FORENSIC ASPECTS OF VISUAL ACUITY AND CAUSATION IN MOTOR VEHICLE CASES
Daniel S. Chamberlain
Doehrman & Chamberlain
10333 North Meridian Street Suite 100
Indianapolis, Indiana 46290
(800) 269-3443
dsc@tortslaw.com
Visual acuity is a measurement of the ability of the eye to resolve fine detail. Visual acuity is the most easily and frequently measured visual function by way of measurement of illuminance (how much light is displayed on the object), luminance (how much light is reflected off an the object), and luminance intensity (output from a light source). These measurements can be useful to infer the ability of a motor vehicle operator to view an object at a distance. This determination may infer whether a plaintiff or defendant was negligent or comparatively negligent. Lower view = Objects close up while viewing at a distance.
There are numerous factors that can contribute to a decrease in visual acuity which would cause an object to be partially obscured by the human eye. These factors/considerations may be presented to a jury, by way of expert testimony, for determination of the degree of fault by a party. It is a difficult proposition to provide admissible testimony as to what a driver could, should, or did see, prior to a motor vehicle incident. As a general rule, motor vehicle operators focus their sight on objects in the distance. When focused on distant objects, light rays reflect parallel to the driver. These light rays are directed at the light sensitive retina in the eye. While the driver's eyes are focused at a distance, nearby objects reflect light behind the retina and appear blurred to the driver. As a result, these nearby objects are more difficult for the driver to detect and react to than objects in the distance. The larger and brighter (conspicuity) the object, the quicker the object will be detected and reaction can occur. In fact, trucking companies market "conspiquity" kits to assist visualization of their trailer tractors.
The fovea (located in the back of the eye) is the anatomical structure upon which an object reflects light rays. This structure will present the clearest view of an object when presented at close range, as a result of the visual receptors known as rods and cones. The greatest concentration of rods (low light receptors) and cones (color/wavelength receptors) are located within the retina. The further the object reflects light rays from the fovea, then visual acuity is reduced as well as a decrease in the likelihood of detection. Thus, the decrease in driver detection results in a delayed reaction time. The fovea is a very small area in the field of sight. Periphery vision is located outside of the area of the fovea. When an object is in the driver's periphery vision, the object must be more conspicuous to be detected by the driver.
A 1991 study demonstrated that a person with a peripheral vision disability may have an increased number of accidents. This increase in accidents is caused by a compromised detection and reaction time.
There are three categories of light measurement: luminous intensity, illuminance, and luminance. Luminous intensity is the measurement of the output of light from a source. This is measured in candelas. One candela is roughly equal to the output of a common candle. Illuminance is the amount of light reaching a surface. Illuminance is measured in foot-candles. The human eye is designed to discern objects best at high intensities of illuminance (as a result of cones). One candela (source output/luminance) will provide one foot-candle of illuminance at a distance of one foot. This relationship of luminous intensity to illuminance is described as the distance squared law. For example, a luminance of 8 candelas will yield 8 foot-candles at a distance of 1 foot. By increasing the distance from the source to 16 feet the foot-candles will decrease to 0.5, and increasing the distance from the source to 32 feet will decrease the illuminance to 0.25 foot candles. Luminance is the measurement of light reflected from a surface of an object. Luminance is measured in footlamberts. A surface that reflects all available light reaching it uniformly in all directions has a luminance of one footlambert. Luminance (or reflected light) produces a brightening effect on objects. An object with a high luminance will be easily discernible, for example, reflective clothing, reflective "conspicuity" tape, and neon signs, provided that the objects have a dark background. The measurement of luminance is important when determining the contrast of an object. Contrast is the difference in the luminance of the target object and the background area of the object. The higher the contrast between an object and the background results in an increase in the conspicuity of the object. For example, automobile headlights work by making the object brighter than the background. On the other hand, window tinting reduces the candlepower of street and headlights which decreases the brightness and contrast of objects; thus, rendering the object less discernible. There are many factors that decrease visual acuity and detection of objects.
Camouflage effects occur when the contrast of the object from its background is relatively minute. For example, a gray or dark colored car on an overcast day will have a camouflage effect. A camouflage effect can be measured by subtracting the luminance of the object from the luminance of the background (contrast). In a Pennsylvania case, the state Supreme Court reversed a lower court judgment that there was contributory negligence, as a matter of law, against a plaintiff who was momentarily blinded by oncoming lights. The operator struck an unlit, parked crane, covered by a black tarpaulin while positioned upon a background of black asphalt. In making this ruling, the court held that it was the plaintiff's burden to overcome the Pennsylvania, "Assured Clear Distance Ahead" statute. That statute provided, in part, that a driver has a duty to keep a proper lookout while making certain that the traveled portion of the roadway was clear from obstacles, such as the crane at issue. Thus, the court established an exception to the "Assured Clear Distance Ahead" statute. Other important factors are the type of lights equipped on a vehicle and where the lights are aimed. The aim of the headlights can be critical as to what an operator or oncoming motorist may see. If headlights are aimed as little as one degree too high, the visibility distance is increased by as much as 75 percent. Unfortunately, the higher aim causes an increased amount of glare to oncoming drivers. Extra weight in the trunk of an automobile can also raise the aim of the headlights one degree. If the headlights are aimed one degree too low, visibility distance is decreased by 45 percent. It is common for headlamps to be outside the SAE standard J599 which is plus/minus 4 inches at 25 feet for both horizontal and vertical dimensions. Dirt and slush on headlamps reduce the illumination of headlamps on most cars by one half. Dirt and scratches on the windshield can cause a significant amount of glare. A Texas appellate court ruled that a defendant was negligent for an automobile collision when two oncoming vehicles collided as a result of a dirty windshield. The negligent driver caused the collision and the court held that the tortfeasor's windshield was "in such a dirty, filthy and greasy condition that the view of the driver in front of him was practically destroyed." Polarized sunglasses can protect the driver from sun glare off the hood, top of the dash panel, and the road. Sunglasses decrease the contrast between an object and its background lessening it conspicuity. There are a number of visual impairments that reduces a driver's visual acuity. Persons with glaucoma may have difficulty seeing at night, a reduced contrast sensitivity, and sometimes absolute peripheral vision loss. Peripheral vision loss also occurs from retinal disorders and cataracts. Night blindness results from a deficiency in vitamin A and has varying degrees of severity. Macular degeneration is the predominant cause of blindness in the elderly. This disease stops sending messages to the brain from the retina resulting in a weakened visual acuity and color perception. Peripheral vision is normally unaffected by such diseases, rather the static central visual acuity is compromised. A 1991 case involving macular degeneration was reviewed in a Louisiana Court of Appeals decision. Mr. Tanner, the plaintiff/driver, suffered from macular degeneration. He had come to rely on his peripheral vision for the majority of his sight. Mr. Tanner hit an 18-wheeler straddling a two-lane road. The defendants' expert opined that Mr. Tanner should have seen the truck at 650-810 feet away and that if he had he would have seen the truck he would have been able to stop. To the contrary, Mr. Tanners' ophthalmologist testified that it was reasonable for Mr. Tanner to believe he was a safe driver because the degeneration progresses slowly. Mr. Tanner's eyesight was 20/400 almost twice the standard to be determined as "legally blind." The Department of Public Safety and Corrections was held 30 percent at fault for not performing the required, statutory eye testing and for licensing an unsafe driver. Mr. Tanner's fault was assessed at 35 percent because he was unaware that he was unsafe to drive a vehicle and the owner of the 18-wheeler was deemed 35 percent at fault.
Stereopsis is the ability of a person to see out of both eyes simultaneously which provides a stereo awareness of spatial relationships. A person without stereopsis (also known as a monocular operator) is a person that has vision impairment in one eye. This person will have a slower reaction time because their spatial perception is either absent or will take more reaction time to interpret. However, this will not affect distance vision but may impair near range driving, such as parking. Visual analysis standards and terminology varies among jurisdictions. The Ohio Supreme Court (citing the Pennsylvania Supreme Court) wrote: The Court stated that none of the cases revealed an intention to ascribe to the word "discernible" a fixed and rigid meaning applicable to every possible situation. The word "discernible" ordinarily implies something more than "visible." Visible means perceivable by the eye whereas "discernible" means mentally perceptible or distinguishable-capable of being discerned by the understanding and not merely by the senses. Reasonably discernible is an objective standard for determination of whether two persons, under the same or similar circumstances and weather conditions, would have reasonably discerned an object. Visible means capable of perception by the human eye.
Using the McFadden analysis (as set forth above), the authors of Forensic Aspects of Vision and Highway Safety concluded that the mental perception of an obstacle requires: 1. Detection, 2. Identification, 3. Recognition (before it can or cannot be perceived as a danger), and 4. Reaction (i.e., message sent to the muscular skeleton system before a maneuver can occur). Plainly and clearly visible takes into consideration the size and contrast of the object and possibly the case history of that jurisdiction. Visual analysis may be used to determine whether a plaintiff was negligent, negligent per se or whether a defendant was comparatively at fault.
A judge or jury may find that an operator could not have reasonably discerned the object in question and is therefore, not negligent or vice versa depending on the law applied and the instructions given to the jury. Depending on the state, negligence per se findings may have exceptions that include objects that are not reasonably discernible. For example, in 1976, the Supreme Court of Ohio held that a: Violation of the statute and a finding of negligence per se depends on whether there is evidence that the driver collided with an object which (1) was ahead of him in his path of travel, (2) was stationary or moving in the same direction as the driver, (3) did not suddenly appear in the driver's path, and (4) was reasonably discernible. The Ohio courts have held that "where there is conflicting evidence and reasonable minds could differ concerning any one of the elements necessary to constitute a violation of the statute, a jury question exists with regard to that element." The Court went further by stating that Ohio has on numerous cases ruled that a collision that occurred at night during extraordinary weather conditions was a jury question as to whether the object that the driver hit was "reasonably discernible." Conversely, the court stated that it has also held "[a]n automobile, van, or truck stopped on a highway in a driver's path during daylight hours is, in the absence of extraordinary weather conditions, a reasonably [**479] discernible object as a matter of law." Contributory/comparative negligence is a question of fact for the jury in most states.
Depending on the instructions given to the jury, conspicuity, may be proven under a plainly visible, clearly visible, discernible, or reasonably discernible standard. For instance, an Indiana case where a defendant pulled out of a parking lot into the path of a three-wheeler, the defendant contended that the plaintiff was contributorily negligent because the owner's manual stated that the three-wheeler was for off road use only. The Indiana Appeals Court stated, in the context of determining contributory negligence that, "a proper lookout has been defined to mean the duty to see that which is clearly visible or which in the exercise of due care would be visible." Later the next year, the Indiana Appeals Court cited the Conway jury instructions and stated that the proper lookout/clearly visible concept may be evidence of negligence. There are several factors to consider when presenting evidence to the jury. When presenting photographic evidence to the jury, the jury is provided significantly greater exposure to the evidence than the "real time" situation experienced by an on the road driver. Furthermore, the jury already knows what to look for and where to look in the photograph prior to reviewing the evidence, unlike the party involved.
When retaining an expert, it is important to provide the following information. Vehicle Scene Documentation Visibility Aspects Pre-Impact A. Minimum view 1000 Fee Prior to Impact 1. Written Description B. Obtain Light Level 1. Time: Environmental: Luminaire: Other: 2. Sun Rise: Sun Set Both C. Obtain Vehicle Windshield Data 1. Windshields: Clear Tint Color Dirty Scratched Sloped Other Photo D. Color of Car Pantone Y X 1. Sample Paint 2. Percent Reflectance E. Inspect Lighting System 1. Headlight a. Lens: Dirty Scratched b. Filament c. Low/High d. Ground to bulb: to center: e. Separation: f. Type: 2. Taillight a. Dirty Pitted Scratch SAE# Lens Color Stop Turn Regular Transmission % Y X Each Other F. Sight Distance/Site Distance 1. Day 2. Night 3. Obstruction-describe G. Road: Asphalt % Ref. Concrete % Ref. H. Background: Visual Clutter: Clear Luminance: Absolute % Other: I. Driver V-1 a. Wear Glasses Tint b. Age c. Size Driver V-2 a. Wear Glasses Tint b. Age c. Size J. Other Involved a. Pedestrian Clothes Color: Pants Shirt Size Shoes Other b. Locomotive (See Railroad Work Up) c. Bicycle Color Headlamp Reflector % Size Location: K. Weather/Climatology Rain Estimate Light, Medium, Heavy Fog Estimate Light, Medium, Heavy Snow Estimate Light, Medium, Heavy Mist Estimate Light, Medium, Heavy Condition: Wet Dry Snow Ice L. Road Design: 1000 Feet Prior to Scene Draw Map Items: Signs, Houses, Driveways, Contour, etc. 2 Lane 4 Lane Other M. Visual Clutter - Describe N. Traffic Controls/Location 1000 Feet Prior Signs Road Berm Signals Other O. Special Conditions a. Construction Describe Controls b. School c. Hospital d. Urban City Township e. Other Describe Post-Impact Documentation Visibility Aspects Scene Data Required 1. Moon evaluation as to light quantity, azimuth, bearing. 2. Sun evaluation as to azimuth and location. 3. Percent transmission to windshield 4. Taillight/Headlight SAE Number: Height/Ground Center Bulb Angular Separation: Center to Center 5. Retro-Reflection Signs a. Age b. Type c. Condition 6. Truck Light/Lens Inspection a.. Age b. Condition c. Emission d. Lens 7. Retro-Reflection Tapes a. Location b. Condition c. Type 8. Photographs The type of evidence needed depends on the type of incident that has occurred. For accidents that question the visibility or discernability of an object, it will be important to obtain the sight distance, lighting, and the weather conditions at the time of the accident. If the accident occurred at night, the positioning of any light that may have distracted or blinded a driver is a critical determination. Light intensities at accidents that occur at dawn or dusk are dependent upon the sky conditions. An overcast sky will decrease light while a sunset will increase the amount of light that existed at the time of the accident. Finally, the driver's medical records will be necessary to determine any medical condition that may affect the participant's visual acuity. Visual acuity can be very useful in determining whether negligence is involved in an accident. It is important to remember that numerous factors can affect the visual acuity of a party which increases or decreases reaction times. Depending on the law applied and the instructions given to the jury, visual acuity can prove causation or disprove negligence, comparative negligence, or negligence per se.
Doehrman & Chamberlain
10333 North Meridian Street Suite 100
Indianapolis, Indiana 46290