Transscleral Nd:YAG Laser Cyclophotocoagulation With a Contact Lens Ruthanne B. Simmons, M.D., M. Bruce Shields, M.D., Marino Blasini, M.D., Mark Wilkerson, M.D., and Robert A. Stern, Ph.D.
Transscleral Nd:YAG laser cyclophotocoagulation was performed on 100 consecutive patients. A contact lens designed specifically for this operation was used, and the results were compared to those of a previously reported series of 100 patients in which the same procedure was performed without the lens. The lens provided intraoperative advantages of eyelid separation, compression and blanching of the conjunctiva at the treatment site, and precise measurements for placement of the laser applications. Early postoperative advantages were reduced conjunctival burns and less hyperemia. However, the long-term results were comparable between the two series, with the exception of a higher incidence of phthisis when the lens was used. The thinning and blanching of the conjunctiva may increase the percentage of laser energy reaching the ciliary processes, which suggests a need for reduced energy levels when using the lens.
T HE CONCEPT OF transscleral laser cyclophoto-
coagulation was introduced by Vucicevic and associates' in 1969 and pioneered by Beckman and colleagues' in the early 1970s. A ruby laser was initially used, but Beckman and Sugar subsequently observed that a neodymium laser provided a more useful wavelength for penetrating sclera and enhancing energy absorption at the level of the ciliary epithelium. With the commercial availability of Nd:YAG lasers, transscleral Nd:YAG laser cyclophotocoagulation has become an increasingly popular cyclodestructive procedure.r"
Accepted for publication Sept. 19, 1991. From the Duke University Eye Center, Durham, North Carolina. Reprint requests to M. Bruce Shields, M.D., Duke University Eye Center, Box 3802, Durham, NC 27710.
©AMERICAN
JOURNAL OF OPHTHALMOLOGY
112:671-677,
Several techniques have been used in performing transscleral Nd:YAG laser cyclophotocoagulation. The laser energy may be delivered by either a slit lamp or fiberoptic contact probe, and the laser mode may be either pulsed or continuous-wave. One of the most extensively studied techniques utilizes the slit-lamp delivery of laser energy in a pulsed, thermal mode."? Originally this procedure involved laser application through air without a lens interface. To facilitate the operation, we developed a contact lens that maintains eyelid separation, compresses and blanches the conjunctiva, and provides measurements for accurate laser placement.? A study of the contact lens in human autopsy eyes disclosed similar histologic results" to those previously observed for transscleral Nd:YAG laser cyclophotocoagulation without a contact lens." This study contains the results of a prospective clinical evaluation of transscleral Nd:YAG laser cyclophotocoagulation with the contact lens. We compared these findings to a previously reported series of 100 patients, in which the same protocol was used with no contact lens."
Patients and Methods All patients were entered prospectively and consecutively from the Glaucoma Service of the Duke University Eye Center. The patients selected for transscleral Nd:YAG laser cyclophoto coagulation were those at high risk of failure with standard glaucoma filtering surgery, including failed filtering operations, glaucoma in aphakia or pseudophakia, neovascular glaucoma, glaucoma associated with inflammation, and glaucoma after penetrating keratoplasty. All patients had an intraocular pressure that was thought to be inadequately controlled despite maximally tolerated medical therapy and DECEMBER,
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despite conventional laser or intraocular surgery where appropriate. All patients received and signed an informed consent. All laser procedures in the study were performed by one of us (M.B.S., M.B., M.W.). Retrobulbar anesthetics containing a 50:50 mixture of 4% lidocaine and 0.75% bupivacaine with 150 USP U of hyaluronidase were given in all cases. With the patient positioned at the slit lamp, the eyelids were separated, and the contact lens was applied to the cornea and sclera with a viscous bridge of methylcellulose. If a prominent brow forced the lens inferiorly, preventing adequate vertical alignment, the lens was rotated so that the section removed from the peripheral holding portion was in the superior quadrant. The innermost of three etch marks was then aligned with the corneoscleral limbus at the 12 0' clock position. The other two marks, located 1 and 2 mm peripheral to this reference point, were used for placement of the laser applications. Three additional sets of marks, placed at the 3, 6, and 9 o'clock positions, aided in placement in all quadrants. Pressure was then applied to the eye with the contact lens in the area of treatment to compress and blanch the conjunctiva (Fig. 1). The Nd:YAG laser was used in the free-running, thermal mode with a duration of 20 msec. The offset between the therapeutic and aiming
Fig. 1 (Simmons and associates). Slit-lamp view of the contact lens in position. The upper eyelid and lashes rest against the edge of the lens. Note the blanching of the conjunctival vessels (black arrow) adjacent to an area of unblanched vessels, and the central corneal protector (white arrow).
beams was set at the maximum of 9, which corresponds to 3.6 mm in air. An average energy level of 7.6 J was used, with a mean of 32 evenly spaced applications for 360 degrees. Burns were placed 1.5 mm posterior to the surgical corneoscleral limbus superiorly and inferiorly and 1.0 mm nasally and temporally. Dexamethasone, 12 mg, was injected subconjunctivally immediately after the procedure. The patients were given atropine 1 % twice daily and an antibiotic/corticosteroid combination four times daily for ten days, or longer as required by the degree of inflammatory response. Miotic therapy was discontinued, but all other preoperative glaucoma medications were continued. Measurement of intraocular pressure and slit-lamp examination were performed two hours after the procedure. Subsequent examinations at one day, two to four weeks, and every two to four months thereafter included measurement of visual acuity and intraocular pressure, slit-lamp examination and fundus examination, and recording a history of discomfort or other complaints. A decrease in vision was defined as a decrease of more than two lines of Snellen acuity or one low-vision category. Glaucoma medications were coded numerically, on the basis of a point value scale described previously.P A change of two or more in this scaled medication number in either direction was considered remarkable and recorded as an increase or decrease in medical therapy. A change in intraocular pressure of 2 mm Hg or more in either direction was considered remarkable. A change of less than 2 mm Hg was recorded as no change. Phthisis was defined as an intraocular pressure of zero with shrinkage of the globe. When the intraocular pressure reduction was inadequate one month or more after the treatment, one or more repeat procedures was performed, using the same basic protocol. Only one eye per patient was included in the analysis of data. When both eyes of a patient were treated, one was randomly selected for analysis. In assessing the relationship between potential risk factors and intraocular pressure outcome, categoric data were analyzed by chi square and continuous data were analyzed by univariate analysis of variance.
Results
One hundred consecutive patients were included in the study. There were 55 women and
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673
Transscleral Nd: YAG Cyclophotocoagulation
TABLE 1
TABLE 2
DIAGNOSTIC GROUPS
INTRAOCULAR PRESSURE CHANGE AT TWO AND 24 HOURS PATIENTS
GLAUCOMA DIAGNOSIS
Neovascular glaucoma Glaucoma in aphakia Glaucoma in pseudophakia Glaucoma after penetrating keratoplasty Other
(N = 100)
17
27 33 10·
·Four aphakic; five pseudophakic; one phakic. tThree congenital glaucoma; three traumatic glaucoma; two primary open-angle glaucoma; two angle-closure glaucoma; one juvenile glaucoma; one pigmentary glaucoma; one glaucoma in aniridia.
45 men with a mean age of 62.0 years (range, 22 to 90 years). Eighty-one subjects were white and 19 were black. Fifteen patients were phakic, 41 were aphakic, and 44 were pseudophakic. The most common diagnostic categories were glaucoma in aphakia, glaucoma in pseudophakia, and neovascular glaucoma (Table 1). Seventy patients had previous intraocular glaucoma surgery, including argon laser trabeculoplasty in 18, a single filtering operation in 23, two or more filtering operations in eight, cyclocryotherapy in 14, transpupillary argon cyclophotocoagulation in two, previous transscleral Nd:YAG laser cyclophotocoagulation without the contact lens in two, and peripheral iridectomies in three patients. The median pretreatment visual acuity was 20/400. Fifty-two patients had visual acuities better than or equal to 20/400 (median, 20/70), whereas the remaining 48 patients had visual acuities worse than 20/400 (median, hand motion). Two patients had no light perception. The mean pretreatment intraocular pressure was 34.6 mm Hg (range, 12 to 78 mm Hg). Ten patients with pretreatment intraocular pressures less than 20 mm Hg were treated because of either medication intolerance or diurnal pressure spikes of 21 to 28 mm Hg with documented progressive visual loss. The mean value of pretreatment medical therapy for the entire sample, on the basis of the medication point value scale described previously, was 9.2 (range, 0 to 21). Patients were followed up from four to 24 months (mean, 11 months). At two and 24 hours after transscleral Nd: YAG laser cyclophotocoagulation, 81 (83 %) and 68 (85%) patients, respectively, had no change or a decrease in intraocular pressure
MEAN INTRAOCULAR PRESSURE
PATIENTS NO. (0/0)
CHANGE (RANGE. MMHCl)
MEAN % CHANGE
2 hrs
(N = 98)· Decrease/same
81 (83)
Increase
17 (17)
24 hrs (N =
-10.2 (+1 to -39) +8.2 (+2 to +28)
-25.5 (+6 to -94) +33.4 (+10 to +109)
-16.5 (+1 to -41) +6.0 (+2 to +14)
-41.9 (+6 to -82) +29.1 (+6 to +67)
80)·
Decrease/same
68 (85)
Increase
12 (15)
·N = patients with available data.
(Table 2). Of those patients who had an increase in intraocular pressure, the average increase was 8.2 mm Hg at two hours and 6.0 mm Hg at 24 hours. At the two-month examination, 78 of 91 patients (86%) had a decreased intraocular pressure of greater than 2 mm Hg. Five of 91 patients (5%) had no change in intraocular pressure of more than 2 mm Hg, and eight of 91 (9%) had an increase in intraocular pressure. The mean intraocular pressure change for these groups is shown in Table 3. At the final visit after the initial treatment, 56 patients had intraocular pressures between 7 and 20 mm Hg and required no further treatment. Eleven patients had a pressure less than 7 mm Hg, and ten were above 20 mm Hg, but no further treatment was thought to be indicated for these patients. In the remaining 23 patients, the final intraocular pressure after the initial treatment was thought to be inadequate (Table 4). Twenty patients underwent repeat transscleral Nd:YAG laser cyclophotocoagulation treatments at our institution. An additional three patients underwent repeat transscleral Nd:YAG laser cyclophotocoagulation elsewhere, but the data on their repeat procedures are not included in this study. After the first repeat treatment at our institution, ten patients had final intraocular pressures between 7 and 20 mm Hg and required no further surgical treatment. One patient developed phthisis, and two had final intraocular pressures of 22 mm Hg, but no further laser
674
TABLE 3 INTRAOCULAR PRESSURE CHANGE AT TWO MONTHS
PATIENTS INTRAOCULAR
NO.(%)
PRESSURE
(N = 91)*
Decrease/same
83 (91)
Increase
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AMERICAN JOURNAL OF OPHTHALMOLOGY
8 (9)
TABLE 4
FINAL INTRAOCULAR PRESSURE AFTER FIRSTTREATMENT
MEAN CHANGE
PATIENTS
(RANGE, MMHG)
MEAN % CHANGE
-19.9 (+1 to -54)
-54.7 (+4 to -100)
+11.0
+45.9 (+9 to +115)
(+3
to +37)
*N = patients with available data.
treatment was recommended. Seven patients had additional repeat transscleral Nd:YAG laser cyclophotocoagulation; four required two repeats, two had three repeats, and one patient had four repeats. After one or more treatments, 69 patients had final intraocular pressures between 7 and 20 mm Hg (Table 5). Eighty-four patients had a decrease in their intraocular pressure, ranging from -2 to -45 mm Hg with a mean of -20.8 mm Hg, which represents a mean percentage decrease of 53.8%. Five patients did not have a pressure change of more than 2 mm Hg, five had an increase of more than 2 mm Hg, and six patients developed phthisis. None of the six patients who developed phthisis had had previous cyclodestructive surgery. One patient with neovascular glaucoma had two transscleral Nd:YAG laser cyclophotocoagulation treatments because his intraocular pressure was 56 mm Hg one month after initial treatment. The other five patients underwent only a single treatment. Two patients had undergone previous trabeculectomies, and one patient had undergone cyclodialysis. Three patients had neovascular glaucoma: one had had no previous surgery, and two had had vitrectomies with membrane peeling and fluid-gas exchange. Three patients were phakic, two were aphakic, and one was pseudophakic. At the final visit, five patients required an increase in their glaucoma medications as compared to their pretreatment medications, and 62 required fewer medications. Fifty-one patients had no change in visual acuity. Twelve had an improvement, and 35 patients had a decrease. The visual acuity in six patients decreased to no light perception. Of these six individuals, the preoperative visual acuity was counting fingers in two, hand motions in three, and light perception in one. Five of these six patients had neovascular glaucoma.
INTRAOCULAR PRESSURE
(N = 100)
7-20 mm Hg
56
< 7 mm Hg
11
> 20 mm Hg. no repeat treatment > 20 mm Hg, with repeat treatment
23
10
Of the 52 patients with pretreatment visual acuities greater than or equal to 20/400, 22 lost two or more Snellen lines of visual acuity by the final visit (nine lost two lines, seven lost three to four lines, three lost five to six lines, and three patients lost seven to nine lines). Of the 48 patients with pretreatment visual acuity worse than 20/400, ten patients had an improvement (five improved to better than 20/ 400, with 20/25 and 20/60 in two patients), 20 had no change, and 17 patients had a decrease in their visual acuity. The following variables were significantly associated with the final intraocular pressure result: (1) pretreatment visual acuity (27 of 48 [56%] of patients with a pretreatment visual acuity worse than 20/400 had final pressures of 7 to 20 mm Hg, compared to 42 of 52 [81 %] of those with a visual acuity better than or equal to 20/400; P = .025); (2) race (60 of 81 [74%] of white patients had final intraocular pressures of 7 to 20 mm Hg, compared to nine of 19 [47%] of the black patients; P = .019); and (3) type of glaucoma (patients with neovascular glaucoma had the lowest success, whereas patients with glaucoma in pseudophakia had the best intraocular pressure outcome [Table 6]). There was also a significant correlation between the final intraocular pressure and the intraocular pressure at two months (r = .46, P = .001). Factors that were analyzed and found not to be significantly associated with the final intraocular pressure included age, pretreatment intraocular pressure, gender, the amount of laser energy delivered, and the number of spots delivered. Postoperative complications included white conjunctival burns at the sites of the laser applications, which usually were not detectable by the first postoperative day, and conjunctival hyperemia, which was typically mild and cleared within the first one to two weeks. Anterior uveitis was also seen in all patients, although this was judged to be mild in approxi-
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TABLE 5 FINAL INTRAOCULAR PRESSURE AFTER ONE OR MORE TREATMENTS
TABLE 6 RELATIONSHIP BETWEEN GLAUCOMA TYPE AND FINAL INTRAOCULAR PRESSURE
MEAN
MEAN
MEAN
INTRAOCULAR
PATIENTS
PRESSURE
CHANGE
%
PRESSURE
(N = 100)
(MMHo)
(MMHo)
CHANGE
DIAGNOSTIC
7-20 mm Hg 20mm Hg
69 13 18
14.5 2.2 26.3
-18.5 -36.6 -11.8
-49.3 -92.9 -19.8
mately one half of the patients, moderate in 20%, and severe in 30%. Most patients retained a chronic, low-grade flare. Only two patients complained of severe pain. Other complications included four hyphemas, four vitreous hemorrhages, one vitreitis, four posttreatment choroidal detachments, one acute cystoid macular edema, and one patient with possible malignant glaucoma.
Discussion
In vitro studies with human autopsy eyes disclosed no histologic differences when transscleral Nd:YAG laser cyclophotocoagulation was performed with'? and without" the contact lens used in this study. This was not surprising, since two of the main advantages of the contact lens are believed to be compression and blanching of the conjunctiva, neither of which would be a factor in the autopsy eyes. In the living eye, however, these two factors might enhance the percentage of laser energy reaching the ciliary body and influence the surgical outcome. The purpose of this study, therefore, was to compare the results of a clinical trial in which the contact lens was used to the results of a previously reported trial in which 100 patients were treated with the same transscleral Nd:YAG laser cyclophotocoagulation protocol, except for the absence of a contact lens." The patient populations in the two studies were comparable. In the previous study with no contact lens, the baseline mean intraocular pressure was 38 mm Hg with a range of 18 to 80 mm Hg; the baseline visual acuity was equal to or better than 20/400 in 53 of the 100 patients; and the most common glaucoma types were neovascular glaucoma in 27, glaucoma in aphakia in 27, and glaucoma in pseudophakia in 31 patients. Twenty-five patients in the previous study, as opposed to 18 patients in this study,
675
INTRAOCULAR PRESSURE OUTCOME GLAUCOMA
7-20 MM Ho
20MMHo
GROUP
NO.(%)
NO.(%)
NO.(%)
Neovascular In aphakia In pseudophakia After penetrating keratoplasty Other
10 (59) 19 (70) 25 (76) 7 (70)
4 (24) 3 (11) 3 (9) 2 (20)
3 (18) 5 (19) 5 (15) 1 (10)
1 (8)
4 (31)
8 (62)
had undergone previous cyclodestructive surgery. The postoperative results were also similar in the two groups treated with and without the contact lens. Two hours after the initial treatment, there was either no change or a decrease in intraocular pressure in 81 of 98 (83%) and 68 of 87 (79%) of the patients, respectively, whereas 68 of 80 (85%) and 78 of 86 (91 %), respectively, had either the same or a decreased pressure from baseline on the first postoperative day. After the initial treatment, 56 of 100 (56%) and 51 of 100 (51 %) patients, respectively, had a final intraocular pressure between 7 and 20 mm Hg. Those for whom further surgical reduction of the intraocular pressure was thought to be indicated after the initial treatment were 23 of 100 (23%) and 32 of 100 (32%) patients, respectively. When the results of all treatments were included, a final intraocular pressure between 7 and 20 mm Hg was seen in 69% and 65%, respectively. However, there were six cases of phthisis among the 100 patients in whom the lens was used, compared to none when it was not used. Factors associated with the final intraocular pressure result differed somewhat between the two groups. In both study populations, neovascular glaucoma was associated with the poorest result, whereas patients with glaucoma in pseudophakia had the best intraocular pressure response. However, a higher mean age and a lower baseline intraocular pressure correlated with a better pressure result in the group without the contact lens, but not in those patients in whom the lens was used. Conversely, those in whom the lens was used had a better final intraocular pressure result in association with a better baseline visual acuity, white race, and a
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favorable intraocular pressure at two months after treatment. Visual acuity results were similar between the two groups. The final visual acuity was unchanged or improved, as compared to the baseline level, in 63 of 100 (63%) of those treated with the lens and 50 of 100 (50%) of the group in which it was not used. The extent of visual reduction among those who lost visual acuity was comparable between the two groups. Postoperative complications were also similar between the two groups with one notable exception. By compressing and blanching the conjunctiva, the contact lens markedly reduced the degree of conjunctival burn, as compared to the same amount of laser treatment without the lens (Fig. 2). The reduction in conjunctival burns resulted in a more rapid resolution of the conjunctival hyperemia when the lens was used. Both groups had relatively low rates of other postoperative complications, especially as compared to those reported with cyclocryotherapy." In addition to the low incidence of transient postoperative intraocular pressure increase, which is a significant complication of cyclocryotherapy, trans scleral Nd:YAG laser cyclophotocoagulation, with or without the use of the contact lens, was associated with a much
December, 1991
lower incidence of severe pain and inflammation, as compared to that with cyclocryotherapy. Schuman and colleagues," using a fiberoptic contact probe delivery of continuous-wave Nd:YAG laser, reported intraocular pressure results comparable to those in this study, with a lower rate of visual acuity reduction. Furthermore, lower energy levels were required with the contact probe, which may be explained by a combination of conjunctival compression and reduced light scatter. Fankhauser, Rol, and Kwasniewska!' stated that using a contact lens with the slit-lampdelivery of trans scleral Nd:YAG laser cyclophotocoagulation eliminates most of the differences in results between the slit-lamp and contact probe techniques of laser delivery. When slitlamp delivery transscleral Nd:YAG laser cyclephotocoagulation is performed without the contact lens, between 20% and 50% or more of the light may be reflected from the sclera by surface scatter and bulk scatter." Backscattered rays within the sclera may also cause heating of the sclera. However, when a contact lens is used, reflected light can be reduced to less than 1%, and backscatter within the sclera can be decreased, allowing energy to exit through the contact lens.":" Compression and blanching of
Fig. 2 (Simmons and associates), Slit-lamp view of an eye immediately after transscleral Nd:YAG laser cyclophotocoagulation in which 180 degrees was treated without the use of the contact lens (left) and 180 degrees with the use of the contact lens (right). The black arrows indicate areas of conjunctival burning that are decreased when the contact lens is used. (All eyes in the present study were treated for 360 degrees with the lens.)
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Transsc1eral Nd: YAG Cyc1ophotocoagulation
the conjunctiva, along with reduced light scatter, may increase the amount of laser energy reaching the ciliary body and decrease heating within the sclera when the contact lens is used. This possibility is supported by the results of Schuman and colleagues" and Fankhauser, Rol, and Kwasniewska.P:" as well as the increased phthisis rate found in this study when the contact lens is used. The higher rate of phthisis found when the contact lens is used cannot be explained on the basis of previous cyclodestructive surgery. None of the patients in whom phthisis developed had had cyclodestructive surgery. It is possible that the study done with the contact lens more accurately reflects the expected outcome of cyclodestructive surgery in these patients with advanced glaucoma. Alternatively, the contact lens may actually increase the amount of energy being delivered to the ciliary body, although this cannot be proved in our study. This study supports the value of a contact lens for the slit-lamp delivery of transscleral Nd:YAG laser cyclophotocoagulation. The only late postoperative difference, as compared to the same operation without a contact lens, was a higher incidence of phthisis when using the lens. On the basis of these observations, we are now evaluating lower energy levels to find the optimum parameters for transscleral Nd:YAG laser cyclophotocoagulation with a contact lens.
References 1. Vucicevic, Z, M., Tsou, K. c., Nazarian, I. H., Scheie, H. G., and Burns, W. P.: A cytochemical approach to the laser coagulation of the ciliary body. Bibl. Ophthalmol. 79:467, 1969. 2. Beckman, H., Kinoshita, A., Rota, A. N., and Sugar, H. S.: Transscleral ruby laser irradiation of the ciliary body in the treatment of intractable glaucoma. Trans. Am. Acad. Ophthalmol. Otolaryngol. 76:0P423, 1972.
677
3. Beckman, H., and Sugar, H. S.: Neodymium laser cyclocoagulation. Arch. Ophthalmol. 90:27, 1973. 4. Devenyi, R. G., Trope, G. E., Hunter, W. H., and Badeeb, 0.: Neodymium:YAG transscleral cyclocoagulation in human eyes. Ophthalmology 94:1519, 1987. 5. Klapper, R. M., Wandel, T., Donnenfeld, E., and Perry, H. D.: Transscleral neodymium:YAG thermal cyclophotocoagulation in refractory glaucoma. A preliminary report. Ophthalmology 95:719, 1988. 6. Hampton, c.. Shields, M. B., Miller, K. N., and Blasini, M.: Evaluation of a protocol for transscleral neodymium:YAG cyclophotocoagulation in one hundred patients. Ophthalmology 97:910,1990. 7. Trope, G. E., and Ma, S.: Mid-term effects of neodymium:YAG transscleral cyclophotocoagulation in glaucoma. Ophthalmology 97:73, 1990. 8. Schuman, ]. S., Puliafito, C. A., Allingham, R. R., Belcher, C. D., Bellows, A. R., Latina, M. A., and Shingleton, B. J.: Contact transscleral continuous wave neodymium:YAG laser cyclophotocoagulation. Ophthalmology 97:571, 1990. 9. Shields, M. B., Blasini, M., Simmons, R. B., and Erickson, P. J.: A contact lens for transscleral Nd:YAG cyclophotocoagulation. Am. J. Ophthalmol. 108:457,1989. 10. Simmons, R. B., Blasini, M., Shields, M. B., and Erickson, P. J.: Comparison of transscleral Nd:YAG cyclophotocoagulation with and without a contact lens in human autopsy eyes. Am. J. Ophthalmol. 109:174, 1990. 11. Hampton, C; and Shields, M. B.: Transscleral neodymium-YAG cyclophotocoagulation. A histologic study of human autopsy eyes. Arch. Ophthalmol. 106:1121, 1988. 12. Farrar, S. M., Shields, M. B., Miller, K. N., and Stoup, C. M.: Risk factors for the development and severity of glaucoma in the pigment dispersion syndrome. Am. J. Ophthalmol. 108:223, 1989. 13. Brindley, G., and Shields, M. B.: Value and limitations of cyclocryotherapy. Graefes Arch. Clin. Exp. Ophthalmol. 224:545, 1986. 14. Fankhauser, F., Rol, P., and Kwasniewska, S.: Considerations and methods for laser surgery in the anterior and posterior segments. Int. Ophthalmol. Clin. 30:130, 1990. 15. - - : Optical aids and their application. Int. Ophthalmol. Clin. 30:123, 1990.
Transscleral Nd:YAG laser cyclophotocoagulation was performed on 100 consecutive patients. A contact lens designed specifically for this operation was used, and the results were compared to those of a previously reported series of 100 patients in which the same procedure was performed without the lens. The lens provided intraoperative advantages of eyelid separation, compression and blanching of the conjunctiva at the treatment site, and precise measurements for placement of the laser applications. Early postoperative advantages were reduced conjunctival burns and less hyperemia. However, the long-term results were comparable between the two series, with the exception of a higher incidence of phthisis when the lens was used. The thinning and blanching of the conjunctiva may increase the percentage of laser energy reaching the ciliary processes, which suggests a need for reduced energy levels when using the lens.
T HE CONCEPT OF transscleral laser cyclophoto-
coagulation was introduced by Vucicevic and associates' in 1969 and pioneered by Beckman and colleagues' in the early 1970s. A ruby laser was initially used, but Beckman and Sugar subsequently observed that a neodymium laser provided a more useful wavelength for penetrating sclera and enhancing energy absorption at the level of the ciliary epithelium. With the commercial availability of Nd:YAG lasers, transscleral Nd:YAG laser cyclophotocoagulation has become an increasingly popular cyclodestructive procedure.r"
Accepted for publication Sept. 19, 1991. From the Duke University Eye Center, Durham, North Carolina. Reprint requests to M. Bruce Shields, M.D., Duke University Eye Center, Box 3802, Durham, NC 27710.
©AMERICAN
JOURNAL OF OPHTHALMOLOGY
112:671-677,
Several techniques have been used in performing transscleral Nd:YAG laser cyclophotocoagulation. The laser energy may be delivered by either a slit lamp or fiberoptic contact probe, and the laser mode may be either pulsed or continuous-wave. One of the most extensively studied techniques utilizes the slit-lamp delivery of laser energy in a pulsed, thermal mode."? Originally this procedure involved laser application through air without a lens interface. To facilitate the operation, we developed a contact lens that maintains eyelid separation, compresses and blanches the conjunctiva, and provides measurements for accurate laser placement.? A study of the contact lens in human autopsy eyes disclosed similar histologic results" to those previously observed for transscleral Nd:YAG laser cyclophotocoagulation without a contact lens." This study contains the results of a prospective clinical evaluation of transscleral Nd:YAG laser cyclophotocoagulation with the contact lens. We compared these findings to a previously reported series of 100 patients, in which the same protocol was used with no contact lens."
Patients and Methods All patients were entered prospectively and consecutively from the Glaucoma Service of the Duke University Eye Center. The patients selected for transscleral Nd:YAG laser cyclophoto coagulation were those at high risk of failure with standard glaucoma filtering surgery, including failed filtering operations, glaucoma in aphakia or pseudophakia, neovascular glaucoma, glaucoma associated with inflammation, and glaucoma after penetrating keratoplasty. All patients had an intraocular pressure that was thought to be inadequately controlled despite maximally tolerated medical therapy and DECEMBER,
1991
671
672
December, 1991
AMERICAN JOURNAL OF OPHTHALMOLOGY
despite conventional laser or intraocular surgery where appropriate. All patients received and signed an informed consent. All laser procedures in the study were performed by one of us (M.B.S., M.B., M.W.). Retrobulbar anesthetics containing a 50:50 mixture of 4% lidocaine and 0.75% bupivacaine with 150 USP U of hyaluronidase were given in all cases. With the patient positioned at the slit lamp, the eyelids were separated, and the contact lens was applied to the cornea and sclera with a viscous bridge of methylcellulose. If a prominent brow forced the lens inferiorly, preventing adequate vertical alignment, the lens was rotated so that the section removed from the peripheral holding portion was in the superior quadrant. The innermost of three etch marks was then aligned with the corneoscleral limbus at the 12 0' clock position. The other two marks, located 1 and 2 mm peripheral to this reference point, were used for placement of the laser applications. Three additional sets of marks, placed at the 3, 6, and 9 o'clock positions, aided in placement in all quadrants. Pressure was then applied to the eye with the contact lens in the area of treatment to compress and blanch the conjunctiva (Fig. 1). The Nd:YAG laser was used in the free-running, thermal mode with a duration of 20 msec. The offset between the therapeutic and aiming
Fig. 1 (Simmons and associates). Slit-lamp view of the contact lens in position. The upper eyelid and lashes rest against the edge of the lens. Note the blanching of the conjunctival vessels (black arrow) adjacent to an area of unblanched vessels, and the central corneal protector (white arrow).
beams was set at the maximum of 9, which corresponds to 3.6 mm in air. An average energy level of 7.6 J was used, with a mean of 32 evenly spaced applications for 360 degrees. Burns were placed 1.5 mm posterior to the surgical corneoscleral limbus superiorly and inferiorly and 1.0 mm nasally and temporally. Dexamethasone, 12 mg, was injected subconjunctivally immediately after the procedure. The patients were given atropine 1 % twice daily and an antibiotic/corticosteroid combination four times daily for ten days, or longer as required by the degree of inflammatory response. Miotic therapy was discontinued, but all other preoperative glaucoma medications were continued. Measurement of intraocular pressure and slit-lamp examination were performed two hours after the procedure. Subsequent examinations at one day, two to four weeks, and every two to four months thereafter included measurement of visual acuity and intraocular pressure, slit-lamp examination and fundus examination, and recording a history of discomfort or other complaints. A decrease in vision was defined as a decrease of more than two lines of Snellen acuity or one low-vision category. Glaucoma medications were coded numerically, on the basis of a point value scale described previously.P A change of two or more in this scaled medication number in either direction was considered remarkable and recorded as an increase or decrease in medical therapy. A change in intraocular pressure of 2 mm Hg or more in either direction was considered remarkable. A change of less than 2 mm Hg was recorded as no change. Phthisis was defined as an intraocular pressure of zero with shrinkage of the globe. When the intraocular pressure reduction was inadequate one month or more after the treatment, one or more repeat procedures was performed, using the same basic protocol. Only one eye per patient was included in the analysis of data. When both eyes of a patient were treated, one was randomly selected for analysis. In assessing the relationship between potential risk factors and intraocular pressure outcome, categoric data were analyzed by chi square and continuous data were analyzed by univariate analysis of variance.
Results
One hundred consecutive patients were included in the study. There were 55 women and
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Transscleral Nd: YAG Cyclophotocoagulation
TABLE 1
TABLE 2
DIAGNOSTIC GROUPS
INTRAOCULAR PRESSURE CHANGE AT TWO AND 24 HOURS PATIENTS
GLAUCOMA DIAGNOSIS
Neovascular glaucoma Glaucoma in aphakia Glaucoma in pseudophakia Glaucoma after penetrating keratoplasty Other
(N = 100)
17
27 33 10·
·Four aphakic; five pseudophakic; one phakic. tThree congenital glaucoma; three traumatic glaucoma; two primary open-angle glaucoma; two angle-closure glaucoma; one juvenile glaucoma; one pigmentary glaucoma; one glaucoma in aniridia.
45 men with a mean age of 62.0 years (range, 22 to 90 years). Eighty-one subjects were white and 19 were black. Fifteen patients were phakic, 41 were aphakic, and 44 were pseudophakic. The most common diagnostic categories were glaucoma in aphakia, glaucoma in pseudophakia, and neovascular glaucoma (Table 1). Seventy patients had previous intraocular glaucoma surgery, including argon laser trabeculoplasty in 18, a single filtering operation in 23, two or more filtering operations in eight, cyclocryotherapy in 14, transpupillary argon cyclophotocoagulation in two, previous transscleral Nd:YAG laser cyclophotocoagulation without the contact lens in two, and peripheral iridectomies in three patients. The median pretreatment visual acuity was 20/400. Fifty-two patients had visual acuities better than or equal to 20/400 (median, 20/70), whereas the remaining 48 patients had visual acuities worse than 20/400 (median, hand motion). Two patients had no light perception. The mean pretreatment intraocular pressure was 34.6 mm Hg (range, 12 to 78 mm Hg). Ten patients with pretreatment intraocular pressures less than 20 mm Hg were treated because of either medication intolerance or diurnal pressure spikes of 21 to 28 mm Hg with documented progressive visual loss. The mean value of pretreatment medical therapy for the entire sample, on the basis of the medication point value scale described previously, was 9.2 (range, 0 to 21). Patients were followed up from four to 24 months (mean, 11 months). At two and 24 hours after transscleral Nd: YAG laser cyclophotocoagulation, 81 (83 %) and 68 (85%) patients, respectively, had no change or a decrease in intraocular pressure
MEAN INTRAOCULAR PRESSURE
PATIENTS NO. (0/0)
CHANGE (RANGE. MMHCl)
MEAN % CHANGE
2 hrs
(N = 98)· Decrease/same
81 (83)
Increase
17 (17)
24 hrs (N =
-10.2 (+1 to -39) +8.2 (+2 to +28)
-25.5 (+6 to -94) +33.4 (+10 to +109)
-16.5 (+1 to -41) +6.0 (+2 to +14)
-41.9 (+6 to -82) +29.1 (+6 to +67)
80)·
Decrease/same
68 (85)
Increase
12 (15)
·N = patients with available data.
(Table 2). Of those patients who had an increase in intraocular pressure, the average increase was 8.2 mm Hg at two hours and 6.0 mm Hg at 24 hours. At the two-month examination, 78 of 91 patients (86%) had a decreased intraocular pressure of greater than 2 mm Hg. Five of 91 patients (5%) had no change in intraocular pressure of more than 2 mm Hg, and eight of 91 (9%) had an increase in intraocular pressure. The mean intraocular pressure change for these groups is shown in Table 3. At the final visit after the initial treatment, 56 patients had intraocular pressures between 7 and 20 mm Hg and required no further treatment. Eleven patients had a pressure less than 7 mm Hg, and ten were above 20 mm Hg, but no further treatment was thought to be indicated for these patients. In the remaining 23 patients, the final intraocular pressure after the initial treatment was thought to be inadequate (Table 4). Twenty patients underwent repeat transscleral Nd:YAG laser cyclophotocoagulation treatments at our institution. An additional three patients underwent repeat transscleral Nd:YAG laser cyclophotocoagulation elsewhere, but the data on their repeat procedures are not included in this study. After the first repeat treatment at our institution, ten patients had final intraocular pressures between 7 and 20 mm Hg and required no further surgical treatment. One patient developed phthisis, and two had final intraocular pressures of 22 mm Hg, but no further laser
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TABLE 3 INTRAOCULAR PRESSURE CHANGE AT TWO MONTHS
PATIENTS INTRAOCULAR
NO.(%)
PRESSURE
(N = 91)*
Decrease/same
83 (91)
Increase
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8 (9)
TABLE 4
FINAL INTRAOCULAR PRESSURE AFTER FIRSTTREATMENT
MEAN CHANGE
PATIENTS
(RANGE, MMHG)
MEAN % CHANGE
-19.9 (+1 to -54)
-54.7 (+4 to -100)
+11.0
+45.9 (+9 to +115)
(+3
to +37)
*N = patients with available data.
treatment was recommended. Seven patients had additional repeat transscleral Nd:YAG laser cyclophotocoagulation; four required two repeats, two had three repeats, and one patient had four repeats. After one or more treatments, 69 patients had final intraocular pressures between 7 and 20 mm Hg (Table 5). Eighty-four patients had a decrease in their intraocular pressure, ranging from -2 to -45 mm Hg with a mean of -20.8 mm Hg, which represents a mean percentage decrease of 53.8%. Five patients did not have a pressure change of more than 2 mm Hg, five had an increase of more than 2 mm Hg, and six patients developed phthisis. None of the six patients who developed phthisis had had previous cyclodestructive surgery. One patient with neovascular glaucoma had two transscleral Nd:YAG laser cyclophotocoagulation treatments because his intraocular pressure was 56 mm Hg one month after initial treatment. The other five patients underwent only a single treatment. Two patients had undergone previous trabeculectomies, and one patient had undergone cyclodialysis. Three patients had neovascular glaucoma: one had had no previous surgery, and two had had vitrectomies with membrane peeling and fluid-gas exchange. Three patients were phakic, two were aphakic, and one was pseudophakic. At the final visit, five patients required an increase in their glaucoma medications as compared to their pretreatment medications, and 62 required fewer medications. Fifty-one patients had no change in visual acuity. Twelve had an improvement, and 35 patients had a decrease. The visual acuity in six patients decreased to no light perception. Of these six individuals, the preoperative visual acuity was counting fingers in two, hand motions in three, and light perception in one. Five of these six patients had neovascular glaucoma.
INTRAOCULAR PRESSURE
(N = 100)
7-20 mm Hg
56
< 7 mm Hg
11
> 20 mm Hg. no repeat treatment > 20 mm Hg, with repeat treatment
23
10
Of the 52 patients with pretreatment visual acuities greater than or equal to 20/400, 22 lost two or more Snellen lines of visual acuity by the final visit (nine lost two lines, seven lost three to four lines, three lost five to six lines, and three patients lost seven to nine lines). Of the 48 patients with pretreatment visual acuity worse than 20/400, ten patients had an improvement (five improved to better than 20/ 400, with 20/25 and 20/60 in two patients), 20 had no change, and 17 patients had a decrease in their visual acuity. The following variables were significantly associated with the final intraocular pressure result: (1) pretreatment visual acuity (27 of 48 [56%] of patients with a pretreatment visual acuity worse than 20/400 had final pressures of 7 to 20 mm Hg, compared to 42 of 52 [81 %] of those with a visual acuity better than or equal to 20/400; P = .025); (2) race (60 of 81 [74%] of white patients had final intraocular pressures of 7 to 20 mm Hg, compared to nine of 19 [47%] of the black patients; P = .019); and (3) type of glaucoma (patients with neovascular glaucoma had the lowest success, whereas patients with glaucoma in pseudophakia had the best intraocular pressure outcome [Table 6]). There was also a significant correlation between the final intraocular pressure and the intraocular pressure at two months (r = .46, P = .001). Factors that were analyzed and found not to be significantly associated with the final intraocular pressure included age, pretreatment intraocular pressure, gender, the amount of laser energy delivered, and the number of spots delivered. Postoperative complications included white conjunctival burns at the sites of the laser applications, which usually were not detectable by the first postoperative day, and conjunctival hyperemia, which was typically mild and cleared within the first one to two weeks. Anterior uveitis was also seen in all patients, although this was judged to be mild in approxi-
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TABLE 5 FINAL INTRAOCULAR PRESSURE AFTER ONE OR MORE TREATMENTS
TABLE 6 RELATIONSHIP BETWEEN GLAUCOMA TYPE AND FINAL INTRAOCULAR PRESSURE
MEAN
MEAN
MEAN
INTRAOCULAR
PATIENTS
PRESSURE
CHANGE
%
PRESSURE
(N = 100)
(MMHo)
(MMHo)
CHANGE
DIAGNOSTIC
7-20 mm Hg 20mm Hg
69 13 18
14.5 2.2 26.3
-18.5 -36.6 -11.8
-49.3 -92.9 -19.8
mately one half of the patients, moderate in 20%, and severe in 30%. Most patients retained a chronic, low-grade flare. Only two patients complained of severe pain. Other complications included four hyphemas, four vitreous hemorrhages, one vitreitis, four posttreatment choroidal detachments, one acute cystoid macular edema, and one patient with possible malignant glaucoma.
Discussion
In vitro studies with human autopsy eyes disclosed no histologic differences when transscleral Nd:YAG laser cyclophotocoagulation was performed with'? and without" the contact lens used in this study. This was not surprising, since two of the main advantages of the contact lens are believed to be compression and blanching of the conjunctiva, neither of which would be a factor in the autopsy eyes. In the living eye, however, these two factors might enhance the percentage of laser energy reaching the ciliary body and influence the surgical outcome. The purpose of this study, therefore, was to compare the results of a clinical trial in which the contact lens was used to the results of a previously reported trial in which 100 patients were treated with the same transscleral Nd:YAG laser cyclophotocoagulation protocol, except for the absence of a contact lens." The patient populations in the two studies were comparable. In the previous study with no contact lens, the baseline mean intraocular pressure was 38 mm Hg with a range of 18 to 80 mm Hg; the baseline visual acuity was equal to or better than 20/400 in 53 of the 100 patients; and the most common glaucoma types were neovascular glaucoma in 27, glaucoma in aphakia in 27, and glaucoma in pseudophakia in 31 patients. Twenty-five patients in the previous study, as opposed to 18 patients in this study,
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INTRAOCULAR PRESSURE OUTCOME GLAUCOMA
7-20 MM Ho
20MMHo
GROUP
NO.(%)
NO.(%)
NO.(%)
Neovascular In aphakia In pseudophakia After penetrating keratoplasty Other
10 (59) 19 (70) 25 (76) 7 (70)
4 (24) 3 (11) 3 (9) 2 (20)
3 (18) 5 (19) 5 (15) 1 (10)
1 (8)
4 (31)
8 (62)
had undergone previous cyclodestructive surgery. The postoperative results were also similar in the two groups treated with and without the contact lens. Two hours after the initial treatment, there was either no change or a decrease in intraocular pressure in 81 of 98 (83%) and 68 of 87 (79%) of the patients, respectively, whereas 68 of 80 (85%) and 78 of 86 (91 %), respectively, had either the same or a decreased pressure from baseline on the first postoperative day. After the initial treatment, 56 of 100 (56%) and 51 of 100 (51 %) patients, respectively, had a final intraocular pressure between 7 and 20 mm Hg. Those for whom further surgical reduction of the intraocular pressure was thought to be indicated after the initial treatment were 23 of 100 (23%) and 32 of 100 (32%) patients, respectively. When the results of all treatments were included, a final intraocular pressure between 7 and 20 mm Hg was seen in 69% and 65%, respectively. However, there were six cases of phthisis among the 100 patients in whom the lens was used, compared to none when it was not used. Factors associated with the final intraocular pressure result differed somewhat between the two groups. In both study populations, neovascular glaucoma was associated with the poorest result, whereas patients with glaucoma in pseudophakia had the best intraocular pressure response. However, a higher mean age and a lower baseline intraocular pressure correlated with a better pressure result in the group without the contact lens, but not in those patients in whom the lens was used. Conversely, those in whom the lens was used had a better final intraocular pressure result in association with a better baseline visual acuity, white race, and a
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AMERICAN JOURNAL OF OPHTHALMOLOGY
favorable intraocular pressure at two months after treatment. Visual acuity results were similar between the two groups. The final visual acuity was unchanged or improved, as compared to the baseline level, in 63 of 100 (63%) of those treated with the lens and 50 of 100 (50%) of the group in which it was not used. The extent of visual reduction among those who lost visual acuity was comparable between the two groups. Postoperative complications were also similar between the two groups with one notable exception. By compressing and blanching the conjunctiva, the contact lens markedly reduced the degree of conjunctival burn, as compared to the same amount of laser treatment without the lens (Fig. 2). The reduction in conjunctival burns resulted in a more rapid resolution of the conjunctival hyperemia when the lens was used. Both groups had relatively low rates of other postoperative complications, especially as compared to those reported with cyclocryotherapy." In addition to the low incidence of transient postoperative intraocular pressure increase, which is a significant complication of cyclocryotherapy, trans scleral Nd:YAG laser cyclophotocoagulation, with or without the use of the contact lens, was associated with a much
December, 1991
lower incidence of severe pain and inflammation, as compared to that with cyclocryotherapy. Schuman and colleagues," using a fiberoptic contact probe delivery of continuous-wave Nd:YAG laser, reported intraocular pressure results comparable to those in this study, with a lower rate of visual acuity reduction. Furthermore, lower energy levels were required with the contact probe, which may be explained by a combination of conjunctival compression and reduced light scatter. Fankhauser, Rol, and Kwasniewska!' stated that using a contact lens with the slit-lampdelivery of trans scleral Nd:YAG laser cyclophotocoagulation eliminates most of the differences in results between the slit-lamp and contact probe techniques of laser delivery. When slitlamp delivery transscleral Nd:YAG laser cyclephotocoagulation is performed without the contact lens, between 20% and 50% or more of the light may be reflected from the sclera by surface scatter and bulk scatter." Backscattered rays within the sclera may also cause heating of the sclera. However, when a contact lens is used, reflected light can be reduced to less than 1%, and backscatter within the sclera can be decreased, allowing energy to exit through the contact lens.":" Compression and blanching of
Fig. 2 (Simmons and associates), Slit-lamp view of an eye immediately after transscleral Nd:YAG laser cyclophotocoagulation in which 180 degrees was treated without the use of the contact lens (left) and 180 degrees with the use of the contact lens (right). The black arrows indicate areas of conjunctival burning that are decreased when the contact lens is used. (All eyes in the present study were treated for 360 degrees with the lens.)
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Transsc1eral Nd: YAG Cyc1ophotocoagulation
the conjunctiva, along with reduced light scatter, may increase the amount of laser energy reaching the ciliary body and decrease heating within the sclera when the contact lens is used. This possibility is supported by the results of Schuman and colleagues" and Fankhauser, Rol, and Kwasniewska.P:" as well as the increased phthisis rate found in this study when the contact lens is used. The higher rate of phthisis found when the contact lens is used cannot be explained on the basis of previous cyclodestructive surgery. None of the patients in whom phthisis developed had had cyclodestructive surgery. It is possible that the study done with the contact lens more accurately reflects the expected outcome of cyclodestructive surgery in these patients with advanced glaucoma. Alternatively, the contact lens may actually increase the amount of energy being delivered to the ciliary body, although this cannot be proved in our study. This study supports the value of a contact lens for the slit-lamp delivery of transscleral Nd:YAG laser cyclophotocoagulation. The only late postoperative difference, as compared to the same operation without a contact lens, was a higher incidence of phthisis when using the lens. On the basis of these observations, we are now evaluating lower energy levels to find the optimum parameters for transscleral Nd:YAG laser cyclophotocoagulation with a contact lens.
References 1. Vucicevic, Z, M., Tsou, K. c., Nazarian, I. H., Scheie, H. G., and Burns, W. P.: A cytochemical approach to the laser coagulation of the ciliary body. Bibl. Ophthalmol. 79:467, 1969. 2. Beckman, H., Kinoshita, A., Rota, A. N., and Sugar, H. S.: Transscleral ruby laser irradiation of the ciliary body in the treatment of intractable glaucoma. Trans. Am. Acad. Ophthalmol. Otolaryngol. 76:0P423, 1972.
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3. Beckman, H., and Sugar, H. S.: Neodymium laser cyclocoagulation. Arch. Ophthalmol. 90:27, 1973. 4. Devenyi, R. G., Trope, G. E., Hunter, W. H., and Badeeb, 0.: Neodymium:YAG transscleral cyclocoagulation in human eyes. Ophthalmology 94:1519, 1987. 5. Klapper, R. M., Wandel, T., Donnenfeld, E., and Perry, H. D.: Transscleral neodymium:YAG thermal cyclophotocoagulation in refractory glaucoma. A preliminary report. Ophthalmology 95:719, 1988. 6. Hampton, c.. Shields, M. B., Miller, K. N., and Blasini, M.: Evaluation of a protocol for transscleral neodymium:YAG cyclophotocoagulation in one hundred patients. Ophthalmology 97:910,1990. 7. Trope, G. E., and Ma, S.: Mid-term effects of neodymium:YAG transscleral cyclophotocoagulation in glaucoma. Ophthalmology 97:73, 1990. 8. Schuman, ]. S., Puliafito, C. A., Allingham, R. R., Belcher, C. D., Bellows, A. R., Latina, M. A., and Shingleton, B. J.: Contact transscleral continuous wave neodymium:YAG laser cyclophotocoagulation. Ophthalmology 97:571, 1990. 9. Shields, M. B., Blasini, M., Simmons, R. B., and Erickson, P. J.: A contact lens for transscleral Nd:YAG cyclophotocoagulation. Am. J. Ophthalmol. 108:457,1989. 10. Simmons, R. B., Blasini, M., Shields, M. B., and Erickson, P. J.: Comparison of transscleral Nd:YAG cyclophotocoagulation with and without a contact lens in human autopsy eyes. Am. J. Ophthalmol. 109:174, 1990. 11. Hampton, C; and Shields, M. B.: Transscleral neodymium-YAG cyclophotocoagulation. A histologic study of human autopsy eyes. Arch. Ophthalmol. 106:1121, 1988. 12. Farrar, S. M., Shields, M. B., Miller, K. N., and Stoup, C. M.: Risk factors for the development and severity of glaucoma in the pigment dispersion syndrome. Am. J. Ophthalmol. 108:223, 1989. 13. Brindley, G., and Shields, M. B.: Value and limitations of cyclocryotherapy. Graefes Arch. Clin. Exp. Ophthalmol. 224:545, 1986. 14. Fankhauser, F., Rol, P., and Kwasniewska, S.: Considerations and methods for laser surgery in the anterior and posterior segments. Int. Ophthalmol. Clin. 30:130, 1990. 15. - - : Optical aids and their application. Int. Ophthalmol. Clin. 30:123, 1990.
