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As one of the most important aspects of aviation physiology, vision is a virtual sine qua non of the aviation field. A basic understanding of vision is vitally important in the field of aviation medicine. Following is a summary of some aspects of visual physiology, including visual acuity, night vision, dark adaptation, and acceleration effects on vision.
PURPOSE: To describe the phenotype caused by a retinol deficiency in a family with compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the gene for serum retinol binding protein (RBP). METHODS: The two affected sisters, 17 (BR) and 13 (MR) years old, were examined clinically and with perimetry, color vision tests, dark adaptometry, rod- and cone-isolated electroretinograms (ERGs), multifocal ERGs, electrooculograms (EOGs), and laboratory tests. RESULTS: There were no complaints besides night vision problems and no history of systemic disease. Visual acuity was reduced to 20/40 (BR) and 20/25 (MR). Anterior segments were normal except for a discrete iris coloboma. Both patients showed a typical "fundus xerophthalmicus," featuring a progressed atrophy of the retinal pigment epithelium. Dark adaptation thresholds were elevated. In the scotopic ERG, only reduced mixed responses were recordable. The photopic ERG was reduced in BR and normal in MR; implicit times were highly (BR) to slightly (MR) elevated. There was no (BR) to little (MR) light reaction in the EOG. All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test. RBP was below detection threshold, and retinyl esters were normal. CONCLUSIONS: Both affected siblings had no detectable serum RBP, one sixth of normal retinol levels, and normal retinyl esters. The retinal pigment epithelium was severely affected, but besides acne there were no changes to other organs. This gives evidence for an alternative tissue source of vitamin A, presumably retinyl esters from chylomicron remnants. The normal retinol levels in the tear fluid explain the lack of xerophthalmia. However, considering the role of RBP in the tear fluid and, during development, in the yolk sac there is also evidence that there are organ-specific RBP forms not affected by the genetic defect.
Nocturnal animals are said to sacrifice colour vision in favour of increased absolute sensitivity. This is true for most vertebrates that possess a dual retina with a single type of rod for colour-blind night vision and multiple types of cone for diurnal colour vision. However, among the nocturnal vertebrates, geckos are unusual because they have no rods but three cone types. Here, we show that geckos use their cones for colour vision in dim light. Two specimens of the nocturnal helmet gecko Tarentola (formerly Geckonia) chazaliae were able to discriminate blue from grey patterns by colour alone. Experiments were performed at 0.002 cd m(-2), a light intensity similar to dim moonlight. We conclude that nocturnal geckos can use cone-based colour vision at very dim light levels when humans rely on colour-blind rod vision.
Thirty employees of an industrial plant involved in the manufacture of silver nitrate and silver oxide underwent ophthalmologic evaluation in an effort to evaluate the frequency and extent of ocular argyrosis. The most frequently noted ocular abnormality was pigmentation of the conjunctiva, present in 20 workers; corneal pigmentation occurred in 15 workers. A direct relationship existed between the levels of pigmentation and duration of employment. Ocular pigmentation was seen more frequently than cutaneous pigmentation. Ten workers noted decreased night vision, but electrophysiologic and psychophysiologic studies of seven of these ten workers demonstrated no functional deficits.
Proliferative retinopathies account for the majority of cases of vision loss throughout the world. Currently accepted therapy for retinopathy consists of retinal ablation by panretinal laser photocoagulation or cryotherapy. This technique is not without deleterious effects to patients, including diminished night vision, reduced peripheral vision and loss of precise vision, decreasing visual acuity by one to two lines in magnitude. One promising area of research into pharmacotherapeutics for retinopathies, especially proliferative diabetic retinopathy, involves the use of synthetic analogues of somatostatin. The rationale for somatostatin as a therapeutic agent for retinal neovascularization is discussed. Somatostatin analogues such as octreotide have shown promise as a safe and effective treatment for severe proliferative diabetic retinopathy by blocking the local and systemic production of growth hormone and insulin-like growth factor type 1 associated with angiogenesis and endothelial cell proliferation. There are also observations suggesting an autocrine and paracrine effect of somatostatin, perhaps directly on retinal cells, which are known to express somatostatin receptors (SSTR). SSTR2 and SSTR3 are the most important receptor subtypes mediating growth hormone secretion and endothelial cell cycle arrest, retinal endothelial cell apoptosis and release of insulin. Thus, analogues that target these receptor subtypes may prove more useful. Long-acting somatostatin analogues are currently being tested for treatment of diabetic retinopathy and are, in fact, the only therapeutic alternative for patients who fail panretinal photocoagulation. Whether such a therapy may also prove effective for other retinal vascular proliferative diseases such as retinopathy of prematurity and age-related macular degeneration remains an open question that deserves attention, given our new understanding of the cellular and molecular mechanisms by which somatostatin may exert its antiangiogenic effects.
Hereditary degenerations of the human retina are genetically heterogeneous, with well over 100 genes implicated so far. This Seminar focuses on the subset of diseases called retinitis pigmentosa, in which patients typically lose night vision in adolescence, side vision in young adulthood, and central vision in later life because of progressive loss of rod and cone photoreceptor cells. Measures of retinal function, such as the electroretinogram, show that photoreceptor function is diminished generally many years before symptomic night blindness, visual-field scotomas, or decreased visual acuity arise. More than 45 genes for retinitis pigmentosa have been identified. These genes account for only about 60% of all patients; the remainder have defects in as yet unidentified genes. Findings of controlled trials indicate that nutritional interventions, including vitamin A palmitate and omega-3-rich fish, slow progression of disease in many patients. Imminent treatments for retinitis pigmentosa are greatly anticipated, especially for genetically defined subsets of patients, because of newly identified genes, growing knowledge of affected biochemical pathways, and development of animal models.
A 30 year old white female with known retinitis pigmentosa of autosomal dominant transmission was placed on thyroid medication for weight control purposes for nearly one year. The unusually rapid progression of visual field changes and the increased severity of night vision problems are documented by serial functional studies.
A lysine to glutamic acid substitution at codon 296 in the rhodopsin gene has been reported in a family with autosomal dominant retinitis pigmentosa. This mutation is of particular functional interest as this lysine molecule is the binding site of 11-cis-retinal. The clinical features of a family with this mutation have not been reported previously. We examined 14 patients with autosomal dominant retinitis pigmentosa and a lysine-296-glutamic acid rhodopsin mutation. Four had detailed psychophysical and electrophysiological testing. Most affected subjects had severe disease with poor night vision from early life, and marked reduction of visual acuity and visual field by their early forties. Psychophysical testing showed no demonstrable rod function and severely reduced cone function in all patients tested.
BACKGROUND AND METHODS: Optometry has played a significant role in the USAF vision research program since the early 1960s. The Air Force Institute of Technology (AFIT) sponsors active duty optometry officers for Ph.D. and masters programs in Physiological Optics at civilian universities. After training, they are assigned to research laboratories at Brooks AFB, TX, or Wright-Patterson AFB, OH. Senior research optometrists manage vision and medical research programs and have served on the staff of the United States Air Force (USAF) Surgeon General. RESULTS AND CONCLUSIONS: Research papers reporting on USAF vision research programs, especially those germane to improving aircrew combat effectiveness, have been published extensively by USAF optometrists in Air Force and joint services technical reports as well as the open literature. These programs include: refractive error trends, contact lenses, ophthalmic materials, night vision, aircraft transparency measurement, nuclear flashblindness, laser, and space flight. As long as vision remains the most important sensory input to the pilot, USAF optometrists will remain an integral part of the aerospace medical research team.
Scotopic visual thresholds and time courses for dark adaptation were determined in eight patients with Sorsby's fundus dystrophy. Rhodopsin regeneration also was recorded in two. All patients had poor night vision and a visible yellow deposit at the level of Bruch's membrane that was confluent in the posterior pole. In retinal regions with the yellow deposit, scotopic thresholds were elevated, the rod-cone break was delayed or indistinct, the time courses for the rod portion of the dark adaptation curve was prolonged, and rhodopsin regeneration was slow in the one patient in whom measurements were made. In regions of ophthalmoscopically normal retina, dark adaptation was affected minimally, and in one patient, rhodopsin was regenerated at a normal rate. It was hypothesized that the abnormal dark adaptation and rhodopsin kinetics might be caused by reduced metabolic exchange across a thickened Bruch's membrane.
INTRODUCTION: Presbyopia is a problem in refraction attributed to loss of near vision. Monovision (MV) is a strategy to compensate for presbyopia whereby one eye is corrected for distance and the other eye corrected for near vision. The patient should be able to suppress the blurred image from one eye and see clearly at all distances without glasses. PURPOSE: To measure binocular function and patient satisfaction with MV induced by laser in situ keratomileusis (LASIK) in myopic and hyperopic presbyopic patients. METHODS: Patients 39 years or older who underwent MV LASIK and minimum 90 days follow-up were included in the study. The following parameters were used: distance and near corrected/uncorrected visual acuity, manifest refraction before and after surgery and near stereopsis postoperatively. Patient satisfaction was evaluated by a questionnaire. RESULTS: One hundred and fourteen patients (100 myopes, 14 hyperopes) were included. After surgery, 79% had distance binocular uncorrected visual acuity of 6/7.5 or better and 97% of the patients had near binocular uncorrected visual acuity of J2 or better. The median of the near steroacuity was 100 seconds of arc. A total of 80% of the patients were very satisfied. The surgical score was 85. An overall 89.5% of the patients felt that their main goal had been achieved and 89% would choose to have surgery if they had it to do over. Eight percent of the patients used glasses for distance and 24% used reading glasses after surgery. The quality of life while driving at night improved in 55% and deteriorated in 15% of the patients. The quality of life while driving during the day improved in 69% and deteriorated in 1%. CONCLUSIONS: Monovision induced by LASIK may be a valuable option for both myopic and hyperopic presbyopic individuals considering refractive surgery. However, due to the risk of decreased night vision and continued use of reading glasses during the day, this surgery may not be suitable for patients in whom night driving and/or reading are an essential part of their life.
The standard for dark adaptation has long been the Goldmann-Weekers Dark Adaptometer(Haag-Streit). More recently, portable, relatively inexpensive LED-based dark adaptometers have become commercially available. These devices have potential use in areas with limited resources to screen for night-blindness, commonly caused worldwide by vitamin A deficiency. In order to determine the sensitivity to detecting changes in night vision, this study compared one such device, LKC Technologies Scotopic Sensitivity Tester-1 (SST-1) to the Goldmann-Weekers in patients with hereditary retinal degeneration and loss of rod function. Dark-adapted final thresholds and rod full-field ERG responses were obtained from 87 patients and 24 normal subjects. Linear regression analysis, discrepancy analysis, and receiver operator characteristic curves for both devices show that the SST-1 quantifies psychophysical rod function nearly as well as the Goldmann-Weekers, within some limitations. We conclude, therefore, that the SST-1 is a viable alternative to the Goldmann-Weekers for the screening of night-blinding retinal disorders.
Microspectrophotometry (MSP) shows rhodopsin highly concentrated (about 3.0 mmol/l) in rod outer segments (ROS). Calculation of the in vivo absorption spectrum of human rhodopsin from such data reveals a striking failure to agree with the action spectrum of human rod vision. Agreement is good between the spectral distribution of absorption coefficients and the action spectrum, but the "concentration-broadening" (or "self-screening") introduced by the high end on absorbance at this concentration results in a misfit among the largest in the 93 years comparisons of this kind have been made! To deal with this anomaly, it has been suggested that "concentration-broadening" is inappropriate for rhodopsin in rod vision. This proposal was tested by comparing rod action spectra of 15-day-old and adult rats, since the lengths of ROS increase by a factor of about two in maturation. Three lines of evidence are inconsistent with it. Although the conundrum remains unexplained, it cannot be dismissed by supposing "self-screening" inappropriate for night vision.
Isotretinoin (Accutane Capsules) is a synthetic vitamin A compound used for treatment of recalcitrant cystic acne. It has numerous ocular toxic side effects which include anterior segment inflammation, dry eye syndrome, contact lens intolerance, altered refraction, photosensitivity, and reduced night vision. Eye care practitioners should be aware of these potential side effects and be prepared to communicate with the prescribing physician if side effects present.
PURPOSE: To evaluate factors related to the quality of vision after LASIK. DESIGN: Survey study. PARTICIPANTS: One hundred consecutive patients. INTERVENTION: LASIK with a 6.0-mm elliptical ablation pattern without transition zone to treat mild to moderate myopia or astigmatism (preoperative manifest spherical equivalent [MSE], -4.79 +/- 1.33 diopters [D]; range, -2.88 to -9.25 D). The second eye was treated 1 month after the first. MAIN OUTCOME MEASURES: Completed questionnaires assessing night vision problems (glare, haze, and halo symptoms) before surgery and at 1, 3, and 6 months after surgery in 97, 75, 81, and 66 subjects, respectively. Mesopic pupil size and preoperative and postoperative variables were analyzed with questionnaire data using an analysis of variance (ANOVA) and multivariate regression analysis. RESULTS: Patients with large mesopic pupils had significantly more reports of glare, haze, and halo than did those with smaller pupils in the treated eye at 1 month after surgery (P=0.02, P=0.03, and P=0.02, respectively ANOVA) and of glare at 3 months (P=0.05). Significant predictors of symptoms at 6 months, identified through multivariate regression analysis, included preoperative MSE (for glare and haze), preoperative contrast acuity (glare), postoperative uncorrected visual acuity (UCVA; haze), and residual cylinder (haze). Together, these factors accounted for only 19% of the overall variability in glare and 37% of the variability in haze responses. No relationship between pupils and symptoms was noted at 6 months after surgery in either the ANOVA or regression analysis group. CONCLUSIONS: Patients with large pupils had more quality of vision symptoms in the early postoperative period, but no correlation was observed 6 months after surgery. Factors related to long-term symptoms include the level of treatment (preoperative myopia), preoperative contrast acuity, postoperative UCVA, and residual cylinder. Most of the variability in visual quality could not be explained by preoperative or clinical outcome measures, including pupil size.
A five generation family with an X linked ocular disorder has been investigated. The major clinical features were reduced visual acuity, nystagmus, and myopia. Although impaired night vision was not a symptom, using psychophysical and electrophysiological testing both rod and cone function were found to be abnormal in all affected males. No abnormality was detected in carrier females. Gene location studies showed X linked transmission of a gene that maps to proximal Xp11. The findings observed in this cohort are similar to those previously reported in both congenital stationary night blindness type 2 (CSNB2) and Aland Island eye disease (AIED). This study addresses whether CSNB2 and AIED are a single entity or whether the latter is a subset of the former.
UNLABELLED: Excimer laser photorefractive keratectomy (PRK) to reduce myopia has been studied the past 3 yrs at multicenters authorized by the FDA. The excimer laser ablates the central cornea to a new calculated power. A review of the cases reported in the literature reveals the following information: Corneal scarring may be reflected in the loss of best-corrected vision. Regression of the refractive effect is a complication. Predictability was the percentage of eyes obtaining 20/40 or better vision; this varied from 62.5-91%. Conversely, 9.0-37.5% were 20/50 or worse. Low to moderate myopes had better visual success. Accuracy was the refractive correction within +/- 1.00 D (spherical equivalent); this varied between 64.7-93%. The higher percentages were with low to moderate degrees of myopia. Loss of best corrected vision was due to scarring and haze, and occurred more frequently with high myopia and deeper ablations. Patient satisfaction after 2 yrs was reported as 82.6-90%; 17.4% were not satisfied. ADVANTAGES: a) PRK effectively and safely corrected myopia and myopic astigmatism; b) there was no diurnal variation of refraction or vision; c) vision remained fairly stable with some regression up to 24 mo and; d) accuracy of correction to +/- 1.00 D was fair. Disadvantages: a) post-operative scarring and haze was present after 6 mo to 2 yrs of follow-up in some cases. Scarring was less with low myopia and worse with high myopia; b) regression of correction and blur; and c) poor night vision, halos, and glare sensitivity occurred after pupil dilation.(ABSTRACT TRUNCATED AT 250 WORDS)
PURPOSE: Congenital stationary night blindness (CSNB) is a group of nonprogressive retinal disorders characterized by impaired night vision that occurs in autosomal dominant, autosomal recessive, or X-linked forms. Autosomal recessive (ar)CSNB seems to be very rare. Mice lacking the metabotropic glutamate receptor 6 (Grm6) have a defect in signal transmission from the photoreceptors to ON-bipolar cells. In the current study, the human orthologue (GRM6) was screened as a likely candidate for arCSNB. METHODS: arCSNB individuals of five families were screened for mutations in GRM6. Subsequently, they were examined with standard and 15-Hz flicker electroretinography (ERG). These recordings were compared with those of patients with X-linked CSNB1. RESULTS: Affected individuals in three of five families carried either compound heterozygous or homozygous mutations in GRM6. Strikingly, all of them displayed a distinctive abnormality of the rod pathway signals on scotopic 15-Hz flicker ERG. CONCLUSIONS: The novel profile identified in this study suggests the existence of more than two rod pathways. The distinctive ERG feature was not observed in patients with X-linked CSNB1 and additional affected individuals with unknown molecular defect. These observations will help to discriminate autosomal recessive from X-linked recessive cases by ERG and molecular genetic analysis.