Converting a conventional wired-halogen illuminated indirect ophthalmoscope to a wireless-light emitting diode illuminated indirect ophthalmoscope in less than 1000/- rupees.

AIM: To report the "do it yourself" method of converting an existing wired-halogen indirect ophthalmoscope (IO) to a wireless-light emitting diode (LED) IO and report the preferences of the patients and the ophthalmologists. SUBJECTS AND METHODS: In this prospective observational study, a conventional IO was converted to wireless-LED IO using easily available, affordable electrical components. Conventional and the converted IO were then used to perform photo-stress test and take the feedback of subjects and the ophthalmologists regarding its handling and illumination characteristics.
RESULTS: The cost of conversion to wireless-LED was 815/- rupees. Twenty-nine subjects, mean age 34.3 [formula in text] 10 years with normal eyes were recruited in the study. Between the two illumination systems, there was no statistical difference in the magnitude of the visual acuity loss and the time to recovery of acuity and the bleached vision on photo-stress test, although the visual recovery was clinically faster with LED illumination. The heat sensation was more with halogen illumination than the LED (P = 0.009). The ophthalmologists rated wireless-LED IO higher than wired-halogen IO on the handling, examination comfort, patient's visual comfort and quality of the image. Twenty-two (81%) ophthalmologists wanted to change over to wireless-LED IO.
CONCLUSIONS: Converting to wireless-LED IO is easy, cost-effective and preferred over a wired-halogen indirect ophthalmoscope.

An indirect ophthalmoscope (IO) is an indispensable instrument universally used by the ophthalmologists to perform peripheral retinal evaluation. The conventional/older IOs were illuminated with a halogen bulb and required a transformer with a long cable that compromised on the portability of the instrument. With newer illumination methods using a light emitting diode (LED) and a wireless electrical supply, the newer IOs [Table 1] have become more portable and eco-friendly (more energy efficient along with lower heat emission). However, the wireless-LED IOs are priced considerably higher than the wired-halogen ones and many older versions are still in perfectly fine condition for a daily and rigorous clinical usage.

Table 1

List of modern wireless-LED ophthalmoscope models and their manufacturer's details that are currently available in India

In this study, we present a cost-effective method to convert a wired-halogen IO to a wireless-LED IO and present a feedback of the patients and the ophthalmologists using both the types of illumination system in the same model of IO.

Subjects and Methods

Two binocular IOs (model AAIO 7, Appasamy Associates, Chennai, India) were used for the study. One was converted into wireless-LED system in the following manner.

The halogen bulb with it power supply was first removed from the head mount and discarded. The LED illumination was made in the following manner.

A 3 W white LED bulb was glued to a standard printed circuit board (PCB) and mounted on an aluminum heat sink [Fig. 1]. The entire assembly was then mounted in the illumination housing of the IO.

Figure 1

Shows the illumination assembly

A rechargeable battery pack was then made using battery, battery case, potentiometer, external knob, an on/off switch, red LED, resistor and a charging port connected with each other as shown in the circuit diagram [Fig. 2].

Figure 2

Circuit diagram for the battery pack

The detailed description of the components, the place of its availability and cost per piece is mentioned in Table 2.

Table 2

The electrical components for making a wireless-LED indirect ophthalmoscope

The power pack [Fig. 3] was then mounted on the headband [Fig. 4] and connected to the PCB of the illumination system.

Figure 3

The inside view of the battery pack

Figure 4

The battery pack mounted on the head band and connected to the charging adapter

The rechargeable battery was charged for 6 h and the wireless-LED IO was commissioned in to use.

Twenty-nine adult subjects with normal eyes underwent an eye examination using the wireless-LED IO in the right eye followed by wired-halogen IO in the left eye. The illumination level used for each examination was kept equal using a light meter (HTC Luxmeter LX-101A).

A photo-stress test was performed prior to the above mentioned examination using illumination level of 200 lux and 10 s exposure; first with wireless-LED in front of the right eye and then wired-halogen LED in front of the left eye after a gap of 5 min. The loss in best corrected visual acuity after 10 s, time to recovery to the pretest best corrected visual acuity and complete recovery of light-induced bleaching were noted down.

In a different clinical setting, the IOs were given to 27 ophthalmologists to provide their feedback on the predefined parameter.

The data for wireless-LED IO were compared with wired-halogen IO using a two-tailed paired t-test.

Before recruiting the subjects, an oral informed consent was taken. Most subjects were working as the clinical/paraclinical/nonmedical staff in our organization.

Results

The cost of conversion was 815/- rupees. We included 29 subjects with a mean age 34.3 ± 10 years of which 19 were females. There was no statistical difference in the visual acuity loss and the subsequent recovery of acuity and the bleached vision between the two illumination systems although the visual recovery was clinically faster with LED illumination [Table 3]. The subjects clearly felt the heat sensation more with halogen illumination than the LED [Table 4].

Table 3

The results of the photo stress test-LED IO versus halogen IO (n=29)

Table 4

Feedback of the patients (n=29)

We included 27 ophthalmologists (6 residents, 2 retinologists and 19 pediatric ophthalmologists) with a mean age 35 ± 6 years of which 11 were females. All the handling and illumination parameters were graded little better on LED IO versus halogen IO [Table 4]. Majority ophthalmologists preferred to change over to wireless-LED IO [Table 5].

Table 5

Feedback of the ophthalmologists (n=27)

Discussion

An IO is a frequently used instrument by the ophthalmologists all over the world. The newer models from various ophthalmic instrument manufacturers are available with the option of wireless and LED illumination. However, those models are significantly (2–3 times) higher priced. They offer an advantage of excellent portability and the advantages of a LED illumination. In comparison to halogen, LED consumes 1/4th electricity, life is around 100 times longer, and the illumination character is closer to natural sun light albeit the cost is higher.

In the present study, wireless-LED IO was made using easily available and cheap electrical components [Table 2]. The cost of the LED was 60/- rupees only and that of all the components together was 815/- rupees. Although, such a conversion can be done by anyone with the basic knowledge of science of electrical engineering, we took help of the professional who were already in the business of medical instrument manufacturing. It makes sense to take their help as they would have an easy access to these electrical components and used to purchase such components in bulk.

We are using the modified wireless-LED IO since 10 months in a high volume pediatric ophthalmology practice (with considerable movement for retinopathy of prematurity screening) without any problems. The charging of the instrument is needed once in every 4–6 months. The life of the Ni-Cd rechargeable battery is estimated to be 1000 charging cycle.

When the LED demonstrates a minimal flicker at higher illumination level, it is an indication of the time for battery recharge. It usually takes 4–6 h for the battery to be recharged fully. Although the manufacturers suggest that it is advisable to recharge the battery after it is completely discharged, it is not necessary. Nevertheless, if the battery malfunctions/is discharged when an ophthalmologist needs to use the instrument, the IO would continue to function with direct electrical supply using any travel adapter.

There are reports of retinal/macular toxicity (photo-thermal/photo-chemical/photo-radicals injury) following excessive exposure to microscope/endoscope light in vivo (rabbit model) and in vitro (retinal pigment epithelium).[12345] However, there are no comparisons available for halogen with LED IO in human. In this study, we found LED illumination comparable (if not superior) to the halogen bulb in terms of photo-stress vision loss and recovery and comfort to the patient. The sensation of heat was more due to higher light energy in the halogen light.

All the ophthalmologists were used to yellow light and preferred a yellow LED instead of a white LED, especially for the evaluation of the disc pallor.

Conclusion

Wireless-LED IO was found to be more portable and its LED illumination system was preferred by the patients as well as the ophthalmologists. With a simple knowledge of electrical engineering, using easily available electrical components from the market, a conventional IO can be converted to a wireless-LED IO in <1000/- rupees.