Industrial visual screening
- 2. The term occupational ophthalmology was first used in 1946 by Dr. Kuhn. Hedwig Kuhn stressed the need to assess the vision needs of the worker and then to match those needs to the ophthalmic evaluation conducted for that worker. She summarised the key elements of the visual screening programme as: 1. Selecting adequate pre-employment tests 2. periodic rechecks of specific groups, 3. conducting a practical visual survey of the plant
- 3. The Joint Industrial Ophthalmology Committee (1944) published the following definition of normals for job Acuity—In considering job classification “Normal” is of two varieties, the “clinical” or standard (theoretical) normal, and the “job normal.”The latter makes it possible for a person whose vision deviates from the perfect acuity standard to qualify for certain jobs.The term, “substandard,” is often used instead of “defective.” Stereopsis—There is no generally accepted percentage standard although Dr. Marshall Parks considers 40 seconds or better as representing bifoveal fixation and 60 seconds or worse representing extrafoveal fixation. Color Perception—This should be recorded by pseudoisochromatic plates and interpreted on the basis of the job requirement. Muscle Balance—Arbitrary standards of not more than 3 degrees (6 prism diopters) of esophoria and 5 degrees (10 prism diopters) of exophoria for distance, and 2 degrees (4 prism diopters) of esophoria and 8 degrees (16 prism diopters) of exophoria for near, are used as a matter of recording normal or substandard.
- 4. Analysis of the visual tasks involved while performing the job in terms of: Distance of the task Detail involved in the visual task Body , head and eye postures required Eye movements required Need for depth percetion Need for good color discrimination Field of peripheral vision required
- 5. Alternative is to demand that those visual functions considered important to the job must be normally perfect. Another method is to adopt standards for different classes of jobs as specified by various authorities.
- 6. Job description (including qualifications relative to type of training and skills) Distance or distances (distance for acuity and/or near acuity) in inches or feet from eyes of worker to point of operation, fixed or changing. Motion of work (distance and near muscle balance): slow or rapid rotation, vertical or horizontal, fixed or intermittent. Size of central working area, depth perception factors (stereopsis). Type of visual attention required: fixed or changing, casual or concentrated Colors to be perceived and discriminated. Foot candles of illumination at workpoint, as well as in surrounding area. Direction of light (note any harmful shadows). Reflected or direct glares (to be eliminated if possible). Brightness ratios (avoid sharp contrasts). Color of light source and work area (functional painting, etc.). Type of working surface: glossy or nonglossy, slightly or grossly uneven. Angle of working surface. Position of work in relation to normal level of eyes, viz., does worker have to look down, ahead or upward (determine whether bifocals are permissible or a handicap). Eye hazards: flying objects, particles of dust, fumes, splashing chemicals, or molten metal; airborne matter; radiation, and so forth. Type of eye protection required.
- 7. I. MODIFIED CLINICALTECHNIQUE Administered by qualified clinical personnel Tests chosen according to visual factors considered important for the job performance. A comprehensive screening programme would include: 1. History taking 2. Visual acuity measurement with snellen chart 3. External ocular examination and fundoscopic examination. 4. Retinoscopy to determine if extent of refractive error exceeds the predetermined limits 5. Near visual acuity testing and assessment of amplitude of accomodation by advancing the card until it becomes blurred. 6. Eye movements test, Cover test, testing for convergence. 7. Heterophoria measurement 8. Stereopsis measurement using stereoscopes or systems using polarisers that enable separation of two monocular targets. 9. Color vision testing using selected plates from ishihara test.
- 8. I. INSTRUMENTAL VISION SCREENERS They are variants of brewster stereoscopes with eye piece lenses arranged so that their power and prismatic components simulate viewing of a distant object. Right and left eyes view separate halves of the stereogram target. Near vision can be tested by moving the half stereograms closer or changing the lenses Most machines also test for heterophorias and visual fields color vision and astigmatism. They can be operated by lay persons, they present standardised tests useful for statistical comparison and maintenance costs are negligible.
- 9. Master orthorater(Bausch and lomb) Fleming master vision screeners(MAVIS) Sight screener(American optical corporation) Titmus vision tester Orthoscope(Keystone view company U.S.A) RODATEST(germany) Topcon sreenoscope(Japan)
- 10. Use of modified clinical method advisable when the visual tasks are demanding, When the consequence of substandard operation could be serious, and a large range of working distances need to be tested.eg airway pilot. In case of machine visual screeners the awareness of nearness causes some people to accommodate and converge excessively. so a hyperope with substandard distance visual acuity may acievean improved rating on instrument and emmetropes will score poorly in distance visual acuity tests. However machine based visual screening is cheaper and more convenient for screening examinations.