Abstract
Eye examination plays an important role when living individuals are forensically investigated. The iris colour, retinal scans and other biometric features may be used for identification purposes while visual impairments may have legal implications in employment, driving and accidents. Ocular manifestations provide clues regarding substance abuse, poisoning and toxicity, and evidence of trauma, abuse or disease can be revealed along with psychological traits and lifestyle. Thus, the eye is a valuable tool in forensic investigations of living subjects, providing identifying characteristics along with health information. This review focuses on the medico-legal aspects of the eye's contribution when the living are subjected to forensic examination.
Keywords
Introduction
The eye, when forensically examined, can provide important information about the living person: it can reveal health issues, provide biometric identification, disease clues, trauma evidence, toxicity signs and psychological traits. Notwithstanding, eye exams are frequently overlooked in standard forensic evaluations. Modern techniques can unlock pivotal ocular secrets for investigations.
There is little literature synthesising this wealth of knowledge with relevance to its application in forensic practice. An updated review synthesising the wealth of eye exam utility in the living is needed. We aim to provide a overview to highlight the vital clues and evidence the eye may reveal, guiding forensic experts, clinicians, researchers and law enforcement to fully utilise this procedure.
Medico-legal importance of the eye in living people
The eye as a tool in identification
The human eye shows various individual characteristics that can be utilised to identify a person 1 and is now considered one of the most reliable tools for identification. Various eye-related parameters used for this purpose are discussed below.
Biometrics
Iris colour
Genetic and epidemiological studies show that iris colour is a phenotypic feature which can be used to determine population characteristics. Iris pigmentation defines iris colour, which can be clinically classified into light, mixed and dark eyes, or digitally into more accurate colour definitions. 2 Iris colour has been associated with specific genetic markers related to pigmentary traits. 2 In certain diseases like Wilson's disease, excess copper accumulation causes Kayser-Fleischer rings, a dark ring around the iris that persists for 3–5 years before disappearing with chelation therapy. 3
Iris scan
Iris scanning uses near-infrared light (NIR) to image unique patterns and lines in the iris, which were first encoded into biometric data by John Daugman in 1993. 4 It generates a highly specific black and white infrared scan of the iris. 4 Since an individual's iris pattern is stable over their lifetime, iris scanning can be used for unique identification. 4 Iris biometry has been widely used for personal identification of an individual. Even after undergoing cataract surgery, it is still possible to accurately identify a person through iris pattern recognition. 5
Retinal scan
Like iris scanning, retinal scanning is an accurate biometric identification method, based on the unique vascular pattern of the retina that is distinctive for each person. 6
Genetics
Genetics can provide information related to specific physical traits of the eye for an individual. Forensically validated DNA test systems that can categorise the eye according to colour of the eye can be useful in determining biogeographic ancestry.7 –9
Age
Ageing affects all parts of the human body including the eyes. Even minor age-related changes can greatly impact vision and are associated with various eye dysfunctions that are also relevant forensically.
Retina
Age-related macular degeneration (ARMD) is a major cause of blindness in older adults by damaging the central retina and precise central vision. 10 The lens also stiffens, leading to presbyopia – difficulty seeing near objects due to loss of ability to accommodate or focus. 10 Other age-related changes include nerve swelling and loss of axons and thickness in the optic nerve. 10 Fundus changes include loss of fundal reflex and fading, along with a senile tigroid pattern emerging with age. 10
Lens
In the elderly, vision is affected by senile cataracts where the crystallin protein in the ocular lens loses its transparency over time. 11
Vitreous humour
After age 50, people can develop vitreous floating, caused by changes in collagen and hyaluronic acid in the vitreous humour. With further ageing, there is increasing vitreous liquefaction, eventually leading to posterior vitreous detachment. 10
Cornea
Ageing leads to changes in corneal curvature, causing refractive alterations such as presbyopia and astigmatism in the elderly. Other corneal changes include loss of shine and sensitivity, increased fragility, and changes in the dystrophic layer. Arcus senilis, a deposit along the corneal periphery, is another common age-related corneal finding. 10
Identification from tears
Tears maintain eye health and homeostasis. Excessive tearing occurs reflexively from irritants such as pepper spray or emotionally from distress. Tear production declines with age.10,12 Tears can serve as biological evidence on items from crime scenes such as sexual assaults, kidnappings or murders, enabling identification. 13 Tears fluoresce when exposed to light between 254–410 nm, allowing detection up to three months later. 13 Epithelial cells in dried tears can provide DNA for profiling. 14
Ethnicity
Corneal thickness varies among ethnicities, with African-Americans and Japanese people having thinner corneas compared to Caucasians. 15 Optic disc and rim/disc area ratio differences exist between those of African versus European descent. 15 Foveal thickness also differs among ethnicities, with greater thickness in African-Americans reported in some studies,15,16 but conflicting differences found in others. 17 Macular pigment density is higher in Africans. 15 Additionally, age-related macular degeneration has higher prevalence among Caucasians compared to those of African ancestry. 15
Personality traits
There are some personality traits that can be evident when looking into the eyes of a person.
Aesthetic eyebrow piercing
Eyebrow aesthetic features are influenced by age, sex, culture, ethnicity and lifestyle factors. Body piercing is popular in Western cultures and growing globally, primarily as a form of personal self-expression and personality display rather than just fashion. Those with piercings often have risk-taking personalities as well as traits such as low constraint, unconventionality and less self-consciousness. 18 Ultimately, eyebrow piercings allow people to use their bodies to outwardly express inner personality characteristics. 19
Blinking
Excessive blinking (blepharospasm) of one or both eyes is an abnormal nervous tic that can serve to identify persons based on habitual traits. 20 Similarly, eyelid twitching (ocular myokymia) occurs in healthy, anxious, stressed, fatigued or caffeine-affected adults, commonly called “medical student’s disease”. 20
Trichotillomania
Trichotillomania is a psychiatric condition characterised by the recurrent urge to remove one's own body hair, typically from the scalp but also eyebrows and eyelashes. It can thus serve as a distinguishing behavioural trait for identification purposes. 21
Eye tattooing
Keratopigmentation (corneal tattooing) is a medical procedure to treat corneal scars and iris defects. 22 Corneal tattooing by tattoo artists is an extreme body modification that can cause ocular complications such as uveitis, globe perforation and blindness.22 –24 Distinctive corneal tattoos can help identify individuals, and the tattoo artists themselves may recognise their own work to aid identification.
Identification from eyewear/eye accessories
Contact lenses and eyewear found at the scene of the incident can unravel the identity of the person wearing them. Although refractive errors are common in the general population, it is unique to an individual. 25 Refractive errors can be single or dual affecting both the eyes and the error is usually corrected by prescription eyewear (sphere correction −15 to +15, cylinder correction −10 to +10, axis 0 to 180) by bifocal lenses of +1 to 3.5 dioptre. 26 If the prescription exceeds this range of value then it is considered rare and helps with identification. 26 Applications such as “OptoSearch” can be used to identify the person from a prescription database. 27
Lifestyles and living conditions
Ocular larva infestations by nematodes can occur in the conjunctiva, lacrimal duct and gland, caused by poor living conditions globally. 28 Maggots normally infest dead bodies but can also, known as myiasis, infest live patients, typically immobilised, paralysed or severely injured patients. 29 Additional risk factors for live maggot infestations include poor hygiene, moisture, poverty, rural residence and inadequate care. 29
Forensic toxicology
Examination of the eyes can reveal clues about toxic substances consumed or to which the eyes were exposed. This includes pupil dilation or constriction, nystagmus, effects of substance abuse and illicit drugs, blindness from heavy metals, and ocular injuries from tear gases and lachrymators. Specific poisons may cause mydriasis (e.g. atropine, cocaine, methanol), miosis (e.g. opium, nicotine), horizontal, vertical or gaze-evoked nystagmus (e.g. ethanol, phenytoin). 30 Intravenous drug abuse can cause retinal ischemia. 31 Heavy metal poisoning, such as lead and mercury, can diminish vision and cause blindness. Tear gases irritate the eyes, causing burning, tearing and blepharospasm, along with other possible ocular injuries. 32
Medico-legal importance of vision
The primary function of eyes is vision. Any compromise in vision can lead to accidents and deaths. There are many instances in clinical practice where assessment of vision is required.
Employment
Certain employments require adequate vision for applicants to be accepted or trained. In most countries, a pilot should have normal vision unaided and should not be colour blind; this may also apply to the police, army or paramilitary services. Examination of the eye for vision and colour blindness is mandatory to acquire a driving licence in many countries, including Nepal.
Accidents
Visual impairments such as night-blindness, colour blindness or diseases such as senile cataract are very prone to cause accidents. Pedestrians with mature cataracts are in danger if they are not assisted, e.g. to cross a road. 33
Jurisprudence
Eyes play an important role in medical jurisprudence. A wide range of ocular trauma may be encountered during treatment. Commonly encountered injuries include blowout injuries, fist injury, lid laceration, orbital contusion, muscle injury, foreign body, chemical injury, blast injury, gunshot injuries, etc. All such injuries may be accidental or deliberate or sometimes the result of defensive acts, e.g. the use of pepper spray by women to fend off an attempted assault. 34 Ocular injuries compromising vision are medico-legally significant. It is considered one of the six leading causes of blindness globally. 35
Ocular trauma and assault
Permanent deprivation of sight of either eye is a grievous injury.35,36 Disfigurement of the face by vitriolage from jealousy may cause ocular injury and blindness. One of the key features of “shaken baby syndrome” is retinal detachment where there is peripheral bleeding in the retinal layers due to acceleration-deacceleration forces and associated with retinoschisis. 37 Intraocular lens dislocation can occur as a consequence of head injury, traumatic or accidental. 38 Penetrating ocular injury can cause retained intraocular foreign bodies, such as air gun pellets, wood, glass or metals, that require immediate medical attention. 39
Theft, robbery and sexual offence
Eyes are the prime target in case of robbery or other offences. Application of pepper or counter pain rub analgesic balm will incapacitate victims.
Torture
Eyes can also be targeted for physical and psychological torture using blindfolds and sham executions. A blindfolded person is made to appear in front of an armed squad in the belief he will be executed.
Medical negligence
Retinopathy of prematurity (ROP) is a leading cause of preventable childhood blindness worldwide. 40 It is diagnosed by screening the eyes of the premature newborn, with prospects of cure with early intervention. Failing to screen the eyes for ROP is negligent and the physician may be sued. 40
Interrogation and riot control
Lachrymators (tear gas) and pepper spray are used by police in most countries for riot control. 41 Similarly, eye tracking can be used for lie-detection during custodial interrogation of a suspect. 42
Occupational eye injury
Work-related eye injuries are more common in agricultural workers from low and middle income countries. 43 Occupational eye injuries are preventable if proper face shields and other protective equipment are used. Under International Labour Organisation (ILO) standards, most countries have guidelines and laws that compensate employees, including for blindness, in case of occupational hazards.
Eye and the crime scene
Forensic experts thoroughly examine the scene for significant evidence, using knowledge gained from experience to identify disturbances. Eye-tracking technology collects gaze patterns and movements of experts at crime scenes, understanding how they evaluate scenes and make decisions. 44 This trains younger practitioners on evidence collection and supports continuing professional development.
Eye and mental illness
Evidence shows that eye movement desensitisation and reprocessing (EMDR) can be an effective treatment for post-traumatic stress disorder (PTSD). 45 In EMDR patient is instructed to briefly contemplate the traumatic incident while concurrently tracking the therapist’s fingers moving side-to-side with their eyes. 45 This bilateral brain stimulation is believed to activate information processing pathways, enabling the brain to form more adaptive associations related to the trauma. Over time, the brain processes the traumatic memory so that the patient becomes desensitised and symptoms remit as quality of life improves. 45 In cases of mental disorders resulting from head trauma, cooperation and non-cooperation can be distinguished using an image completion test that tracks eye blinking and movement parameters. 46 This eye-tracking data helps evaluate the patient's response. 46
Conclusions
The eye exam provides valuable forensic insights in the living through biometric identification features, health manifestations, trauma and toxicity clues, vision implications and psychological traits. Ocular structures reveal a wealth of data to aid investigations through ID markers, disease signs, toxicology, medicolegal issues and personality evidence. Standardised forensic eye protocols and more research into ocular changes can further realise the eye's immense potential in living forensic inquiries today, with promising possibilities tomorrow through ongoing advances.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
