Characteristics of Diode Laser-Induced Chorioretinal Adhesions for Experimental Retinal Detachment in Rabbit Eyes
Histopathologic William E.
Smiddy, MD, Eleut Hernandez, LAT
\s=b\ A retinal break and localized retinal detachment were induced in 10 rabbit eyes. The retinal break was treated within regions of detached retina using diode laser transscleral retinopexy (four eyes), diode laser indirect ophthalmoscopy (two eyes), or retinocryopexy (two eyes). Two eyes were left as untreated controls. The clinical and histopathologic effects were studied 1 day and 3 weeks after initial treatment. Suitable chorioretinal adhesions were induced with all treatment modalities. The extent of tissue effects was greater in cryopexy and smaller in laser treatment. The histopathologic characteristics of the lesions induced by diode laser indirect ophthalmoscopy were similar to those seen with transscleral diode treatment and were more focal than those seen with cryopexy. Transscleral and transpupillary diode laser photocoagulation were effective in inducing chorioretinal adhesions in detached retina in this experimental model in rabbits.
(Arch Ophthalmol. 1992;110:1630-1633) diode laser delivers energy in the nphe -*- infrared (810 nm) energy
range.1
Intravitreal,24 transpupillary slit lamp,6"11 transpupillary laser indirect ophthalmoscopic,12'1:iandtransscleral4·14"16 delivery modes have been developed
Accepted
for publication June 11, 1992. From the Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami (Fla) School of Medicine. The authors have no proprietary interest in any equipment used. Reprint requests to Bascom Palmer Eye Institute, PO Box 016880, Miami, FL 33101 (Dr
Smiddy).
Diode Laser Treatment Variables Case No.
Diode Modality Laser indirect Laser indirect Transscleral
Interval Between Treatment and Death, d
No. of
1 21
46 159 80 186 156 72
Transscleral Transscleral Transscleral
1 1 21 21
and tested in animal models. Since di¬ ode laser energy is delivered in the infrared wavelength range, it shares the advantages of increased transmis¬ sion through lens opacities, vitreous hemorrhage, and macular xanthophyll pigments found with krypton (red) la¬ ser photocoagulation.17"22 The principal site of energy absorption is melanin in the retinal pigment epithelium (RPE) and choroid. The efficacy of the diode laser in retinal photocoagulation has been demonstrated in several small clinical studies.7·9·10·23 However, its prime advantages may be logistic by providing a clinically useful source of laser photocoagulation that uses stan¬ dard electrical service, avoids cooling system needs, is portable, is less ex¬ pensive, and is adaptable to multiple delivery modes. The purpose of this study was to evaluate the clinical and histopathologic effects of a commercially available diode laser system using transpupillary laser indirect ophthalmoscopic and trans¬ scleral delivery systems in an animal model of detached retina to evaluate its efficacy in inducing a chorioretinal adhesion.
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/05/2015
Spots
Power, mW 200 1140 300 1250 300 300
Duration,
s
0.5 0.5 0.5 1.0 0.5 0.5
MATERIALS AND METHODS One diode laser was used for all aspects of this study (Oculite SLx, IRIS Medical In¬ struments Ine, Mountain View, Calif). Laser indirect ophthalmoscopy and transscleral modes were tested as detailed below. Pig¬ mented rabbits (2 to 3 kg) were anesthetized with intramuscular injections of ketamine hydrochloride (14 mg/kg) and xylazine hydrochloride (14 mg/kg). Pupillary dilation was attained using 0.5% tropicamide and 2.5% phenylephrine hydrochloride. Only one eye of each animal was used. All procedures were performed using sterile techniques and in accordance with the Association for Research in Vision and Ophthalmol¬ ogy Resolution on the Use of Animals in Research. One week before the procedure, 0.5 mL of 40% perfluoropropane gas was injected intravitreally. This allowed for a slightly ex¬ pansile air bubble, yet one that never ex¬ ceeded approximately 25% of the vitreous cavity. Its effect was to induce a largely liq¬ uefied vitreous cavity while maintaining a clear crystalline lens. A sclerotomy was performed 3 mm poste¬ rior to the limbus. Coaxial illumination from the operating microscope and a corneal lens provided visualization. No complications were noted despite the peripheral transretinal entry. All entry sites healed without de-
Fig 1.—Left, Histopathologic findings 1 day after induced retinal break and localized detachment. The retinal break is discrete, its edge is el¬ evated (asterisk), and there is mild photoreceptor outer segment degeneration. The attached material appears to represent fibrin (arrowhead). Right, Three weeks after inducing a retinal break, the retina is reattached and there is a mild subretinal scar (asterisk). The curled edge of the original break is still seen (arrow) (periodic acid-Schiff, original magnification 125 [left] and x250 [right]).
Fig 2.—Left, One day after retinocryopexy treatment at margin of induced retinal break and detachment. There is broad distribution of full-thickness retinal necrosis (between arrowheads). Right, Three weeks after cryotreatment, there is a prominent chorioretinal scar (arrow¬ heads) (periodic acid-Schiff, original magnification
tachment. A single 80-0 black silk suture was used to close the incision made on sclerotomy after inducing the retinal break and retinal detachment. A retinal break measuring 1 to 2 mm was induced by alternately aspirating and injecting balanced salt solution directly over the retina using a 25-gauge blunt can¬ nula, which was placed under the edge of the break to create a 5x5-mm retinal detach¬ ment by hydrodissection. The maximal ele¬ vation of the retinal detachment was esti¬ mated to be 1 mm. Two animals received no further treat¬ ment after retinal detachment was induced, allowing for comparison with the untreated controls. Retinocryopexy and indirect oph¬ thalmoscopic laser treatment were applied to one longitudinal side of the retinal break to allow for comparison with the control in the same eye. Transscleral treatment was given around the retinal break. Retinocryopexy was applied using ap¬ proximately six slightly overlapping spots along one half the extent of the retinal break in two eyes. The treatment end point was the first occurrence of whitening of the retina. Diode laser indirect ophthalmoscopy was applied in two eyes using 46 to 159 spots of 200- to 1140-mW power and 0.5-second duration (Table). Pigment variation be¬ tween subjects accounted for the wide
125).
range of treatment variables needed to achieve a standardized appearance. The treatment end point was choosen as RPE whitening with minimal retinal whitening. The laser indirect ophthalmoscope was used with scierai indentation to allow reapproximation of the RPE to the retina to determine if such treatment was sufficient to induce a chorioretinal adhesion in de¬ tached retina. Transscleral diode laser photocoagulation was applied around the break in four eyes using 72 to 186 spots of 300-mW power and 0.5-second duration (in three eyes, but one lightly pigmented eye required 1250 mW for 1.0 second) (Table). Three contiguous rows of spots were placed, achieving similar ophthal¬ moscopic end points as with laser indirect ophthalmoscopic treatment. Three animals each were killed 1 day and 3 weeks after treatment, using a lethal dose of intravenous sodium pentobarbitol. The globes were enucleated and fixed in a 10% formaldehyde solution, examined grossly by removing the superior cap of the globe, and prepared for light microscopy using stan¬ dard stains. The study was designed to use only as many animals as necessary, but the consistency and extent of treatment effect across these two time points obviated the need for more.
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RESULTS
Spontaneous
occurred in all
retinal reattachment cases.
Untreated Control
Histopathologic study
on day 1 discrete retinal break with photoreceptor cell loss in the area of the retinal detachment (Fig 1, left). Three weeks after inducing a retinal break and detachment, there was a mild subretinal scar within the area of previous detach¬ ment and a mild chorioretinal scar at the edge of the retinal break (Fig 1, right).
showed
a
Retinocryopexy Retinal edema in the treated
area
adjacent to the break was present 1 day after treatment, while RPE changes were present 3 weeks after treatment. Histopathologic examination revealed
broad areas of full-thickness retinal cell necrosis 1 day after treatment with cryopexy (Fig 2, left). Three weeks af¬ ter treatment, extensive chorioretinal adhesion was noted (Fig 2, right).
Fig 3.—Left, One day after diode laser indirect ophthalmoscopic treatment of the induced retinal break, the coagulated area involves the deep retinal layers, with mild ganglion cell attenuation (between arrows). Right, Three weeks after treatment, a chorioretinal scar is evident with marked attenuation of the retina (arrowheads) (periodic acid-Schiff, original magnification 125).
Fig 4.—Left, One day after transscleral retinopexy, the outer portion of detached retina has early coagulation necrosis (between arrows). Right, Three weeks after treatment, a chorioretinal scar has developed (between arrows). The previously detached margins of retina are evident (ar¬ rowheads) with photoreceptor cell loss and attenuation of the inner nuclear layer (periodic acid-Schiff, original magnification 125). Laser Indirect
Ophthalmoscopy
Retinal whitening was observed with laser indirect ophthalmoscopic treat¬ ment. Compared with cryopexy, spots were smaller, more discrete, and not as intensely white in clinical appearance. Histopathologic study one day after laser indirect ophthalmoscopic treat¬ ment showed coagulative necrosis in¬ volving all retinal layers (Fig 3, left). The pattern of cell destruction was sim¬ ilar to that seen with retinocryopexy treatment, but its extent was narrower. Treatment areas bordering on attached retina yielded a more consolidated, py¬ ramidal pattern of coagulative necrosis, while treatment in retina detached from the RPE was less consolidated. Three weeks after laser indirect ophthalmo¬ scopic treatment, there was marked ret¬ inal attenuation and chorioretinal scar¬
ring (Fig 3, right). Transscleral Laser
Retinopexy
The clinical appearance was similar to that seen in laser indirect-treated cases, but with somewhat more regular, discrete, pigmentary changes in the retina and RPE. One day after trans-
scierai laser retinopexy, full-thickness coagulative necrosis was evident in the retina (Fig 4, left). The treated areas generally showed a consolidated pat¬ tern of necrosis, but in some areas sub¬ retinal pigment elements were more
dispersed.
Three weeks after treatment, a wellchorioretinal scar was con¬ centrated in the treated area with fullthickness retinal cell destruction (Fig 4,
developed right). In
one
transscleral laser-treated eye
epiretinal membrane developed. No treatment complications such as hem¬ orrhage, Bruch's membrane rupture, or scierai damage was observed in any study eye. an
COMMENT
Chorioretinal adhesion has two ef¬ fects in closing a retinal break. It in¬ duces a watertight seal preventing the ingress of vitreous fluid into the sub¬ retinal space. Second, it provides im¬ mediate additional tensile strength to counteract the vitreoretinal forces that tend to cause reopening of the break.24·2" The strength of the chorioretinal adhe¬ sion increases with time.2"28 Diathermy,
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/05/2015
laser photocoagulation, and cryotherapy have been found experimentally to produce adhesion of approximately equal strength.26"28 The sealing effect is probably more important in maintain¬ ing retinal attachment than the tensile effect since the induced chorioretinal adhesion is only moderately increased from the normal, and retinal detach¬ ment
can
spread through cleavage over
the chorioretinal scars.29 The histo¬ pathologic characteristics of the chori¬ oretinal adhesion induced by dia¬ thermy, retinocryopexy, and photocoagulation are similar.30·31 The advantages of laser photocoagu¬ lation over cryotherapy and diathermy include its ability to induce more precise and selective chorioretinal adhesion, disperse fewer viable RPE cells,32 and create less breakdown of the bloodretinal barrier.33 These factors may de¬ crease the risk of subsequent proliferative vitreoretinopathy. Diode laser photocoagulation may cause less break¬ down of the blood-retinal barrier than argon laser photocoagulation.34 Transpupillary photocoagulation is most effective in attached retina since the laser energy is poorly transmitted
detached retina. Transscleral laser treatment, like cryotherapy, allows treatment of the RPE underlying the retinal break even in ar¬ eas of detached retina. The infrared light of the diode laser can be transmit¬ ted transsclerally for this purpose as demonstrated in this and other studies.4·14"16 This study has shown the feasibility of applying transscleral diode laser energy in experimentally de¬ tached rabbit retinas. Scierai indenta¬ tion by the retinopexy probe allowed direct reapproximation of the retina to the RPE. Retinal whitening was more consistently observed with transscleral than with laser indirect ophthalmo¬ scopic treatment. Chorioretinal adhe-
through edematous,
where transscleral without visible retinal uptake, as has been observed with cryotherapy in bullous retinal de¬ tachment.35 Indeed, the standard de¬ gree of treatment applied in retinal reattachment surgery may be far more than necessary to effect a suitable chori¬ oretinal adhesion. A potential disadvantage is that transscleral laser treatment of the RPE with overlying retinal detachment may allow dispersion of viable RPE cells in the subretinal space, which may subse¬ quently migrate into the vitreous cavity, as is hypothesized with cryotherapy.32 A limitation of this model is that the retinal detachment induced was relasion
was seen even
treatment
was
applied
tively small and that the rabbit is able to spontaneously reattach the retina in virtually all cases without chorioretinal scar induction. Still the histopathologic
appearance of the induced chorioretinal scars appeared similar to that created in standard retinal reattachment surgery. However, laser treatment probably ac¬ complishes this with less breakdown of the blood-brain barrier and dispersion of viable precursor elements. This study confirms the promise for the use oftransscleral diode laser retino¬ pexy in the treatment of rhegmatogenous retinal detachments. Clinical stud¬ ies are necessary to confirm its efficacy. This study was supported in part by a grant from IRIS Medical Instruments Ine, Mountain View, Calif.
References 1. Brancato R, Pratisi R. Applications of diode laser in ophthalmology. Lasers Light Ophthalmol.
1987;1:119-129. 2. Puliafito CA, Deutsch TF, Holl JK. Semicon-
ductor laser endophotocoagulation of the retina. Arch Ophthalmol. 1987;105:424-427. 3. Duker JS, Federman JL, Schubert HD, Talboc C. Semiconductor diode laser endophotocoagulation. Ophthalmic Surg. 1989;20:717-719. 4. Smiddy WE, Hernandez E. Histopathology of retinal diode laser photocoagulation in rabbit eyes. Arch Ophthalmol. 1992;110:693-698. 5. Brancato R, Pratesi R, Leoni G, Trabucchi G, Giovannoni L, Vanni U. Retinal photocoagulation with diode laser operating from a slit lamp microscope. Lasers Light Ophthalmol. 1988;2:73-78. 6. McHugh JDA, Marshall J, Capon M, Rothery S, Raven A, Naylor RP. Transpupillary retinal photocoagulation in the eyes of rabbit and human using a diode laser. Lasers Light Ophthalmol.
1988;2:125-143. 7. McHugh JDA, Marshall J, Ffytche TJ, HamilAM, Raven A, Keeler CR. Initial clinical experience using a diode laser in the treatment of retinal vascular disease. Eye. 1989;3:516-527. 8. McHugh JDA, Marshall J, Ffytche TJ, Hamilton AM, Raven A. Macular photocoagulation of human retina with a diode laser: a comparative histopathological study. Lasers Light Ophthalmol. 1990; ton
3:11-28. 9. Balles MW, Puliafito CA, D'Amico DJ, Jacobsen JJ, Birngruber R. Semiconductor diode laser photocoagulation in retinal vascular disease. Oph-
thalmology. 1990;97:1553-1561. 10. Noyori K, Noyori S, Ohki R. Clinical trial of diode laser photocoagulator: preliminary report. Lasers Light Ophthalmol. 1990;3:81-87. 11. Wallow IHL, Sponsel WE, Stevens TS. Clinicopathologic correlation of diode laser burns in monkeys. Arch Ophthalmol. 1991;109:648-653. 12. Benner JD, Huang M, Ishigooka H, et al. A comparison of argon, krypton and diode binocular indirect ophthalmoscopic laser photocoagulation in the
rabbit. Invest Ophthalmol Vis Sci. 1991;32:2764. 13. Avery RL, Repka MX, Green WR, D'Anna S, Goldberg MF. A comparative study of diode and argon laser indirect photocoagulation of primate retina. Invest Ophthalmol Vis Sci. 1991;32(suppl): 2766. 14. Jennings T, Fuller T, Vukich JA, et al. Trans-scleral retinal photocoagulation with 810-nm semiconductor diode laser. Ophthalmic Surg. 1990; 21:492-496. 15. Peyman GA, Naguib K, Gaasterland DE. Trans-scleral application of semi-conductor diode laser. Lasers Surg Med. 1990;10:569-575. 16. Okamoto S, Takahashi H, Fukado Y, Ozawa T. Laser diode application for trans-scleral photocoagulation. Lasers Light Ophthalmol. 1990;3:29\x=req-\ 37. 17. Marshall J, Bird A. A comparative histopathologic study of argon and krypton laser irradiations of the human retina. Br J Ophthalmol. 1979; 63:657-668. 18. Peyman GA, Li M, Yoneya S, Goldberg MF, Raichand M. Fundus photocoagulation with the argon and krypton lasers: a comparative study.
Ophthalmic Surg. 1981;12:481-490. 19. Smiddy WE, Fine SL, Quigley AJ, Hohman RM, Addicks EM. Comparison of krypton and argon laser photocoagulation in primate retina. Arch Ophthalmol. 1984;102:1086-1092. 20. Blankenship GW, Gerke E, Batlle JF. Red krypton and blue-green argon laser diabetic panretinal photocoagulation. Graefes Arch Clin Exp Ophthalmol. 1989;227:364-368. 21. L'Esperance FA. The ocular histopathologic effect of krypton and argon laser radiation. Am J Ophthalmol. 1969;68:263-273. 22. Blankenship GW. Red krypton and blue\x=req-\ green argon panretinal laser photocoagulation for proliferative diabetic retinopathy: a laboratory and clinical comparison. Trans Am Ophthalmol Soc. 1986;84:967-1003.
23. Smiddy WE. Diode laser endophotocoagulation. Arch 1992;110:693-698.
Ophthalmol.
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/05/2015
24. Johnson
RN, Irvine AR, Wood IS. Endola-
ser, cryopexy, and retinal reattachment in the air-
a clinicopathologic correlation. Arch Ophthalmol. 1987;105:231-234. 25. Yoon YH, Marmor MF. Rapid enhancement of retinal adhesion by laser photocoagulation. Ophthalmology. 1988;95:1385-1388. 26. Zauberman H. Tensile strength of chorioretinal lesions produced by photocoagulation, diathermy, and cryopexy. Br J Ophthalmol. 1969;53:
filled eye:
749-752. 27. Kain HL. A new model for examining chorioretinal adhesion experimentally. Arch Ophthalmol. 1984;102:608-611. 28. Kita M, Negi A, Kawano S, Honda Y. Photothermal, cryogenic, and diathermic effects on retinal adhesive force in vivo. Retina. 1991;11:441-444. 29. Zauberman H. Experimental cleavage of chorioretinal scars by traction and subretinal fluid. Ann Ophthalmol. 1976;8:1301-1308. 30. Curtin VT, Fujino T, Norton EWD. Comparative histopathology of cryosurgery and photocoagulation. Arch Ophthalmol. 1966;75:674-682. 31. Lincoff H, O'Connor P, Bloch D, Nadel A, Kreissig I, Grinberg M. The chorioretinal adhesion. Trans Am Acad Ophthalmol Otolaryngol. 1970;74: 98-107. 32. Campochiaro PA, Kaden IH, Vidauri-Leal J, Glaser BM. Cryotherapy enhances intravitreal dispersion of viable retinal pigment epithelial cells. Arch Ophthalmol. 1985;103:434-436. 33. Jaccoma EH, Conway BP, Campochiaro PA. Cryotherapy causes extensive breakdown of the blood-brain barrier. Arch Ophthalmol. 1985;103: 1728-1730. 34. Sato Y, Berkowitz BA, Wilson CA, DeJuan E Jr. Blood-retinal barrier breakdown caused by diode vs argon laser endophotocoagulation. Arch
Ophthalmol. 1992;110:277-281. 35. Laqua H, Machemer R. Repair and adhesion mechanism of the cryotherapy lesion in experimental retinal detachment. Am J Ophthalmol. 1976;81: 833-844.
Histopathologic William E.
Smiddy, MD, Eleut Hernandez, LAT
\s=b\ A retinal break and localized retinal detachment were induced in 10 rabbit eyes. The retinal break was treated within regions of detached retina using diode laser transscleral retinopexy (four eyes), diode laser indirect ophthalmoscopy (two eyes), or retinocryopexy (two eyes). Two eyes were left as untreated controls. The clinical and histopathologic effects were studied 1 day and 3 weeks after initial treatment. Suitable chorioretinal adhesions were induced with all treatment modalities. The extent of tissue effects was greater in cryopexy and smaller in laser treatment. The histopathologic characteristics of the lesions induced by diode laser indirect ophthalmoscopy were similar to those seen with transscleral diode treatment and were more focal than those seen with cryopexy. Transscleral and transpupillary diode laser photocoagulation were effective in inducing chorioretinal adhesions in detached retina in this experimental model in rabbits.
(Arch Ophthalmol. 1992;110:1630-1633) diode laser delivers energy in the nphe -*- infrared (810 nm) energy
range.1
Intravitreal,24 transpupillary slit lamp,6"11 transpupillary laser indirect ophthalmoscopic,12'1:iandtransscleral4·14"16 delivery modes have been developed
Accepted
for publication June 11, 1992. From the Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami (Fla) School of Medicine. The authors have no proprietary interest in any equipment used. Reprint requests to Bascom Palmer Eye Institute, PO Box 016880, Miami, FL 33101 (Dr
Smiddy).
Diode Laser Treatment Variables Case No.
Diode Modality Laser indirect Laser indirect Transscleral
Interval Between Treatment and Death, d
No. of
1 21
46 159 80 186 156 72
Transscleral Transscleral Transscleral
1 1 21 21
and tested in animal models. Since di¬ ode laser energy is delivered in the infrared wavelength range, it shares the advantages of increased transmis¬ sion through lens opacities, vitreous hemorrhage, and macular xanthophyll pigments found with krypton (red) la¬ ser photocoagulation.17"22 The principal site of energy absorption is melanin in the retinal pigment epithelium (RPE) and choroid. The efficacy of the diode laser in retinal photocoagulation has been demonstrated in several small clinical studies.7·9·10·23 However, its prime advantages may be logistic by providing a clinically useful source of laser photocoagulation that uses stan¬ dard electrical service, avoids cooling system needs, is portable, is less ex¬ pensive, and is adaptable to multiple delivery modes. The purpose of this study was to evaluate the clinical and histopathologic effects of a commercially available diode laser system using transpupillary laser indirect ophthalmoscopic and trans¬ scleral delivery systems in an animal model of detached retina to evaluate its efficacy in inducing a chorioretinal adhesion.
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/05/2015
Spots
Power, mW 200 1140 300 1250 300 300
Duration,
s
0.5 0.5 0.5 1.0 0.5 0.5
MATERIALS AND METHODS One diode laser was used for all aspects of this study (Oculite SLx, IRIS Medical In¬ struments Ine, Mountain View, Calif). Laser indirect ophthalmoscopy and transscleral modes were tested as detailed below. Pig¬ mented rabbits (2 to 3 kg) were anesthetized with intramuscular injections of ketamine hydrochloride (14 mg/kg) and xylazine hydrochloride (14 mg/kg). Pupillary dilation was attained using 0.5% tropicamide and 2.5% phenylephrine hydrochloride. Only one eye of each animal was used. All procedures were performed using sterile techniques and in accordance with the Association for Research in Vision and Ophthalmol¬ ogy Resolution on the Use of Animals in Research. One week before the procedure, 0.5 mL of 40% perfluoropropane gas was injected intravitreally. This allowed for a slightly ex¬ pansile air bubble, yet one that never ex¬ ceeded approximately 25% of the vitreous cavity. Its effect was to induce a largely liq¬ uefied vitreous cavity while maintaining a clear crystalline lens. A sclerotomy was performed 3 mm poste¬ rior to the limbus. Coaxial illumination from the operating microscope and a corneal lens provided visualization. No complications were noted despite the peripheral transretinal entry. All entry sites healed without de-
Fig 1.—Left, Histopathologic findings 1 day after induced retinal break and localized detachment. The retinal break is discrete, its edge is el¬ evated (asterisk), and there is mild photoreceptor outer segment degeneration. The attached material appears to represent fibrin (arrowhead). Right, Three weeks after inducing a retinal break, the retina is reattached and there is a mild subretinal scar (asterisk). The curled edge of the original break is still seen (arrow) (periodic acid-Schiff, original magnification 125 [left] and x250 [right]).
Fig 2.—Left, One day after retinocryopexy treatment at margin of induced retinal break and detachment. There is broad distribution of full-thickness retinal necrosis (between arrowheads). Right, Three weeks after cryotreatment, there is a prominent chorioretinal scar (arrow¬ heads) (periodic acid-Schiff, original magnification
tachment. A single 80-0 black silk suture was used to close the incision made on sclerotomy after inducing the retinal break and retinal detachment. A retinal break measuring 1 to 2 mm was induced by alternately aspirating and injecting balanced salt solution directly over the retina using a 25-gauge blunt can¬ nula, which was placed under the edge of the break to create a 5x5-mm retinal detach¬ ment by hydrodissection. The maximal ele¬ vation of the retinal detachment was esti¬ mated to be 1 mm. Two animals received no further treat¬ ment after retinal detachment was induced, allowing for comparison with the untreated controls. Retinocryopexy and indirect oph¬ thalmoscopic laser treatment were applied to one longitudinal side of the retinal break to allow for comparison with the control in the same eye. Transscleral treatment was given around the retinal break. Retinocryopexy was applied using ap¬ proximately six slightly overlapping spots along one half the extent of the retinal break in two eyes. The treatment end point was the first occurrence of whitening of the retina. Diode laser indirect ophthalmoscopy was applied in two eyes using 46 to 159 spots of 200- to 1140-mW power and 0.5-second duration (Table). Pigment variation be¬ tween subjects accounted for the wide
125).
range of treatment variables needed to achieve a standardized appearance. The treatment end point was choosen as RPE whitening with minimal retinal whitening. The laser indirect ophthalmoscope was used with scierai indentation to allow reapproximation of the RPE to the retina to determine if such treatment was sufficient to induce a chorioretinal adhesion in de¬ tached retina. Transscleral diode laser photocoagulation was applied around the break in four eyes using 72 to 186 spots of 300-mW power and 0.5-second duration (in three eyes, but one lightly pigmented eye required 1250 mW for 1.0 second) (Table). Three contiguous rows of spots were placed, achieving similar ophthal¬ moscopic end points as with laser indirect ophthalmoscopic treatment. Three animals each were killed 1 day and 3 weeks after treatment, using a lethal dose of intravenous sodium pentobarbitol. The globes were enucleated and fixed in a 10% formaldehyde solution, examined grossly by removing the superior cap of the globe, and prepared for light microscopy using stan¬ dard stains. The study was designed to use only as many animals as necessary, but the consistency and extent of treatment effect across these two time points obviated the need for more.
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/05/2015
RESULTS
Spontaneous
occurred in all
retinal reattachment cases.
Untreated Control
Histopathologic study
on day 1 discrete retinal break with photoreceptor cell loss in the area of the retinal detachment (Fig 1, left). Three weeks after inducing a retinal break and detachment, there was a mild subretinal scar within the area of previous detach¬ ment and a mild chorioretinal scar at the edge of the retinal break (Fig 1, right).
showed
a
Retinocryopexy Retinal edema in the treated
area
adjacent to the break was present 1 day after treatment, while RPE changes were present 3 weeks after treatment. Histopathologic examination revealed
broad areas of full-thickness retinal cell necrosis 1 day after treatment with cryopexy (Fig 2, left). Three weeks af¬ ter treatment, extensive chorioretinal adhesion was noted (Fig 2, right).
Fig 3.—Left, One day after diode laser indirect ophthalmoscopic treatment of the induced retinal break, the coagulated area involves the deep retinal layers, with mild ganglion cell attenuation (between arrows). Right, Three weeks after treatment, a chorioretinal scar is evident with marked attenuation of the retina (arrowheads) (periodic acid-Schiff, original magnification 125).
Fig 4.—Left, One day after transscleral retinopexy, the outer portion of detached retina has early coagulation necrosis (between arrows). Right, Three weeks after treatment, a chorioretinal scar has developed (between arrows). The previously detached margins of retina are evident (ar¬ rowheads) with photoreceptor cell loss and attenuation of the inner nuclear layer (periodic acid-Schiff, original magnification 125). Laser Indirect
Ophthalmoscopy
Retinal whitening was observed with laser indirect ophthalmoscopic treat¬ ment. Compared with cryopexy, spots were smaller, more discrete, and not as intensely white in clinical appearance. Histopathologic study one day after laser indirect ophthalmoscopic treat¬ ment showed coagulative necrosis in¬ volving all retinal layers (Fig 3, left). The pattern of cell destruction was sim¬ ilar to that seen with retinocryopexy treatment, but its extent was narrower. Treatment areas bordering on attached retina yielded a more consolidated, py¬ ramidal pattern of coagulative necrosis, while treatment in retina detached from the RPE was less consolidated. Three weeks after laser indirect ophthalmo¬ scopic treatment, there was marked ret¬ inal attenuation and chorioretinal scar¬
ring (Fig 3, right). Transscleral Laser
Retinopexy
The clinical appearance was similar to that seen in laser indirect-treated cases, but with somewhat more regular, discrete, pigmentary changes in the retina and RPE. One day after trans-
scierai laser retinopexy, full-thickness coagulative necrosis was evident in the retina (Fig 4, left). The treated areas generally showed a consolidated pat¬ tern of necrosis, but in some areas sub¬ retinal pigment elements were more
dispersed.
Three weeks after treatment, a wellchorioretinal scar was con¬ centrated in the treated area with fullthickness retinal cell destruction (Fig 4,
developed right). In
one
transscleral laser-treated eye
epiretinal membrane developed. No treatment complications such as hem¬ orrhage, Bruch's membrane rupture, or scierai damage was observed in any study eye. an
COMMENT
Chorioretinal adhesion has two ef¬ fects in closing a retinal break. It in¬ duces a watertight seal preventing the ingress of vitreous fluid into the sub¬ retinal space. Second, it provides im¬ mediate additional tensile strength to counteract the vitreoretinal forces that tend to cause reopening of the break.24·2" The strength of the chorioretinal adhe¬ sion increases with time.2"28 Diathermy,
Downloaded From: http://archopht.jamanetwork.com/ by a University of Iowa User on 06/05/2015
laser photocoagulation, and cryotherapy have been found experimentally to produce adhesion of approximately equal strength.26"28 The sealing effect is probably more important in maintain¬ ing retinal attachment than the tensile effect since the induced chorioretinal adhesion is only moderately increased from the normal, and retinal detach¬ ment
can
spread through cleavage over
the chorioretinal scars.29 The histo¬ pathologic characteristics of the chori¬ oretinal adhesion induced by dia¬ thermy, retinocryopexy, and photocoagulation are similar.30·31 The advantages of laser photocoagu¬ lation over cryotherapy and diathermy include its ability to induce more precise and selective chorioretinal adhesion, disperse fewer viable RPE cells,32 and create less breakdown of the bloodretinal barrier.33 These factors may de¬ crease the risk of subsequent proliferative vitreoretinopathy. Diode laser photocoagulation may cause less break¬ down of the blood-retinal barrier than argon laser photocoagulation.34 Transpupillary photocoagulation is most effective in attached retina since the laser energy is poorly transmitted
detached retina. Transscleral laser treatment, like cryotherapy, allows treatment of the RPE underlying the retinal break even in ar¬ eas of detached retina. The infrared light of the diode laser can be transmit¬ ted transsclerally for this purpose as demonstrated in this and other studies.4·14"16 This study has shown the feasibility of applying transscleral diode laser energy in experimentally de¬ tached rabbit retinas. Scierai indenta¬ tion by the retinopexy probe allowed direct reapproximation of the retina to the RPE. Retinal whitening was more consistently observed with transscleral than with laser indirect ophthalmo¬ scopic treatment. Chorioretinal adhe-
through edematous,
where transscleral without visible retinal uptake, as has been observed with cryotherapy in bullous retinal de¬ tachment.35 Indeed, the standard de¬ gree of treatment applied in retinal reattachment surgery may be far more than necessary to effect a suitable chori¬ oretinal adhesion. A potential disadvantage is that transscleral laser treatment of the RPE with overlying retinal detachment may allow dispersion of viable RPE cells in the subretinal space, which may subse¬ quently migrate into the vitreous cavity, as is hypothesized with cryotherapy.32 A limitation of this model is that the retinal detachment induced was relasion
was seen even
treatment
was
applied
tively small and that the rabbit is able to spontaneously reattach the retina in virtually all cases without chorioretinal scar induction. Still the histopathologic
appearance of the induced chorioretinal scars appeared similar to that created in standard retinal reattachment surgery. However, laser treatment probably ac¬ complishes this with less breakdown of the blood-brain barrier and dispersion of viable precursor elements. This study confirms the promise for the use oftransscleral diode laser retino¬ pexy in the treatment of rhegmatogenous retinal detachments. Clinical stud¬ ies are necessary to confirm its efficacy. This study was supported in part by a grant from IRIS Medical Instruments Ine, Mountain View, Calif.
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