18th annual Frank Costenbader Lecture. Fusion and suppression: development and loss

Hess Lancaster Screen Test with Eye Tracker: An Objective Method for the Measurement of Binocular Gaze Direction

Background: To objectively measure with an eye tracker both eye movement conjugacy and gaze direction in different positions when performing the Hess Lancaster Screen Test (HLST) in a sample of control subjects without binocular dysfunction and compare the results with those of the traditional subjective HLST performance. Methods: The sample was selected avoiding subjects who suffered from suppression of one of the two eyes, visual acuity less than 20/25 on the Snellen chart in each eye, strabismus, or any symptom of binocular dysfunction that could alter the results. While performing the HLST, the examiner wrote down each of the points on a template in a traditional way while the eye tracker (Tobii Pro Fusion, Tobii AB, Danderyd, Sweden), placed in front of the subject, took objective measurements of the position of both eyes at each point. Of the 29 subjects recruited in this study, 13 subjects between 18 and 27 years old underwent the complete optometric examination and the HLST wearing anaglyph glasses; meanwhile, 16 people were excluded because of binocular or accommodative dysfunctions or because they didn’t give reliable eye-tracking results. Additionally, a specific program called Etracker Parse Video (University of Zaragoza, Zaragoza, Spain) was developed to analyse the prismatic deviation between both eyes at each evaluated point. Results: Similar horizontal prismatic deviations of visual axes were obtained in the different gaze positions with the Maddox rod, the manually annotated HLST, and the eye-tracker measurement. Variations were found in the magnitude of the deviation between methods but not in the direction. On the other hand, vertical deviations were more difficult for the examiner to detect and quantify, especially those with small magnitudes; more exact values were obtained when measuring objectively with the eye tracker. Conclusion: The HLST is very useful and allows the amount of heterophoria or heterotropia to be recorded in the patient’s medical record in all the main gaze positions. This test is complementary; by itself, it is not diagnostic and does not replace a complete examination of binocular vision. The eye tracker is an objective method with which we can evaluate the HLST in patients with no binocular problems, obtaining more accurate results than when it is performed in the traditional manner.

Objective measurement of nine gaze-directions using an eye-tracking device

Purpose: To investigate the usefulness and efficacy of a novel eye-tracking device that can objectively measure nine gaze-directions.

Methods: We measured each of the nine gaze-directions subjectively, using a conventional Hess screen test, and objectively, using the nine gaze-direction measuring device, and de-termined the correlation, addition error, and proportional error. We obtained two consecu-tive measurements of the nine gaze-directions using the newly developed device in healthy young people with exophoria and investigated the reproducibility of the measurements. We further measured the nine gaze-directions using a Hess screen test and the newly developed device in three subjects with cover test-based strabismus and compared the results. Results: We observed that the objective measurements obtained with the newly developed gaze-direction measuring device had significant correlation and addition error compared to the conventional subjective method, and we found no proportional error. These measure-ments had good reproducibility.

Conclusion: The novel device can be used to observe delayed eye movement associated with limited eye movement in the affected eye, as well as the associated excessive movement of the healthy eye in patients with strabismus, similar to the Hess screen test. This is a useful device that can provide objective measurements of nine gaze-directions.

Dorsal midbrain syndrome with loss of motor fusion: a rare association

INTRODUCTION

Dorsal midbrain syndrome (DMS) is characterized by upgaze paralysis, convergence-retraction nystagmus, and eyelid retraction. Impaired downgaze and pupillary light-near dissociation may co-exist, while less common features including exotropia and convergence paralysis have also been described. However, loss of motor fusion is not a well recognised finding in DMS.

PURPOSE

To describe DMS associated with loss of motor fusion.

METHODS

Retrospective case series.

RESULTS

Five patients (age 21-80 years) presented with features of DMS due to severe head injury (n=1), brainstem stroke (n=3) and pinealoma (n=1). All five complained of constant diplopia with horizontal and vertical separation and had an exotropia (range 20Δ to 70Δ), absent convergence and motor fusion. Two underwent strabismus surgery and subsequently had a variable improvement in their motor fusion. The remaining three patients were managed with occlusion.

CONCLUSION

This case series illustrates the complexity of ocular motility findings associated with DMS and highlights the potential difficulties in the management of patients with loss of motor fusion.

Changes in the functional binocular status of older children and adults with previously untreated infantile esotropia following late surgical realignment

BACKGROUND

Most studies of infantile esotropia concern patients diagnosed in infancy and treated throughout childhood. This prospective study addresses changes in the functional binocular status of older children and adults with previously untreated infantile esotropia, following late surgical realignment.

SUBJECTS AND METHODS

Seventeen patients aged 8 years or more with a history of untreated esotropia occurring within the first 6 months of life were included in this study. All had monocular optokinetic asymmetry, a visual acuity of 20/30 or better in the worse eye, and binocular function assesment preoperatively and postoperatively. All were surgically aligned within 8(Delta) of orthotropia. None had neurologic disease.

RESULTS

Preoperatively, all 17 patients demonstrated a monocular response to Bagolini lenses, while postoperatively 15 (88%) of the 17 demonstrated binocular function with Bagolini lenses (in that they could constantly perceive the major part of both arms of the X generated by the Bagolini lenses) and 13/17 (76%) demonstrated an increase in the binocular field. All 17 had no sensory fusion, either preoperatively or postoperatively, when tested with the Worth 4-Dot test or synoptophore, and no stereopsis with the Titmus stereo test.

CONCLUSIONS

Older children and adults with previously untreated infantile esotropia derive some functional benefits following late surgical realignment. The degree of binocular function may be lower than that achieved in patients aligned before 24 months of age.

Relationships between visual acuity and anomalous head posture in patients with congenital nystagmus

PURPOSE

To determine whether patients with congenital nystagmus and an anomalous head posture have better binocular visual acuity than such patients without an anomalous head posture.

PATIENTS AND METHODS

This was an observational case series of prospectively collected data for 125 patients with clinical and oculographically confirmed congenital nystagmus. Clinical data were tabulated using computer software. Statistical analyses compared binocular visual acuity with and without the presence of a clinically evident anomalous head posture and visual acuity with and without associated sensory disease.

RESULTS

The mean visual acuity was 20/42 (log of the minimal angle of resolution [MAR], 0.32) in patients with an anomalous head posture and 20/83 (logMAR, 0.62) in patients with no anomalous head posture (P < .001). Among patients with disease of the sensory system, those with an anomalous head posture had a mean visual acuity of 20/55 (logMAR, 0.44) and those without an anomalous head posture had a mean visual acuity of 20/108 (logMAR, 0.73; P < .001).

CONCLUSIONS

Visual acuity was found to be significantly better in patients with congenital nystagmus who had an anomalous head posture versus those without such a head posture. Our findings indicate that the presence of an anomalous head posture in a patient with congenital nystagmus correlates with good vision and thus may be considered a positive prognostic sign in a preverbal child.

Untreated essential infantile esotropia: factors affecting the development of amblyopia

PURPOSE

A concomitant esotropia, presenting within the first 6 months of life, associated with a high incidence of dissociated vertical deviation, manifest latent nystagmus and asymmetric optokinetic nystagmus is termed essential infantile esotropia. Most studies concern patients diagnosed in infancy and treated throughout childhood. This paper addresses the factors that may influence the development of amblyopia in patients who remain untreated until visual adulthood.

METHODS

During a 3 year period 113 patients aged 8 years or more with a history of esotropia occurring within the first 6 months of life were examined for the study. All patients underwent full ocular motility assessment and cycloplegic refraction, and only those with one or more signs of essential infantile esotropia were included.

RESULTS

Of the 113 patients, 16 (14.3%) had a difference of 2 or more lines in the visual acuity of the two eyes and were diagnosed as having amblyopia. Anisometropia was present in 10 of the 16 (62.5%). The correlation between anisometropia and amblyopia was statistically significant (p = 0.0001).

CONCLUSIONS

Amblyopia following early surgical intervention in essential infantile exotropia is well documented, but the risk is outweighed by the chance of obtaining some form of binocular vision. However, where access to ongoing therapy is not available, patients with essential infantile esotropia, free alternation and no anisometropia have a significant chance of retaining good visual acuity in both eyes if surgery is delayed until visual adulthood.

Binocular function and amblyopia after early surgery in infantile eosotropia

We report on binocular function and amblyopia in children who had surgery for infantile eosotropia in the first 24 months of life. Fourteen (56%) achieved peripheral fusion and no child obtained high grade stereopsis. Following surgery and treatment for amblyopia 20% remained amblyopic.

Loss of stereopsis in monkeys following prismatic binocular dissociation during infancy

Prismatic binocular dissociation was used during infancy to mimic conditions of strabismus in macaque infants. Prisms worn continuously produce a diplopia unfavorable for the maintenance and development of the binocular visual system. Prism-reared monkeys were tested as young adults and found to be permanently stereoblind for dynamic random dot stereograms. Control monkeys did comparably to humans on such tests. It is concluded that short periods of diplopia attendant with strabismus are sufficient to produce permanent stereoblindness.

Acquired central fusion disruption following cataract extraction

Central sensory and motor fusion of images, once established, is usually maintained throughout life. Under certain circumstances, this ability may be lost. This gives rise to the syndrome known as horror fusionis, or acquired disruption of central fusion. We report the development of central fusion disruption in three patients with uniocular mature senile cataract. We postulate that this is the result of prolonged sensory deprivation in the cataractous eye. The loss of fusion results in a particularly troublesome type of intractable diplopia, characterized by the inability to either fuse or suppress images. To the best of the authors' knowledge, this is the first report of central fusion disruption following cataract surgery for senile cataract.

Results of early surgery for infantile esotropia in normal and neurologically impaired infants

A prospective study was performed over a 4-year period of 56 infants presenting with infantile esotropia to assess development of binocularity after surgical alignment before 2 years of age. In 50% of cases infantile esotropia was associated with neurological problems or prematurity. Forty-three cases have undergone surgery (mean age 15.7 months +/- 3.46); 86% were aligned (+/- 10 dioptres) at 2 years. Eighty-seven per cent of normal children and 74% of children with neurological problems or prematurity were aligned at last follow-up (mean 27.2 months since surgery). Tests of fusion and stereopsis have to date been possible upon 21 'successfully' aligned infants and although most have evidence of peripheral sensory fusion none showed stereopsis to more than one test. Although early surgery achieves a good cosmetic result in normal children and those with neurological problems, our findings question its ability to promote the development of even gross stereopsis in most children.