In 1904, Elschnig1 recognized vitreous changes in eyes with retinitis pigmentosa (RP); other investigators also documented these changes.2·3 In 1975, Pruett,4 who studied 116 eyes with the disease, illustrated these vitreous abnormalities and classified them into four stages based on the degenerative process in the vitreous: stage I, tiny, dust-like, reflective particles uniformly distributed throughout the gel; stage II, particles plus posterior vitreous detachment (PVD); stage III, particles and PVD plus formation of a posterior matrix of dense, white opacities and interconnecting fibers on the posterior hyaloid membrane; and stage W, particles, PVD, and a coarse posterior matrix plus a collapsed residual gel of reduced volume.
Vitreous changes already had been observed in children, and the progression of these changes appeared to parallel the magnitude of the gross retinal malfunction estimated by visual field measurements. Furthermore, such degeneration was reported to progress rapidly to its final form in young adults.4 However, the prevalence of PVD or other vitreous changes in eyes with RP vis-à-vis patient age has not been established with certainty.
In the present study, the vitreous condition in 218 eyes with RP was observed biomicroscopically to determine the prevalence of PVD and PVD with collapse in relation to age.
SUBJECTS AND METHODS
Two hundred eighteen eyes of 109 patients with RP (52 males, 57 females; median age, 34 years; range, 6 to 78 years) (Fig 1) were examined from 1978 through 1992 at the Retina Associates in Boston. All had been diagnosed with primary RP, as evidenced by the characteristic bilateral fundus appearance, loss of peripheral vision, and abnormalities of dark adaptation and/or electroretinography (ERG).5 Electrophysiologic and psychophysiologic studies (ERG, visual-evoked response, dark adaptation, color-vision testing, flicker perimetry) were performed on 96 of the 109 patients to verify the diagnosis. We did not include patients with atypical disease forms, such as paravenous, sector, and unilateral RP, clumped pigmentary retinal degeneration, or patients with a history or serologic evidence that suggested another cause of pigmentary retinal degeneration such as lues, rubella, or toxin or drug exposure. We also excluded eyes with a history of ocular trauma or ocular surgery.
FIGURE 1: Age and sex distribution of 109 patients with retinitis pigmentosa. Open bars, males; hatched bars, females.
FIGURE 2: Age and sex distribution of 115 control subjects. Open bars, males; hatched bars, females.
Eyes with high myopia (more than - 6 diopters), in which PVD develops nearly 10 years earlier than in emmetropic eyes,6'8 were excluded to avoid overestimating the prevalence of PVD. Sixty of the 109 patients had no definite history of familial ocular disease. In the remaining 49, there was evidence that other family members also had RP: 29 were classified as autosomal dominant, 18 as autosomal recessive, and two as having an X-linked recessive trait. Two hundred thirty healthy eyes of 115 age- and sex-matched subjects were selected at random from 2292 eyes of 1213 normal subjects (age range, 5 to 90 years) to serve as controls (Fig 2).
Complete ocular examinations, including bestcorrected visual acuity measurement using the Snellen chart, slit-lamp biomicroscopy, indirect ophthalmoscopy with scleral depression, Goldmann perimetry, and color fundus photography, were performed. The vitreous condition was studied biomicroscopically with a + 58.6-diopter preset lens (El Bayadi-Kajiura lens, Nikon, Tokyo, Japan).9-10 The entire vitreous cavity was observed before and after rapid vertical and horizontal ocular movements. When PVD was present, ocular movements momentarily displaced the detached vitreous cortex from the retinal surface. As a result, the posterior limits of the detached vitreous gel, delineated by the detached posterior hyaloid membrane, were outlined temporarily.11·12 The vitreous conditions were classified into two groups according to the absence or presence of PVD, with the latter further classified as either simple PVD or vitreous collapse. PVD with collapse was defined as the condition in which the vitreous gel appeared greatly reduced in volume, with the residual matrix floating freely in the optically clear fluid of the posterior vitreous cavity.4·7·13
Statistical analysis was performed using the chisquare test with YaIeS* continuity correction or Fisher's exact test, and the Mann- Whitney U test. A finding was considered statistically significant if the probability that it could have occurred by chance was less than 5% (P < .05).
All 218 eyes with RP, even those of patients in the first decade of life, had translucent and/or pigmented particles throughout the vitreous gel (Pig 3). One hundred eighty-one (83%) of the RP eyes and 27 (12%) of the control eyes had PVD (Fig 4). The prevalence of PVD was significantly higher in the RP eyes than in the controls (P < .01). Among the RP eyes, nine (64%) of the 17 eyes of patients in their first decade had PVD. The prevalence of PVD increased with age in the second through the eighth decades (ie, 67%, 87%, 85%, 90%, 88%, 90%, and 100%, respectively). However, none of the eyes of the control subjects who were 39 years or younger had PVD. The prevalence of PVD in the first through the sixth decades was significantly higher in the RP eyes than in the controls (0%, 0%, 0%, 0%, 7%, and 20%, respectively) (P < .01) (Fig 5).
One hundred forty-five (67%) of the RP eyes and 18 (8%) of the control eyes had PVD with collapse. The prevalence was significantly higher in the RP eyes than in the controls (P < .01). Among the patients in the second decade of life, nine (25%) of 36 RP eyes already had PVD with collapse; no eyes of control subjects 49 years or younger had PVD with collapse. The prevalence in the second through the seventh decades was also significantly higher among the RP eyes (25%, 50%, 81%, 90%, 88%, and 90%, respectively) than in the controls (0%, 0%, 0%, 0%, 17%, and 30%, respectively) (P < .01) (Fig 6).
FIGURE 3: The anterior vitreous in a 9-year-old boy with retinitis pigmentosa. The vitreous photograph shows many fine, dust-like particles in the vitreous gel.
FIGURE 4: Retinitis pigmentosa with complete posterior vitreous detachment in a 29-year-old man. The vitreous photograph shows a posterior hyaloid membrane (arrow heads) completely detached from the retina, and formation of a posterior matrix of dense, white opacities (A) and interconnecting fibers (B).
No retinal breaks, with or without retinal detachment, were observed in the 218 RP eyes.
Diagnosing PVD in eyes with RP is more difficult than in normal eyes. The presence of a large lacuna formation or extensive vitreous liquefaction, which is associated with residual thin cortical vitreous remaining on the inner retinal surface, makes misdiagnosing PVD for RP likely. However, recent advancements in instrumentation and the techniques of vitreous examination enable clear observation of the dynamic movement of the vitreous gel and more accurate diagnosis of PVD.11,12 In eyes with PVD diagnosed biomicroscopically, complete posterior vitreous separation has been distinctly seen, with no residual cortical vitreous detected during vitreous surgery,14 thus confirming the reliability of biomicroscopic diagnosis of PVD. Furthermore, in eyes with RP, no cortical vitreous remains have been detected, and it has been suggested that clear separation of the vitreous body from the retina is associated with a low incidence of vitreoretinal traction phenomena, retinal breaks, and retinal detachment.4 Therefore, although the risk of misdiagnosis in our study was minimal, our findings strongly suggest that PVD and PVD with collapse develop much earlier in eyes with RP than in normal eyes.
FIGURE 5: Comparison of the prevalence of posterior vitreous detachment (PVD) by age in the eyes with retinitis pigmentosa and in the controls. Open circles, controls; solid circles, patients.
FIGURE 6: Comparison by age of the prevalence of posterior vitreous detachment (PVD) with collapse in the eyes with retinitis pigmentosa and in the controls. Open circles, controls; solid circles, patients.
The cellular nature of the particles in the vitreous gel or structural changes in the vitreoretinal interface in eyes with RP recently have been demonstrated.1521 However, the pathologic process of the vitreous changes remains unknown. Finding the answer to this question is difficult because the cells that generate the vitreous and the vitreous metabolism have not been identified. Pruett4 and Albert and colleagues15 speculated that cellular damage or death in the retinal pigment epithelium-neurosensory retinal complex may be responsible for decreased production of hyaluronic acid (which may maintain the vitreous gel formation22) and consequently may induce vitreous collapse in eyes with RP. Newsome and Michels17 stated that the presence of unusual amounts and types of proteins, such as fibronectin, and cells in the vitreous gel caused by breakdown of the blood-ocular barrier might induce vitreous condensation in eyes with RP. In the present study, all of the 218 eyes with RP, even those of patients 10 years of age or younger, had numerous particles throughout the vitreous gel. This change is considered the primary process in the vitreous degeneration that occurs in eyes with RP; it has not been detected in normal eyes. Thus, the mechanism of PVD development and subsequent vitreous collapse in eyes with RP may be quite different from that in normal eyes.
Rhegmatogenous retinal detachment rarely occurs in eyes with RP. In the present series, no eyes with RP had retinal breaks despite a high prevalence of PVD, which can cause retinal breaks. Pruett4 suggested that a clear separation of the vitreous body from the retina at an early age and an abnormal retinal-choroidal bond in eyes with RP might partially explain the low incidence of vitreoretinal traction phenomena in these eyes.
In the present study, although the sample size in each age group was small, we found that vitreous changes such as PVD or PVD with collapse developed much earlier in eyes with RP
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