical pathways. A handgun firing two barbed darts delivering pulses of electrical shocks therefore poses a potential threat to the structural integrity as well as to the electrical conduction of the organs. Largely protected by clothing and the thorax from direct mechanical impact, the induction of ventricular fibrillation is the main concern for the heart.[1] For the exposed eyeballs with a wall thickness of less than 1 mm, the danger situation is much less favourable. The following article gives an overview of ocular injury patterns and prognosis after TASER injuries.

In the 1960s, NASA researcher Jack Clover developed the TASER, whose name is derived from the initial letters of Thomas A. Swift Electric Rifle. Thomas Swift, in turn, was the developer's favourite childhood book character, a brilliant teenager who, among other things, developed an electric rifle firing bolts of electricity.[2] Originating from a juvenile American science fiction novel and commercially available since 1974, TASER pistols are enjoying ever-growing widespread distribution among police forces as less lethal, electric weapons for self-defence or to stun criminal subjects.

Indeed, the arrest-related death rate has been reported to have declined from 1:1000 to approximately 1:3500.[3] To cause an effective loss of regional muscle control conducted electric weapons deploy electric pulses through two contact points in the target subject's skin. Ideally, these contact points need to be separated by at least 30 cm and the two contact probes shot from the pistol need to penetrate the clothing and achieve a stable anchorage in the subject's superficial tissue. This is achieved by simultaneously deploying two dart probes with barbed arrow tips (Figure 1). While the fire line of one probe follows the aiming laser beam, a second probe flies along an eight-degree lowered trajectory which results in a probe separation of approximately 1 m in case of a shooting distance of 6 m.

Figure 1.

A probe used in X26 TASER pistols; the model most widespread among police forces. The arrow part is 13 mm long.

The TEASER manufacturer recommends the lower torso as a preferred point to aim for with the laser beam. However, to increase the likelihood of a successfully anchoring of the lower probe in the lower body region the TASER gun needs to be aimed at the upper body region, bringing the eye into the target area.[4] The TEASER probes travel at a low speed of initially 42 m/s which is rapidly reduced to 11 m/s by the trailing electric wire. This low speed allows time for reflex movements of the target subject such as turning the face towards the pistol or bending the head down, thereby exposing the face and the eye even more to the probes. It is estimated, that approximately 1% of the fired probes strike the face. As the eye with the retina is a neural tissue with an extremely sensitive electrical signal transduction, the effect of TASER pistols to the eye may also be of interest in other organs with a complex electric signal transduction, such as the heart.

So far there have been approximately 30 reported eye injuries in the last 20 years with a calculated risk of 1:123 000 per TASER shot, resulting in about two reported injuries per year based on estimated 300 000 world-wide field uses of TASER pistols annually.[5] However, the risk for eye injuries might be considerably higher due to underreporting and the fact that even subjects with serious TASER pistol induced eye injuries end up in prison and are rapidly lost to follow-up.[6]

Ocular traumas are usually complex and are based on different injury patterns: perforation by the arrowhead, blunt trauma caused by the impact velocity, electrical or thermal trauma with possible burns, cataract development, exudative retinal detachment, or impaired photoreceptor function.[6] The majority of reported cases have suffered from penetrating trauma with often blinding consequences (Figure 2).[4] The tip of the arrow measures 9–13 mm in length. The sharp arrow of the dart probe easily penetrates the sclera or cornea and will reach through the globe to the retina. In addition, the trailing body of the probe has enough kinetic energy to rupture an eye even without the sharp tip if deployed closer than 6 m from the subject.

Figure 2.

Corneal penetrating injury by a TASER dart with prolapse of dark iris tissue. Source: Figure 6A+C Moysidis et al.6 Permission to use Elsevier see pdf.

These injuries usually result in an open globe situation with vitreous loss, severe intraocular bleeding and retinal detachment. Despite surgical repair, approximately 50% of these eyes became blind or had to be surgically removed early after the incident. In addition, there is an ongoing discussion of the possibility of eye injuries caused by the electric current itself. The eyeball represents a liquid-filled globe with thin walls, making it prone to electrical damage.[7]

The retina has very delicate electric activity and applying a non-physiological current by TASER probes may cause additional electrical injuries. The gun manufacturer's scientific board argues that the electric power of less than 2 W that is exhibited by the TEASER gun is lower than the electric power used during surgery for electrocoagulation of periocular structures and therefore too low to cause damage to the eye.[8]

However, there has been a case report where it was possible to examine the patient with an electroretinogram, assessing the electric function of the retinal cells.[9] This patient had a TASER probe embedded in his lower eyelid without penetrating eye injury and only a visually non-relevant circumscribed peripheral subretinal haemorrhage. Despite this minor trauma of his peripheral retina, his vision had dropped dramatically to 0.05 (5% of normal visual acuity) and the electroretinogram showed a 60–70% decrease of the electric activity of his rod cells in the retina compared to his fellow eye. The pattern of the electroretinogram was in accordance with diffuse damage to a large area of the retina. Over a period of 2 months, the visual acuity recovered to approximately 80% of normal vision and the patient was lost to follow-up before the electroretinogram could be repeated. However, there is another similar incidence with a TASER probe landing on an eyelid but without any visual consequences.[10]

Hence due to the rarity of cases, the discussion about electric damage to the eye remains open, especially as most ocular injuries result in severe globe perforation and retinal detachment which makes it impossible to diagnose only electrical damage to the retina.

In summary, ocular injuries by TASER pistols are rare and most often are caused by kinetic perforation of the sharp dart tip hitting the eye or lid. Purely electrical damage to the retina remains a controversial possibility, that is, if really existing, difficult to diagnose and usually overlooked due to the usually severe and blinding mechanical trauma to the eye, caused by TASER pistol probes.

Unlike the heart, the visual system protects itself from a total TASER-induced loss of function not by the musculo-skeletal thorax, but by the paired arrangement of the eyes.