Comparison of visual function after foveal translocation with 360 degrees retinotomy and with scleral shortening in a patient with bilateral myopic neovascular maculopathy

PURPOSE

To compare the visual outcome after foveal translocation by scleral shortening and that after 360 degrees retinotomy with extraocular muscle surgery in a patient with bilateral myopic neovascular maculopathy.

METHODS

Case report.

RESULTS

A 52-year-old woman with bilateral myopic neovascular maculopathy underwent foveal translocation with scleral shortening in the left eye, and visual acuity improved from 20/70 to 20/30. However, choroidal neovascularization recurred, and the final visual acuity was 20/40 after excision of the choroidal neovascularization. Foveal translocation with 360 degrees retinotomy was performed on the right eye, and visual acuity improved from 20/150 to 20/30. The critical print size was better, and the retinal sensitive area was larger in the right eye.

CONCLUSION

The better reading ability shown by foveal translocation by a 360 degrees retinotomy compared with scleral shortening may stem from a larger retinal sensitive area obtained by this method.

Amsler grid examination and optical coherence tomography of a macular hole caused by accidental Nd:YAG laser injury

PURPOSE

To compare a macular hole from accidental Nd:YAG laser injury with idiopathic macular holes.

METHODS

Case report. In a 24-year-old man with accidental Nd:YAG laser injury, right eye, Amsler grid testing and optical coherence tomography were performed.

RESULTS

Nd:YAG laser injury was responsible for a macular hole about 700 microm in diameter. The visual acuity was 20/100. Amsler grid testing displayed a central scotoma with no surrounding distortion. Optical coherence tomography showed a defect in all retinal layers at the macula.

CONCLUSION

The scotoma caused by Nd:YAG laser injury is not surrounded by distortion; the hole is produced by the defect of all retinal layers. In contrast, idiopathic macular holes generally produce a pincushion pattern on Amsler grid testing and have no tissue loss.

Rapid detection of M1S1 mutations by the protein truncation test

PURPOSE

To determine a method of rapid detection of M1S1 gene mutations in patients with gelatinous droplike corneal dystrophy.

METHODS

Forty-one patients from 35 families with gelatinous drop-like corneal dystrophy were studied. The entire coding region of the M1S1 gene was screened using the protein truncation test (PYT), with a polymerase chain reaction fragment amplified from genomic DNA serving as a template of in vitro translation.

RESULTS

Homozygous or compound heterozygous mutations were detected in all patients by a single reaction of the PTT. This result matched those obtained using the polymerase chain reaction-restriction fragment length polymorphism and direct sequence analyses. The Q118X mutation was present in 63 of the 70 alleles, accounting for 90% of the disease-associated chromosomes in Japanese patients.

CONCLUSIONS

The PTT is useful for detecting mutations in the M1S1 gene. This technique showed that the Q118X mutation is a founder mutation in Japanese patients with gelatinous droplike corneal dystrophy, and it reflects the linkage disequilibrium reported previously.

Gas stress test for assessment of corneal endothelial function

PURPOSE

This study was undertaken to evaluate the endothelial pump function by monitoring both corneal swelling response under hypoxia and dehydration response following hypoxia in vivo.

METHODS

Humidified nitrogen gas was used to obtain corneal swelling, and humidified gas mixed with oxygen and nitrogen was used for corneal dehydration. First, in 6 young volunteers, we investigated the most suitable oxygen level for evaluating pump function by changing oxygen levels. Then, with the optimal oxygen level, we attempted to evaluate pump function in 53 normal subjects, 5 Fuchs' dystrophy patients, and 3 iridocorneal endothelial syndrome (ICE) patients.

RESULTS

Swelling rate showed similar values regardless of age, but both dehydration rate and swelling rate plus dehydration rate decreased with aging. The swelling rate of 5 guttata corneas was significantly higher than that of age-matched control corneas. In contrast, dehydration rate markedly decreased in guttata corneas, while the swelling rate plus dehydration rate of guttata corneas was comparable to that of age-matched corneas. In the 3 ICE corneas, however, swelling rate, dehydration rate, and swelling rate plus dehydration rate were markedly lower than those of both the fellow corneas and the age-matched control corneas.

CONCLUSION

These observations lead us to conclude that in order to evaluate pump function, it is necessary to monitor not only dehydration response following hypoxia but also swelling response under hypoxia.

Retinal fascin: functional nature, subcellular distribution, and chromosomal localization

PURPOSE

To investigate the functional properties, subcellular localization, and chromosomal location of retinal fascin.

METHODS

Recombinant retinal fascin protein was prepared by using a baculovirus-insect expression system. Actin-binding and -bundling assays were performed with chick actin purified from skeletal muscle. Western blot analysis and immunohistochemistry were performed with a polyclonal antibody raised against bovine retinal fascin. A human retinal cDNA library was screened with an expressed sequence tag cDNA fragment. Chromosomal location was determined with fluorescent in situ hybridization.

RESULTS

The actin-binding and actin-bundling activities of retinal fascin were demonstrated by high- and low-speed centrifugation assays. Formation of filamentous (F)-actin bundles by retinal fascin in vitro was also morphologically confirmed by fluorescence microscopy and electron microscopy. Immunohistochemical analysis revealed that retinal fascin protein was localized specifically in the outer and inner segments of the photoreceptor cells in the retina. Two splicing variants of human retinal fascin cDNA were also located. One clone encoded 492 amino acids, and the other encoded 516 amino acids. The gene encoding retinal fascin was localized to human chromosome 17, region q24 -25.

CONCLUSIONS

These results suggest that retinal fascin may play a role in formation of unique morphologic structures of the photoreceptor cells and is a candidate gene for retinal degenerative disorders.

Multicenter retrospective study of retinal detachment associated with atopic dermatitis

PURPOSE

Epidemiological and clinical study of retinal detachment associated with atopic dermatitis.

METHODS

A multicenter retrospective study.

RESULTS

We analyzed the records of 417 eyes of 348 patients operated on during 5 years from 1989 to 1993 and followed up for more than 6 months by vitreo-retinal specialists in 33 hospitals throughout Japan. The number of eyes operated on increased yearly from 42 in 1989 to 132 in 1993. These cases associated with atopic dermatitis were 2.3% of the average number of eyes operated on for rhegmatogenous retinal detachment during the same period, but when restricted to the Kanto area or further to Tokyo only, the percentage was as high as 3.8% and 4.7%, respectively.

CONCLUSION

Clinical characteristics of retinal detachment previously reported, such as traumatic slapping or rubbing of the lids by patients as the most likely pathogenetic factor, and high incidence of cataract and proliferative vitreoretinopathy, were confirmed. The primary surgical procedure was scleral buckling in 78% of the cases and vitreous surgery in 22%, and initial and final reattachment rates were 75.3% and 92.6%, respectively.

Optical coherence tomography patterns of choroidal osteoma

PURPOSE

To determine the optical coherence tomographic images that are commonly observed in eyes with choroidal osteoma (choroidal ossification).

METHODS

Three patients with choroidal osteoma were examined by optical coherence tomography.

RESULTS

We found two optical coherence tomographic patterns in the eyes with choroidal osteoma. First, multiple tracks of high refractivity were present posterior to the tumor lesion. Second, thick and irregular plate-like, high-signal intensity areas were present in the choroid in the region of the tumor.

CONCLUSIONS

Optical coherence tomography can be useful in the diagnosis of choroidal osteoma.

Fixation patterns of idiopathic macular holes after vitreous surgery

BACKGROUND

Evaluation of idiopathic macular holes with the scanning laser ophthalmoscope (SLO) has shown fixation to be located at or near the margin of the hole and above the horizontal meridian in most cases. However, changes between preoperative and postoperative fixation have not been well studied.

METHOD

We used SLO microperimetry to determine scotomas and fixation points in 13 patients with idiopathic macular holes before and after vitreous surgery. The distance between preoperative and postoperative fixation points and the direction of movement were measured.

RESULTS

Preoperatively, fixation was found to be at or near the margin of the macular hole in all eyes and was located above the horizontal meridian in most (84.6%) eyes. Postoperatively, there was a shift in the position of the fixation points. The distance between preoperative and postoperative fixation correlated with the degree of visual improvement (P = 0.032), but the direction of movement was variable.

CONCLUSION

A shift in the position of fixation occurs after macular hole surgery, and the amount of shift correlates with visual improvement. From this observation, we define the term functional macular hole closure, characterized by centripetal movement of the neurosensory retina and improvement in vision, and the broader term anatomic macular hole closure, in which apparent hole closure may result from gliosis in the absence of movement of the neurosensory retina, not associated with visual improvement.

Prediction of letter contrast sensitivity using videokeratographic indices

PURPOSE

To analyze the relationship between corneal topography and letter contrast sensitivity.

METHOD

Experiments were conducted on 59 eyes of 51 patients who had best spectacle-corrected visual acuity of 20/20 or better and no ocular pathology except for the corneal shape. Thirty-nine eyes had an abnormal topographic pattern resulting from keratoconus, and the other 20 eyes showed a normal topographic pattern. Videokeratography was performed with the TMS-2 videokeratoscope, and the surface regularity index, surface asymmetry index, and coefficient of variation of power were obtained for each subject. Letter contrast sensitivity was measured with the CSV-1000LV with spectacle correction. The correlation between the number of correct letters and topographic indices was calculated.

RESULTS

The abnormal topography group had a significantly greater loss of letter contrast sensitivity (median = 20 letters) than the normal control (median = 23 letters; P =.0001). There were statistically significant correlations between number of correct letters and the coefficient of variation of power (r = -.77; P =. 001), number of correct letters and surface regularity index (r = -. 76, P =.001), and the number of correct letters and surface asymmetry index (r = -.64; P =.001). The linear regression equation between number of correct letters and the coefficient of variation of power was the number of correct letters = -0.05 x the coefficient of variation of power + 23.2.

CONCLUSIONS

Our results suggest that subtle visual deteriorations, which are barely detected by contrast sensitivity testing, can be predicted objectively by the corneal topographic indices.

Molecular cloning of a novel membrane glycoprotein, pal, specifically expressed in photoreceptor cells of the retina and containing leucine-rich repeat

We have isolated a novel retina-specific gene in a screen for genes of which expression is not apparent neonatally in rat retina but is abundant postnatally on day 14 (P14). This gene, named Pal, encodes a putative type I transmembrane protein containing five leucine-rich repeats (LRRs), a single C2-type Ig-like domain, and a single fibronectin type III domain and is considered to be a new member of the LRR and Ig superfamily. No expression of Pal was found in rat retina at P1, but it was detected at P7 and markedly increased with subsequent development. These expression patterns of Pal appeared to be correlated with the development of the photoreceptor outer segments, because in the adult rat retina it was specifically localized in these segments. Ultrastructually, Pal immunoreactivity was distributed diffusely on the disk membrane in the lamellar regions. On the basis of its structural features and localization pattern, Pal may act as a receptor for a certain trophic factor or for an adhesion molecule participating in morphogenesis. The human homolog of Pal was mapped to chromosome 10q23.2-23.3 using fluorescence in situ hybridization.

The spectrum of beta ig-h3 gene mutations in Japanese patients with corneal dystrophy

PURPOSE

This study was undertaken to identify beta ig-h3 gene mutations in Japanese patients with granular corneal dystrophy (GCD), Avellino corneal dystrophy (ACD), lattice corneal dystrophy (LCD), and Reis-Bücklers' corneal dystrophy (RBCD). R124H, R124C, R555W, and R555Q mutations have been reported in Europe to cause ACD, LCD type I, GCD, and RBCD, respectively.

METHODS

In total, 91 Japanese patients who had been clinically diagnosed with GCD, LCD, or RBCD were investigated to determine whether they had mutations in the beta ig-h3 gene. Genomic DNA was amplified using the polymerase chain reaction and analyzed using single-strand conformation polymorphism techniques. Mutations were identified using the direct sequencing method.

RESULTS

In 68 unrelated patients who had been diagnosed with GCD, 62 patients (91%) were found to have the R124H mutation, which has been reported to cause ACD, whereas only six patients (9%) had the R555W mutation. In LCD patients, 10 patients with type I disease had the R124C mutation, and 10 patients with type IIIA disease had a P501T mutation. One patient with atypical LCD had an L527R mutation. In two patients with RBCD, one had an R555Q mutation and the other patient with geographic opacities was found to have an R124L mutation.

CONCLUSIONS

Depending on the specific mutation in the beta ig-h3 gene, the phenotypes of corneal dystrophy may differ. Our results indicate that assay of mutations in the beta ig-h3 gene is required to establish a correct diagnosis.

Effects of penetrating keratoplasty rejection on the endothelium of the donor cornea and the recipient peripheral cornea

PURPOSE

To determine the effects of penetrating keratoplasty rejection on the recipient endothelium.

METHODS

Twenty transplanted corneas of 20 keratoconus patients were enrolled in this study. Ten of the corneas had undergone allograft rejection and the other 10 grafts had an uneventful postsurgical course. The endothelium of the donor cornea and the endothelium of the recipient peripheral cornea were evaluated by wide-field specular microscopy.

RESULTS

The transplanted corneas that underwent allograft rejection showed a marked decrease in endothelial cell density not only in central donor cornea but also in the recipient peripheral cornea compared with that in the uneventful transplanted corneas. Additionally, the recipient endothelium had significant pleomorphism in the rejection group. There were no morphologic differences in the peripheral donor cornea between the control group and the rejection group.

CONCLUSIONS

Our findings indicate that the recipient peripheral endothelium is also affected by allograft rejection, perhaps because of the contribution of recipient endothelium to the wound healing process after allograft rejection.

Comparison of topographic indices that correlate with visual acuity in videokeratography

OBJECTIVE

To evaluate the relationship between the best spectacle-corrected visual acuity (BSCVA) and two quantitative indices of the anterior corneal surface obtained by videokeratography.

DESIGN

Prospective, single center, comparative, observational study.

PARTICIPANTS

Eighty-nine normal eyes and 52 eyes with keratoconus with contact lens-corrected visual acuity of 20/20 or better.

INTERVENTION

Videokeratography was performed with the TMS-2 and the CAS system 2000.

MAIN OUTCOME MEASURES

The relationship between the BSCVA recorded in log minimal angle of resolution (logMAR) units, the surface regularity index (SRI), and the predicted corneal acuity (PCA) were assessed by linear regression analysis.

RESULTS

The BSCVAs for all eyes ranged from 0.82 to -0.30 logMAR units. BSCVA was highly correlated with the SRI (r = 0.70, P < 0.0001) and the PCA (r = -0.61, P < 0.0001). There was no statistical difference in the regression slopes and the intercepts for the estimated BSCVA using the SRI and measured BSCVA, and the estimated BSCVA using PCA and measured BSCVA.

CONCLUSIONS

Two quantitative topographic indices, SRI and PCA, are useful for estimating the effect of irregular astigmatism on visual acuity even though both indices quantify different aspects of the anterior surface of the cornea.

Intraoperative adjunctive agents in vitrectomy: serum, cytokines, and glue

The surgical goal in the treatment of retinal breaks is to seal the edges of the break, and traditionally, photocoagulation and cryocoagulation have been used to accomplish this. However, it is sometimes difficult in complicated retinal detachments to maintain the seal against tractional forces. Adhesion is achieved through a process of cell necrosis, inflammation and subsequent fibrovascular proliferation. This strategy, however, may not be appropriate in vision-sensitive areas such as macular holes. To improve the success rate of macular hole surgery, a number of authors have advocated the use of biological modifiers, such as transforming growth factor beta, human autologous serum, tissue glue, or platelet concentrates. These materials may enhance the adhesion of the detached retina and therefore lead to a better anatomical and functional success. We have reviewed the advances of intraoperative application of synthetic or biological adhesives. However, through the improvement of surgical techniques and surgeons' skills in recent years, the anatomical success rate of macular hole surgery has increased in most institutions without adjunctive additives. Thus, many surgeons believe that adjunctive additives may not be necessary for most idiopathic macular holes.

The effects of binocular suture and dark rearing on the induction of c-fos protein in the rat visual cortex during and after the critical period

It has been demonstrated in kittens that binocular lid suture has more deleterious and irreversible effects on plasticity of the developing visual system than rearing in complete darkness. The present study using immunocytochemistry focuses on the effects of the two types of visual deprivation on the inducibility of c-fos protein in visual cortical neurons of rats. Rats were subjected to binocular suture or dark rearing for 1 week during (postnatal days 14-21; P14-P21) and after (P50-P57) the critical period for activity-dependent modifiability of cortical ocular dominance. In rats of both age groups reared in the normal light-dark condition, only a small number of Fos-immunoreactive neurons was obtained in the visual cortex. By contrast, in dark-reared pups and adult rats, numerous c-fos neurons were detected in the layers II-IV and VI of the visual cortex following a brief light exposure (1 h). In rats of both ages subjected to binocular suture, Fos neurons were detected in the same layers as in the dark-reared rats, but significantly less in number. We speculate that the reduced plasticity of the visual cortex in the rats subjected to binocular suture may be due partly to the repressed AP-1 activity in visual cortical neurons. No significant difference was detected in c-fos expression in the visual cortex between visually manipulated pups and adult rats.

Substance P-induced cadherin expression and its signal transduction in a cloned human corneal epithelial cell line

Although the absence of Substance P (SP), a neurotransmitter in the trigeminal nerve, has been speculated as a cause for developing neurotrophic keratitis, its exact pathogenesis is still not clarified. In a previous report, we showed with electron microscopic examination that epithelial cell attachment was weakened in denervated corneas. In this study, SV40-transformed human corneal epithelial cells (HCE-Ts) were used to explore the molecular mechanisms responsible for mediating regulation of E-cadherin expression in response to Substance P receptor stimulation. Expression of the mRNAs for specific SP receptors, neurokinin (NK)-1R, NK-2R, and NK-3R, was demonstrated with RT-PCR. The cells were treated with various concentrations of SP in vitro, and the expression of an adhesion molecule E-cadherin was analyzed by immunofluorescence, immunoblotting, and enzyme-linked immunosorbent assay (ELISA) using an anti-E-cadherin antibody. E-cadherin expression was increased by SP in a dose-dependent manner both in the cytosolic fraction and in the cell membrane fraction. This increase in E-cadherin expression was completely inhibited by Calphostin C (PKC inhibitor) and KN-62 (CaMK inhibitor), but not by H-89 (PKA inhibitor), indicating that SP-induced E-cadherin expression involves the activation of protein kinase C (PKC) and calmodulin kinase (CaMK). SP did not affect cell proliferation at all. All these findings indicate that SP induced E-cadherin expression through PKC and CaMK activation and suggest that a lack of SP may account in part for the pathogenesis of neurotrophic keratitis.

X-linked retinoschisis with point mutations in the XLRS1 gene

BACKGROUND

X-linked retinoschisis (XLRS) is a relatively rare vitreoretinal dystrophy that causes visual loss in young men. Recently, a gene responsible for this disease, designated XLRS1, was identified, and several deleterious gene mutations were reported.

OBJECTIVE

To analyze Japanese patients clinically diagnosed as having XLRS formutational changes in the XLRS1 gene.

METHODS

Ten patients with XLRS underwent full ophthalmologic examination, including slitlamp biomicroscopy and dilated funduscopy. Genomic DNA was isolated from leukocytes, and all exons of the XLRS1 gene were amplified by polymerase chain reaction and analyzed using a direct sequencing method.

RESULTS

Point mutations in the XLRS1 gene were identified in all 10 patients. The mutations were identical in each of 2 pairs of brothers. Six of the point mutations represented missense mutations, 1 was a nonsense mutation, and 1 was a frameshift mutation. Five of the mutations are newly reported herein.

CONCLUSIONS

The discovery of new point mutations in this study increases the available information regarding the spectrum of genetic abnormalities and clinical manifestations of XLRS. However, the limited data failed to reveal a correlation between mutation and disease phenotype.

CLINICAL RELEVANCE

Identification of mutations in the XLRS1 gene and expanded information on clinical manifestations will facilitate early diagnosis, appropriate early therapy, and genetic counseling regarding the prognosis of XLRS.

Corneal changes in spondyloepiphyseal dysplasia tarda

BACKGROUND

A new type of corneal opacity with prominent corneal nerve fibers as an ocular complication of spondyloepiphyseal dysplasia tarda (SEDT).

CASE

A 58-year-old woman, diagnosed with SEDT at 5 years of age, underwent a complete ophthalmological examination.

OBSERVATIONS

The patient had no complaints and no history of eye disease. No relatives were reported to have suffered from SEDT. Slit-lamp examination disclosed a diffuse opacity in the central cornea in both eyes, which was localized in the middle to deep stroma. Dot opacities in the central and paracentral cornea were located in the middle of the stroma in both eyes. Optically clear regions were observed in the peripheral cornea of both eyes. More interestingly, corneal nerve fibers were visible passing from the limbus to the central cornea in both eyes.

RESULTS

The etiology of the corneal opacities of this patient with SEDT is unknown. However, collagen and proteoglycan abnormalities in the skin of patients with SEDT have been reported. Therefore, such abnormalities may also be present in the cornea and these alterations may lead to corneal complications.

Corneal guttata associated with the corneal dystrophy resulting from a betaig-h3 R124H mutation

AIMS

To investigate the frequency of corneal guttata in patients with a corneal dystrophy resulting from an Arg124His (R124H) mutation of betaig-h3 gene.

METHODS

Slit lamp examination was performed on 30 eyes with corneal dystrophy from a genetically confirmed betaig-h3 R124H mutation and on 50 age matched control eyes. The stage of the corneal dystrophy was classified as stage 0, I, or II and the degree of guttata was classified as none, mild, or severe. Specular microscopic examinations were performed to evaluate the morphology of the corneal endothelium.

RESULTS

Slit lamp examination disclosed the presence of corneal guttata in 21 eyes (70%) of the 30 eyes with the corneal dystrophy, but in only one (2%) of the 50 eyes in the age matched control group (p<0.001, chi(2) with Yates's correction). Of the 12 eyes with stage I betaig-h3 R124H corneal dystrophy, seven had no corneal guttata and five had a mild degree of guttata. Of the 18 eyes with stage II, the degree of guttata was none in two, mild in nine, and severe in seven. The degree of corneal guttata was significantly related to the stage of the corneal dystrophy (p<0.0001, Kruskul-Wallis test ANOVA on ranks). There was no significant differences between eyes with betaig-h3 R124H corneal dystrophy and normal eyes in cell density, coefficient of variation, and cell hexagonality of corneal endothelium.

CONCLUSION

Corneal guttata are one of the characteristics of the corneal dystrophy resulting from betaig-h3 R124H mutation.

The visual performance and metamorphopsia of patients with macular holes

BACKGROUND

Most patients attain better visual acuity with the elimination of metamorphopsia after successful closure of a macular hole (MH) by vitrectomy.

OBJECTIVE

To determine the presurgical visual function of eyes with an MH.

METHODS

We examined 54 eyes of 51 patients with an idiopathic MH using the Amsler chart. We evaluated the types of subjective metamorphopsia and compared them with the clinical factors associated with MHs. In a prospective study, we performed a montage test on a separate group of 16 patients with unilateral idiopathic MHs. The patients were asked to choose, while viewing with their better eye, the computer-modified picture that best matched the unmodified image seen by the eye with the MH.

RESULTS

From the results of the Amsler chart test, we divided the subjective changes into 2 types of metamorphopsia; of the 54 eyes, pincushion distortion (bowed toward the center) was found in 33 (61%), and unpatterned distortion (no specific pattern) was found in 21 (39%). Pincushion distortion was significantly associated with an MH of shorter duration (< or =6 months) (P = .03) and an early stage (stage 2) of MH formation (P = .02). A scotoma was hard to detect, and patients had difficulty describing their scotomata and distortions. In the montage test, patients with early MHs chose portraits modified with a pincushion type of distortion.

CONCLUSIONS

We found concentric pincushion metamorphopsia without subjective scotomata, which we suggest arises from an eccentric displacement of the photoreceptors. This accounts for the main characteristic of the visual performance of patients with idiopathic MHs.

Analysis of vitrectomy for idiopathic macular hole by optical coherence tomography

PURPOSE

To evaluate foveal structure after vitrectomy for idiopathic macular hole in relation to postoperative visual outcome.

METHODS

Optical coherence tomography was performed postoperatively to assess retinal thickness at the foveal center in patients who underwent vitrectomy, posterior hyaloid membrane removal, and perfluoropropane gas tamponade for idiopathic macular hole. Thirty-seven eyes of 36 patients documented to have achieved anatomic hole closure by optical coherence tomography were included in the study.

RESULTS

Increased visual acuity significantly correlated with greater foveal thickness assessed at a median of 5 months postoperatively (Spearman analysis; R = .453, P = .005).

CONCLUSION

Visual outcome after anatomic closure of macular holes by vitrectomy is closely related to the structure of the center of the fovea postoperatively.

Expression and polarized distribution of an inwardly rectifying K+ channel, Kir4.1, in rat retinal pigment epithelium

1. In the eye, different substances and ions including potassium (K+) are transported between neural retina and choroid via the subretinal space. Inwardly rectifying K+ channels (Kir) on the apical membrane of retinal pigment epithelial (RPE) cells are thought to play an essential role in K+ transport in the subretinal space. 2. Single-channel recordings from the apical membrane of RPE cells exhibited functional expression of a Kir channel with properties identical to those of Kir4.1, while recordings from the basolateral membrane showed no detectable Kir channel currents. 3. The expression of Kir4.1 mRNA in RPE cells was confirmed by RT-PCR analysis and in situ hybridization. Furthermore, using immunohistochemistry, we found that Kir4.1 was prominently expressed in RPE cells and localized specifically on the processes on their apical membrane. 4. Developmental studies revealed that expression of Kir4.1 started to appear 10 days or later after birth in RPE cells, in parallel with the maturation of retinal neuronal activity as represented by the a- and b-waves of the electroretinogram. 5. These data suggest that Kir4.1 is one of the Kir channels involved in RPE-mediated control of K+ ions in the subretinal space.