Objective evaluation of sensorial and sensorimotorial status in esotropia: their importance in surgical prognosis

Recent understanding of binocular vision in the natural environment with clinical implications

Technological advances in recent decades have allowed us to measure both the information available to the visual system in the natural environment and the rich array of behaviors that the visual system supports. This review highlights the tasks undertaken by the binocular visual system in particular and how, for much of human activity, these tasks differ from those considered when an observer fixates a static target on the midline. The everyday motor and perceptual challenges involved in generating a stable, useful binocular percept of the environment are discussed, together with how these challenges are but minimally addressed by much of current clinical interpretation of binocular function. The implications for new technology, such as virtual reality, are also highlighted in terms of clinical and basic research application.

Late Surgical Correction of Longstanding Constant Strabismus in Adults: Is Fusion Possible in All Successfully Aligned Patients?

PURPOSE

To determine whether late surgical correction provides fusion in adults who have constant strabismus beginning in early childhood.

MATERIALS AND METHODS

This was a prospective study that included 34 consecutive adults with a history of early onset strabismus who had not previously undergone surgery. They were tested with the Bagolini striated glasses (BSG), Worth four-dot (W4D) test, cover test, and four-prism diopter (4-PD) test, preoperatively, and 6 weeks after surgery.

RESULTS

The mean age was 23.8 years, 17 patients had esotropia and 17 patients had exotropia. Preoperatively, all patients demonstrated a manifest horizontal deviation ranging from 30^∆ to 60^∆ and had suppression. At 6 weeks postoperatively, 33 patients had a horizontal manifest deviation of <15^∆ (range, 2^∆-14^∆; median, 6^∆), and none were orthotropic as determined by the cover test together with the 4-PD test. All of these 33 patients achieved anomalous retinal correspondence (ARC) with the BSG at near, and 25 (75%) had ARC with the W4D test at near.

CONCLUSIONS

Although our study has limited number of patients its findings suggest it is possible to develop ARC after surgery in almost all adult patients with childhood-onset strabismus associated with suppression, and who have not previously been operated upon, if satisfactory alignment is achieved in adulthood.

A pilot study of the value of prism adaptation in planning strabismus reoperations

PURPOSE

To evaluate the value of prism adaptation in planning strabismus reoperations.

METHODS

Of 15 patients with persistent strabismus, 9 underwent prism adaptation prior to strabismus reoperation and 6 underwent strabismus reoperation without preoperative prism adaptation. Corrective surgery was performed on the same or new muscles. Follow-up ranged from 3 months to 2 years. A horizontal deviation of 10 prism diopters or less was considered a successful outcome. Statistical analysis of the results was done.

RESULTS

Of the 9 patients who had prism adaptation, 3 (33%) were responders and 6 (67%) were nonresponders. A successful outcome was achieved in 6 patients (67%) who had prism adaptation and 3 patients (50%) who did not. The difference between groups was statistically insignificant (P > .05).

CONCLUSION

These results suggest that the benefits of prism adaptation are not significant enough to justify the time consumption and expenses of this test when planning strabismus reoperations, but a larger group of patients should be studied.

The irvine prism test: does the positive response indicate suppression scotoma?

PURPOSE

To investigate whether the positive prism test response is due to the presence of a suppression scotoma or the absence of bifoveolar fixation.

METHODS

Fifty-one subjects with esotropia (microtropia, small-, moderate- or large-angle esotropia), and 22 subjects with nonstrabismic anisometropic amblyopia were examined. The prism test was performed by using base-out prisms of two different powers (4-PD and 30-PD), and base-in prism of 20-PD, as well as base-down prism of 10-PD for each subject.

RESULTS

All the subjects with esotropia showed a positive prism test response, whereas all the subjects with nonstrabismic anisometropic amblyopia had a negative prism test response. All the esotropic subjects showed positive response to all magnitudes and positions of the prisms tested.

CONCLUSIONS

The positive response to the prism test does not indicate suppression scotoma in subjects with microtropia and small-angle esotropia because all the esotropic subjects showed the positive response regardless of the amount of deviation or the sensorial adaptation mechanisms. Also, the positive response, seen in the esotropic subjects, did not alter to negative by using the prisms of different powers and directions.

Effects of anisometropia on binocularity

PURPOSE

To investigate the effects of anisometropia on binocular function and the relationship between stereopsis and fusion in anisometropia.

METHODS

Twenty-five patients with anisometropia were studied. The manifest refraction and best-corrected Snellen visual acuity of each patient was recorded. Patients, corrected with spectacles, were evaluated using Bagolini glasses, the 4-diopter (D) prism test, Worth four-dot test, and TNO stereotest.

RESULTS

All patients indicated fusion by the Bagolini glasses. Although the 4-D prism test was positive in the anisometropic eye of all 25 patients, it was slower than the response of the other eye in 19 patients with reduced stereoacuity. On the distant Worth four-dot test, fusion response was positive in 15 patients. On theTNO test, stereoacuity levels were reduced or absent in 19 patients.

CONCLUSION

The depth of amblyopia is more effective than the amount of anisometropia in causing a deterioration in binocularity. Even if fusion is weak, almost all patients with anisometropia have bifoveal fusion. Fusion becomes weak and stereoacuity decreases in proportion to the anisometropic amblyopia. Stereoacuity is related to the strength of fusion, and the TNO stereotest effectively detects those patients with significant anisometropic amblyopia.

Binocular interactions and steady-state VEPs. A study in normal and defective binocular vision (Part II)

BACKGROUND

Recent evidence indicates that an index of binocular activity may be found in some properties of steady-state visual evoked potentials (VEPs), such as amplitude facilitation and phase shortening. We evaluated binocular interactions with steady-state VEPs in normal subjects as well as in patients with concomitant strabismus and defective binocular vision.

METHODS

Steady-state (8-Hz) VEPs to counterphased sinusoidal gratings (1.2 c/deg spatial frequency) of low contrast (3.2%) were recorded in 19 esotropic patients and in 18 age-matched controls. Patients had either anomalous retinal correspondence (ARC, n = 10) or suppression (n = 9) in casual seeing conditions (striated glasses). In all subjects, both binocular and monocular VEPs displayed a major component at twice the stimulation frequency (second harmonic), whose amplitude and phase were measured. A binocular interaction index was obtained by comparing binocular VEPs (BVEPs) with the sum (vectorial) of the two monocular VEPs (SMVEPs).

RESULTS

In normal subjects, BVEPs were larger in amplitude than SMVEPs (facilitation), and shortened in latency (phase). On average, both ARC and suppression patients displayed loss in amplitude facilitation and absence of phase shortening. However, 50% of ARC patients showed clear VEP facilitation. In both ARC and suppression patients, the amplitude ratio BVEP/SMVEP was negatively correlated with the amount of the angle of deviation.

CONCLUSION

These results suggest that losses in amplitude facilitation and phase shortening of binocular steady-state VEPs reflect abnormal binocular interactions associated with different forms of sensorial adaptation in concomitant strabismus.

Influence of existing retinal correspondence on the results of squint operations in alternating convergent strabism

In our study we examined the influence of existing retinal correspondence on the result of squint operations for alternating convergent strabism. 157 patients under 10 years of age at the time of their first or only operation were included. They were divided into groups, depending on their age at the onset of squint and subgroups according to their type of retinal correspondence. The development of distance and near deviation was investigated separately. Covariance analysis demonstrated that the preoperative sensorial state is a predictor for the motor outcome of surgery with regard to postoperative distance deviation. Statistically we found at least noticeable results (p < 0.15) in all groups of patients--for acquired esotropia a significant result (p < 0.01). With regard to the postoperative near deviation we found a significant influence of the preoperative sensorial state only in the group of patients with a late onset of squint (p = 0.05). For patients with an earlier onset (before the 30th month) of strabismus, the preoperative angle of near deviation proved to have a significant impact on the postoperative development of near deviation (p < 0.05). Sensorio-motorial adaptational phenomena in esotropia are presumed to be the major cause for this difference.

Prolonged preoperative prismatic treatment in alternating convergent squint

Our 10-year retrospective study includes 178 children below the age of 10 years, operated for alternating convergent squint. Inclusion criteria were: Absence of amblyopia and an angle of squint less than 45 pdpt so that alignment of the eyes in only one operation could be expected. One hundred children received preoperatively a prismatic correction of the distance deviation for a period of 6-15 months; 78 cases were treated with glasses and occlusion. In the prism-treated group a significantly better alignment (p = 0.0001) with a motorial gain of 7-8 pdpt was observed 6 months after surgery; also better sensorial results with significantly (p = 0.0001) more cases of stable NRC or harmonious ARC and improved binocularity were achieved. Unlike the type of esotropia, the preexisting retinal correspondence significantly influenced the motorial outcome (p < 0.05). Fewer reoperations were necessary in the prism-treated group (p = 0.001). Our results indicate that a prolonged prismatic correction is an effective preoperative treatment in patients with alternating convergent squint.

Surgical correction of convergent strabismus: its relationship to prism compensation

Esotropic patients whose angle of strabismus has been corrected by prisms frequently increase their angle deviation to compensate for the prismatic correction. This sensorio-motorial reaction to prism correction has been given the name of anomalous movements (a.m.). Quantification of a.m. has been made according to the amount of prisms that an esotropic patient is capable of compensating for (progressive prism compensation test--p.p. test). Some esodeviation does not compensate for any prisms at all since a.m. have not yet developed. Other cases compensate for as much as 40 or 60 prism diopters and more of over-correction of the angle deviation and they therefore have powerful a.m. The interference of these innervational forces acting on the medial recti to corrective surgery has been studied in 126 operated esotropic patients. A significant decrease from the expected surgical result (p less than 0.001) has been found in patients having powerful a.m., as can be judged by the p.p. test. It is believed that a.m. are an important drawback contributing to vitiate any formula on the amount of muscle surgery to be performed in patients having no possibilities of restoring normal binocular vision. Practical advice on how to eliminate this drawback and theoretical reasoning on the significance of a.m. are offered.