Evaluation of Visual Disabilities

PURPOSE: This rule sets forth procedures to evaluate visual disability. (1) Compensable disability for loss of vision should be based on that proportional part of the compensation provided by law for loss of use or loss of function of one (1) or of both eyes which expresses the percentage loss of visual efficiency of the individual. (A) Visual acuity as used in this rule means the best acuity obtainable at twenty feet fourteen inches (20'14") without the use of ophthalmic lenses, except that corrective lenses shall be used for natural presbyopia and other conditions clearly not the result of injury. (B) Visual efficiency is defined as that degree or percentage of competence of the eye to accomplish its physiologic function. (C) Loss of binocular single vision is equivalent to the loss of use of one (1) eye. (D) The reduction in visual acuity to 20/200 (6/60 where the metric system is used) or a reduction in visual efficiency to ten percent (10%) or less constitutes industrial blindness. (E) When both eyes are involved in a permanent visual disability, the efficiency of the coordinate function of both eyes should be determined on the basis of permanent partial disability of the body as a whole. (2) There are three (3) elements of vision, each of which has an interdependent and coordinate relation to full visual efficiency. These coordinate factors are acuteness of vision (central visual acuity), field of vision and muscle function. Although these factors do not possess an equal degree of importance, no act of vision is perfect without the coordinate action of all. Other functions, though secondary and dependent, are recognized as important, such as, for instance, depth perception, stereoscopic vision, fusion sense, color perception, adaptation to light and dark and accommodation. These secondary functions are inherently dependent on the status of the three (3) primary coordinate functions of vision and they also depend upon the condition of the central nervous system. (3) In order to determine the various degrees of visual efficiency, a) normal or maximum, and b) minimum limits for each coordinate function must be established, that is, the one hundred percent (100%) point and the zero percent (0%) point. (A) The maximum efficiency for each of these is established by existing and accepted standards. 1. Central visual acuity. The ability to recognize letters or characters with subtend an angle of five (5) minutes, each unit part of which subtends a one (1) minute angle, is accepted as standard. Therefore a 20/20 (6/6 metric) Snellen is employed as the maximum acuity of central vision or one hundred percent (100%) acuity. 2. Field vision. A visual field having an area which extends from the point of fixation outward eighty-five degrees (85°), down and out eighty-five degrees (85°), down sixty-five degrees (65°), down and in fifty degrees (50°), inward sixty degrees (60°), in and up fifty-five degrees (55°), upward forty-five degrees (45°), and up and out fifty-five degrees (55°) is accepted as one hundred percent (100%) industrial visual field efficiency. 3. Muscle function. A maximum normal muscle function is present when binocular single vision is present in all parts of the field of binocular fixation or when there is no limitation of motion in either eye. (B) The minimum limit or the zero percent (0%) of each of the coordinate functions of vision is established as that degree of deficiency which reduces vision to a state of uselessness. 1. Central visual acuity. Experience, experiment and authoritative opinion establish that a distance central visual acuity of 20/200 Snellen and a near central visual acuity of 14/140 is the accepted threshold of industrial blindness. 2. Field of vision. The minimum limit for this function is established as a concentric central contraction of the visual field to five degrees (5°). This degree of contraction of the visual field reduces the visual efficiency to zero (0). 3. Muscle function. The minimum limit for this function is established by the presence of diplopia in all parts of the motor field, the loss of binocular single vision or inability to rotate the eye to any point of fixation in the normal motor field. These conditions constitute zero visual efficiency. TABLE NO. 1 Percentage Loss of Visual Efficiency Corresponding to Snellen Notations for Distant and for Near Vision for Measurable Range of Quantitative Visual Acuity Using 20/200 = 100% Loss Percent- Percent- Snellen age of age of Notation Visual Visual at 20 feet Snellen at Efficiency Efficiency or 6 m 14 inches Retained Loss 20/20 14/14 100.0 0.0 20/25 14/17.5 94.0 6.0 20/30 14/21 88.0 12.0 20/35 14/24.5 82.4 17.6 20/40 14/28 77.4 22.6 20/45 14/31.5 72.8 27.2 20/50 14/35 68.1 31.9 20/60 14/42 60.0 40.0 20/70 14/49 52.5 47.5 20/80 14/56 46.4 53.6 20/90 14/63 41.2 58.8 20/100 14/70 35.9 64.1 20/120 14/84 27.8 72.2 20/140 14/98 20.2 79.8 20/160 14/112 13.0 87.0 20/180 14/126 6.0 94.0 20/200 14/140 0.0 100.0 (4) Visual acuity shall be measured both for distance and for near, using the Snellen notation, each eye being measured separately. Central visual acuity for distance shall be measured at a test distance of twenty feet (20') or six meters (6 m). Central visual acuity for near shall be measured at a test distance of fourteen inches (14") or thirty-five centimeter (35 cm). The best central visual acuity obtainable without the use of ophthalmic lenses shall be used in determining the degree of visual efficiency, except when natural presbyopia or other conditions clearly not the result of injury exist; then it is permissible to measure the visual acuity both for distance and near with correction. As an example, a high myopia with a vision without correction of 20/200 or less in each eye should be measured with the best corrective lenses, using the best vision of the uninjured eye as a standard. The practical difficulties of fitting, expense of and tolerance of wearing contact lenses are too great at the present time to favor the use of other than regular ophthalmic lenses to determine the best corrected vision. Having determined the best visual acuity for twenty feet fourteen inches (20'14"), the visual efficiency is ascertained by the weighted values assigned for central visual acuity at twenty feet (20') and central acuity at fourteen inches (14"). A one-fold value is given the distance vision and a twofold value is given for near vision. As an example: best visual acuity twenty feet (20'), 20/40; best visual acuity fourteen inches (14"), 14/35. Reference to Table No. 1 shows 20/40 equals 77.4 retained visual acuity and 14/35 equals 68.1 retained visual acuity. Thus the visual acuity efficiency for one eye would be ((77.4 × 1) plus (68.1 × 2)) divided by 3 equals .712 or 71.2% visual acuity efficiency (or a 28.8% loss). (5) The extent of the field of vision shall be determined by the use of the usual perimetric test methods, a white target being employed which subtends a one degree (1°) angle under illumination of not less than seven (7) footcandles and the result plotted on an ordinary visual field chart as shown on Figure No. 1. (A) Normal Field. A visual field having an area which extends from the point of fixation outward eighty-five degrees (85°), down and temporally eighty-five degrees (85°), down sixty-five degrees (65°), down and nasally fifty degrees (50°), nasally sixty degrees (60°), up and nasally fifty-five degrees (55°), up forty-five degrees (45°), up and temporally fifty-five degrees (55°), giving a total of five hundred (500) is established as a normal field of vision. (B) An Abnormal Field. The amount of radial contraction in the eight (8) field sectors, measured in their principal meridians, shall be determined. The sum in degrees of the eight (8) principal radii of the visual field (which normally is five hundred (500)) will give the visual field efficiency of one (1) eye in percent when divided by 5.00. Example: The following represent the findings in an abnormal field of vision in one (1) eye Upward 40 degrees Up and Out 40 degrees Outward 70 degrees Down and Out 60 degrees Down 50 degrees Down and In 50 degrees In 45 degrees Up and In 35 degrees TOTAL 390 5.00 78% which is the field of vision efficiency of the affected eye. (See Field of Vision Chart). (6) Muscle function shall be measured in all parts of the motor field, recognized methods being used for testing. A maximum normal extraocular muscle function is present when there is absence of diplopia (double vision) in all parts of the field of binocular fixation. Where diplopia is present, it shall be plotted on the motor field chart. This chart is divided into twenty (20) rectangles twenty by twentyfive degrees (20° × 25°) in size, as shown in Figure No. 2. Motor field chart at 40 inches is approximately 40 inches square, and the 20 rectangles measure 8 inches by 10 inches. The partial loss of muscle function due to diplopia is that proportional area which shows diplopia, as indicated on the plotted chart, compared with the entire motor field area. It shall be measured without corrective lenses, red glass or prism. For example, to determine the motor field efficiency of the eyes, assume the motor field chart shows a diplopia in eight (8) out of twenty (20) rectangles of the entire field. By referring to the Motor Field Chart, Figure No. 2 and Table No. 2, it is found that a loss of 8/20 gives a forty percent (40%) motor field loss or an efficiency of sixty percent (60%). TABLE NO. 2 Loss in Muscle Function Loss Retained 1/20 = 5% 95% 2/20 = 10% 90% 3/20 = 15% 85% 4/20 = 20% 80% 5/20 = 25% 75% 6/20 = 30% 70% 7/20 = 35% 65% 8/20 = 40% 60% 9/20 = 45% 55% 10/20 = 50% 50% 11/20 = 55% 45% 12/20 = 60% 40% 13/20 = 65% 35% 14/20 = 70% 30% 15/20 = 75% 25% 16/20 = 80% 20% 17/20 = 85% 15% 18/20 = 90% 10% 19/20 = 95% 5% 20/20 = 100% 0% (7) The industrial visual efficiency of one (1) eye is determined by obtaining the product of the computed coordinate efficiency values of central visual acuity of field vision and of muscle function. Thus, if central visual acuity efficiency is forty percent (40%), visual field efficiency is eighty-one percent (81%) and the muscle function efficiency is one hundred percent (100%), the resultant visual efficiency of the eye will be 0.40 × 0.81 × 1.00 equal 32.4% (a loss of 67.6%). Should the motor efficiency be reduced fifty percent (50%) in the example given, the visual efficiency would be 0.40 × 0.81 × 0.50 equal 16.2% (a loss of 83.3%). (8) It is a fact, established by common experience, that visual efficiency is by no means reduced to one-half (1/2) by the complete loss of one (1) eye, the vision in the fellow eye remaining normal; and it is also a fact that a permanent visual disability, total or partial, involving both eyes is not equivalent to the sum of the visual disabilities computed separately for each eye. Hence, the necessity arises to give a weighted average when a permanent binocular disability is present. For the complete loss of the sight of one (1) eye, the Missouri Workers’ Compensation Law allows one hundred forty (140) weeks; when there is permanent partial loss in both eyes, the disability evaluation is on the basis of four hundred (400) weeks (disability to the body as a whole). It should be noted that when an employee has sustained a permanent partial disability involving both eyes and a part of this disability is due to a loss in the binocular motor fields (determined by the area of diplopia), the loss of motor field efficiency is used only in computing the loss in the less efficient of the two (2) eyes. Therefore, the estimation of visual efficiency in the more efficient of the two (2) eyes is determined by using only the factors of central visual acuity and the field of vision efficiency. The formula for computing binocular visual efficiency loss in weeks is as follows: To the loss of visual efficiency of the poorer eye in weeks (based on the percentage of value of one (1) eye in weeks, one hundred and forty (140) being the basis) add the loss of visual efficiency of the second eye in weeks (based on the percentage of the difference between the value of one (1) eye in weeks and the value of both eyes in weeks, that is, four hundred (400) less one hundred forty (140) or two hundred sixty (260) weeks). For examples: poorer eye (right eye), seventy-five percent (75%) loss, 140 ×.75 = 105 weeks; second eye (left eye), five percent (5%) loss, 260 ×.05 = 13 weeks; binocular visual efficiency, loss one hundred eighteen (118) weeks. (9) Certain types of ocular disturbance are not included in the foregoing computations and these may result in disabilities, the value of which cannot be accurately measured by any scientific method available. Among them are disturbance of accommodation, of color vision, of adaptation to light and dark, metamorphopsia, entropion, ectropion, lagophthalmos, epiphora and muscle disturbances not included under diplopia. For such disabilities, additional compensation shall be allowed, but in no case shall such additional compensation make the total for loss in industrial visual efficiency greater than that provided by law for the total loss of the sight of one (1) eye when only one (1) eye is involved and that for permanent partial disability of the body as a whole when both eyes are involved. (A) Compensation for loss in industrial visual efficiency, as provided for previously in this rule, does not include compensation for any cosmetic defect, for mental or physical suffering, for cost of medical attention or for time lost from gainful occupation during the period of treatment previous to final computation of compensation as provided for in the following subsections. Additional compensation should be allowed for the various losses hereinafter enumerated. (B) Defects of form or structure of the eye, congenital or developmental in origin, such as regular astigmatism, myopia, hyperopia and presbyopia will not in themselves be regarded as traumatic in origin. (C) Irregular astigmatism may be due to corneal scars, inflammation, injury or operation and is compensable if it is. (D) Combined ratings of disabilities of the same eye shall not exceed the amount for total loss of sight of that eye. However, any cosmetic defect shall be noted in the report. (E) Although no scientific deductions can as yet be made as a basis for determining disabilities arising from those secondary ocular defect not included in the foregoing computations in the three (3) primary and coordinate factors of vision, experience and sound judgment, as expressed in the following table, give a yardstick for estimating losses due to so-called secondary ocular disabilities. (F) Compensable disability shall not be computed until all adequate and reasonable operations and treatment known to medical science have been offered to correct the defect. Final examination on which compensation is to be based shall not be made until at least three (3) months shall have elapsed after all visible evidences of inflammation have disappeared, except in cases of disturbance of extrinsic ocular muscles, optic nerve atrophy, sympathetic ophthalmia, traumatic cataract and paralysis of accommodation; in such cases at least twelve (12) months and preferably not more than sixteen (16) months shall intervene before the examination shall be made on which final compensable disability is to be computed. (G) In cases of additional loss in visual efficiency when it is known by the examining physician that there was present a pre-existing subnormal vision, compensable disability shall be based on the loss incurred as a result of eye injury or occupational condition specifically responsible for the additional loss. In cases in which there exists no record or no adequate and positive evidence of preexisting subnormal vision, it shall be assumed that the visual efficiency prior to any injury was one hundred percent (100%) or at least equal to the visual efficiency of the uninjured eye. TABLE NO. 3 TYPES OF OCULAR INJURY NOT INCLUDED IN THE DISTURBANCE OF COORDINATE FACTORS (The percentages are for unilateral losses unless otherwise noted) Disability Approximate Rating Not to Exceed Traumatic Cataract: When a traumatic cataract has been successfully treated by surgical or medical methods, the best visual acuity for that eye with ophthalmic lenses shall be measured. Fifty percent (50%) of this best visual acuity efficiency with an ophthalmic lens shall represent the central visual acuity efficiency of the eye for rating purposes. Dislocation of Lens—Traumatic: Partial—Withhold rating for 12 months; then rate as visual loss plus 50% (not to exceed 100%). Total—The loss shall be 100% unless the lens has been successfully removed by surgery or has been absorbed. When the lens has been successfully removed by surgery or has been absorbed, the eye shall be rated as an eye where a traumatic cataract has been removed. See: “Traumatic Cataract” preceding. Ptosis Loss is visual efficiency Loss Iridectomy With photo- 30% —Traumatic phobia or or surgical dazzling resulting Scotoma If not cen- 10% —Traumatic trally located Paralysis Unilateral 20% of Accom- *Bilateral See footnote modation Eye Brow Unilateral 10% (complete *Bilateral See footnote loss of) Eye Lashes Unilateral 10% (complete *Bilateral See footnote loss of) Symble- Unilateral 10% pharon (also *Bilateral See footnote limited muscle function) Ectropion Unilateral 10% or Entropion *Bilateral See footnote Lagophthalmus Unilateral 10% *Bilateral See footnote Epiphora Unilateral 10% *Bilateral See footnote * In the event of bilateral disabilities due to paralysis of accommodation, loss of eye brows, loss of eye lashes, symblepharon, ectropion, entripion, lagophthalmus or epiphora, the percentage of unilateral loss in the poorer eye shall be taken of 140 weeks and to that shall be added the percentage of unilateral loss in the better eye taken of 260 weeks. (See section (9) for computation of binocular visual efficiency). (10) When an employee, who has a permanent partial visual disability whether from a compensable injury or otherwise, subsequently receives a compensable injury resulting in additional permanent partial visual disability, the examining doctor shall then determine, as nearly as possible, the permanent disability caused by the last injury and set forth that percentage loss in his/her report. The employer is liable only for the visual loss due to the second injury, taken alone, and the Second Injury Fund is liable for additional disability if it is in excess of the mere sum of all the disabilities. (11) In each case of eye injury resulting in any degree of permanent disability, the employer and insurer shall file Form 9-A, Physician’s Report on Eye Injuries, completed in all the detail the form asks for, as promptly as possible. If the Form 9-A shows final estimation of the visual disabilities, it may be used as a basis for computing the compensation due the injured worker. AUTHORITY: section 287.650, RSMo 1986.* Original rule filed Dec. 23, 1953, effective Jan. 3, 1954. Amended: Filed Nov. 1, 1956, effective Nov. 12, 1956. Amended: Filed June 19, 1958, effective June 30, 1958. Amended: Filed Sept. 4, 1963, effective Sept. 15, 1963. *Original authority: 287.650, RSMo 1939, amended 1949, 1961, 1980, 1993, 1995, 1998.