Division 1

Assessment of the Degree of an Employee's Permanent Impairment Resulting from an Injury

 

Chapter 6 - The Visual System

 

 

6.0 Introduction

In conducting an assessment, the assessor must have regard to the Principles of Assessment and the definitions contained in the Glossary.

Chapter 6 provides a standard method for examining the visual system, and for calculating the extent of any visual impairment. Impairment is any loss or abnormality in the anatomy or function of the visual system. The visual system includes the eyes, the ocular adnexa, and the visual pathways.

All visual tests are standardised and impairment assessment follows a strict protocol in order to ensure that different ophthalmologists can closely reproduce results. Wherever possible, impairment assessment should be performed by an ophthalmologist.

Visual impairment exists when there is deviation from any of the normal functions of the eye.

Among the types of visual impairment listed below, the first three (6.1-6.3) contribute the most to the overall impairment (numbers correspond to sections in Chapter 6):

Impairments assessed under Chapter 6 include those caused by secondary conditions accompanying an endocrine system condition. An impairment assessed under Chapter 3 - The Endocrine System should be combined with those resulting from the secondary conditions assessed under Chapter 6.

WPI ratings from Table 4.2: Facial Disfigurement (Chapter 4 -Disfigurement and Skin Disorders), cannot be combined with WPI ratings arising from either:

• section 6.4 - Other Ocular Abnormalities; or
• section 6.5 - Other Conditions Causing Permanent Deformities Causing up to 10% Impairment of the Whole Person.

Facial nerve injury complicated by visual changes, such as occurs with corneal desiccation and scarring, rates as a significant impairment. Such an impairment is assessed under Chapter 6 and a resulting WPI rating may be combined with a WPI rating from Table 12.5.4: The Facial Nerve (VII) (Chapter 12 - The Neurological System).

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Steps in Determining Whole Person Impairment.

See Figure 6-A below for steps in deriving a visual system impairment rating. Use Table 6.1 (following Figure 6-A) to convert a visual system impairment rating to a WPI rating.

Figure 6-A: Steps for Calculating Impairment of the Visual System

Step 1	Determine and record the percentage loss of central vision for each eye separately, combining the losses of near and distance vision. Refer to Figure 6-C.
Step 2	Determine and record the percentage loss of visual fields for each eye separately (monocular) or for both eyes together (binocular).
Step 3	Using the Combined Values Chart (see Appendix 1), combine the results from Step 1 and Step 2 for each eye if any central vision and visual field impairment is present.
Step 4	Determine and record the percentage loss of ocular motility.
Step 5	Using the Combined Values Chart (see Appendix 1), combine the result of Step 3 with Step 4 if there is any ocular motility impairment.
Step 6	Determine and record the percentage loss if other ocular impairments are present.
Step 7	Using the Combined Values Chart (see Appendix 1), combine the result of Step 5 with Step 6 if any other ocular impairment exists.
Step 8	Determine the visual impairment for both eyes. The visual impairment for both eyes is calculated by the formula: 3 x (impairment of better eye) + (impairment of worse eye)= visual system impairment 4 Alternatively use Figure 6-F.
Step 9	Convert the visual impairment for both eyes to a WPI rating using Table 6.1.
Step 10	Using the Combined Values Chart (see Appendix 1), combine the result of Step 9 with any impairment (up to 10% maximum) arising from other conditions causing permanent deformities (see section 6.5).

Table 6.1: Conversion of the Visual System to Whole Person Impairment Rating

Source: American Medical Association Guides to the Evaluation of Permanent Impairment (4^th edition, 1995, Table 6, Chapter 8, page 218).

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Visual System	Whole person	Visual System	Whole person	Visual System	Whole person	Visual System	Whole person
0	0
1	1	26	25	51	48	76	72
2	2	27	25	52	49	77	73
3	3	28	26	53	50	78	74
4	4	29	27	54	51	79	75
5	5	30	28	55	52	80	76
6	6	31	29	56	53	81	76
7	7	32	30	57	54	82	77
8	8	33	31	58	55	83	78
9	8	34	32	59	56	84	79
10	9	35	33	60	57	85	80
11	10	36	34	61	58	86	81
12	11	37	35	62	59	87	82
13	12	38	36	63	59	88	83
14	13	39	37	64	60	89	84
15	14	40	38	65	61	90	85
16	15	41	39	66	62	91	85
17	16	42	40	67	63	92	85
18	17	43	41	68	64	93	85
19	18	44	42	69	65	94	85
20	19	45	42	70	66	95	85
21	20	46	43	71	67	96	85
22	21	47	44	72	68	97	85
23	22	48	45	73	69	98	85
24	23	49	46	74	70	99	85
25	24	50	47	75	71	100	85

6.1 Central Visual Acuity

A Snellen test chart is used to measure the distance of visual acuity. The test distance is 6 metres.

The near vision is measured using a LogMar reading card. If Near Snellen, Jaeger, Sloan or Roman reading cards are used the results need to be converted to LogMar (see Figure 6-B below). The distance in the near reading test is not fixed: the reading distance should be recorded by the ophthalmologist.

Central vision should be tested and recorded for distant and near objects. The employee should be refracted and tested with loose lenses, phoropter, or with their own glasses if they are accurate.

If an employee wears contact lenses each day and wishes to wear them in the test, this is acceptable for measuring acuity. In certain ocular conditions (particularly in the presence of corneal abnormalities) contact lens-corrected vision may be better than that obtained with spectacle correction. However, if an employee does not already wear contact lenses, they should not be fitted for an impairment assessment.

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Figure 6-B: Revised LogMar Equivalent for Different Reading Cards

LogMar	Near Snellen	Equivalent to Snellen	N.	Points Roman	Revised Jaeger Standard
0.3	14/14	6/6	N5	3	1
0.4	14/18	6/7.5	N6	4	2
0.5	14/21	6/9	N7	5	3
0.6	14/24	6/12	N8	6	4
0.65	14/28	6/15	N9	7	5
0.7	14/35	6/18	N10	8	6
0.725	14/40	6/24	N12	9	7
0.75	14/45	6/30	N15	10	8
0.8	14/60	6/36	N17	11	9
0.9	14/70	6/48	N18	12	10
1.0	14/80	6/60	N20	13	11
1.1	14/88	6/90	N24	14	12
1.3	14/112	6/120	N40	21	13
1.6	14/140	6/240	N80	23	14

6.1.1 Determining the Loss of Central Vision in One Eye

The following steps are taken to determine loss of central vision in one eye.

Step 1	Measure the central acuity for distance and near, correcting for any refractive errors and presbyopia, and record the result.
Step 2	Consult Figure 6-C below to derive the overall loss, combining the values for corrected near and distance acuities.
Step 3	If monocular aphakia or pseudoaphakia is present then add 50% to the percentage loss of Central Vision obtained from Figure 6-C.

Figure 6-C: Percentage Loss of Central Vision in One Eye

	Revised LogMar Standard for Near Vision
Distance Vision (metric 6)	0.3	0.4	0.4	0.5	0.6	0.7	0.7	0.7	0.8	0.9	1.0	1.1	1.3	1.6
6/5	0	0	3	4	5	25	27	30	40	43	44	45	48	49
6/6	0	0	3	4	5	25	27	30	40	43	44	46	48	49
6/7.5	3	3	5	6	8	28	30	33	43	45	46	48	50	52
6/10	5	5	8	9	10	30	32	35	45	48	49	50	53	54
6/12	8	8	10	11	13	33	35	38	48	50	51	53	55	57
6/15	13	13	15	16	18	38	40	43	53	55	56	58	60	62
6/20	16	16	18	20	22	41	44	46	56	59	60	61	64	65
6/22	18	18	21	22	23	43	46	48	58	61	62	63	66	67
6/24	20	20	23	24	25	45	47	50	60	63	64	65	68	69
6/30	25	25	28	29	30	50	52	55	58	68	69	70	73	74
6/38	30	30	33	34	35	55	57	60	70	73	74	75	78	79
6/50	34	34	37	38	39	59	61	64	74	77	78	79	82	83
6/60	40	40	43	44	45	65	67	70	80	83	84	85	88	89
6/90	43	43	45	46	48	68	70	73	83	85	86	88	90	92
6/120	45	45	48	49	50	70	72	75	85	88	89	90	93	94
6/240	48	48	50	51	53	73	75	78	88	90	91	93	95	97

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6.2 Determining Loss of Monocular Visual Fields

There are many ways of measuring the visual field. The most common are the manual Goldman field and the Humphrey, Octopus and Medmont computerised field analysers. If using a computerised field it is necessary to test at least a 30-2 Threshold.

An Esterman Binocular Field is suitable for the majority of visual field impairment examinations. The field is tested with the employee wearing their glasses and both eyes open. The binocular field result is determined by using the Esterman 120-unit binocular grid, and the dot count is multiplied by⁵/₆to obtain the percentage of retained or lost field. Note that binocular field-testing is not recommended when double vision is present.

If the automated 30-2 Threshold Field is normal, and the ocular history and examination do not suggest lesions that would affect the outer extent of the field, it is then acceptable to conclude that the entire field is normal. Whatever technique is used to measure the visual field, the test should be performed by the ophthalmologist.

The normal visual field meridians in each of eight principal meridians are given in Figure 6-D below.The total extent summed over 8 meridians is 500.

Figure 6-D: Normal Extent of the Visual Field

Direction of Vision	Degrees of Field
Temporally	85
Down temporally	85
Direct down	65
Down nasally	50
Nasally	60
Up nasally	55
Direct up	45
Up temporally	55
Total	500

The percentage of retained vision is calculated using the following steps.

Step 1	Add the extent of the visual field along each of the 8 meridians (while considering the maximum normal values for the meridians given in Figure 6-D).
Step 2	Divide by 5 to determine the percentage of visual field perception that remains.
Step 3	To obtain the percentage of visual field loss, subtract the percentage of visual field remaining from 100%.

These steps are based upon the following formulae:

Total visual field 5

= % of remaining visual field

 

100 - (% of remaining visual field) = % of visual field lost

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6.3 Abnormal Ocular Motility and Binocular Diplopia

The diplopia within the central 30?is measured by the ophthalmologist with a Tangent screen. Unless there is diplopia within 30?of the centre of fixation, the diplopia does not cause significant visual impairment. The exception is when looking downwards. Double vision within the central 20?signifies the maximum loss of ocular motility (that is, a 50% loss of ocular motility of one eye).

If the double vision is not within the central 20?, the presence of diplopia is then plotted along the 8 meridians (see Figure 6-E below). The largest percentage on any of the meridians in which there is double vision is the impairment percentage for loss of ocular motility.

Figure 6-E: Percentage Loss of Ocular Motility of one Eye in Diplopia Fields

6.4 Other Ocular Abnormalities

If an ocular adnexal disturbance or deformity interferes with visual function and is not reflected in diminished visual acuity, decreased visual fields, or ocular motility problems with diplopia, then the significance of the disturbance or deformity should be evaluated by the examining ophthalmologist. In that situation, using the Combined Values Chart (see Appendix 1), the ophthalmologist may combine up to an additional 10% impairment for that eye.

Problems in the visual system should also be taken into account where they result in symptoms such as epiphoria, photophobia, metamorphopsia, and convergence insufficiency.

 

Using the Combined Values Chart (see Appendix 1), an additional WPI of up to 10% may be combined with WPI ratings for conditions such as permanent deformities of the orbit, scars, and other cosmetic deformities that do not otherwise alter ocular function.

6.6 Calculation of Visual System Impairment for Both Eyes

Figure 6-F (from the American Medical Association's Guides to the Evaluation of Permanent Impairment, Chapter 8, page 219, 4 ^thedition, 1995) is on the three following pages.

Figure 6-F was established using the equation:

3 x (impairment value of better eye) + (impairment value of worse eye) 4

= impairment of visual system

 

Percentages for the worse eye are read from the side of the table.

Percentages for the better eye are read from the bottom of the table.

The impairment of the visual system is at the intersection of the column for the worse eye and the column
for the better eye.

For example, for a 40% impairment of one eye and 10% impairment of the other eye, read down the table
until you come to the large value (40%). Follow across the row until it is intersected with the column
designated by 10% at the bottom of the page (18%). Thus, the impairment to the visual system is 18%.

Figure 6-F: Calculation of Visual System Impairment for Both Eyes