The association of ocular dominance and the preferred eye for fixation in intermittent exotropia: a guide to choosing the eye for unilateral surgery

OBJECTIVE

Recession of the lateral rectus muscle of the more frequently deviating eye in patients with small-angle intermittent exotropia has yielded good results. However, sometimes neither history nor clinical examination can identify this eye. This study sought to determine if the dominant eye of patients with intermittent exotropia is the preferred eye for fixation i.e., not the more frequently deviating eye.

METHODS

We recruited 40 patients (33 males, 7 females) aged 2.5 to 44.0 years (mean 9.5, SD 8.7) who had intermittent exotropia and attended our eye clinic between September 1998 and April 1999. Exclusion criteria included age (patients too young to cooperate), previous strabismus surgery, poor vision, neurological disorders or abnormal ocular motility, and unsuccessful determination of the preferred eye for fixation from history and examination. The preferred eye for fixation was determined by an orthoptist using cover tests, the dominant eye by an ophthalmologist using sighting and convergence near-point tests.

RESULTS

Tests showed that the dominant eye was almost invariably the same eye as the preferred eye for fixation.

CONCLUSIONS

For patients who have small-angle intermittent exotropia, when the more frequently deviating eye cannot be definitely determined before unilateral surgery, the sighting test can help identify the dominant eye.

Vision screening of 4-year-old children in Singapore

AIM OF THE STUDY

To evaluate the feasibility of an improved visual acuity screening program for Singapore 4-year-old preschool children and to draw up an appropriate referral criteria as well as evaluating the rates and outcomes of these referrals.

METHOD

A total of 450 children aged 4 to 4 1/2 years, who attended 3 polyclinics of the Family Health Service (FHS) for their 4-year-old Developmental Health Screening during the study period from 1/4/1997 to 30/6/1997 were recruited for the study. Children who were tested with Snellen (or Sloan) visual acuity chart resulting in visual acuity of 6/9 or worse, or failed to pass the 3 mm medium plate at 30 cm distance (300 seconds of arc) in the Frisby Stereotest, or were found to have strabismus, or were untestable in either visual acuity test or stereotest were offered referral to ophthalmologists in the hospitals for specialist assessment.

RESULT

82.7% of the 450 children were successfully screened with Snellen (or Sloan) chart while 91.6% were successfully screened with Frisby Stereotest. In all, 180 children were evaluated by ophthalmologists. Majority of the children were referred because of their abnormal visual acuity test while only 2 children were referred for failing stereotest alone. Among the 180 children referred, 63 (35.0%) were found to have refractive errors for which spectacles were prescribed. Eight children had amblyopia and 2 children had strabismus which were not detected at the polyclinic screening. The untestable children evaluated had significantly higher abnormality rate (37.5%) than that of children who had 6/9 vision (8.8%) therefore they should be offered referral for further evaluation. There was high "refused referral" rate of 39.0%. Parents of children who were untestable or had 6/9 vision were found to be more likely to refuse offer of referral. If these two groups of children were excluded, the "refused referral" rate dropped to 13.3%. When the referral criteria for visual acuity was reset at 6/12 instead of 6/9, the referral rate dropped from 39.6% to a more manageable 26.7% and the positive predictive value improved from 35.4% to 48.3% and none of the children with amblyopia were missed being screened-out.

CONCLUSION

The study confirmed the feasibility of doing visual acuity screening at 4 to 41/2 year-old. The referral criteria for abnormal visual acuity should be set at 6/12. The efficacy of adding Frisby stereotest needs further evaluation.

A review of 5 years' experience in the use of botulinium toxin A in the treatment of sixth cranial nerve palsy at the Singapore National Eye Centre

INTRODUCTION

This retrospective study reports our experience on the use of botulinum toxin A (BTXA) in the treatment of sixth cranial nerve palsy at the Singapore National Eye Centre. BTXA is derived from clostridium botulinum; it causes temporary paralysis of the extraocular muscle (medial rectus) into which it is injected, thus preventing its contracture and allows the antagonist lateral rectus muscle to take up the slack and reduce or correct the ocular misalignment.

METHODS

Nineteen patients had BTXA injection for estropia due to sixth cranial nerve palsy during the period September 1992 to August 1997. The sixth cranial nerve palsy was related to nasopharyngeal carcinoma in 76.7% of cases. Follow-up after the last injection ranged from zero (defaulted) to 21 months (mean 8, median 6 months).

RESULTS

A total of 25 injections were given to 19 patients. Seven patients (36.8%) had final ocular alignment within 10 prism dioptres of orthotropia of which six achieved fusion at primary gaze position. There was no correlation between the number of injections per patient and the size of strabismus or grade of lateral rectus muscle function. The incidence of ptosis was 48%, subconjunctival haemorrhage 16% and hypertropia 16%.

DISCUSSION

Our results suggest that those patients with smaller strabismus and a shorter time interval between onset of strabismus and botulinum injection tend to achieve better outcome in terms of fusion or ocular alignment within 10 prism dioptres of orthotropia. The treatment of strabismus with BTXA is an acceptable approach in selected patients. The procedure is simple, safe, cheap, effective, and avoids the risks of general anaesthesia. It can substitute for or eliminate the need for strabismus surgery in some cases of sixth nerve palsy.

Case report of Usher's syndrome in two sisters--first reported case in Singapore

A 28-year-old Chinese woman presented with poor night vision since childhood. Ocular examination showed pigmentary retinopathy and systemic examination revealed sensorineural hearing loss. Family history showed a similar condition in her youngest sister. Ocular and systemic examination of her sister showed similar findings. This is presented as the first case report of Usher's syndrome in Singapore. A general discussion of Usher's syndrome is also presented.

Analysis of photorefractive keratectomy patients who have not had PRK in their second eye

BACKGROUND AND OBJECTIVE

Excimer laser photorefractive keratectomy (PRK) is performed at the Singapore National Eye Centre (SNEC) with a minimum period of 3 months between first and second eye treatment. During this period, iatrogenic anisometropia may occur, which can lead to significant visual disability. We analyzed the reasons why some patients delayed or did not receive PRK treatment to their second eye. The reasons for originally electing PRK, and the expectations these patients had, were also studied.

PATIENTS AND METHODS

Between January 1992 and September 1993, 341 patients underwent PRK at SNEC. Of these, 86 (25.2%) did not receive PRK to their fellow eye within 1 year of follow-up and were recruited into the study. Data were collected retrospectively using a standardized questionnaire, and objective clinical data were obtained from the case records. Sixty-eight patients (79%) responded.

RESULTS

Fifty-one patients (14.9%) had not undergone PRK at the conclusion of the study (mean follow-up = 31 months). Of these, 36 were due to dissatisfaction with the results of the procedure. Symptoms relating to hypermetropia (15 patients) and symptoms of glare and halos were the main reasons which discouraged patients from receiving PRK in their fellow eye. Seventeen of the 51 patients (33.3%) who did not have PRK performed in the second eye were overcorrected to hypermetropia, as opposed to 9 out of 255 patients (3.5%) who had PRK in the second eye (P < 0.001, chi-square test). Seventy-five percent of the patients who did not undergo PRK in the second eye expected postlaser unaided vision to be equal to prelaser best corrected vision; however, only 23% of these patients achieved this.

CONCLUSION

Hypermetropia, glare and halos are significant causes of patient dissatisfaction after PRK. Patients who request PRK should be advised against harboring unrealistically high expectations for the procedure.

Mandibulo-facial dysostosis--the eye signs of a case study

The mandibulo-facial dysostosis syndrome (Treacher-Collins syndrome) was first described in 1889. It is a syndrome with multiple presentations, the classification for which was devised by Franceschetti and Zwahlen in 1944. The eye signs are an important part of this syndrome. In addition to the main ocular features of colobomata of the lower eyelids and an anti-mongoloid slant, many other eye signs have been reported. An 18-year-old Indian male was found to have features not previously described. These are high myopia, dermolipoma, lens subluxation and secondary glaucoma.

A study of amblyopia in 18-19 year old males

During a vision screening of 6,556 National Service pre-enlistees aged 18-19 years at the Medical Classification Centre of Central Manpower Base, 48 subjects were found to have visual acuity of 6/12 or less in one or both eyes in the absence of ocular pathology. The prevalence of amblyopia in this population is 0.73%. Amblyopia was due to anisometropia in 24 cases (50%), strabismus in 9 cases (18.7%), high astigmatism (meridional) in 7 cases (14.5%) and other causes or a combination of factors in 8 cases (16.7%). Strabismic amblyopia is most commonly associated with esotropia. There is a positive association between the severity of amblyopia and the degree of strabismus in strabismic amblyopes. Meridional amblyopia tends to be less severe than most other types of amblyopia. The amblyopes were detected late (average 7-10 years of age) and orthoptic treatment of a small minority of them upon diagnosis was unsuccessful.