Timothy C. Hain, MD Page last modified: December 13, 2011
There are two types of Frenzel goggles -- optical and video. The video are far preferable, but they cost substantially more than the optical versions.
|Conventional optical Frenzel goggles.|
Frenzel goggles are extremely useful in evaluation of patients with vestibular disorders. In essence, they consist of the combination of magnifying glasses (+20 lenses placed in front of the patient), and a lighting system. When Frenzel's goggles are placed on the patient, and the room lights darkened, nystagmus can easily be seen because the patients eyes are well illuminated and magnified, and because fixation is removed as the patient can hardly focus through magnifying glasses on a dark room.
Frenzel, a German physician, should not be confused with Augustin-Jean Fresnel, a French physicist. Fresnel is known for his work with optics, and his name is associated with a type of magnifying lens. Fresnel lenses are used in Frenzel's goggles, in the GN-otometrics design (see below).
In the authors practice in Chicago Illinois, we use video Frenzels. A single image of the eye fills the entire screen of a 30 inch monitor. This allows one to see very small amounts of nystagmus from across the room. While some video Frenzel goggles offer the ability to see both eyes simultaneously, this capabilty is usually associated with several small images on a security style TV monitor. We do not think that the ability to see both eyes simultaneously adds much value, and the small images detract from the devices usefulness.
Such video-eye movement recording systems, called "video Frenzels", such as those sold by Micromedical Technology (Chatham IL, USA, 217-483-2122) are usually preferable to optical Frenzel goggles. Video systems provide a mechanism of recording the examination and also are more educational for patients, spouses and students. Video goggles eliminate vision entirely, compared to Frenzel goggles which merely obscure vision. They also provide the capability of showing much larger images. These are very important advantages.
The model that we favor is the "RealEyes" monocular. They cost considerably more (about $2600) than optical Frenzels (typically about $500). We do not favor systems that require a computer, and we also do not favor systems that monitor both eyes at the same time. We prefer "analog" monitors to flat-screens, as display contrast is more reliable and a very large monitor is much more attainable. Because the size and resolution of the image is critical, a "quad splitter" is not recommended. Instead, we favor a "picture in picture" processor (PIP), that puts a small dirigible image in a corner of the display. We are uncertain whether the "record to PC" feature is useful. We STRONGLY advise against models that do not have a focus knob.
The main advantage of optical Frenzels over video Frenzels are their portability and lower cost. If you go this way, we suggest that you buy your own large monitor, as well as a room camera, DVD player, and PIP processor. As of 2010, this costs roughly $1000 more. More about this is found here.
Anyway, there are six sources of the optical Frenzel glasses that I am aware of which are discussed below:
Most people use the Baxter or Bausch and Lomb glasses (which are the same device).
Baxter (cat # Au5050). Baxter often doesn't even seem to know that they sell these things so use the catalog #. Their goggles are actually made in Germany, and are lightweight and sturdy. The bulbs are expensive, about $20, and are the same ones used by Bausch and Lomb, but they don't blow out that frequently. One disadvantage is that you must purchase a power supply to go with them. They work well with a 4-volt supply. Too much and they get hot and the bulbs blow. Too little and you can't see. The bulbs blowing thing is a safety issue as glass shards can be produced. So, we do not recommend using anything but a fixed voltage 4-volt supply. These glasses are not UL approved.
I got mine from the V. Mueller Division (800-323-9088). Another contact # is 708-948-3756. The price in 1996 was $477 for the glasses, but Bausch and Lomb sells them for $100 less (see below). These goggles need a 4 volt power supply. Bome sells an inexpensive one that can be modified to produce 4 volts. Bome's number is 716-436-6584. Bausch and Lomb also sells a power supply.
ICS's Frenzel's goggles are a new player on the block. Personally, I prefer the Baxter goggles, but ICS's goggles aren't bad. They are made of plastic rather than composite like the Baxter and Nagashima brand goggles, and their lighting is a bit dim compared to either. Perhaps they could be brighter if one used a higher voltage supply. I don't know. They are priced similarly to the Baxter/Bausch and Lomb goggles.
ICS is located in 2227 Hammond Drive, in Schaumberg, Illinois, 60173. 708-397-2150. ICS has a distributer network in the US for selling ENG equipment, and you should also be able to get these goggles through them. They can also be reached through the Internet.
The Nagashima Frenzel's goggles are the best optical goggles on the market (excepting the video system), but they are somewhat expensive (>$1200 last priced). They are nicer than the others because of their bright lighting, wide field of view, and relative comfort (for the patient). In my opinion, they are really not worth $1200 -- maybe $600, but if you have lots of money to spend, hey, why not go for the best. On the other hand, if you have lots of money to spend, it might be a better idea to get a video system. I am told (but am not entirely sure) that the Nagashima goggles are the only ones that are UL approved. This may be important if you are planning to use them in a hospital. If you don't have to move the goggles around from room to room, just get a video system - -don't waste your money on these.
Bausch and Lomb sells the same goggles as does Baxter.The part number is n0785. Prices as of 2003 for the goggle is 386.00. The B&L recommended power supply (S1910A) is 136.00.This power supply produces between 0 and 6 volts. In our opinion, it is safer (less blown bulbs) to use a power supply that cannot provide more than 4 volts. Phone: 1-800-338-2020. US neurologicals also sells Frenzel goggles (price $378, in 2006). Their part # is 701. Bome sells an inexpensive power supply that can be modified to produce 4 volts. Bome's number is 716-436-6584.
I have no personal experience with these goggles, but they appear to be an improved design of the Frenzel goggles.
According to the web page marketing these devices, these goggles have a shielded bulb, and several useful accessories. It appears to me that the lens is smaller than is desirable. I prefer the Nagashima size lens. Bigger is better, for Frenzels anyway.
As of 2006, model 721 was being sold for $445 by US neurologicals. It is usually a good idea to have extra bulbs and a provision for power. Bome sells an inexpensive one that can be modified to produce 4 volts. Bome's number is 716-436-6584.
Do it yourself Frenzel goggles
It is possible to make your own video Frenzels. It is generally said that this can be done at roughly 10% of the cost of the commercial goggles. Guevarra and Chiong (2004) provides one design. The components include safety glasses, a web-camera, and various parts. As Frenzel goggles are very useful, we think that this is a good idea. We would prefer a system that used infrared illumination, contained focus mechanism (preferably automatic), had an analog output so that the image could be displayed on a large screen without any lag, and a mechanism of positioning the camera with respect to the eye.
It is also quite possible to make your own optical Frenzel goggles, for even less of an investment. The basic components include a pair of +20 lenses, a method of illuminating the eye (we would recommend high-intensity LED's for safety -- they can't produce any glass fragments), and safety goggles as shown above. A large +20 glass lens can be heavy. Another design involves use of plastic "Fresnel" lenses, which are much lighter. This is somewhat similar to the design of the ICS goggles. Edmund Scientific is a good source for optical components.