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We present a case of ocular deviation and diplopia that developed 9 months after monocular excimer laser photorefractive keratectomy. In this case, decompensation occurred because of a breakdown of fusion at distance. We suggest a cover test to assess the presence of significant phorias in all candidates for refractive surgery procedures.
BACKGROUND: This study was designed to resolve uncertainty concerning whether the position of the examiner is associated with variability in the results of the nearpoint alternate cover test (NACT). Two previous studies have shown that when the examiner is positioned to the side of the patient, rather than directly in front of the patient, the NACT shows greater exophoria in the range of 1.3 to 4.4 prism diopters. In the current study, we sought to determine if proximal cues or effective prism power might be the source of the apparent exo shift associated with examiner position. METHODS: Three conditions of the NACT were performed on 52 young adults with normal visual function. Two measurements using the method of limits were made in each condition and averaged. In all conditions, the fixation target remained on the subject's midline at a distance of 40 cm. RESULTS: Our results showed a small significant increase in measured exophoria when the examiner administered the NACT from a position to the side of the subject. The magnitude of the increase, 0.98 prism diopter, was less than in the previous studies, probably due to the control for proximal effect that was used. Intentionally rotating the measuring prism had a nominal effect on the measured phoria value, consistent with error induced due to effective prism power. DISCUSSION: It appears that examiner position does affect the outcome of the NACT, but that the magnitude of the effect is not clinically significant. A change in proximal cues may contribute to the effect.
This experiment showed that phoria-induced displacement adds to or subtracts from prism-induced displacement. A near stimulus (25 cm) was apparently displaced more than the optical displacement when the base of a prism was out and less when the base was in. In contrast, a far stimulus (200 cm) was displaced less when the base was out and more when the base was in. Moreover, the between-subjects variability of the apparent displacement was greater with monocular than with binocular viewing. Some implications for studies on monocular prism adaptation are discussed.
All patients presenting with double vision as a principal symptom who presented to the Casualty Department of Moorfields Eye Hospital over a nine month period were prospectively investigated. Two hundred and seventy five patients were identified accounting for 1.4% of all casualties. Monocular diplopia was commoner than expected accounting for 69 cases (25.1%) and was almost always a genuine symptom attributable to uniocular pathology, most commonly lenticular or corneal pathology. Two hundred and six patients (74.9%) had binocular diplopia and in most cases an aetiology was established. Cranial nerve palsies were the commonest cause of binocular diplopia accounting for 81 cases. Other causes were classified as convergence or accommodation problems, decompensating phorias, traumatic, muscular, orbital lesions, supranuclear lesions, and other miscellaneous conditions. In eight cases of monocular and 23 cases of binocular diplopia no cause for the symptoms could be identified.
PURPOSE: To define the clinical characteristics of patients presenting with acute onset esotropia and features suggestive of possible underlying central nervous system pathology. To assess the prognosis for the return of binocular function and to consider the most appropriate management. METHODS: A prospective clinical study was carried out of all patients presenting to the department of paediatric ophthalmology at a university teaching hospital over the period January 1994 to April 1997. Each patient underwent a full ophthalmological examination (including assessment of sensory status). All patients were referred to a paediatric neurologist for examination and CT and/or MRI scan. RESULTS: Ten patients presented during the study period. Uncorrected hypermetropia and/or decompensated monofixation syndrome were the commonest aetiological factors. One patient was found to have a cerebellar tumour. In 5 patients prescription of the full hypermetropic correction alone was sufficient to restore binocularity. Five patients required bilateral medial rectus recession. Binocular function was restored in all cases--in 5 cases with bifoveal fusion. CONCLUSION: Decompensation of a pre-existing phoria or monofixation syndrome appears the commonest aetiology. Prescription of the full hypermetropic correction found at cycloplegic refraction forms an essential part of initial management. No single clinical sign can reliably indicate the rare patient harbouring a tumour. A high index of suspicion should be maintained and neuro-imaging considered in the absence of expected findings such as hypermetropia or fusion potential or in the presence of atypical features or neurological signs.
BACKGROUND: Publications on changes of optic disc topography usually illustrate their findings with two-dimensional images. METHODS: With the introduction of computerized imaging, anaglyphs of stereo images can be produced for illustrations. Anaglyphs are viewed three-dimensionally with red-green spectacles that are included in refraction sets and are normally used to assess phoria. An anaglyph of progressive, glaucomatous progression is included to demonstrate the method, along with conventional colour images. RESULTS: We present two cases of severely altered optic disc topography post-trabeculectomy and illustrate these cases with anaglyphs that can be viewed three-dimensionally. CONCLUSION: Three-dimensional viewing of illustrations assists with the visualization, perception and interpretation of optic disc changes.
The characteristics of prism induced fixation disparity curve at near were studied in 56 asymptomatic young adult Hong Kong Chinese (average age 21 years). The percentage distribution of types of fixation disparity curves was found to be similar to some previous studies, with a higher prevalence of Type I curve (64.3%), followed by Type II (28.6%) and Type III (7.1%) curves. No Type IV curve was revealed from the sample. Two modified measurement approaches were applied to study the effect of measurement techniques on the parameters of fixation disparity curve obtained. A thorough description of the techniques was given. Although a significant difference in the x- and y-intercepts was obtained between different methods, the curve type and slope were not affected. The average y-intercepts (fixation disparity) were 2.72 min of arc and 3.54 min of arc from two methods respectively. Forty-one subjects had x-intercept (associated phoria) found from the curve. The average values were 2.42 delta base-out and 3.54 delta base-out from two methods respectively.
The aim of this study was to investigate the incidence of functional vision problems in a large unselected cosmopolitan population of primary school-age children and to investigate whether constant clinical criteria for functional vision problems would be implemented by the practitioners involved in the screening. Refractive errors, near point of convergence, stereopsis, strabismus, heterophoria and accommodative facility were assessed for 2697 children (3-12 years) of varying racial backgrounds living in Australia. The spherical component of the refractive error ranged from -7.75 to +9.50 D (mean +0.54 D, +/-0.79) with a distribution skewed towards hypermetropia; astigmatism ranged from 0 to 4.25 D (mean -0.16 D, +/-0.35). There was a trend towards less hypermetropia and slightly more astigmatism with age. Mean near point of convergence was 5.4+/-2.9 cm, heterophoria at far and near was 0.12+/-1.58delta exophoria and 1.05+/-2.53delta exophoria, respectively, 0.55% of children exhibited vertical phoria at near >0.5delta, accommodative facility ranged from 0 to 24 cycles per minute (cpm) (mean 11.2 cpm, +/-3.7), stereopsis varied from 20 to 800 s (") of arc with 50% of children having 40" or better. The prevalence of strabismus was particularly low (0.3%). Twenty percent of the children were referred for further assessment based on criteria of one or more of: stereopsis >70", accommodative facility <8 cpm, near point of convergence (NPC) >9 cm, near exophoria >10delta or near esophoria >5delta, shift in eso or exophoria > or = 4delta between distance and near, astigmatism > or = 1 D, myopia more than -0.75 D, or hyperopia >+1.50 D. Post-hoc analysis of the record cards seeking the reason for further assessment indicates that referrals appear to have been based upon clinical intuition rather than on a set number of borderline or unsatisfactory results.
BACKGROUND: Previous studies have found that crossed disparities give better stereoacuity than uncrossed. When near phoria is considered, exophores had a better crossed stereoacuity and esophores had a better uncrossed stereoacuity. The current study investigated the effect of heterophoria on distant crossed and uncrossed stereoacuity. METHODS: Seventy-two subjects were recruited and their distant heterophoria measured. Heterophoria within two prism dioptres was considered as orthophoric. Esophoric group had esophoria greater than two prism dioptres. Exophoric group had exophoria greater than two prism dioptres. There were 40 orthophores, 23 exophores and nine esophores. Their stereoacuity was measured with a three-rod apparatus at 6 m. RESULTS: The mean crossed stereoacuity was 4.8" and uncrossed stereoacuity was 7.2" (t = -3.03, p < 0.01). The mean stereoacuity for orthophoric subjects was 5.31", 6.02" for exophores and 8.91" for esophores. The distant crossed stereoacuity is better than uncrossed stereoacuity in all three groups but the difference is only significant for the exophores. Exophoric subjects demonstrated a significant difference between crossed (4.10") and uncrossed (7.95") stereoacuity. CONCLUSIONS: Orthophores have the best stereoacuity, followed by exophores and esophores. Exophoric subjects have a better crossed than uncrossed stereoacuity. More esophoric subjects should be recruited to confirm the difference between crossed and uncrossed stereoacuity.
At the end of a clinical trial of bifocals as myopia treatment, subjects were allowed to select any type of optical correction they wished and were asked to return in 1 year. This report gives results of that last examination with emphasis on how progression rates differed between those remaining in their original type of glasses compared with those who switched to soft contact lenses. We found that myopia progressed at an age-adjusted average rate of 0.74 D in 19 children who switched to soft contact lens wear compared with 0.25 D for 24 children remaining in glasses (p < 0.0001). Increased growth of the vitreous chamber appeared to account for much of this excess myopia progression, although the difference in that variable did not reach statistical significance (p = 0.101). We also noted a 0.203 D steepening in the corneal curvature in contact lens wearers compared with spectacle wearers whose corneas steepened very little (0.014 D, p = 0.007). Soft contact lens wear was also accompanied by a greater change in the near-point phoria which moved 4.5 prism dioptres in the exo direction compared with spectacle wearers who experienced only a 1.4 prism dioptre divergent shift (p = 0.048).
PURPOSE: To report on a 7-year-old boy with a small left-over-right deviation (-VD) which increased when the head was tilted to the left shoulder and during convergence. METHODS: The squint angles were measured by the unilateral and alternate prism cover test at distance and near fixation when the head was in ortho-position and when it was tilted. RESULTS: At distance fixation (D) there was a latent deviation of-VD 3 degrees. With near fixation (N) at 0.3 m the vertical phoria increased to-VD 18 degrees. The angle of deviation was not influenced by (N) convex lenses in front of the fixating eye despite an adequate dis-accommodation. The-VD was fairly comittant in right and left gaze. At 45 degrees head tilt to the right shoulder the-VD decreased to (D) 2 degrees and (N) 12 degrees. At 45 degrees head tilt to the left shoulder the-VD increased to (D) 18 degrees and (N) 26 degrees. A dissociated vertical deviation was excluded by the dark red glass test and by the reversed fixation test. CONCLUSION: The disturbance can be explained by a, presumably congenital, supranuclear misinnervation and has to be differentiated from other types of vertical deviation.
BACKGROUND: Ocular prevalence is defined as an unequal weighting of the eyes in the directional perception of stereo objects. Opinions differ as to the cause and relevance of ocular prevalence. Hans-Joachim Haase suggested that ocular prevalence is due to fixation disparity, brought about by incomplete compensation of heterophoria. He further suggested that prismatic spectacles determined by his "measuring and correcting methodology" (MKH) could restore bicentral fixation and thus establish a perceptual balance between both eyes. METHODS: We examined 10 non-strabismic subjects with a visual acuity of > or = 1.0 in both eyes. It turned out that all 10 had a "fixation disparity type II", characterised according to Haase by a "disparate retinal correspondence". All subjects underwent the automatic Freiburg Ocular Prevalence Test, without and with MKH prisms. In addition we examined ocular prevalence under forced vergence and compared ocular prevalence with stereoacuity. RESULTS: Spontaneous ocular prevalence ranged between 1 and 69 %. Averaged over all 10 subjects, ocular prevalence without and with the MKH prisms were not significantly different. Statistical evaluation of single subjects revealed only in one of the 10 a significant difference (Bonferroni-corrected p = 0.001). In the subgroup of 5 subjects who underwent forced vergence, ocular prevalence remained unaltered between 0 and 18 Delta base out. The stereoscopic threshold of all 10 subjects ranged between 1.5 and 14.5 arcsec. There was no correlation between ocular prevalence and stereoscopic threshold (r = - 0.2, p = 0.5). CONCLUSION: Our results indicate that ocular prevalence is largely independent of phoria correction and vergence stress. The excellent stereoacuity of all subjects suggests that ocular prevalence is abandoned for the sake of optimal resolution when very small differences in depth have to be judged.
A collection of programs has been developed on the Macintosh II computer to generate visual tests for an ophthalmological practice. The large number of available colours makes it possible to emulate most of the available tests and also to develop new ones. The system allows testing of the following visual functions: Visual acuity, Stereopsis, Aniseikonia, Phoria, Cyclophoria, Colour Vision and Contrast sensitivity.
71 patients (average age 64 years) were examined for binocular vision after unilateral posterior chamber lens implantation. Average visual acuity in the pseudophacic as well as the phacic eyes was 0.8. Intact stereoscopic dose-up and long-distance vision was found in 85% of the cases. Patients with vertical phorias or moderately decreased visual acuity more often presented impaired binocular functions. Further investigations will be carried out.
A study was carried out by seven ophthalmologists practising in the Berne region on 473 patients complaining of eye strain. Medical histories were taken by questionnaire, refraction was done and phoria measured, followed by therapy in accordance with the physician's opinion. In 380 cases, glasses were prescribed, including prismatic glasses for 14 patients. In 123 cases, local medical therapy was instituted. The statistica evaluation of pre-treatment findings and results of therapy, was carried out using a computer. The principial complaints before treatment were eyestrain and visual disturbances, followed by conjunctival irritation and headache. Women complained more about headaches, men more about visual disturbances. A majority of the patients with visual disturbances needed minus lenses, while for the treatment of headaches mostly plus lenses were needed. In patients with conjunctival irritation local medical treatment resulted in additional relief of symptoms. Cylindric correction had only a minor influence on the result of therapy. Heterophoric patients did not have more complaints than orthophoric ones, and results with spectacles without prisms were the same as in orthophoric patients.
A report covering 80 cases of esophoria in which surgery was performed. All the patients had previously suffered from severe headache and other complaints. Preoperative treatment consisted of full prismatic correction. The power of the prisms was measured by the "Polatest" method. We observed that the increase of the angle was initially very slow; sometimes two years or more were needed for it to reach 15 degrees. Subsequently the angle increased rapidly, stabilizing a few months later, whereupon surgery was performed. The peroperative angle varied from 15 degrees to 56 degrees. Postoperatively most cases attained orthophoria, some others a residual esophoria; there were only three cases of exophoria, these being among the 14 cases who had to undergo surgery twice. Sixty percent of the patients were subsequently free of complaints and the rest, with two exceptions, showed a distinct improvement. The average follow-up period was 2.2 years after surgery. One may conclude that esophorias which give rise to complaints can be treated with prisms, but that some of them may have to be operated on. For successful treatment a reliable instrument for measuring the angle of the phoria is indispensable. We found the Polatest best for this purpose. In most cases orthophoria and permanent relief of symptoms will result.
Seven female volunteer bank clerks aged between 24 and 32 yr were selected for a laboratory trial after a preliminary ocular examination which showed them to be emmetropic or slightly myopic (less than or equal to 1D) and to have normal ocular motility or only minor deficiencies. Near and far point refraction and phorias and near point fusional vergences were measured before and immediately after a 6 h workday at a PC workstation. Eye screen distance (viewing distance) was monitored. Near and far distance refraction showed an increase and a decrease of accommodation in 13 out of 14 eyes respectively. Fusional convergence decreased in six out of seven cases: a smaller decrease in divergence was recorded in all subjects. These changes were statistically significant. Viewing distance, though showing some interindividual differences, increased considerably during the last 2 h of the trial, without reaching statistical significance.
This experimental study was conducted on 14 volunteer female clerks to measure viewing distance variation and related ophthalmological changes in office activities with (session 1) and without (session 2) VDU. A video camera connected to an electronic elaborator was used to determine eye-screen distance of the VDU operators during the task. Before and after each of the two work sessions far refraction, far phorias, near point of accommodation (APP), and fusional convergence were measured. Blinking rate of each subject was measured by a transducer only during the "VDU session'. The objective measurements of the eye-screen distance, whose range was between 48.42 and 65.33 cm, allowed a precise quantification of the occupational visual load during session 1. The accommodation was about 1.5-2D on average and the fusional convergence 10-13 delta on average. The symptomatology shows a number of disturbances in session 1 (71.4%) clearly higher than in session 2 (35.7%). The study of refraction before and after the task has shown a slight excess of accommodation compared to the theoretical value in both sessions, more marked in session 1. The APP shows no statistical significative variation. A tendency to exophoria was registered at the beginning and at the end of the trial and the fusional convergence clearly decreased, especially in the first session.