Ping-Kang Hou

Epidemiologic Study of Ocular Refraction among Schoolchildren in Taiwan in 1995

PURPOSE In order to understand and update the prevalence of myopia in Taiwan, a nationwide survey was performed in 1995. METHODS We stratified the cluster sampling by developmental grading of the city, using a size proportional to the population. Two cities were randomly selected from each city grading. The total number of students enrolled was 11,178, including 5,676 boys and 5,502 girls. The refractive status and corneal radius of each student were measured with an autorefractometer under cycloplegia and checked with retinoscopy. Axial length was measured with biometric ultrasound. RESULTS The myopic rate was from 12% at the age of 6, it increased to 56% at the age of 12, and then to 76% at the age of 15. A myopic rate of 84% was found for the age range of 16 to 18. The prevalence of high myopia (over -6.0 D) at the age of 18 was 20% in girls and 12% in boys. The mean refractive status became myopic at the age of 9, then increased to -3.92 D in girls and -2.71 D in boys at the age of 18. The increase of axial length is correspondent with the progression of myopia. The anterior chamber depth (ACD) was deeper with age and the severity of myopia, whereas the corneal curvature remained unchanged. The lens thickness became thinner from age 7 to 13, then it became thicker with age and the severity of myopia after age 15. The prevalence and degree of myopia in girls was more severe than in boys. CONCLUSIONS The prevalence of myopia in Taiwan increased year by year. The increase in severity and prevalence of high myopia may be due to earlier onset.

Changes in ocular refraction and its components among medical students : A 5-year longitudinal study

Purpose. Myopic progression has been noted, especially during the period of puberty. It is interesting to investigate whether myopia will progress after the age of puberty and at what rate the changes in ocular components occur during its progression. Methods. A 5-year longitudinal study was made of refraction and its components among 345 National Taiwan University medical students (690 eyes). The examinations included corneal curvature and cycloplegic refraction measured by auto-refractor and retinoscopy, and axial length measurement with A scan ultrasonography. The same procedures and instruments were used again after 5 years. Results. The myopic prevalence increased from 92.8 to 95.8%; 21 new cases of myopia developed in the 5 years. The mean refractive error significantly increased from —4.26 ± 2.66 D of freshmen to -4.94 ± 2.70 D of clerks. The change in refractive error at the 5-year follow-up was 0.70 ± 0.65 D more myopic for males and 0.54 ± 0.64 D for females. The main change in the ocular components was in axial length, which increased from 25.54 to 26.05 mm in males and from 24.60 to 24.95 mm in females. Other optical components—including corneal curvature, anterior chamber depth, lens thickness— all remained relatively unchanged from the initial values. Conclusions. Myopia can progress after the age of puberty, but at a slower rate than during childhood. Axial elongation of the eyeball is the main component that changes in myopic progression.

Study of myopia among aboriginal school children in Taiwan

In various studies there were racial differences as to the refractional status between the white and the black or the natives (Taylor 198 1). Chandran (1972) thus compared the refractive errors of the Malayan, the Chinese and the Indian (or the Indonesian) in West Malaysia. The natives in Solomon Islands were found to have as low a rate as only 1 % of myopia (Verlee 1968). Most people in Taiwan descend from those who came to this island from mainland China some 300 years ago. According to the biostatistics, about one sixtieth of our population are the aboriginals, or the so-called high-mountain people. There are 9 tribes of them. It is believed that the aborigines in Taiwan belong to the Polynesians, which came from the South Pacific islands. In previous studies of the highmountain people Japanese authors reported that the myopic rates were exceptionally low (Motegi et al. 1945; Yamaji et al. 198 1). In order to know how the myopia would affect a different racial group living in the same Formosa, the authors made a refraction survey of 18 junior high schools around the whole island. All the children in the schools were examined, using retinoscopy performed under cycloplegia.

Corneal epithelial recovery following photorefractive keratectomy.

AIMS: To further understand the morphological and functional recovery of corneal epithelium following excimer laser photorefractive keratectomy (PRK). METHODS: The right eyes (group 1) of 15 male, New Zealand white rabbits weighing 2-3 kg underwent PRK. The left eye of each rabbit (group 2) underwent simple mechanical de-epithelialisation and were examined as treated controls. Both eyes of another eight rabbits (group 3) served as untreated controls. All eyes underwent a corneal epithelial permeability study by fluorophotometry at 2, 4, and 8 weeks after surgery. Five animals in groups 1 and 2 were sacrificed at 9, 10, and 12 weeks after surgery. The animals in group 3 were sacrificed at the end of the 12 week experimental period. Both eyes of each sacrificed animal were enucleated immediately and processed for both haematoxylin and eosin stain and electron microscopic study. The electron micrograph was magnified to 14,000x and the extent of hemidesmosome formation was quantified and analysed. RESULTS: The corneal epithelial barrier to sodium fluorescein was subnormal and returned to a normal barrier state 4 weeks after PRK in group 1 whereas it was normal in group 2 throughout the examination period. The extent of hemidesmosome formation was abundant yet subnormal in both groups 1 and 2 up to 12 weeks, when compared with that in group 3. CONCLUSION: The corneal epithelium regained its functional barrier 4 weeks after PRK in rabbits while the extent of hemidesmosome formation was still subnormal 12 weeks after mechanical de-epithelialisation, with or without PRK.

Reticular Dystrophy of the Retinal Pigment Epithelium

A laser flare-cell meter was used to examine blood-aqueous barrier function in a 57-year-old male patient who had typical reticular dystrophy of the retinal pigment epithelium with a bilateral hyperpigmented reticular pattern at the posterior pole in both eyes. Fluorescein angiography showed hypofluorescent reticular net resembling a fishing net with knots associated with a central diffuse hyperfluorescence. Dark adaptation test revealed that the final rod threshold was elevated. Laser photometry showed an increase in the aqueous flare intensity in both eyes, as compared to the results in normal subjects. Quantitative measurement of the aqueous flare intensity by a laser flare-cell meter might indicate abnormalities in the blood-aqueous barrier in patients with reticular dystrophy of the retinal pigment epithelium.

Experimental myopia in chickens induced by corneal astigmatism

Abstract Astigmatism has been suggested to be an important factor in the production and/or progression of myopia. Chickens have been used as a myopic animal model for several years. In the present investigation our aim was to evaluate the importance of surgically induced corneal astigmatism by peripheral corneal incision with compression suture in one eye, the right, of 3‐day‐old chicks. Vertical incision (2 mm) with compression suture (nylon 9‐0, one stitch) induces against‐the‐rule astigmatism, horizontal incision with compression induces with‐the‐rule astigmatism. Four groups were studied 1) with one vertical cut, 2) one horizontal cut, 3) two vertical cuts, 4) two horizontal cuts. The eyes were measured by caliper after 8 weeks. Eye enlargements were induced in all groups, however, less by one cut (astigmatism around 5 diopters) than by two cuts (astigmatism 10 diopters, or more). In the latter groups the pattern of equatorial eye enlargement dependend on the axis of the induced astigmatism, the greater elongation being associated with the strongest refracting corneal meridian. All considered, the results suggest that significant corneal astigmatism could be another factor in the production of myopia, possibly acting by way of optical degradation of retinal image quality.

Blood-aqueous Barrier Function in a Patient with Choroideremia

The purpose was to determine whether there was a breakdown of the blood-aqueous barrier in a patient with choroideremia. A 27-year-old man with typical choroideremia underwent standardized ophthalmo-logical evaluation, including quantitative measurement of aqueous flare intensity, by a laser flare-cell meter. The results showed areas of atrophy of the choriocapillaries and retinal pigment epithelium in the mid-periphery and posterior pole, although not in the macula. Fluorescein angiography showed areas of loss of the choriocapillaries and retinal pigment epithelium. The fovea was spared with a surrounding zone of hy-perfluorescence. Electroretinography showed a subnormal photopic amplitude and extinguished scotopic response. Electrooculography revealed that the light peak/dark trough ratio was reduced. Goldmann perimetry showed constricted peripheral fields. Laser photometry showed an increase in the aqueous flare intensity in both eyes, as compared with normal subjects. We conclude that the function of the blood-aqueous barrier might be affected in patients with choroideremia.

Role of Vascular Endothelial Growth Factor in the Breakdown of the Blood-Aqueous Barrier After Retinal Laser Photocoagulation in Pigmented Rabbits

PURPOSE Retinal laser photocoagulation is used to treat a variety of retinal diseases. Breakdown of the blood-aqueous barrier has been noted after retinal laser photocoagulation. The effect of vascular endothelial growth factor (VEGF) on the function of the blood-aqueous barrier after retinal laser photocoagulation remains undetermined. The current study was designed to evaluate the relationship between intraocular levels of VEGF and breakdown of the blood-aqueous barrier after retinal laser photocoagulation in rabbits. METHODS Pigmented rabbits were treated with retinal laser photocoagulation in one eye; the other served as control. Laser flare photometry was carried out on post-treatment days 1, 3, 7, and 14. Animals were sacrificed at the time period just mentioned postlaser, the eyes were removed, and samples of vitreous and aqueous humor were collected. Intraocular VEGF levels were measured by using an immunoassay. An intravitreal injection of VEGF was administered, and the aqueous flare intensity and VEGF levels in the aqueous and vitreous humor were measured at the time periods just mentioned. RESULTS A significant increase in the aqueous flare intensity after retinal laser photocoagulation was noticed on postoperative day 1, with the values returning to baseline levels on day 14. The VEGF levels in the vitreous of the lasered eyes were significantly increased on day 1 compared with the nonlasered control eyes. The VEGF levels in the aqueous humor of the lasered eyes were also significantly increased on day 1 compared with the control eyes. An intravitreal injection of VEGF induced a significant increase in the aqueous flare intensity and VEGF levels in the aqueous and vitreous humor. CONCLUSIONS The current results suggested that retinal laser photocoagulation can produce a breakdown of the blood-aqueous barrier. VEGF may play a role in the blood-aqueous barrier dysfunction after retinal laser photocoagulation.

Retinal Detachment in a Patient with Microphthalmos and Choroidal Coloboma

We report a rare case of retinal detachment with microphthalmos and choroidal coloboma. A 28-year-old man who had suffered from poor vision since early childhood was examined because of progressive deterioration of vision in his right eye. Examination of the anterior segment showed microphthalmos with microcornea and coloboma of the iris. Fundus examination revealed an inferior choroidal coloboma extending to the optic disc. The patient also had total bullous retinal detachment. Pars plana vitrectomy with silicone oil tamponade was performed, and the retina was reattached. Although rare, retinal detachment may develop in patients with microphthalmos and choroidal coloboma. Pars plana vitrectomy with additional scleral encircling buckle may be performed to treat this condition.

Blood-aqueous barrier function in a patient with combined hamartomas of the retina and retinal pigment epithelium.

Clinical data showing breakdown in the blood-aqueous barrier in patients with combined hamartomas of the retina and retinal pigment epithelium are very limited. We used a laser flare-cell meter to examine blood-aqueous barrier function in a 35-year-old male patient who had typical combined hamartomas of the retina and retinal pigment epithelium characterized by an ill-defined, slightly elevated, grey-white epipapillary lesion with overlying glial proliferation and surrounding vascular tortuosity. Fluorescein angiography showed early hypofluorescence corresponding to the pigmented area with speckled hyperfluorescence in the lesion. Prominent retinal vascular tortuosity and late dye leakage were noted in the late phase. Visual evoked potential demonstrated poor waveform. Laser photometry showed an increase in the aqueous flare intensity in the affected eye, as compared to the results in the unaffected eye and to data from normal subjects. The increase in the aqueous flare intensity in this patient suggests that the function of the blood-aqueous barrier may be affected in combined hamartomas of the retina and retinal pigment epithelium.