Richard A. Stone

The localization of nitric oxide synthase in the rat eye and related cranial ganglia

Nitric oxide synthase is the biosynthetic enzyme for the free radical neurotransmitter nitric oxide. Using an affinity-purified antiserum, nitric oxide synthase was found to be localized to peripheral ocular nerve fibers, related cranial ganglia, and the retina of the rat. In the eye, nitric oxide synthase-like immunoreactive peripheral nerve fibers were visualized mainly in the choroid and about limbal blood vessels. The anterior uvea was quite sparsely innervated, and the cornea was negative. Many principal neurons in the pterygopalatine ganglion were immunoreactive for nitric oxide synthase while very few cells stained in the superior cervical and trigeminal ganglia. Virtually all nitric oxide synthase-like immunoreactive pterygopalatine cells were also immunostained for vasoactive intestinal polypeptide; nitric oxide synthase also partially co-localized with neuropeptide Y in some of the neurons of this ganglion. Pterygopalatine ganglionectomy significantly reduced the number of peripheral nitric oxide synthase-like immunoreactive nerve fibers in the eye. A variety of immunoreactive retinal cells were seen. Most cells in the inner nuclear layer or ganglion cell layer corresponded morphologically to amacrine cells and displaced amacrine cells. Interplexiform cells and occasional faintly stained cells in the outer portion of the inner nuclear layer also were visualized. Nicotinamide adenine dinucleotide phosphate diaphorase histochemistry generally stained cells of similar distribution but did reveal somewhat more extensive localizations in peripheral ocular tissues, the ciliary ganglion, and the retina, compared with nitric oxide synthase immunohistochemistry. Nitric oxide synthase thus localizes to peripheral ocular nerve fibers, chiefly parasympathetic in nature and derived from the pterygopalatine ganglion, and to several cell types in the retina. Nitric oxide probably acts as a choroidal vasodilator of parasympathetic origin in the eye; the neuropeptide co-localizations in the pterygopalatine ganglion suggest complex neuromodulatory interactions. The retinal localizations imply potential neurotransmitter functions for nitric oxide in this tissue.

Retinal Autoregulation in Open-angle Glaucoma

The macular blood flow response to an induced change in intraocular pressure (autoregulation) was studied using the blue field entopic phenomenon in 11 open angle glaucoma patients, eight glaucoma suspects and 13 normal volunteers. A suction cup was used to raise the intraocular pressure (IOP) above its resting state (IOPrest). IOPmax, the highest acutely increased IOP for which blood flow can be maintained constant by autoregulation, was 24.9 +/- 1.5 mmHg (+/- 1 SD) in the glaucoma patients, 30.8 +/- 4.6 mmHg in the glaucoma suspects and 29.9 +/- 3.6 mmHg in the normal subjects. The values for IOPmax - IOPrest were 3.7 +/- 4.3 mmHg, 4.7 +/- 3.3 mmHg, and 14.3 +/- 3.1 mmHg, respectively. After the release of the suction cup, a hyperemic response was observed by 16 of 17 normal eyes, 10 of 14 glaucoma suspect eyes and only 9 of 19 glaucomatous eyes. These results suggest an abnormal autoregulation of macular retinal blood flow in open-angle glaucoma.

In Vivo Human Choroidal Thickness Measurements: Evidence for Diurnal Fluctuations

PURPOSE The authors applied partial coherence interferometry (PCI) to estimate the thickness of the human choroid in vivo and to learn whether it fluctuates during the day. METHODS By applying signal processing techniques to existing PCI tracings of human ocular axial length measurements, a signal modeling algorithm was developed and validated to determine the position and variability of a postretinal peak that, by analogy to animal studies, likely corresponds to the choroidal/scleral interface. The algorithm then was applied to diurnal axial eye length datasets. RESULTS The postretinal peak was identified in 28% of subjects in the development and validation datasets, with mean subfoveal choroidal thicknesses of 307 and 293 microm, respectively. Twenty-eight of 40 diurnal PCI datasets had at least two time points with identifiable postretinal peaks, yielding a mean choroidal thickness of 426 microm and a mean high-low difference in choroidal thickness of 59.5 +/- 24.2 microm (range, 25.9-103 microm). The diurnal choroidal thickness fluctuation was larger than twice the SE of measurement (24.5 microm) in 16 of these 28 datasets. Axial length and choroidal thickness tended to fluctuate in antiphase. CONCLUSIONS Signal processing techniques provide choroidal thickness estimates in many, but not all, PCI datasets of axial eye measurements. Based on eyes with identifiable postretinal peaks at more than one time in a day, choroidal thickness varied over the day. Because of the established role of the choroid in retinal function and its possible role in regulating eye growth, further development and refinement of clinical methods to measure its thickness are warranted.

Prevalence of Myopia between 3 Months and 5 '/-- Years in Preterm Infants with and without Retinopathy of Prematurity

Purpose: The purpose of the study was to examine spherical equivalent refractive errors, especially myopia, at six ages between 3 months and 5’/, years post-term in preterm children with birth weights of less than 1251 g. Design: A cohort study. Participants: There were a total of 827 participants in the multicenter study of cryotherapy for retinopathy of prematurity (ROP). Approximately one third of the eyes did not develop ROP, whereas two thirds developed mildto-severe ROP. None of the eyes underwent ctyotherapy. Intervention: Refractive error was measured at 3 months, 1 year, and 5’/2 years after term due date at the five long-term follow-up centers. In most eyes, refractive error also was measured at 2, 3’/*, and 4’/* years. Main Outcome Measure: Myopia was defined as 0.25 diopter (D) or greater with high myopia as 5 D or greater. Results: The proportion of eyes with myopia in this preterm population was increased compared to published data on full-term children and was related to severity of both acute-phase and cicatricial-phase ROP. The percentage of eyes with myopia varied little across ages, ranging from 21.2% at 1 year to 15.7% at 4’1’~ years. The percentage of eyes with high myopia doubled from 1.8% to 3.9% between 3 months and 1 year and remained stable thereafter. The distribution of refractive errors in eyes with mild acute-phase ROP was similar to that of eyes with no ROP. In contrast, eyes with moderate or severe acute-phase ROP showed an increased prevalence of high myopia. The distribution of refractive errors changed between 3 months and 1 year with little change after 1 year. This pattern of refractive development differs from that of full-term infants. Birth weight, severity of ROP, and degree of myopia at 3 months predicted the presence of myopia and high myopia at 5’1, years of age. Conclusions: The distribution of refractive errors in preterm infants from age 3 months to 51/2 years varies with severity of acute-phase ROP and cicatricial disease. Changes in refractive error distribution occur primarily between 3 months and 1 year and involve a decrease in the proportion of eyes with hyperopia and an increase in the proportion with high degrees of myopia. Ophfhalmology 7998; 705:7292- 7300

Regulatory peptides in the eye

The eye is made up of three coats: a tough outer collagenous coat of cornea or sclera; an intermediate vascular coat, the uvea; and an inner epithelial coat, highly differentiated by region. The transparent and convex cornea not only contributes to the form of the eye but also serves as a powerful lens. A multicomponent tear film secreted by the lacrimal gland and by small glands in the eyelids wets and lubricates the corneal surface. A rich vascular system supplies the junction of cornea and sclera, the limbus, and provides nutrition to the cornea. Just deep to the corneo-scleral limbus are the filtration tissues responsible for the drainage of aqueous humor from the anterior chamber of the eye into the limbal blood vessels. The secretion of aqueous humor generates intraocular pressure and maintains the shape of the eye. The densely pigmented middle or uveal coat contains many specialized structures. Anteriorly within the iris are the sphincter and dilator muscles to regulate pupillary diameter. Just behind the iris, the ciliary body contains the ciliary muscles and the ciliary processes. Acting through zonules connected to the equatorial region of the lens, the ciliary muscle controls accommodation. The innermost part of the ciliary body is thrown up into heavily vascularized, epithelial-lined radial projections termed ciliary processes; these secrete the aqueous humor. In combination, the secretion of aqueous humor by the ciliary processes and the resistance to its drainage in the chamber angle regulate the internal pressure of the eye. The aqueous humor also provides nutrition to the lens and cornea. Posteriorly, the uvea is called the choroid. A heavily vascularized tissue, it provides blood flow so vastly in excess of the nutritional requirement of the retina that it not only guarantees a wide margin of safety but also controls the retinal temperature within strict limits. The third or epithelial layer of the eye has remarkable regional differences. Its two epithelial layers result from the invagination of the optic vesicle during embryogenesis. At the front of the eye, one layer differentiates into the iris dilator muscle cells; the other is heavily pigmented and lines the back surface of the iris. As the two cell layers continue back onto the ciliary body, they are responsible for secretion of aqueous humor. Thereafter, the outer cell layer continues as the retinal pigmented epithelium while the inner differentiates into the neurosensory retina. The retinal pigmented epithelium separates the choroidal circulation and the neurosensory retina. It provides nutrition to the outer retinal layers, mediates photoreceptor renewal and constitutes an essential part of the blood-retinal barrier. The mature retina contains three layers of neurons, the outermost having photosensitive outer segments. Signalling is influenced greatly by laterally integrated neurons in the middle layer, termed horizontal and amacrine cells. In keeping with the optical needs of the eye, all pigment cells, the pigmented epithelia as well as the melanocytes within the uveal coat, absorb light to reduce the random reflection and thus prevent glare. II. Sources of peripheral innervation to the eye

Myopia and ambient lighting at night

Myopia, or short-sightedness, occurs when the image of distant objects, focused by the cornea and lens, falls in front of the retina. It commonly arises from excessive postnatal eye growth, particularly in the vitreous cavity. Its prevalence is increasing and now reaches 70-90% in some Asian populations,. As well as requiring optical correction, myopia is a leading risk factor for acquired blindness in adults because it predisposes individuals to retinal detachment, retinal degeneration and glaucoma. It typically develops in the early school years but can manifest into early adulthood. Its aetiology is poorly understood but may involve genetic and environmental factors,, such as viewing close objects, although how this stimulates eye growth is not known. We have looked at the effects of light exposure on vision, and find a strong association between myopia and night-time ambient light exposure during sleep in children before they reach two years of age.

A1‐, A2A‐ and A3‐subtype adenosine receptors modulate intraocular pressure in the mouse

Despite the potential importance of the mouse in studying the pharmacology of aqueous dynamics, measurement of intraocular pressure (IOP) in its very small eye has been problematic. Utilizing a novel servo‐null electrophysiologic approach recently applied to the mouse, we have identified a diversity of adenosine‐receptor mechanisms in modulating IOP in this species. We report the first evidence that A3 receptors increase IOP in any species, and verify in the mouse reports with larger mammals that A1 receptors lower and A2A receptors increase IOP.

Academic achievement, close up work parameters, and myopia in Singapore military conscripts

AIM To determine the relation of refractive error to environmental factors, including close up work, in Singapore military conscripts. METHODS A cross sectional study was conducted on 429 Singapore military conscripts. Non-cycloplegic refraction and A-scan biometry were performed in both eyes. A detailed questionnaire was administered by in-person interview to obtain information about current and past near work activity, extra tuition lessons, educational experiences, and family demographics. RESULTS Myopia associated with the conscript having been educated in the (gifted, special, or express) educational streams (adjusted odds ratio (OR) = 3.8, 95% confidence interval CI 2.0–7.3), and having completed pre-university education (OR=4.1, 95% CI 1.9–8.8). The reported close up work activity at age 7 years did correlate with age of onset of myopia (p<0.001). In parallel, supplemental tuition lessons in primary school has (OR=2.6, 95% CI 1.4–4.9) associated with conscript myopia. Parental myopia was positively associated with myopia (p<0.001), but this relation disappeared when adjusted for environmental factors. Current (p=0.83) and past close up work activity at age 7 years (p=0.13) did not correlate with myopia. CONCLUSION Educational level and educational stream positively related to myopia. A relation was observed with reported close up work activity in early childhood and with tuition classes during elementary school, but not with current close up work activity. These results underscore the strong influence of environment in myopia pathogenesis but a role for close up work activity remains indeterminate.

Renal vasculature in essential hypertension: racial differences.

In an attempt to explain the greater morbidity from essential hypertension in the black as compared with the white race, we evaluated the intrarenal vasculature of 27 patients with hypertension (19 white and 8 black). All patients had mild-to-moderate hypertension (mean arterial pressure, 110 to 125 mm Hg), normal renal function, and minimal target-organ damage. All patients had selective renal angiograms, which were evaluated for arterial nephrosclerosis. Additionally, renal blood flow was estimated by the clearance of para-aminohippurate. Patient age, blood pressure, and plasma renin activity did not differ between the two races. Black hypertensives had significantly (P less 0.01) more severe nephrosclerosis than the white patients. Renal blood flow was lower (P less than 0.05) in black patients (390 +/- 35 ml/min - m2 body surface area) than white patients (473 +/- 19 ml/min - m2 body surface area). These findings may help to explain racial differences in morbidity and mortality from essential hypertension.

Darkness and near work: Myopia and its progression in third-year law students

PURPOSE To evaluate myopia prevalence, myopia progression, and various potential myopia risk factors in third-year law students. DESIGN Cross-sectional study and survey. PARTICIPANTS One hundred seventy-nine third-year law students at the University of Pennsylvania. METHODS We administered a questionnaire to assess the prevalence of myopia, myopia progression, and risk factors, including near work, family history, and daily light/dark exposure. We conducted a screening eye examination to ascertain myopia status. Myopia was defined as the mean spherical equivalent of the two eyes of </=-0.5 diopters; myopia progression was defined by the self-reported need for a stronger eyeglass prescription during law school. MAIN OUTCOME MEASURES (1) prevalence of myopia, (2) progression of myopia. RESULTS Seventy-nine percent of the class participated (n = 179, two were excluded for amblyopia leaving 177 students). Fifty-eight percent were male, 75% were Caucasian, and the mean age was 27 years. Seventy-nine percent reported parental myopia. The mean amount of near work was 7.4 hours/day; mean sleep was 7.9 hours/day; mean darkness was 5.3 hours/day. Sixty-six percent of the students were myopic. Of 96 participants myopic before law school, myopia increased in 83 (86%) during law school. Among 75 students not myopic at the beginning of law school, 14 (19%) became myopic. The onset of myopia could not be determined for 6 patients. There were trends for higher myopia prevalence among those with a parental myopia history (P = 0.14) and for increased myopia progression among those reporting more daily near work (P = 0.18). Students with </=5.6 hours of daily darkness were more likely to report myopia progression than those with >5.6 hours of darkness per day (95% vs. 80%, P = 0.07). To account for possible confounding effects of risk factors with myopia progression, logistic regression with categorization of the continuous exposure variables (hours of near work, sleep, and darkness) above or below median values weakened the near work association (odds ratio 1.8, 95% confidence interval 0.5-6.7, P = 0.35) but continued to identify darkness association with daily hours of darkness (odds ratio 4.8, 95% confidence interval 1.0 >/= 23.3, P < 0.05). Among the 77 students with myopia onset before college, those with </=5.6 hours of daily darkness were more likely to progress than those with more hours of daily darkness (97% vs. 76%, P = 0.01). CONCLUSIONS This study confirms high rates of myopia prevalence and myopia progression among law students. The strongest association, especially in those with myopia onset before college, was a relation of myopia progression during law school with less daily exposure to darkness, a potential risk factor previously identified in childhood myopia. The role of exposure to darkness in refractive development warrants additional study.