Aviation Medical Society      - New Zealand Web Site

Volume 24 No 2 September 2000
PATHWAYS OF VISION FOR THE OLDER AIR TRAVELLER  

Martin X Hogan

“70% of all sensory input into the human brain is visual.”

DR. JOHN L. COLVIN, AVIATION OPTHAMOLOGIST

“Presbyopia surely is the cause of the commonest disability of pilots – impairment of near visual acuity.”

DR GRAEME DENNERSTEIN AV MEDIA APRIL 1999

In fact presbyopia is the most common disability to afflict every man and woman over 45 years of age.

Presbyopia presents its visual symptoms to the average emmetropic person (male or female) in the mid forties age group.  These symptoms manifest themselves in the person’s inability to achieve a sharp focus on near objects.  There is no escape from presbyopia.

Presbyopia cannot be effectively corrected with contact lenses or laser surgery whilst achieving normal 20/20 vision acuity and binocular function in both reading and distance.

From the onset of the first visual symptom of presbyopia the condition progresses along a predictable path until 60 to 65 years of age, at which time it may stabilize.  During this period a person’s ability to see close objects at varying distances becomes increasingly restricted and inflexible.  Normally eyeglasses are prescribed to correct the visual symptoms of presbyopia.  These eyeglasses may be in the form of full field single vision reading, bifocal, trifocal or graduated multi focal lenses.

Unless otherwise directed by the candidate ophthalmic practitioners generally prescribe and dispense these “presbyopia correcting eyeglasses” for “hand held” reading matter.

The “hand held” reading position evolved with the main influencing factors being:

• the physiology of the human eye

• the skeletal structure of the human frame

• the location of the eyes in the top of the skull

• the effects of the force of gravity.

All close objects held in this position with prescribed reading lenses in situ can be seen clearly. Comfortably and without stress particularly for extended periods of time.

Unless especially prescribed ALL reading glasses and reading segments of bifocals, trifocals and graduated multifocals are prescribed for “hand held” reading.  The “hand held” reading position could be deemed to be approximately 325 millimetres from the eyes and approximately 250 millimetres from and adjacent to the sternum.

In modern passenger transport aircraft presbyopia has adversely affected the patient/passenger in a unique way.  This is a result of the introduction of the personal video screen.  The screen is located in the patient/passenger’s near vision range but sadly outside the scope of their normal reading prescription.

In all sections of the modern passenger transport aircraft the personal video screen is located in what could be deemed to be at a reading distance and at a reading position in relation to the patient/passenger’s eyes – albeit a “long” reading distance and a “high” reading position.  It is this “long” reading distance and the “high” reading position which renders the patient/passenger’s normal reading prescription ineffective.

In the past the “shared” overhead screen was located in the patient/passengers’ distance vision range and was visually accessible to both emmetropic (not requiring corrective lenses) and the ammetropic (wearing corrective lenses) patients/passengers.

Lenses which are prescribed for reading generally focus on about 325 millimetres.  Bifocal, trifocal and graduated multifocal lenses have reading segments located below the level of the pupil for normal use.

Both the focus point and the position of the reading segment of lenses normally prescribed for reading make it difficult and uncomfortable for the presbyopic patient/passenger to see the personal television screen clearly and without strain with the seat in its upright position.  This physical discomfort and visual difficulty is exacerbated when the passenger seat is reclined.  In some cases, particularly those where the advanced presbyopic patient/passenger is wearing bifocals, trifocals or graduated multifocals the details on the personal screen may be lost.

It is understandable with space being at a premium in the aircraft how the separation of the seating and the location of the service tray have influenced the positioning on the personal video screen.  The height of the screen above the service tray is to allow books, bottles, newspapers and laptop computers to be used.  The value of the personal screen should not be discounted as merely an entertainment advice.  Its most important role is its precise visual delivery of general inflight and safety information.

Aural problems associated with “in cabin” aircraft noise, patient/passenger subnormal hearing and the presentation of inflight entertainment and safety information have been addressed with the use of “on loan” personal head sets.

Vision problems created by the “in cabin” environment and seat design in today’s passenger transport have never been identified or addressed.

Our research has shown a significantly high incidence of “in cabin” vision problems are experienced by the presbyopic passenger.

For the patient/passenger presenting to us with these problems there are successfully prescribed remedies.  Although successful these remedies prove to be very expensive, the cost of which can only be warranted if the patient/passenger is a frequent user of long distance, international air travel.  Our successful remedies to these problems contained many common factors of lens design and lens power parameters.

We concluded these common denominators could be used as the basis of a universal design for an effective very low cost device to reduce if not eliminate the visual problems associated with the personal video screen in all sections of the aircraft.

The result was a simple clip-on device to attach to the passenger’s host spectacles.

It would be possible to make this device available to the presbyopic patient/passenger on an “on loan” basis much in the same manner as personal head sets are distributed.

The device is produced in two models.  One model PLUS for use by the presbyopic patient/passenger wears bifocals, trifocals or graduated mutlifocals.

The other MINUS for use by the presbyopic patient/passenger who wears full field, single vision reading glasses.

Each model would be available in two power options.

The LOW option for those passengers between 47 and 53 years of age.

The HIGH option for those over 53 years of age.

SELECTION GUIDE

The device has been designed solely for use by the presbyopic patient/passenger over the age of 45 years wishing to view the personal video screen.

Prior to describing the application of this device, it is necessary to explain some of the basic fundamentals of the way in which eyeglasses are prescribed and also how spectacles whilst performing their prescribed normal function can present the wearer with unwanted visual side effects when used for viewing the personal screen.

“No man’s land” exists in all aspects of the daily life of the presbyopic spectacle wearer.  In the supermarket and the library with products and books on shelves, at the art gallery and museum with hung paintings and exhibits, reading music, women applying cosmetics, men shaving, control panel operators and viewing THE PERSONAL VIDEO SCREEN IN PASSENGER AIRCRAFT.

There is no ‘universal panacea’, no “one pair does it all” lens design for the presbyopic spectacle wearer.  Spectacles should be considered to be “tools” for achieving good, clear and comfortable vision.  The “right tool” for the job will always produce the best result.

The purpose of the device is to temporarily convert the patient/passengers own reading lenses, bifocals, trifocals or graduated multifocals into a lens which will extend the normal r5ange and scope of the host spectacles.  There is no loss of the prescription integrity when the clip-on device is removed.  The temporary conversion of the role of the host spectacles is achieved much in the same manner as clip-on sunglasses temporarily convert the normal non tinted host spectacles into a prescription sunglass.

The clip on device is universal in that it will fit all spectacle frames, male or female designs, be they fabricated from plastic, metal or even rimless.  The clip-on will fit over all lenses irrespective of design or power.

Full field single vision reading lenses have a rather casual predetermined position in relation to the eye, “up the nose” or “down the nose” it does not particularly matter as the total lens area is 325mm reading. (fig. 3a)

Bifocals (fig.3b), trifocals (fig.3c) or graduated multifocals (fig.3d) have a very precise predetermined position in relation to the eye.

Bifocals and trifocals have small accurately positioned “zones” through which reading vision can be achieved.  There is little margin for error.

Graduated multifocals have a strategically located “window” through which reading vision at different distances can be had.  There is absolutely no margin for error.

Denotes the 325mm reading section or :window” (figs. 3a, b, c, d)

With the clip-on device (MINUMS MODEL) in situ over the host reading glasses (fig 4a) the host single vision full field reading lenses will convert to a two focus lens.  The upper section will have its focus lengthened to say 450mm to 600mm for intermediate reading or viewing the personal television screen.  The lower section will remain as originally prescribed for “hand held” reading at 325mm.

With the clip-on device (PLUS MODEL) in situ over the host bifocals, trifocals or graduated multifocals the distance portion of the hose spectacles immediately converts to lens to focus at, say 450mm to 600mm for “intermediate reading” or viewing the personal television screen.  The lower section will remain as originally prescribed for “hand held” reading at 325mm.

Presbyopia does significantly affect the daily lives of the aged or aging patient in their pursuit of business, leisure and social activities.  Care and in depth patient/practitioner communication regarding lifestyle will provide the necessary basis for prescribing effective, individual solutions.

(Note: Diagrams not available in web version of paper)

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