ABR thresholds in infants born with CLP and OME and infants with OME.

OBJECTIVES: The aim of this study was to investigate and compare auditory brainstem response (ABR) thresholds related to otitis media with effusion (OME) in infants with and without cleft palate and/or lip (CP±L). METHODS: Forty-seven infants with CP±L and 67 infants with OME participated in the study. Hearing thresholds of ears of infants with OME were compared between groups and within the group with CP±L. RESULTS: Infants with CP±L and OME presented with similar hearing thresholds as infants with OME and not CP±L. Within the cleft group, infants with isolated cleft palate and OME demonstrated significantly higher hearing thresholds than infants with unilateral cleft lip and palate and OME. CONCLUSION: A high prevalence of infants with CP±L present with OME early in life. Hearing thresholds of these infants are similar to infants without CP±L, but with OME. The ear status and hearing thresholds of infants with CP±L needs to be monitored to be able to provide the best access to hearing in order to fully allow speech and language development.

Light transmittance of ocular media in living rabbit eyes.

PURPOSE: The purpose of this study was to measure the transmittance of electromagnetic radiation, particularly visible light, through the ocular media of living and whole rabbit eyes. Previous determinations have been carried out on excised cadaver eyes. METHODS: A specially designed fiberoptic probe (outer diameter, 0.9 mm) was placed in the vitreous in front of the retina using a microsurgical technique. In eight living albino rabbits (under general anesthesia), ocular transmittance was determined in the wavelength range 350 to 1100 nm using a reversed beam path (from vitreous to cornea). RESULTS: A maximum optical transmittance of 94% to 96% (standard deviation, 2%-3%) was found between 630 and 730 nm (reflection losses in the cornea-air interface excluded). In the blue portion of the spectrum, transmittance decreased rapidly for shorter wavelengths, and was 50% at 400 nm and less than 1% at 380 nm. In the infrared part of the spectrum, transmittance was close to 90% up to 900 nm but declined at longer wavelengths, coinciding with the absorption in pure water. Calibration recordings showed a 1% to 2% accuracy of the method. CONCLUSIONS: This experimental technique using an intraocular fiberoptic probe yields a high accuracy and indicates that light transmittance is very high in vivo and superior to that reported from cadaver eyes.

Dopaminergic transmission in the rat retina: evidence for volume transmission.

The study was designed to determine whether dopaminergic neurotransmission in the retina can operate via volume transmission. In double immunolabelling experiments, a mismatch as well as a match was demonstrated in the rat retina between tyrosine hydroxylase (TH) and dopamine (DA) immunoreactive (ir) terminals and cell bodies and dopamine D2 receptor-like ir cell bodies and processes. The match regions were located in the inner nuclear and plexiform layers (D2 ir cell bodies plus processes). The mismatch regions were located in the ganglion cell layer, the outer plexiform layer, and the outer segment of the photoreceptor layer, where very few TH ir terminals can be found in relation to the D2 like ir processes. In similar experiments analyzing D1 receptor like ir processes versus TH ir nerve terminals, mainly a mismatch in their distribution could be demonstrated, with the D1 like ir processes present in the outer plexiform layer and the outer segment where a mismatch in D2 like receptors also exists. The demonstration of a mismatch between the localization of the TH terminal plexus and the dopamine D2 and D1 receptor subtypes in the outer plexiform layer, the outer segment and the ganglion cell layer (only D2 immunoreactivity (IR)) suggests that dopamine, mainly from the inner plexiform layer, may reach the D2 and D1 mismatch receptors via diffusion in the extracellular space. After injecting dopamine into the corpus vitreum, dopamine diffuses through the retina, and strong catecholamine (CA) fluorescence appears in the entire inner plexiform layer and the entire outer plexiform layer, representing the match and mismatch DA receptor areas, respectively. The DA is probably bound to D1 and D2 receptors in both plexiform layers, since the DA receptor antagonist chlorpromazine fully blocks the appearance of the DA fluorescence, while only a partial blockade is found after haloperidol treatment which mainly blocks D2 receptors. These results indicate that the amacrine and/or interplexiform DA cells, with sparse branches in the outer plexiform layer, can operate via volume transmission in the rat retina to influence the outer plexiform layer and the outer segment, as well as other layers of the rat retina such as the ganglion cell layer.

Readaptation time after photo stress. Alcohol-induced acute and post-alcohol 'hangover' changes in ocular readaptation time.

The effect of alcohol intake on readaptation time (RAT) after photo stress is studied. Ten healthy subjects were given 0.72 g alcohol per kg body weight to be consumed within 20 min. The tests were made during a total period of 11-12 h. The findings demonstrate that moderate blood alcohol concentrations induce definite changes in RAT. An average RAT-prolongation of 60-70% was seen during the acute phase of intoxication. RAT-prolongation ended before the blood alcohol concentration had reached zero, but did not have the same downward slope. Following a period of reduction, a new prolongation of RAT was observed. The lack of congruence between the RAT-curve and the blood alcohol curve in the acute phase of intoxication and the post-alcohol increase are discussed. It is concluded that the alcohol-induced RAT-changes probably are CNS-effects and that the equipment used constitutes a sensitive method of estimating these effects.

Excimer retreatment of regression after photorefractive keratectomy.

Regression of effect is a well-established complication of excimer laser photorefractive keratectomy for the correction of myopia. In 17 eyes retreated with excimer photorefractive keratectomy, minimum follow-up time was six months. Mean (+/- SD) refraction at six months postoperatively was -0.97 +/- 2.10 diopters, significantly different (P < .01) from the pre-retreatment mean of -2.91 +/- 0.86 diopters. The 11 best eyes (six-month refraction < -1.00 diopter) had a mean refraction of +0.32 +/- 0.67 diopter. At six months after retreatment, 64.7% had an uncorrected visual acuity greater than or equal to 20/40, and 58.8% were within 1.00 diopter of emmetropia. Two eyes showed a loss of one to two Snellen lines at six months. There was no significant increase in mean haze after retreatment. While the percentage of eyes with uncorrected visual acuity greater than or equal to 20/40 and the percentage of eyes within 1.00 diopter of emmetropia were lower than in eyes which did not require retreatment, the results of this study indicate that the majority of photorefractive keratectomy regressions can be successfully retreated.

Photorefractive keratectomy for 1.5 to 18 diopters of myopia.

The purpose of this study was to evaluate the refractive outcome and the stability of refraction after excimer laser photorefractive keratectomy (PRK). Forty-five eyes were treated in three different refractive groups: low myopes, 23 eyes, -1.50 diopters (D) to -6.00 D; intermediate myopes, 14 eyes, -6.10 D to -10.00 D; and high myopes, 8 eyes, -10.10 D to -18.00 D. At 9 months after surgery the low myopes had a mean refraction of -0.14 D (range -1.00 D to + 1.50 D) and were easy to refract. Intermediate myopes mean refraction was +0.14 D (range -1.50 D to +2.50 D). In the high myope group the mean refraction was -0.47 D (range -10.00 D to +2.50 D) and four eyes (50%) lost more than two lines of spectacle corrected visual acuity. Refraction the high myopes was more difficult compared to the lower myopes. PRK produced good results for myopes from -1.50 D to -10.00 D. Myopes greater than -10.00D are not stable at 9 months after PRK and are difficult to refract.

Patient satisfaction following photorefractive keratectomy for myopia.

This study was conducted to evaluate the subjective response of patients who underwent photorefractive keratectomy (PRK) for myopia with the Summit Technology UV 200 LA excimer laser (Summit Technology, Inc., Waltham, Mass.) (3.5 to 5.0 mm diameter ablation zone) 36 months previously. One-hundred thirteen patients with preoperative myopia between -1.50 diopters (D) and -6.50 D with an ablation diameter of 3.5 mm to 5.0 mm answered a questionnaire at the 36-month examination. Sixty-two percent of patients had both eyes treated. Halo problems were experienced always by 34% of patients in the group, 26% sometimes, and 40% never. Permanent night vision problems were experienced by 40%; 30% reported them sometimes and 30% reported no problems at all. Sixty percent never needed to use glasses after treatment, 30% sometimes did, and 10% always wore glasses. Seventy percent of patients thought the results were very good; the remaining 30% experienced different degrees of halo and night vision problems.

Failure of mechanical epithelial removal to reverse persistent hyperopia after photorefractive keratectomy.

BACKGROUND: Residual hyperopic overcorrection after photorefractive keratectomy (PRK) using early algorithms is a rare but serious complication. Anecdotal evidence suggests that epithelial removal can stimulate epithelial hyperplasia, thereby reducing overcorrection. The aim of this study was to determine if epithelial removal effectively reduced hyperopia after PRK for myopia and, concurrently, to correlate the healing response with the refractive outcome. METHODS: Enrolled were seven eyes of seven patients (mean age, 44 +/- 13 years) who had undergone PRK with a mean manifest refractive error of +2.21 +/- 0.74 diopters (D). All had undergone PRK an average of 24 +/- 9 months previously. Epithelial removal was performed over the excimer-treated zone with a surgical blade. Subjective refraction, epithelial thickness, corneal topography, and subepithelial haze were measured up to 1 year postoperatively. RESULTS: Reduction in hyperopia between the baseline and 1-year visit was not statistically significant (mean difference, 0.55 D reduction; p = .102). That epithelial removal did not stimulate a wound-healing response is further supported by the absence of change in epithelial thickness over the first month and the small amounts of subepithelial haze. Central corneal power was reduced by a mean of 0.64 D after 1 month (p < .05). CONCLUSIONS: Epithelial removal alone did not reduce the hyperopic overcorrection present after PRK, nor did it stimulate epithelial hyperplasia in the majority of these eyes. However, a trend toward improvement was noted with time was noted.

Epithelial alterations following photorefractive keratectomy for myopia.

BACKGROUND: A retrospective observational study was conducted to test the hypothesis that there is clinically measurable epithelial hyperplasia after photorefractive keratectomy (PRK), and to determine its effect on the epithelial oxygen uptake rate. METHODS: One hundred myopic eyes who had been previously treated unilaterally with PRK were examined. Fifty eyes were treated with the Summit excimer laser (Summit Technology, Waltham, Mass) 27 +/- 7 months previously with ablation zone diameters of 4.1, 4.3, 4.5, or 5.0 mm. Fifty eyes were treated with the VISX excimer laser (VISX Inc, Sunnyvale, Calif) 5 +/- 4 months previously with one ablation zone diameter of 6.0 mm. The untreated eyes served as controls. Epithelial thickness was measured at a standardized central area within the ablation zone with a modified optical pachometer. Oxygen uptake rate was measured in a subgroup of 30 eyes (20 Summit and 10 VISX). RESULTS: The epithelium after PRK was 24% thicker than in the control eye in the Summit group (mean difference 13 +/- 10 microns; p < .01) and 7% thinner in the VISX group (mean difference -4 +/- 10 microns; p < .01). A higher oxygen uptake rate correlated with a thicker epithelium (r = 0.42; p < .05). CONCLUSIONS: The epithelium was significantly thicker after PRK between 13 and 37 months after treatment with the Summit excimer laser using ablation zone diameters of 4.1 to 5.0 mm. The epithelium was thinner between 1 and 15 months after treatment with the VISX laser using an ablation zone diameter of 6.0 mm. An increase in oxygen uptake rate reflected the metabolic rate of a greater number of cells in the hyperplastic layer.

Collagen distribution in the lamina cribrosa and the trabecular meshwork of the human eye.

Tengroth and Ammitzböll found the collagen content of the optic disc in glaucoma to differ from that of normal eyes. A theory was advanced that a primary collagen disturbance might be involved in the pathogenesis of glaucoma. The connective tissue in the body has a supportive function in almost all the organs. The tensile strength and elasticity of connective tissue is mainly due to the presence of collagen fibres and elastic fibres, which also maintain the shape of the tissues. There are many different types of collagen, three of which are discussed in this paper. Type I collagen is found in tendons, skin, and numerous other organs, for example the eye. Type III is found mainly in the blood vessels but is also present in other tissues with a mesodermal origin, and type IV is found in the basement membranes. To elucidate the precise distribution of collagen types in the ocular structures an immunhistochemical study was undertaken in normal human eyes. The amino acids proline, hydroxyproline, and hydroxylysine, which are characteristic of collagen, were also analysed. Collagen types I, III, and IV were found in the lamina cribrosa, the trabecular meshwork, and the retrolaminary optic nerve. In contrast, only type I was found in the sclera.

Role of epithelial hyperplasia in regression following photorefractive keratectomy.

AIM: To determine the relation between epithelial hyperplasia and regression of effect after photorefractive keratectomy (PRK). METHODS: Seventy unilaterally treated patients with PRK were examined. All eyes had been treated with the Summit excimer laser 27 (SD 7) months previously with zone diameters of 4.1 to 5.0 mm. The untreated fellow eyes served as controls. Epithelial thickness was measured centrally with a thin slit optical pachometer and manifest subjective refraction was performed. RESULTS: The epithelium was 21% thicker in the treated eye (p < 0.0001). The relation between refractive regression and epithelial hyperplasia was significant (r = 0.41; p < 0.001). CONCLUSIONS: Epithelial hyperplasia after PRK correlated with the myopic shift (including hyperopia reduction) after treatment with the Summit laser. A model is proposed suggesting that both subepithelial and epithelial layers contribute to regression in the Summit treated eyes with 18 microns of epithelial hyperplasia contributing each dioptre of regression.

Effect of postoperative steroids on the refractive outcome of photorefractive keratectomy for myopia with the Summit excimer laser.

To assess the role of topical steroids following excimer laser photorefractive keratectomy (PRK) for myopia, we compared the refractive outcome in 100 eyes that did not receive steroids in the immediate postoperative period (untreated eyes) with 100 eyes that were treated with topical dexamethasone for three months postoperatively. Photorefractive keratectomy was performed with the Summit laser, using 4.3 mm and 4.5 mm ablation zones. At three months after surgery, the untreated eyes had a mean refraction of -0.97 +/- 1.15 diopters (D), significantly different (P < .01) from the mean refraction (+0.46 +/- 0.74 D) of the steroid-treated eyes. By six months postoperatively, 86% of the untreated eyes had regressed to a myopia of at least 0.50 D, whereas only 23% of the steroid-treated eyes had regressed. In a second study, we compared the results in 25 patients whose first PRK eye was treated with steroids after surgery but whose second eye was not. At three months postoperatively, mean refraction in the steroid-treated eyes was +1.23 +/- 0.71 D, significantly different (P < .01) from the mean of -0.45 +/- 1.29 D in the untreated eyes. The refractive results in PRK eyes treated with the Summit unit and with relatively small ablation zone diameters showed that eyes that received dexamethasone postoperatively were less likely to regress to myopia.

Factors affecting epithelial hyperplasia after photorefractive keratectomy.

PURPOSE: To determine the effect of patient age, postoperative time, ablation zone diameter and depth, attempted correction, and corneal topography on postoperative corneal epithelial thickness after photorefractive keratectomy (PRK). SETTING: Private clinic and university hospital, Stockholm, Sweden. METHODS: This retrospective, unmasked study comprised 136 myopic patients treated unilaterally with PRK. Seventy eyes had been treated with the Summit excimer laser 27 months +/- 7 (SD) earlier using ablation zone diameters of 4.1 to 5.0 mm. Sixty-six eyes had been treated with the VISX excimer laser 6 +/- 3 months earlier using a 6.0 mm zone diameter. The untreated fellow eyes served as controls. Epithelial thickness was measured at a standardized central corneal area with a modified optical pachymeter, and corneal topography was determined using computerized videokeratoscopy. RESULTS: In the Summit group, the epithelial layer in the PRK eyes was 12.0 microns (21%) thicker than in the control eyes (P < .001; 95% confidence interval [CI] 9.35 to 14.3 microns). This thickness differential correlated significantly with increased ablation depth and attempted correction. In the VISX group, the epithelium in the treated eyes was 7.0 microns (7%) thinner (P = .0009; 95% CI -1.9 to -6.7 microns) and thickness did not correlate with ablation depth or attempted correction. There was no correlation between epithelial hyperplasia and patient age or postoperative follow-up. With the laser groups combined, epithelial hyperplasia was greater with smaller zone sizes and a greater rate of change in power at the edge of the ablation zone. CONCLUSION: The factors associated with an increase in epithelial thickness were small ablation zones, greater attempted corrections, and deeper ablations. Larger, smoother ablation profiles may result in less epithelial hyperplasia.

Steroid treatment of myopic regression: acute refractive and topographic changes in excimer photorefractive keratectomy patients.

We documented acute changes in corneal topography and refraction after readministration of topical steroids in five patients with myopic regression after photorefractive keratectomy (PRK). One was a high myope (-10.00 sphere); the others were moderate myopes (preoperative spherical equivalents -4.25 to -6). All patients had been off steroids for 3 to 8 months before reinstitution. The changes in refractive spherical equivalents ranged from +0.75 to +3.00 diopters, and were observed from 6 days to 4 weeks later. Refractive hyperopic shifts were accompanied by pronounced corneal flattening as measured by computer-assisted corneal topographic analysis. Two to seven months later, three patients have become even less myopic, and two patients have again become slightly more myopic. Topical steroid use can modulate refractive changes after excimer laser treatments in some patients.

Preliminary notes on vulnerability of the retina to injury from peripheral laser exposure conditions.

If laser exposures to the periphery of the retina from low-energy lasers cause a hemorrhage obscuring the optical pathway to the fovea, resulting in loss of visual function, the risks for soldiers on the battlefield may be greater than previously expected. Two off-axis experiments were undertaken to obtain an indication of the hazards involved in exposing the peripheral retina to visible laser irradiation. Both off-axis exposures caused immediate vitreal hemorrhages in the periphery. After 80 min, the hemorrhage in the first eye had diminished, and in the other it was significantly smaller than immediately after exposure; even the central hemorrhage was smaller. Another observation after 120 min revealed the same result. These results indicate that an obvious risk exists on the battlefield for peripheral hemorrhages due to lasers operating within the retinal hazard spectrum. However, it is necessary to make more observations to establish the findings firmly.

Vulnerability of the retina to injury from a military ruby rangefinder at battlefield distances.

This study investigates the possibility of causing a vitreal hemorrhage with a standard ruby rangefinder at battlefield engagement distances when the laser is observed with the naked eye or through magnifying optics or filters. The experiments were undertaken on the eyes of anesthetized pigs. The pigs were anesthetized with Mebumal and given 0.5% thropicamid in the eyes. They were then exposed to the radiation from a standard military ruby rangefinder (pulsewidth 25 ns, pulse energy 180 mJ). The rangefinder was aligned with a He-Ne laser and a beamsplitter. Eight experiments were performed, each with several exposures. The range was varied from 0.5-850 m. Some of the experiments were made using the naked eye, some with a filter, some with binoculars (7 x 50) and some with a combination of filter and binoculars. The pulse energy was varied from 91-6500 muJ. Vitreal hemorrhages were caused at distances of 410 and 850 m when a pair of binoculars (7 x 50) was placed in front of the eyes. The intraocular energy varied between 1500 and 4400 microJ. Results indicate that there is a possibility of causing a vitreal hemorrhage in a soldier who is using standard field binoculars and looking in the direction of an ordinary military rangefinder at distances at least up to 850 m.

Effect of spectral flash on readaptation time.

The effects of an adapting flash of different colors on human vision were investigated with various flashes and target luminances. The readaptation time (RAT) was measured using optokinetic nystagmus elicited by a projected moving striped pattern in a hemisphere. The RATs were recorded from 26 subjects with a multichannel pen recorder. Two target luminances (1.1 X 10(-5) cd/m2 and 2.6 X 10(-5) cd/m2) and 12 flash wavelengths (449 nm, 456 nm, 468 nm, 477 nm, 498 nm, 502 nm, 520 nm, 565 nm, 580 nm, 591 nm, 622 nm, and 703 nm) were used. A spectral RAT curve was obtained, which showed that the chromatic response of RAT follows this order: green greater than blue greater than yellow greater than red. A larger influence of the variation of the target luminance on the RAT was demonstrated at shorter wavelengths. The results also showed that the energy density of the flash has a larger variation with the RAT in blue and green than in red.

Thirty-six month follow-up of excimer laser photorefractive keratectomy for myopia.

BACKGROUND AND OBJECTIVE: The aim of the study was to evaluate the refractive outcome 36 months following excimer laser photorefractive keratectomy (PRK) performed on myopic eyes. We analyzed the refractive stability between 24 and 36 months. PATIENTS AND METHODS: PRK was performed on 457 eyes with a pre-operative refraction ranging from -1.25 to -7.50 diopters (D). Ablation zone diameters of 4.3 to 4.5 mm were used. The follow up time was 36 months. RESULTS: The mean refraction 36 months following surgery was -0.22 to 0.75 D for the whole group, which was not significantly different from the mean at 24 months (-0.27 +0.74D). If we analyze the subgroups at 36 months, we find a significantly better refractive outcome in the low myopia group (up to -2.90D) compared with those with higher myopia. At 36 months, 91% of the 456 eyes had an uncorrected visual acuity of at least 20/40, and 88% of the eyes were within 1.00 D of emmetropia. CONCLUSION: These results show stability between 24 and 36 months.

One year follow-up of photoastigmatic keratectomy (PARK) with the VISX 20/20 excimer laser.

BACKGROUND AND OBJECTIVE: One hundred thirteen eyes were treated with photoastigmatic keratectomy using the VISX 20/20 excimer laser. The results were evaluated after 1 year. PATIENTS AND METHODS: The patients were divided into 2 groups, low astigmatism group with less than 2.00 diopters (D) of pre-operative astigmatism, the second group having 2.00 D or more. RESULTS: Astigmatism was reduced by 43.9% in the low astigmatic group and by 71.7% in the high astigmatic group. Eighty percent of the eyes in the low astigmatic group and 90% in the high astigmatic group achieved an uncorrected visual acuity of 20/40 (0.5) or better. Eighty-four percent in the low astigmatic group and 80% in the high astigmatic group were within +/- 1.00 D in spherical equivalent results. The mean spherical equivalent results were about -0.45 D in both groups using this algorithm. CONCLUSION: The results are very promising at this early stage of algorithm development.