Pars Plana Region Research Articles

Effect of twisting of intravitreal injections on ocular bio-mechanics: a novel insight to ocular surgery.

Although intravitreal (IVT) injections provide several advantages in treating posterior segment eye diseases, several associated challenges remain. The current study uses the finite element method (FEM) to highlight the effect of IVT needle rotation along the insertion axis on the reaction forces and deformation inside the eye. A comparison of the reaction forces at the eye's key locations has been made with and without rotation. In addition, a sensitivity analysis of various parameters, such as the needle's angular speed, insertion location, angle, gauge, shape, and intraocular pressure (IOP), has been carried out to delineate the individual parameter's effect on reaction forces during rotation. Results demonstrate that twisting the needle significantly reduces the reaction forces at the penetration location and throughout the needle travel length, resulting in quicker penetration. Moreover, ocular biomechanics are influenced by needle insertion location, angle, shape, size, and IOP. The reaction forces incurred by the patient may be reduced by using a bevel needle of the higher gauge when inserted close to the normal of the local scleral surface toward the orra serrata within the Pars Plana region. Results obtained from the current study can deepen the understanding of the twisting needle's interaction with the ocular tissue.

Bruch's membrane and Brücke's muscle in the pars plana region

Aims/Purpose: To examine Bruch's membrane (BM) in association with the longitudinal part of the ciliary muscle (LPCM) in the pars plana region.Methods: Using light microscopy, we histomorphometrically assessed BM and the LPCM in the pars plana region.Results: The histomorphometric study included 51 eyes (51 patients; mean age: 60.8 ± 15.0 years; axial length: 26.0 ± 3.3 mm; range: 21.0–36.0 mm). The LPCM (total length: 4.60 ± 1.10 mm) ended 1.15 ± 0.56 mm anterior to the ora serrata. Within the pars plana region, the LPCM (length: 2.58 ± 0.98 mm) had direct contact with BM for 1.95 ± 0.99 mm (71.1 ± 18.4% of the BM undersurface), while a capillary layer was interposed between BM and the LPCM for 0.70 ± 0.40 mm (29.0 ± 18.4%). In the pars plana region free of LPCM close to the ora serrata, the percentage of BM covered by the capillary layer was higher than in the pars plana region containing the LPCM (63.0 ± 42.1% versus 29.0 ± 18.4%; p < 0.001). At the LPCM end, BM was in direct contact with collagenous tissue from the LPCM and was focally thickened as compared to BM (with an underlying capillary layer (9.5 ± 5.3 μm vs. 4.3 ± 1.2 μm; p < 0.001).Conclusions: The direct contact of BM with the LPCM in the pars plana in association with focal BM thickening at the LPCM end suggests an insertion of LPCM on BM. Taking into account the biomechanical strength of BM, it may imply a functional unit of the LPCM with BM in the process of accommodation with a secondary movement of the posterior BM and tertiary thickening of the subfoveal choroidal space.

Bruch's membrane and Brücke's muscle in the pars plana region.

To examine Bruch's membrane (BM) in association with the longitudinal part of the ciliary muscle (LPCM) in the pars plana region. Using light microscopy, we histomorphometrically assessed BM and the LPCM in the pars plana region. The histomorphometric study included 51 eyes (51 patients; mean age: 60.8 ± 15.0 years; axial length: 26.0 ± 3.3 mm; range: 21.0-36.0 mm). The LPCM (total length: 4.60 ± 1.10 mm) ended 1.15 ± 0.56 mm anterior to the ora serrata. Within the pars plana region, the LPCM (length: 2.58 ± 0.98 mm) had direct contact with BM for 1.95 ± 0.99 mm (71.1 ± 18.4% of the BM undersurface), while a capillary layer was interposed between the BM and the LPCM for 0.70 ± 0.40 mm (29.0 ± 18.4%). In the pars plana region free of LPCM close to the ora serrata, the percentage of BM covered by the capillary layer was higher than in the pars plana region containing the LPCM (63.0 ± 42.1% vs. 29.0 ± 18.4%; p < 0.001). At the LPCM end, BM was in direct contact with a collagenous tissue from the LPCM and was focally thickened as compared to BM with an underlying capillary layer (9.5 ± 5.3 μm vs. 4.3 ± 1.2 μm; p < 0.001). The direct contact of BM with the LPCM in the pars plana in association with focal BM thickening at the LPCM end suggests an insertion of LPCM on the BM. Taking into account the biomechanical strength of BM, it may imply a functional unit of the LPCM with BM in the process of accommodation with a secondary movement of the posterior BM and tertiary thickening of the subfoveal choroidal space.

Zinn's zonule.

The Zonule of Zinn, or ciliary zonule, is the elaborate system of extracellular fibers that centers the lens in the eye. In humans, the fibers transmit forces that flatten the lens during the process of disaccommodation, thereby bringing distant objects into focus. Zonular fibers are composed almost entirely of 10-12nm-wide microfibrils, of which polymerized fibrillin is the most abundant component. The thickest fibers have a fascicular organization, where hundreds or thousands of microfibrils are gathered into micrometer-wide bundles. Many such bundles are aggregated to form a fiber. Dozens of proteins comprise the zonule. Most are derived from cells of the non-pigmented ciliary epithelium in the pars plana region, although some are probably contributed by the lens and perhaps other tissues of the anterior segment. Zonular fibers are viscoelastic cables but their component microfibrils are rather stiff structures. Thus, the elastic properties of the fibers likely stem from lateral interactions between microfibrils. Rupture of zonular fibers and subsequent lens dislocation (ectopia lentis) can result from blunt force trauma or be a sequela of other eye diseases, notably exfoliation syndrome. Ectopia lentis is also a feature of syndromic conditions caused typically by mutations in microfibril-associated genes. The resulting ocular phenotypes raise the possibility that the zonule regulates lens size and shape, globe size, and even corneal topology, in addition to its well-recognized role in accommodation.

Fleck-like deposits and swept source optical coherence tomography characteristics in a case of confirmed ocular chalcosis

A 36-year-old male presented with history of injury in the left eye 3 years back with a copper wire. Examination revealed the presence of typical sunflower cataract with golden yellow deposits over the anterior lens capsule with dull glow and old vitreous hemorrhage. Non-contrast computerized tomography revealed retained intraocular foreign body in the pars plana region. The patient underwent phacoemulsification with intraocular lens implantation followed by pars plana vitrectomy and foreign body removal. Intraoperatively, fleck-like deposits were noted on the retinal surface in a circinate manner around the fovea and also over mid-peripheral retina. Postoperative swept source optical coherence tomography (SS-OCT) was performed to document the location of deposits and their characteristics. Limited literature exists regarding SS-OCT characteristics of ocular chalcosis.

Wide-field fundus imaging with trans-palpebral illumination.

In conventional fundus imaging devices, transpupillary illumination is used for illuminating the inside of the eye. In this method, the illumination light is directed into the posterior segment of the eye through the cornea and passes the pupillary area. As a result of sharing the pupillary area for the illumination beam and observation path, pupil dilation is typically necessary for wide-angle fundus examination, and the field of view is inherently limited. An alternative approach is to deliver light from the sclera. It is possible to image a wider retinal area with transcleral-illumination. However, the requirement of physical contact between the illumination probe and the sclera is a drawback of this method. We report here trans-palpebral illumination as a new method to deliver the light through the upper eyelid (palpebra). For this study, we used a 1.5 mm diameter fiber with a warm white LED light source. To illuminate the inside of the eye, the fiber illuminator was placed at the location corresponding to the pars plana region. A custom designed optical system was attached to a digital camera for retinal imaging. The optical system contained a 90 diopter ophthalmic lens and a 25 diopter relay lens. The ophthalmic lens collected light coming from the posterior of the eye and formed an aerial image between the ophthalmic and relay lenses. The aerial image was captured by the camera through the relay lens. An adequate illumination level was obtained to capture wide angle fundus images within ocular safety limits, defined by the ISO 15004-2: 2007 standard. This novel trans-palpebral illumination approach enables wide-angle fundus photography without eyeball contact and pupil dilation.

SCLERAL AND CHOROIDAL THICKNESS IN SECONDARY HIGH AXIAL MYOPIA.

To assess differences in scleral and choroidal thickness between eyes with secondary high axial myopia caused by congenital glaucoma, eyes with primary high axial myopia, and nonhighly myopic eyes. The study consisted of 301 Chinese individuals with a mean age of 23.9 ± 22.6 years and mean axial length of 24.8 ± 4.2 mm. It included the "secondary highly myopic group" (SHMG) because of congenital glaucoma (n = 20 eyes; axial length >26.0 mm), the "primary highly myopic group" (PHMG) (n = 73; axial length >26.0 mm), and the remaining nonhighly myopic group (NHMG). The secondary highly myopic group versus the primary highly myopic group had significantly thinner sclera in the pars plana region (343 ± 71 μm versus 398 ± 83 μm; P = 0.006), whereas scleral thickness in other regions did not differ significantly between both highly myopic groups and was significantly thinner in both highly myopic groups than in the NHMG. Mean total scleral volume did not differ significantly (P > 0.20) between any group (SHMG: 659 ± 106 μm; PHMG: 667 ± 128 μm; NHMG: 626 ± 135 μm). Choroidal thickness was significantly thinner in both highly myopic groups than in the NHMG, with no significant differences between both highly myopic groups. Choroidal volume did not differ significantly (P > 0.40) between any of the groups (SHMG: 43 ± 12 μm; PHMG: 43 ± 13 μm; NHMG: 46 ± 17 μm). In secondary high axial myopia, the sclera gets thinner anterior and posterior to the equator; whereas in primary high axial myopia, scleral thinning is predominantly found posterior to the equator. Because volume of sclera and choroid did not differ between any group, scleral and choroidal thinning in myopia may be due to a rearrangement of tissue and not due to the new formation of tissue.

Scleral Thickness in Chinese Eyes.

We measured scleral thickness in eyes of Chinese, and assessed interregional differences and associations with age and axial length. Using light microscopy, we histomorphometrically measured scleral thickness at various locations in eyeballs from Chinese patients that had been enucleated due to retinoblastoma, uveal melanoma, or absolute painful glaucoma. The study included 281 globes from patients with a mean age of 24.8 ± 23.1 years (range, 1-83 years) and mean axial length of 24.3 ± 3.9 mm (range, 17.0-35.7 mm). In multivariate analysis in children aged ≤2 years, thicker posterior scleral thickness was marginally significantly associated with older age (P = 0.07; standardized correlation coefficient β, 0.21; correlation coefficient B, 62.2; 95% confidence interval [CI], -4.3,128.8) after adjusting for shorter axial length (P = 0.01). In participants aged ≥5 years, larger posterior scleral thickness was significantly associated only with shorter axial length (P < 0.001; β, -0.49; B, -24.1; 95% CI, -30.6,-17.6), but not with age (P = 0.93). The ratio of posterior scleral thickness to scleral thickness in the pars plana region decreased significantly with increasing axial length. The correlation coefficients were higher for the ratio of scleral thickness posterior pole/pars plana region than for posterior pole/ora serrata, posterior pole/equator, or posterior pole/midpoint posterior pole to equator. Scleral thickness measurements were not significantly (all P > 0.10) associated with adult glaucoma. Scleral thickness increased up to an age of 2 years, while afterwards scleral thickness was independent of age and decreased with longer axial length. Differences in the associations between the regional scleral thickness ratios and axial length suggested a scleral thinning taking place in axially elongated eyes predominantly in the posterior globe segment.

Bruch′s membrane thickness in high myopia

To measure the thickness of Bruch's membrane (BM) and assess its associations with axial length. Using a light microscope, we measured the thickness of Bruch's membrane, choroid and sclera on horizontal anterior-posterior histological sections of enucleated human globes. The study included 54 eyes (42 with glaucomatous optic nerve damage; 23 globes with axial length ≥26.5mm) with a mean axial length of 26.6±3.3mm (range: 21.0-34.0mm). In the non-highly myopic eyes, BM was significantly thicker at the pars plana region (6.6±1.1μm) than at the equator (4.1±1.5μm; p<0.001), the midpoint between equator and posterior pole (4.1±1.5μm; p<0.001), the parapapillary region (4.5±1.0μm; p=0.006) or the posterior pole (4.4±1.7μm; p=0.001). At any measurement location at or behind the ora serrata, BM thickness did not differ significantly (all p≥0.40) between the non-glaucomatous non-highly myopic group and the glaucomatous non-highly myopic group, or between the non-highly myopic group and the highly myopic group. BM thickness at any location was not significantly (all p>0.45) related to axial length. The ratio of scleral thickness to BM thickness and the ratio of choroidal thickness to BM thickness significantly decreased with longer axial length for measurements taken behind the equator. BM is physiologically thickest in the pars plana, with no major thickness differences between locations at or behind the ora serrata. In contrast to choroidal and scleral thickness, BM thickness is not significantly related to axial length. Axially elongated eyes have a normal BM thickness, despite a thinned choroid and sclera.

Activation of neural progenitor cells in human eyes with proliferative vitreoretinopathy

In addition to the ability for self-renewal and functional differentiation, neural stem/progenitor cells (NSCs) can respond to CNS injuries by targeted migration. In lower vertebrates, retinal injury is known to activate NSCs in the ciliary marginal zone (CMZ). Cells expressing markers of NSCs are also present in the ciliary body epithelium (CE) and in Müller glia in the peripheral retina (PR) of the adult human eye. However, these cells seem to be quiescent in the adult human eye and recent reports have shown that CE cells have limited properties of NSCs. In order to further clarify whether NSCs exist in the adult human eye, we tested whether NSC-like cells could be activated in eyes with proliferative vitreoretinopathy (PVR). The PR and CE were studied for NSC-associated markers in human enucleated control eyes and eyes with confirmed PVR, as well as in a mouse model of PVR. Furthermore, cells isolated from vitreous samples obtained during vitrectomies for retinal detachment were directly fixed or cultured in a stem cell-promoting medium and compared to cells cultured from the post-mortem retina and CE. In situ characterization of the normal eyes revealed robust expression of markers present in NSCs (Nestin, Sox2, Pax6) only around peripheral cysts of the proximal pars plana region and the PR, the latter population also staining for the glial marker GFAP. Although there were higher numbers of dividing cells in the CE of PVR eyes than in controls, we did not detect NSC-associated markers in the CE except around the proximal pars plana cysts. In the mice PVR eyes, Nestin activation was also found in the CE. In human PVR eyes, proliferation of both non-glial and glial cells co-staining NSC-associated markers was evident around the ora serrata region. Spheres formed in 7/10 vitreous samples from patients with PVR compared to 2/15 samples from patients with no known PVR, and expressed glial – and NSC-associated markers both after direct fixation and repetitive passages. In conclusion, the adult human eye may harbor two different populations of neuroepithelial stem/progenitor cells; a non-glial population located in the proximal pars plana around peripheral cysts in addition to a population with Müller glia characteristics. Yet, we only found that the glial population was able to respond to retinal injury by targeted migration into the vitreous.

Changes of the vasculature and innervation in the anterior segment of the RCS rat eye

Investigating the anterior eye segment vasculature and innervation of dystrophic RCS rats, two major unique findings were observed: in the iris, young adult animals with retinal dystrophy showed an increase in substance P nerve fibres and a dilation of arterioles and capillaries. This finding continued during ageing. In the pars plana region, the surface covered by venules decreased continuously with age. In older animals, this decrease was parallelled by a local decrease of sympathetic TH-positive nerve fibres supplying these venules. For both conditions, no comparable data exists so far in the literature. They might point to a unique situation in the anterior eye segment of the dystrophic RCS rat.

Scleral Thickness following Fluocinolone Acetonide Implant (Retisert)

Purpose: To evaluate whether intravitreal fluocinolone acetonide (FA) implantation (Retisert) leads to scleral thinning.Methods: Scleral thickness was measured at the pars plana region (4 quadrants) with anterior segment OCT (Visante) in FA implanted eyes (18) with noninfectious posterior uveitis in comparison to eyes with prior vitrectomy (8), and normal eyes without prior surgery (30).Results: Mean scleral thickness in normal (nonsurgical) eyes was 0.99/0.93/0.88/0.86, and 0.92 mm in the inferonasal/inferotemporal/superotemporal/superonasal quadrants, and overall, respectively. Sclera was thinner in each quadrant of the FA implanted eyes compared to the fellow or nonsurgical eyes, although none reached statistical significance, as the differences were small. However, a few FA implanted eyes demonstrated more dramatic scleral thinning than others.Conclusions: FA implant appears to lead to statistically nonsignificant scleral thinning overall with few exceptions. Clinicians should be aware of potential scleral thinning in select cases, important for reimplantation and long-term follow-up.

Effects of repeated injection of intravitreal triamcinolone on macular oedema in central retinal vein occlusion

To investigate the effectiveness of repeated injections of intravitreal triamcinolone acetonide (IVTA) in the treatment of macular oedema caused by central retinal vein occlusion (CRVO). Seventeen pseudophakic or aphakic eyes of 17 patients (10 male, seven female) with macular oedema caused by CRVO received a repeat injection of 4 mg IVTA, 16 weeks after the first injection of the same dose. The examination included measurements of best-corrected visual acuity (BCVA) for distance and central foveal thickness (CFT) by optical coherence tomography (OCT), preoperatively and 1, 2, 3 and 4 months postoperatively. The values were compared by paired-t test. Side-effects were monitored. BCVA and CFT were not significantly different before initial and repeat injections. Transient improvements of BCVA and CFT were achieved after both injections. At the end of follow-up, BCVA and CFT were significantly different compared to pre-injection values in the same group (P = 0.032, 0.049 in the initial-injection group and P = 0.001, 0.008 in the repeat-injection group, respectively). However, compared to the initial injection, BCVA measurements were significantly worse at each time-point (P = 0.043, 0.011, 0.010 and 0.012, respectively) after the repeat injection, as were CFT at 1, 2 and 3 months post-injection (P = 0.040, 0.015 and 0.025, respectively). The achieved maximum mean intraocular pressures were 20.00 [standard deviation (SD) 2.06] mmHg and 18.56 (SD 3.65) mmHg after the first and repeat injections, respectively. These values were not significantly different (P = 0.467). No other significant adverse events were noted during the study. A repeat injection of 4 mg IVTA may not be as effective as an initial injection for the treatment of macular oedema caused by CRVO.

Clinical Case Notes

AbstractThe case is presented of a highly aggressive congenital epithelial cyst of the anterior chamber. The patient underwent four primary procedures to remove the cyst and its three recurrences, and one procedure for secondary glaucoma. The primary cyst and first recurrence occurred in the anterior chamber, whereas the second and third recurrences occurred in the pars plana region. Attempts at optical correction of the eye were weighed against complications arising from further procedures, and a conservative approach favouring preservation of the eye became the management strategy in this case.

PII: S0886-3350(04)00446-8

In addition to the ability for self-renewal and functional differentiation, neural stem/progenitor cells (NSCs) can respond to CNS injuries by targeted migration. In lower vertebrates, retinal injury is known to activate NSCs in the ciliary marginal zone (CMZ). Cells expressing markers of NSCs are also present in the ciliary body epithelium (CE) and in Müller glia in the peripheral retina (PR) of the adult human eye. However, these cells seem to be quiescent in the adult human eye and recent reports have shown that CE cells have limited properties of NSCs. In order to further clarify whether NSCs exist in the adult human eye, we tested whether NSC-like cells could be activated in eyes with proliferative vitreoretinopathy (PVR). The PR and CE were studied for NSC-associated markers in human enucleated control eyes and eyes with confirmed PVR, as well as in a mouse model of PVR. Furthermore, cells isolated from vitreous samples obtained during vitrectomies for retinal detachment were directly fixed or cultured in a stem cell-promoting medium and compared to cells cultured from the post-mortem retina and CE. In situ characterization of the normal eyes revealed robust expression of markers present in NSCs (Nestin, Sox2, Pax6) only around peripheral cysts of the proximal pars plana region and the PR, the latter population also staining for the glial marker GFAP. Although there were higher numbers of dividing cells in the CE of PVR eyes than in controls, we did not detect NSC-associated markers in the CE except around the proximal pars plana cysts. In the mice PVR eyes, Nestin activation was also found in the CE. In human PVR eyes, proliferation of both non-glial and glial cells co-staining NSC-associated markers was evident around the ora serrata region. Spheres formed in 7/10 vitreous samples from patients with PVR compared to 2/15 samples from patients with no known PVR, and expressed glial – and NSC-associated markers both after direct fixation and repetitive passages. In conclusion, the adult human eye may harbor two different populations of neuroepithelial stem/progenitor cells; a non-glial population located in the proximal pars plana around peripheral cysts in addition to a population with Müller glia characteristics. Yet, we only found that the glial population was able to respond to retinal injury by targeted migration into the vitreous.

Endoscopic photocoagulation of the ciliary body after repeated failure of trans-scleral diode-laser cyclophotocoagulation

PURPOSE: To report the successful control of intraocular pressure with endoscopic cyclophotocoagulation after repeated failure of trans-scleral diode-laser cyclophotocoagulation. DESIGN: Interventional case report. METHODS: A 3 1/2-year-old child had intraocular pressure around 30 mm Hg in one eye despite full medical treatment and three procedures of trans-scleral diode laser photocoagulation. RESULTS: Endoscopic view of the ciliary body revealed many misplaced laser burns in the pars plana region. Using direct endoscopic visualization of the ciliary body, precise, confluent burns were applied to the ciliary body. Six months after the procedure, intraocular pressure has remained under 20 mm Hg. CONCLUSION: Endoscopic cyclophotocoagulation can effectively lower intraocular pressure after recurrent external diode-laser photocoagulation has failed to do so. The direct visualization during the endoscopic procedure is particularly advantageous in cases with atypical ciliary body morphology, such as in pediatric glaucoma.

Cataract extraction combined with trans-pupillary silicone oil drainage by planned posterior capsulorhexis

A cataract is frequently observed after pars plana vitrectomy with silicone oil endotamponade. Forty-three consecutive patients underwent cataract surgery combined with transpupillary removal of silicone oil. After phacoemulsification of the lens material through a sclerocorneal tunnel incision, a planned posterior capsulorhexis with a diameter of 3-4 mm was performed. By injecting saline through the capsulorhexis into the vitreous cavity, the silicone oil was rinsed out. Widening of the sclerocorneal tunnel facilitated the drainage of the silicone oil through the pupil and tunnel. After ophthalmoscopic evaluation of the fundus, a plano-convex PMMA posterior chamber lens was implanted into the capsular bag or ciliary sulcus, and the corneoscleral tunnel was closed by a 10-0 nylon suture. Depending on the underlying retinal disease the visual acuity improved in some eyes. Silicone oil bubbles left behind in the vitreous cavity were smaller than 0.5 mm in diameter. Persisting corneal decompensation or a clinically detectable cystoid macular edema related to cataract surgery did not occur. Due to the posterior capsulorhexis, secondary cataract did not develop postoperatively. Small postoperative vitreous hemorrhages resolved during the first three post-operative days. Retinal detachment recurred in 11 eyes (11/42 or 26.2%). In one eye, dislocation of the pseudophacos occurred which had to be corrected surgically. Since the pars plana region remained untouched, direct retinal lesions in the periphery of the fundus or marked vitreous hemorrhages were not encountered. Silicone oil removal can be combined with cataract surgery with transpupillary drainage of the silicone oil.

Specialized neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle.

There are many regional differences in cell morphology and neurochemistry in the retina. This study examined a specialized population of neuropeptide Y- and glucagon-like immunoreactive amacrine cells in the peripheral retina of the turtle. Some of the dendritic processes from these peptidergic amacrine cells formed a dense circumferentially oriented nerve fiber plexus which ran parallel to the ora serrata. Collaterals from this plexus projected into and innervated the nonpigmented ciliary epithelium in the pars plana region of the ciliary body. Electron microscopy revealed that the neuropeptide Y- and glucagon-like immunoreactive processes in the ciliary epithelium contained many labeled, large dense-cored vesicles. Small crystals of lipid-soluble fluorescent dye were implanted in the retina near the ora serrata in fixed retinal tissue to search for other peripheral retinal specializations. Numerous thick and thin cell processes oriented parallel to the ora serrata were labeled in the retina by the dye. In addition, many dye-labeled somata with circumferentially oriented dendritic arborizations were seen in the extreme periphery of the retina. Many of these dye-labeled cells and processes were clearly not associated with the neuropeptide Y- and glucagon-like immunoreactive cells described above. This study has shown that some peptidergic neurons in the peripheral retina have a unique morphology in comparison to more centrally located cells. The function of these specialized peripheral cells is not established, but the innervation of the ciliary epithelium by peptidergic amacrine cells suggests that they may be involved in control of aqueous inflow.

Mechanism of Intraocular Pressure Decrease after Contact Transscleral Continuous-Wave Nd:YAG Laser Cyclophotocoagulation

Twenty-two eyes of 11 cynomolgus monkeys were subjected to contact transscleral cyclophotocoagulation with a continuous-wave Nd:YAG laser. The right eye of each monkey was coagulated at the pars plicata region by the contact probe placed 1.0 mm from the limbus, while the left eye of each monkey was coagulated at the pars plana region by the contact probe placed 3.0 mm from the limbus. Physiological and morphological studies were carried out up to 6 months after the treatment. The postoperative intraocular pressure showed a significant decrease within 1 week, corresponding to the inflammation of the anterior chamber. A gradual increase of the intraocular pressure occurred from the 2nd week on and returned to the preoperative value 8 weeks after pars plicata coagulation. The pars plana coagulation group maintained the intraocular pressure lower than the preoperative value until the end of the observation period. Histopathological examinations were carried out by the use of tracer particle perfusion into the anterior chamber. The pathologic features of pars plicata coagulation were necrosis, followed by atrophy of the ciliary process. The tracer particles accumulated at the anterior portion of the space between the bundles of ciliary muscle. The pathologic features of pars plana coagulation were necrosis followed by extension of proliferative tissue into the vitreous. The surrounding extracellular space of the stroma was enlarged, and the ciliary muscles were separated from the sclera. The tracer particles accumulated at the enlarged extracellular space of the stroma and the opened suprachoroidal space. These results suggest that the decrease of the intraocular pressure after pars plicata cyclocoagulation resulted from the reduction of aqueous secretion, whereas that after pars plana cyclocoagulation resulted from enhancement of the uveoscleral outflow through the enlarged extracellular space from the anterior chamber into the suprachoroidal space.

Differential Expression of the Cellular Retinaldehyde-binding Protein in Bovine Ciliary Epithelium

Differential expression of the cellular retinaldehyde-binding protein (CRALBP), a likely component of the visual cycle, has been observed in the ocular ciliary epithelium, a bilayer of neurepithelial cells involved in the active transport of aqueous humor. Antibody probes raised to bovine ciliary epithelium were used to isolate a cDNA encoding CRALBP from a bovine ciliary epithelium cDNA expression library. Northern analysis of poly A + RNA isolated from three different regions of the neonate ciliary epithelium revealed a three-fold higher level of CRALBP expression in the most anterior portion of the pars plicata region relative to the posterior pars plana region. Western blot analysis using CRALBP-specific antibodies also demonstrated that the level of CRALBP expression was higher in the most anterior portion of the ciliary epithelium and gradually decreases toward the posterior region in both neonate and adult bovine eyes. Using indirect immunofluorescence and frozen-sectioned bovine ciliary epithelium, CRALBP was localized to the pigmented ciliary epithelial cell layer along the entire ciliary epithelium. In the nonpigmented ciliary epithelial cell layer, CRALBP was only detected in the pars plana region. Pigmented ciliary epithelial cells have also been cultured and CRALBP expression demonstrated for several continuous passages by Northern and Western analysis. These results raise questions regarding the physiological role of CRALBP in the ciliary epithelium and the involvement of the protein in defining regional and functional boundaries within this tissue.