I first took delivery of a Falcon fitting set from Ocutech last summer and so was pleased to be able to offer an autofocusing telescope as an option when meeting a patient with quite specific visual needs, for whom magnification of multiple distances seemed necessary and where manual adjustment had been previously dismissed as too cumbersome.
The Ocutech VES Falcon
The Falcon makes manual focusing obsolete. The system includes an autofocusing function not dissimilar to that in a modern digital camera device. The telescope is mounted on a metal frame and adjusted such that the eye piece is above the pupil (figure 1). This allows the wearer the option of normal viewing through the spectacle lens (figure 2) and telescopic viewing by a single tilt of the head downwards (figure 3), hence a bioptic viewing system. The eyepieces may be adjusted to correct ametropia of up to ±8.00DS, and further sphere power or a cylinder correction of up to -3.00DC may be ordered.
Figure 2
Figure 3
The telescope is powered by a portable charging system attached to the telescope and which is easily carried in the patient’s pocket (figure 4). A full charge overnight allows up to eight hours of continuous use the next day. Despite the incorporated technology, the device weighs just 90g (excluding any corrective lenses in the frame) which is well-distributed horizontally. So, according to the manufacturers (Ocutech), the unit may be worn comfortably for long periods.
Figure 4
The Falcon is a monocular Keplerian device. This means it uses positive lenses to increase the angle of subtense at the retina allowing magnification of even the furthest objects (figure 5). The redirected light forms an exit pupil near coincidental with that of the viewer’s eye. For this reason, the system presents a better quality image than that of Galilean telescopes. Magnification of shorter working distance is possible by changing lens separation within the telescope. In standard telescopes and binoculars this is done manually by changing the tube length. Autofocusing uses an infrared light sensor to detect distance and then automatically adjusts the lens positioning accordingly.
Figure 5
One downside of traditional telescopes is that the distance of the objective lens from the eye results in a restricted field of view. The Falcon offers 15 degrees for the 3x model, 12.5 degrees for the 4x and 9.5 degrees for the 5.5x.
Case Study
EM is a 36-year-old woman with oculocutaneous albinism and a small oscillation manifest nystagmus. She has been registered as severe sight impaired for many years. Her vision has been stable for some time and, like so many such patients, she has learned to adapt to her sight well with very few interventions from practitioners in recent years.
She is currently sub-contracted to the NHS as a Social Prescription Link Worker where she ‘tears out her hair helping others.’ For this work, she uses a fully adapted desktop and smartphone, a close working distance and no additional optical aid. Like many with a nystagmus, her near uncorrected near vision far exceeds what would be predicted from the distance vision, and she also has a degree of uncorrected myopia to help.
EM is a keen theatregoer and, for this, uses a distance spectacle correction. She uses sunshields when needed as, like many but by no means all albinos, has some light sensitivity. She enjoys museums and art galleries, but here the viewing distances are too great to benefit from the convergence and myopia, and too near and variable for any distance spectacles to have major benefit. She has tried spotting telescopes and binoculars. The former can exacerbate the nystagmus while the latter are cumbersome and difficult to focus.
One major challenge, however, is being able to read sheet music while playing the cello – ‘this is pretty much impossible.’ Estimated viewing distance for this was 80cm.
Other points of interest include the following:
- EM was not aware of having a null point (a specific viewing position where the nystagmus oscillation is minimised) and, indeed, had never heard of this
- EM has some grittiness and dry eye symptoms after prolonged viewing of anything or when outdoors, especially when it is windy
- EM has never tried, nor wants to try contact lenses; her myopia, somewhat unusually with her albinism, was near spherical and she was used to exploiting this for near vision benefit
- Both mother and father have glaucoma; this, as well as her myopia, helped me reinforce the importance of annual checks from now on
Assessment
Findings of relevance to this feature:
- Unaided visions 1.30 R and L (top line of logMAR at half distance)
- Refraction:
- R; -11.00 DS (0.90)
- L; -9.50 DS (0.80)
- Binocular 0.80 and more comfortable
- Unaided vision @ 10cm N15 binocular/left preference
- Slight right head turn to achieve visual comfort, but no measurable improvement
- 4x Falcon used without myopia correction (0.4)
- Mid to low contrast sensitivity (1.50 R&L on Pelli-Robson)
- No subjective viewing preference with range of selective contrast tints
- Poor lipid layer on interferometry (IDRA) but full blink, healthy lid margins and no stain
Management
Some distance and intermediate magnification seemed desirable. Uncorrected myopia will increase the magnification from a Keplerian device. If, for example, the objective is +20D and the eye piece is +50D, the magnification is 2.5x. Uncorrected myopia of -10D makes the eyepiece the equivalent of +60D, and the magnification now is 3x. Susceptibility to wind made side shields an option worth considering. The jury was still out on whether tinting gave any benefit. A device that did not occlude (or encouraged eye shutting) of the non-sighting eye was preferred. Autofocusing seemed worth a go.
After much discussion we decided upon the following plan:
- Preservative ocular lubricant (Thealoz Duo) prescribed for use as needed
- 4 x Falcon to be used for all viewing tasks other than near
I suggested trying the trial unit out for one week, partly for my own curiosity and also to ensure that what would be a big investment would be worth it.
Dispensing the trial unit was easy. After selecting the best fit frame, the eyepiece was adjusted and set horizontally before the viewing eye and accounting for the small head turn, and then focused at the default viewing distance by means of a small screw adjustment on the side of the device (figure 6). This setting was locked (figure 7). The unit automatically refocused for different viewing distances and, when demonstrated in the waiting area of our clinic, in a matter of a fraction of a second for even large distance viewing changes.
Figure 6
Figure 7
Order
This was the request sent to Associated Optical for supply of the unit.
- Falcon Unit; 4x seemed adequate
- Small eye frame (the smaller of the two in trial set)
- Centration distances; R 32.5mm L 32.5mm
- Mount eyepiece before left eye
- Colour; black
- Plano lenses in frame; tinted overlays were requested to help with reported glare when outdoors and using the unit
- Side shields, if possible, on frame to reduce wind exposure outdoors; it was possible (figure 8)
Figure 8
Collection
Upon collection, EM agreed to write a daily log of her activity with the Falcon unit. This will form the second part of this
feature.