Experimental retinal detachment. II. Role of the vitreous

Detached retina affects morphologic and biochemical changes in the retina adjacent to bullous retinal detachment in rabbits

PURPOSE

Long-term results, more than 10 years after successful retinal detachment surgery, have shown gradually decreasing visual acuity in some cases. It is unclear if reduced functional recovery postoperatively is caused by anatomic changes or biochemical disorders. To determine the etiology of the reduced visual acuity, we cytochemically examined the changes in the cellular responses of the edges of retinal detachments.

METHODS

We histochemically studied the glucose-6-phosphatase (G6P) and 5'-nucleotidase (5'-Nase) activity in the rabbit retina. Experimental rhegmatogenous retinal detachment was produced in a rabbit model after partial vitrectomy, followed by retinal tear formation.

RESULTS

Although 5'-Nase activity gradually decreased during the period of detachment, activity was still detectable after 24 weeks. G6P activity increased in the region of the detached neural retina. Around the border of the detached retina, the decrease in 5'-Nase activity extended approximately 140 micrometers into the adjacent attached retina at 2 weeks after detachment and 270 micrometers at 24 weeks.

CONCLUSIONS

These observations suggest that some anatomical and biochemical damages may occur in the retina adjacent to bullous retinal detachment and may explain the reduction in postoperative vision in some clinical cases.

Alterations in rabbit vitreal fine structure following C3F8 injection

This study examines the morphological and histochemical changes in the cortical vitreous of 36 rabbit eyes following C3F8 intravitreal gas injection. Eyes were examined by light microscopy (LM) using a modified cryofixation and cryosectioning technique that prevented the loss of soluble tissue moieties and permitted collagen and proteoglycan histochemistry as well as enzyme digestion with hyaluronidase. LM and scanning electron microscopy (SEM) of cryosectioned normal eyes revealed an elaborate fibrillar matrix extending 100-190 microns from the basal lamina of the retina into the vitreous proper, which seemed to be composed of collagen fibrils intimately associated or wrapped in proteoglycan. Following the full expansion of the C3F8 gas bubble in the vitreous, the cortical fibrillar meshwork was absent from the retinal surface and a dense, collagenous material accumulated in the anterior vitreous, especially between the ciliary processes and over the posterior face of the lens. At 41 days postinjection, the fibrillar matrix was reforming and the vitreal cavity was filled with fluid and numerous fibrillar-mucinous islands. These islands did not form sheets or membranes, nor did they attach to either the posterior or the anterior retinal surface. The cortical fibrillar meshwork had reformed at 61 days' recovery; however, the condensed fibrillar material against the lens and filling the spaces between the ciliary processes had not resorbed. Neither shearing of the cortical gel or fibrillar matrix nor congestion of the anterior vitreous was observed in eyes only partially filled with gas.

Comparison of pneumatic retinopexy with alternative surgical techniques

To determine the efficacy of pneumatic retinopexy, the authors conducted a retrospective study of 56 cases of uncomplicated retinal detachments (RDs) treated with this technique (follow-up, 6-18 months). These were compared with 28 similar cases treated with a Lincoff balloon and 78 similar cases treated with a scleral buckle. The long-term success rates for these three groups were 71, 64, and 96%, with the incidence of new breaks being 20, 18, and 1.3% respectively. In aphakic or pseudophakic patients with an absent or ruptured posterior capsule, the success rate for pneumatic retinopexy was only 43%. In phakic and aphakic patients with an intact posterior capsule, the success rate for pneumatic retinopexy improved to 81%. These data suggest that this technique is less effective in aphakic or pseudophakic patients with an absent or ruptured posterior capsule and that careful follow-up to detect new breaks is necessary in all cases. A prospective randomized study is needed to verify these data.

Laser treatment of macular holes

Macular holes have not been treated with the laser because of the rarity of subsequent total retinal detachment (RD). The authors attempted to clear the subretinal fluid of the halo by laser coagulation of the rim of the hole. Eighteen eyes with visual acuity of 20/200 or less were treated with a laser and followed for a mean of 34.8 months. Ten eyes (55.6%) improved three to eight lines, five eyes (27.8%) remained the same, and the vision of three (16.6%) deteriorated three to five lines. The best visual results noted in three eyes (20/400-20/70, 20/200-20/80, and 20/200-20/60) correlated with the least late loss of pigment epithelium and pigment migration.

Apparent disappearance of a macular hole associated with development of an epiretinal membrane

A macular hole in a 78-year-old man participating in a long-term follow-up study changed its biomicroscopic appearance dramatically as a result of changes in an epiretinal membrane. The macular hole became invisible and visual acuity improved from 20/70-2 to 20/30-2+2.

Resorption of subretinal fluid by transepithelial flow of the retinal pigment epithelium

The efficiency of flow through the retinal pigment epithelium (RPE) was calculated by studying the postoperative course of the subretinal fluid after nondrainage surgery of rhegmatogenous retinal detachment. In ten eyes of ten patients the preoperative volume of the subretinal fluid, area of the RPE participating in resorption of the fluid, elapsed time until resorption of the fluid, and efficiency of the flow were studied using B-scan ultrasonography. The flow through the RPE was 261 microliter/cm2 per day and could drain more than 50% of the vitreous volume to the choroidal circulation. These data coincide well with early reattachment of neural retina in nondrainage surgery. No statistically significant difference in this flow was seen between young and old patients.