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Archive for the ‘Harmon distance’ Category

Posture and Vision (3)

Visual Hygiene and Near Work Visual Habits

 

Some tips in brief:

  • Do all near point activity at HARMON distance or slightly further.
  • For reading, writing, and other near vision tasks it is important that the object being viewed be kept adequately far from the eyes.  The working distance should be at least 40 cm (sixteen inches) for adults and older children, and at least 30-33 cm (twelve to thirteen inches) for younger children.  When the viewing distance is shorter, the demands upon the focusing system become increased out of proportion to the few inches involved.  This increases demand can lead to severe stress and strain.
  • Therefore, maintaining an adequately long working distance is the foundation of good visual hygiene and depends upon good relaxed posture and proper lighting.  Reading and writing while lying down, reading in bed, and other inappropriate postures tend to result in shortened viewing distances.  Insufficient lighting also causes one to hold reading material inappropriately close in order to see it.
  • When reading, occasionally look off at a specific distant object and let its details come into focus. Maintain awareness of other objects and details surrounding it. Do this at least after two or three pages.
  • Desk work should be performed at an appropriately sized desk and on a surface inclined at an angle of 20 degrees. The chair should be of such size to allow the feet to rest comfortably on the floor. The buttocks should be flat and tucked fully to the back of the seat.  Kitchen or dining room tables were not designed for studying or writing.  They are usually too high and inappropriate for use by a child.  Tilt the book up about 20o.  Read in bed only when sitting upright – if at all.
  • For proper lighting when reading in a chair, illuminate the entire area using overhead/full-room lighting.  Next, have another light on your book – one that avoids bright reflection on the task.
  • When performing any prolonged near work, take breaks if you begin to feel your neck, shoulder, or back muscles beginning to tighten.
  • Don’t get “locked in” when doing close work.  Read or study no longer than fifteen to thirty minutes without interruption.  Look up at a distant object as you turn each page, and try to get the distant object clear before beginning to read the next page.  Looking back and forth from distance to near while reading reduces the tendency of the focusing muscles to become cramped.
  • Be aware of your general surroundings while reading or viewing TV.  Do not place desks against walls. Do not sit any closer to TV than is necessary.  A minimum viewing distance of 2,5 to 3 meters is reasonable.
  • Active outdoor play is an essential part of normal and healthy development.  Play activities that require seeing beyond arm’s length should be encouraged.

Inspired from:  http://www.gallopintovision.com/visual_hygiene.htm

In summary:

 The essential elements of visual hygiene tips are:

  • posture
  • distance
  • furniture
  • lighting
  • relaxation (breaks)

Posture: Sit with a straight back, with head straight, aligned for the task, neither tilted excessively forward nor backward, nor tilted to either side. This position should be maintained throughout all near activities.  Avoid reading in bed or lying down. No lying on the stomach, no slouching, no curling up or other asymmetric positions.

Distance: for reading, writing, drawing, hand-held video game, etc.: everything must be done at forearm’s length. For desktop computer, the screen should be placed at arm’s length (fingers must just barely touch the screen). For a laptop, a working distance of 50 to 60 cm is recommended.

For television: At least 2 to 3 meters, with head and back straight.

Furniture:

If children or shorter people are working on a regular table (ex kitchen table), they should sit on a higher stool or a cushion.  Otherwise, use a smaller table adjusted for their height.

Lighting:  Use general overall lighting in the room and add supplemental lighting as needed for the task.  Make sure there is even lighting across your work.  Never work in the dark.

Taking breaks: a 10 minute break after a 60 minute period is beneficial.

Note: This ends all that I had to say about myopia and the control of this condition. I hope these texts have made you more aware about myopia and that you will be able to help your child in the prevention or control of his or her myopia.

Posture and Vision (2)

Slant desk or slant board with a 20 degree angle

Ideal work surface (http://www.visualedgesb.com/)

 Many years after Harmon’s studies, Drs Pierce and Greenspan have also studied the relationship between posture and vision. Once again, they have shown that there is an integral working relationship between posture, work distance and work surface.  Their research has proven that learning performance improves when the proper conditions are established for near-point visual activities such as reading and writing.

Their studies show when work is presented on a sloped work surface, with an angle at between 20 and 23 degrees, sitting no closer than fist to elbow length from the work surface, the worker experiences a reduced heart rate, neck, muscle and overall body tension as well as a more regular and deeper breathing pattern. A slanted surface compels your body to sit in a more upright posture

  • Dr. John Pierce Rev Optometry 1977; 114:48-63
  • Dr. Steven Greenspan; Optometry Weekly 1971; 62(33): 754-757, Optometry Weekly 1971; 62(34): 776-780

Source: http://www.visualedgesb.com/

A century ago, classroom designers and teachers understood the importance of proper ergonomics in the classroom and the use of slanted desks in a learning environment. It is amazing how something so simple in concept, is so effective in application and can have such huge benefits. It begs the question: why were slanted desks taken out of the classroom in the first place?  The simple answer is most likely the right one: it was more cost effective. Since flat desks were introduced to the classroom, reading scores have dropped considerably.  European schools are now reintroducing slanted desks in their school classrooms and we too should rethink the ergonomics of learning.

Finally, Sampedro et al. observed the characteristics of the spontaneous reflex reading distance (RRD) in 351 children in two stages, first in reading then writing, and comparing their RRD with the Harmon distance in the same environmental conditions. The results show that 72, 08% of the population analyzed (65% while reading and 53% while writing) had a normal RRD. Also, 50, 96% of people who had too short a RRD were myopic, 38, 46% were emmetropic and 10.58% were hyperopic. Conclusions: the shorter the RRD, the more mental effort is required in near vision; the situation creates more visual stress. So in this study, one third of the children were standing too near their work plan and the RRD was shorter in writing than in reading. More myopic individuals had a tendency to read closer than they should.

  •  Gené Sampedro, Andrés; Montalt, Juan C.; Alemany, Antonio L. Estudio del reflejo visuopostural. Gaceta Óptica, 1997 JUL-AGO; (307)

Posture and Vision (1)

No program that addresses myopia control would be complete without talking about the important concepts of posture and visual hygiene advices.

There is ample evidence that conditions which lead to muscle tension and place undue stress on the visual system will, over a period of time, lead to eye problems such as myopia, and other disorders such as focusing and binocular coordination problems.  Many authorities blame our culture’s emphasis, for both children and adults, upon prolonged near vision tasks (such as reading, writing, drawing, video games, computer work) for an increase in visual problems.

While we cannot eliminate those tasks that need to be done, and may even be pleasurable, they can be carried out in a manner that imposes minimal stress on the visual system.

If followed, these suggestions may result in easier and more productive study and desk work and will have value in preventing or retarding the development of visual problems.

Reading distance

For reading, writing, and other near vision tasks, it is important to read or write at an appropriate distance.

When the working distance is too short, both children and adults, it creates substantial additional effort on the focusing system and alignment of the eyes (convergence) This added stress can lead to eye strain and a which will increase stress symptoms.

The spontaneous distance at which we read is called the reflex reading distance (RRD). This must always be compared to the Harmon distance.

Harmon distance

 In the fifties, D.B. Harmon, an educator and a kinesiologist, has shown that the ideal reading distance for each individual was the distance between the center of the middle joint of the elbow to the center measured outside of the arm. Working at the Harmon distance reduces visual stress at close. Harmon believed that environmental factors were related to the development of visual problems and had an excellent understanding of the relationship between movement, posture and vision.

How to measure Harmon distance

Harmon has conducted studies of posture and vision of a phenomenal number of children (over 160,000!) in the forties and fifties. His main findings were:

  • In 1958 he showed that 30.2% of schoolchildren tested had postural problems that may be related to vision.
  • He had also found an increased prevalence of visual problems with age in children in primary school from 20% at entry to primary school and 80% after five years of school. His investigations in the school environment led him to believe that certain visual problems appeared when subjects were subjected to near vision work in awkward postures in order to maintain an effective visual function. (1958)
  • Poor posture not only causes visual problems. A postural imbalance requires a greater expenditure of energy, which reduces the effectiveness of the subject to perform its task. Thus the child will have a smaller amount of energy for school learning. (1951, 1958) 
  • Harmon also noted that using horizontal surfaces tend to require the student to lean forward and to approach its work plan. It is therefore preferable to use work plans inclined at 10 ° or even better at 20 °.
  • Why 20 degrees? Harmon demonstrates that it is the physiological angle that everyone adopts between the horizontal plane passing through the elbows and forearms while reading, in an unconstrained outdoor environment. This position is accompanied by the facial plane parallel to the plane of the forearms. 
  • When we bend forward to read, this induces cervical stress, makes digestion more difficult and prevents adequate respiration necessary for the proper functioning of metabolism. 

When doing his study, Harmon raised the work-surface to a 20 degree angle, bringing the surface more parallel to the face.  This significantly reduced the compression of the intervertebral discs. See the following image which shows an ideal working posture with a surface tilted 20 degrees.

Ideal working posture 

http://www.visualedgesb.com/

In the fall of 1942, after six months in the remodeled classroom, “only 18.6% of those examined in November showed visual difficulties, as compared with 53.3% tested six months previously.”  There was also a significant reduction of posture problems (reduced by 25%) and chronic fatigue (55%).

It is unfortunate that these studies and conclusions have been relegated to oblivion. Many postural problems and vision could be avoided if we applied simple changes in our schools…

References:

Harmon DB. Notes on a Dynamic Theory of Vision, 3rd Revision. Austin TX, Self Published, 1958.

Harmon DB., Some preliminary observations of the developmental problems of 160,000 elementary school children. Med Woman’s J 1942:49:75-