Dear Scientific Friends,

    This is Francis Young's remark about phoria in the bifocal
study -- for your interest.

    The statement about "phoria" was most casual.  The
majority-opinion ODs on sci.med.vision imply that

1.  The whole study must be thrown out because "prevention" only
   works for kids with esophoria or,

2.  Only kids with "esophoria" can avoid -1/2 diopters per year
   progression.  In effect they insist that a strong plus was
   not the reason the the "down" rate was 0.025 diopters for the
   "plus" group.

    This was a large scale study -- conducted for three to four
years and the results are very good for the concept of prevention
with the plus.  I doubt that this type of study could be repeated
given the expense and effort it took to do this.

    Otis

    ++++++++++++++++

BIFOCAL CONTROL OF MYOPIA

Authors:
Kenneth H. Oakley, MD.
Bend, Oregon

and

Francis A. Young, Ph.D.
Primate Research Center
Washington State University
Pullman, Washington

             ABSTRACT

    Forty-three Native American bifocal wearers grouped by yearly
age levels from 9 to 15 with a mixed group of 6 to 8 year olds are
matched on beginning age, sex, beginning refractive error and
ending age with 104 Native American control subjects.

    Similarly, 226 Caucasian bifocal wearers are matched on the
same criteria against 382 control subjects.  Although the
comparisons are made on each age group, the average annual rate of
progression for the bifocal Native American subjects is -0.12 and
-0.10 diopters in the right and left eyes respectively against a
comparable rate of progression of -0.38 and -0.36 diopters for the
control subjects.

    These differences are significant but not as significant as
those found on the Caucasian subjects of -0.02 and -0.03 diopters
right and left eyes against -0.53 and -0.52 diopters for the
controls.  The meaning of these differences is discussed.

           < snip >

           Procedures

    All refractions and prescriptions were performed by the
senior author.  When a young child was referred for an initial
refraction which indicated that the child was in or close to
myopia, the author discussed with the parents the possibility of
fitting a reading lens or bifocal which would provide 3/4 to 1
diopter (D) of plus lens magnification over the minus distance
prescription which was usually under-corrected by 0.50 diopter.
For example, if the child's refraction indicated -1.00 diopters,
the prescription would be written for -0.50 D with a plus 1.50
diopter add.

    If the child responded positively to this lens combination,
the minus distance correction would be dropped but a reading lens
of +1.00 diopter would be retained.

    In the case of older children who were already myopic more
than -2.00 diopters the distance correction would be cut 0.50
diopter and a plus 1.50 to 2.00 diopter add would be prescribed.

    In all cases a flat top add would be prescribed and
positioned so that the top of the add would reach the middle of
the pupil when the eyes are in the primary position.

    This location of the add would require the child to tilt his
head slightly forward and to look slightly up to avoid the add at
distance but would make it virtually impossible to read without
using the add even if the glasses slide downward on the nose as
they so frequently do in children.

[Comment:  This is Francis Young's only commentary about
      "esophoria".  OSB]

    Virtually all children fitted with bifocals in this study
demonstrated a near point esophoria as did most of the control
children who were progressing.

    If the parents did not wish to try the bifocal approach, the
child was fitted with a slight under-correction for distance (0.50
diopters) and told to wear his glasses at all times.

++++++++++++++++++++

[Comment:  The children were assigned randomly to a "plus" or
      "single-minus".  The remark about "phoria" was simply casual.
      It has NOTHING to do with the selection or random assignment
      process.  OSB]

    Best,

    Otis