Reflections from spectacle lenses

1. Reflections from spectacle lenses
Ghost images
Any highly polished object will produce a reflection when light is incident upon the surface. For
spectacle wearers, the reflections from their highly polished lenses can cause visual fatigue as
well as being extremely frustrating. Jalie1 refers to them as ‘troublesome reflections’ and lists five
ghost images that can be formed by:
 Total internal reflection at the lens surfaces (Ghost image 1)
 Reflection at the cornea and the back surface of the lens (Ghost image 2)
 Reflection at the cornea and front surface of the lens (Ghost image 3)
 Reflection at the back surface of the lens (Ghost image 4)
 Reflection at the front surface of the lens (Ghost image 5).
Ghost image 1 is generally the most troublesome to the spectacle wearer.
Spectacle lens surfaces will always reflect any available light and in the presence of a suitable
light source will form ghost images of that light source. Ghost images are visible if three
conditions are met simultaneously.
 The first condition concerns the intensity of the ghost image with respect to the
surrounding illumination. Usually, reflections are more noticeable at night and spectacle
wearers often complain of ghost images of street lamps or car headlights because the
reflected images are viewed against a dark background.
 The second condition concerns the vergence of the reflected image as for a ghost image
to be noticeable the vergence of the light that forms the ghost image must be the same
as, or close to the vergence of the light refracted by the spectacle lens.

2.  The third condition concerns the position of the ghost image within the field of view. If the
ghost image coincides with the source itself it won’t be seen. It also won’t be noticed if it
is formed at the edge of the field of view.
Interestingly, ghost image 1 will be in sharp focus if the power of the spectacle lens is plano and
this reflection is often commented upon by wearers of plano sunspectacles. Ghost image 1 is not
of course restricted to plano lenses but it does remind us of the fact that a RF coating should be
considered for all lenses regardless of power. So practitioners who restrict the dispensing of RF
coatings to patients with high-power lenses should question the wisdom of such advice. In
addition, ghost image 1 is often noticed by wearers of low-power spectacle lenses withh small
prismatic corrections. Such lenses should always be dispensed with a RF coating. A RF coating
is the only solution for eliminating this reflection.
In summary:
 Ghost images arise due to bright sources surrounded by poor illumination
 The images must be bright enough to stand out against the background, so are rarely
noticed by the wearer during the day
 Images 1 and 3 are only in focus for plano or positive lenses
 An RF coating may help to eliminate ghost image 1
 Dispensing solution for image 2: Change lens form/vertex distance
 Dispensing solution for image 3: Change form/thickness/vertexdistance
 Ghost images 4 and 5 are formed due to sources behind the head and are only a
problem when lenses are large enough to collect light from behind the head
 Dispensing solutions for images 4 and 5: RF coat the lens or change the lens form