TECHNICAL NOTE A NEW CORNEAL ELECTRODE

FOR ELECTRORETINOGRAPHY

I

JOHNP. SCHOESSLER and RONALDJONES 5epartment of Physiological Optics, The Ohio State University. College of Optometry. Columbus Ohio 43210, U.S.A. (Received I April 1974; in revisedfirm 20 Mny 1974)

Electroretinography is most often carried out through the use of a fiuid haptic Lens with an implanted electrode. Severaf lenses of this type have been described (Riggs. 1941; Burian, 1953; Jacobson, 1955; Karpe, 1961).There are a number of disadvantages in using a Burian-Allen or Riggs type of electrode, however. These include discomfort, difficulty in maintaining fluid beneath the lens, difficulty in inserting and removing the lens on many patients (especially chiIdren). and the need for several different sizes of haptic shells. The use of some of these devices also may result in considerable cornea1 damage (Dawson, Zimmerman and Houde, 1974) and it is generally recommended that cornea1 anesthetics be used before apply ing the ERG electrode (Karpe, 1961). In order to eliminate most of the disadvantages of the electrodes presentiy being used for efectroretinography, a cornea1 electrode was constructed from two Bausch and Lomb Soflens” contact lenses (polymacon). This material is durable and is not easily torn or damaged. The lens was made by sandwiching a fine platinum or gold wire between two C-series Soflenses (polymacon~ which were hydrated with Q9 per cent saline soiution. The wire lead emerges through a hole in the outermost lens (see Fig. I)_ The hole is easily drilled in the lens in the dehydrated state. When placed one on top of the other, the two hydrated Soflenses adhere together strongly enough to easily keep the wire in place. An electrode from hydrophiIic material has previously been described by &nshein, Wichterle and Wtindsch (1966). However, their lens must be custommolded around a silver-silver chloride button and the lens cannot be used for optical correction. The cornea1 electrode described here can be made from clinically available hydrophiIic lenses and is not expensive in terms of the time and materials necessary for its construction.

Electroretinograms obtained using this soft hydrophilic contact lens cornea1 electrode are not significantly different from those obtained with a Riggs type haptic lens electrode. A typical recording from the hydrophilic lens electrode and a recording using a Riggs lens under identical experimental conditions are shown for comparison in Fig. 2. The eyes were darkadapted and exposed in an integratmg sphere to IO psec gashes of 4.7 x IO* candles at the rate of 1 Hz. Each response consists of a composite of three curves which are roughly parallel to one another. These represent the average and the upper and lower ninety-five per cent confidence limits obtained from IO successive retinal responses using a LAB 8/e Model 25 Computer (Digital Equipment Corporation). There is a slightly greater variation in the response obtained from the soft cornea1 lens electrode as reflected by the greater separation of the 95 per cent confidence limits. As with the Riggs electrode, no speculum has been provided for use with this lens. Since the hydrophilic material is electrically conductive, the electrode is more sensitive to the electrical activity of the lids and it is felt that the slight difference in variability between the two lens types is due to the greater sensitivity of the soft lens electrode to lid fluctuations. Previous work supports this notion (Bornschein, Wichterle and Wiindsch, 1966).

’ This work was supported in part by a grant from the Ohio Lions Eye Research Foundation and by a grant from the Women’s Auxiliary to the American Optometric Association.

Fig. 1. Schematic drawing of a hydrophilic cornea1 Lens electrode constructed from two hydrophilic cornea1 lenses embracing a line piatinum or gold wire (03 mm dia) which emerges through a hole in the outermost lens. 299

Technical Note

Fig.

1(A).

T2chnical Not2

If in-focus retinal imagery is required a cornea1 elcctrode similar to that described above can be constructed from lathe-cut hydrophilic lenses. By proper selection of radii to be lathed on the two lenses used to sandwich the electrode. one can design a system which will produce in-focus retinal imagery for those subjects with little or no astigmatic refractive error.’ The cornea1 electrode described in this paper can be ascepticized by the normal procedure for Sotlens contact lenses (polymacon) as described by Bausch and Lomb. Other hydrophilic materials from which corneal electrodes can be made may not lend themselves to this ascepticizing procedure if the softening point for the material is below 1OO’C. Hydrophilic lenses have been used previously in electroretinography as cushions under a Burian-Allen electrode (Dawson et al., 1974). Even when used as a “protective” device, cornea1 anesthesia was required and some cornea1 damage was still noted. The electrode described in this paper is purely a cornea1 electrode and unlike hard cornea1 lenses which have been

301

tried for electroretinography. the soft lens electrode will remain centered and stable. The eyes of patients using this lens have been critically inspected with the biomicroscope before and after its use. No cornea1 insult or damage has been noted in any patient. Because of its decided comfort advantage over hard lenses, no cornea1 anesthesia is required. It is easily inserted and removed. is easily constructed. requires little time in patient preparation. and different sizes of electrodes an not required. The electrode can be used easily on a wide variety of clinical patients including children (Schoessler and Jones, 1974). It has been demonstrated that the soft lens electrode has excellent recording properties and meets the requirements for an ideal clectrod2 for clinical electroretinography as set down by Jacobson (1961): (1) com-

fort to patient. (1) undistorted electrical transmission, conducting from the eye to the recorder with minimum loss of response characteristics. and (3) minimum obstruction to the stimulus light. REFERESCES

Bornschein H.. Wichterle 0. and Wiindsch L. (1966) A conract lens elrctrodc for comparative ERG studies. Vision Rrs. 6 733-734. Burian A. (1953) Electroretinographv and its clinical applicarion. .&C/I. OpMnl. 49, 141-156: Dawson W. W.. Zimmerman T. J. and Houde W. L. (197-I) A method for mot2 comfortable electroretinography. .4rch. OplrtM. 91. I-1. F, Jacobson J. (1955) A new contact lens electrode for clinical Fbu= + F2 I - r,,rF, elscrroretinography. .Arch. Ophrhnf. 54, 910. Jacobson J. ( 1961) CIirrical Elecno~rtinograpl~~. Charles C. where Thomas, Spring&Id. Fbv = back vertex power Karpe G. (1961) A routine method of clinical sl2ctroretinoF, = power of the front surface graphy. .4cfn. Oplrrho[. SuppIw~r~t~rr~~ 70, I C3 I. F2 = power of the back surface (ocular surface) Lowthrr G. and Bier N. (1971) Co~~ct &ns Correctiorl. t = sum of the center thicknesws of the component Butterworths. London (in preparation). Icns2s Riggs L. (1941) Continuous and reproducible records on the n = index of refraction of the hydrophilic material. electrical activity of the human retina. Proc. Sot. esp. If the posterior radius of this lens does not equal the COTBiol. Med. 48, 204. neal radius of the eye onto which the lens is to be placed. Schoessler J. and Jones R. (1974) Procedures in clinical electhen the power change due to flexure of the lens must be troretinography. ,401.J. Optorn. Phpsiol. Oprics. (in precomputed (Lowther and Bier. 1974). paration).

’ One can design the system so that ths back radius of the outer lens equals the front radius of the inner lens. thus eliminating that surface, and producing a lens with irs center thickness equal to the sum of the center thicknesses of the two component lenses. One can then choose values for the anterior radius and the posterior radius of this combination which will give the desired power using the formula

A new corneal electrode for electroretinography.

TECHNICAL NOTE A NEW CORNEAL ELECTRODE FOR ELECTRORETINOGRAPHY I JOHNP. SCHOESSLER and RONALDJONES 5epartment of Physiological Optics, The Ohio Sta...
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