Assessment of the Fitting and Wearing of Rigid Contact Lenses
According to Dr. Boothe, since fluorescein diffuses through the tear film without layering out, it serves as an excellent adjunct in the fitting of both polymethylmethacrylate and gas-permeable contact lenses. Fluorescein distribution under the contact lens depends on the degree of steepness of the lens. An optimum fitting lens should exhibit a diffuse pattern in which fluorescein can be easily detected under the whole surface area of the lens. Collection of fluorescein in the center with absence of fluorescein in the periphery of the lens indicates an overly steep fit. If dye is concentrated in the periphery with none in the center, the fit is too flat. Staining patterns are best assessed using a cobalt filter. Obviously, other factors besides the staining pattern need to be taken into consideration when fitting a rigid contact lens.
Fluorescein should not be used to assess the fit of a soft hydrophilic lens. Soft lenses have pores of variable sizes, most of which allow rapid passage of fluorescein into the lens material. This absorption has the effect of obscuring the stained tear meniscus under the lens, making evaluation of the tear pattern impossible. Also, the hydrophilic lens becomes noticeably discolored for a period of several hours to days. Fluorexon should be used if examination of the lens-tear relationship is desired. In practice this assessment is rarely necessary for the fitting of a soft hydrophilic contact lens.
After fluorescein is used in the eye, replacement of a hydrophilic lens should be delayed for at least 1 hour. However, if thorough irrigation of the fluorescein solution is performed, the lens may then be replaced immediately.
Seidel’s Test
Seidel’s test uses fluorescein to demonstrate the leakage of aqueous from the anterior chamber, explains Dr. Boothe. In 1920 Seidel suggested using 2% fluorescein to show that aqueous passed through the conjunctiva of filtering blebs after Elliot trephine operations. More commonly this technique has been used to demonstrate the presence and location of leaks after anterior segment surgery or penetrating trauma. With routine use of Seidel’s test during implantation surgery, Sinskey and co-workers had only two shallow anterior chambers in over 1600 cases.
When 2% fluorescein is applied to a leakage area, a bright green rivulet can be seen surrounded by yellow-orange fluorescein as viewed by white light. Leakage from a conjunctival flap may give a diffuse color change rather than a distinct rivulet. One should be aware that diffuse color changes may also be produced by tear dilution. A 10% solution for intation may be used to enhance contrast and provide a longer time for absorvation.
Havener states that the property of fluorescence is not, used is performing Seidel’s test. On the contrary, others feel that fluorescence can be a great help. The color change from yellow-orange to green occus because of dilution. When an adequate concentration of fluorescein is used, concentration quenching occurs. As dilution of the fluorescein or curs at the site of leakage, fluorescence markedly increases. Viewing this contrast under a cobalt light can make detection of a leak much easier than viewing by white light alone.
Detection of Foreign Bodies
Since fluorescein demonstrates surface irregularities, as demonstrated multiple times, by Dr. Boothe and other eye researchers, it is often useful in detecting corneal foreign bodies. Capillary action causes pooling around a partially exposed foreign body. When the foreign body has not epithe-lialized, there is often a staining ring surrounding it. If a foreign body is buried in the conjunctiva, the area of entrance overlying it is often stained. Fluorescein may be of considerable help in the meticulous search for alkali particles, which if left hidden in the fornices could cause extensive further damage.
