Strabismus Ashok Garg, Emanuel Rosen, Eric R Crouch, Ewa Oleszczynska Prost
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1Clinical Strabismus2

Binocular Vision1

Maria T Depena,
Eva Moreno
Maria T Iradier,
Federico Moreno
(Spain)
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DEFINITION
The term binocular vision refers to normal vision and implies the simultaneous use of both eyes.
The images perceived by each eye, or stimuli from a wide range of wavelengths of the visible spectrum, are simultaneously captured by the brain.
The visual system is one of the best understood sensory systems and is possibly the most complex. For binocular vision, the three components participating in the sense of sight (optical, muscular and neurological) need to function well. If this is not the case, it is impossible that each image formed at each retina will be focussed at the corresponding points, that these images will be of similar size, shape and contrast sensitivity, and that the eye will be capable of placing and keeping each retinal image on the fovea.
Binocular vision is the consequence of the co-ordinated joint action of both eyes. One eye plays a dominant role, and the general rule is that this corresponds to the organism's lateral development. Thus normally, the right eye would be dominant in a right-handed person, and the left in a left-handed individual. When this is not so, the phenomenon is referred to as crossed laterality.
The first degree of fusion, or binocular fusion, is denominated duo-ocular vision, while the term binocular is reserved for the second and third degrees.
Fusion of the image produced by the light stimulus in each eye into a unified perception by the brain is second-degree fusion. This fusion process has two components: a motor component, such that the image is perceived at the fovea, and a sensory fusion process whereby the brain is able to achieve single perception.
The third grade is known as stereopsis and permits the single image to be perceived as raised, having lost the form of a flat image to give the appearance of volume. The eyes would be the peripheral receptors of a perceptive system. We could therefore say that “we don't see with our eyes but with the cerebral cortex”.
Binocular vision does not mean that the images perceived are single images (fusion) only. Their shape, color, luminosity, etc. are also perceived and they are located in the space that surrounds them, denominated relative localization, and positioned in relation to our body, known as egocentric localization.
In order to have binocular vision, the entire optic tract needs to be complete. The presence of anomalies in any of the pathways which convey the image to the brain may lead to binocular vision abnormalities or even to a lack of binocular vision. This impossibility is at times minimized through various compensatory mechanisms.5
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Fig. 1: Monocular visual field
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Fig. 2: Binocular visual field
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INTRODUCTION
Each eye has a particular field of vision formed by two lines. One line runs from the inner side of the nose corresponding to the eye in question, and the other runs towards the ear also on the corresponding side. The normal visual field of each eye is 155°, as shown in the image. Everything that falls inside the 120° angle formed at the nose can be seen by both eyes. Since the eyes are not in the same place, there is a difference in the perception of the object of regard by each eye. This difference, or disparity, is called the “parallax”. The parallax is the apparent change in an object's position resulting from a change in the position of the observer. This concept is used in astronomy to compute the distance between the stars and the earth. A similar phenomenon is that used by the brain to compute the vision produced in each eye.
When the images reach the visual cortex, one of the processes undertaken by the brain is to fuse the images to produce a unified version of the two different images of each eye. If the observer does not have binocular vision, the image shown on the right will be seen if the right eye is dominant. That is, a separate blue ball and red cube. If the left eye is dominant, the image shown on the left will be seen, i.e. the blue ball behind the red block.
If the brain did not unify the images in this manner, double vision would be produced. This is not probable since the brain tends to eliminate one of the images, although it can be artificially induced to perform tests or may be the consequence of certain diseases or surgically induced.
Disorders in binocular vision occur when there is an abnormal functioning of the motor-sensory system which is in turn dependent upon:
  • Anatomical integrity
  • Sensory integrity.
Each ganglionic cell of the retina is stimulated by a particular area of the visual field known as the receptive field. Only stimuli within this field are transmitted to the remaining cells of the optic pathway. Seen in this manner, each ganglionic cell would directly transmit an impulse, but multiple cell interactions dictate the overlapping of contiguous retinal fields.
The receptive fields of retinal ganglionic cells increase from the center towards the periphery and since these have closing and opening regions, action potentials are generated both at the moment of stimulation and when the stimulus is removed.
There are different types of ganglionic cells:
X cells These are generally found in the central area and react to sustained stimuli. They have a large capacity for spatial discrimination since their receptive fields are small and well defined.
Cells 4 With transitory response, these cells are of low discrimination and their receptive fields are extensive and poorly defined. They are highly sensitive towards large high-contrast objects.
W cells These are related to maintaining fixation.7
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Fig. 3: Fusion
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Fig. 4: Pink panther used as object for fixation
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DIAGNOSIS OF BINOCULAR DISORDERS
When testing binocular vision, oculomotor, binocular and accommodative performance are established through the estimation of the five components
  • The magnitude and direction of phorias at near and at distance.
  • Positive and negative fusional vergences.
  • The convergence amplitude (near point of convergence).
  • The sensory state to examine suppression and stereopsis.
  • Accommodative dysfunctions and ocular movements.
 
ACCOMMODATIVE PERFORMANCE
 
COVER TEST
This objective method used to evaluate the presence of phorias provides extensive information on binocular vision.
The cover test consists of occluding one of the patient's eyes and observing the type and magnitude of the ocular movements provoked. The test is performed at 33 cm so that the subject accommodates 3.00 D, and at 6 cm using images as the fixation target. Hypoaccommodation during the cover test, results in the overestimation of the degree of exophoria. Overaccommodation leads to the opposite effect.
To perform this test, certain basic conditions need to be fulfilled.
  • Central fixation and minimum visual acuity: Given that the basic principle of the cover test is refixation, sufficient central fixation and foveal visual acuity are needed to perceive the object of fixation
  • The patient needs to cooperate: For children, more than one figure or cartoons are used since each one stimulates attention for a few seconds only. A luminous object is usually used as the object of fixation although this is not the most appropriate since the appreciation of details of shape are not stimulated, accommodative adjustment by the subject is not induced and no information on accommodation/convergence conditions is provided. We therefore recommend the use of figures and a luminous stimulus.
There are several ways to perform this test:
  • Simple cover test—cover-uncover test
  • Alternating cover test—cover test using prisms
  • Cover-uncover test—simultaneous testing using prisms.
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Fig. 5: Prisms
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Fig. 6: Prisms
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Fig. 7: Worth's four dot test
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SUBJECTIVE TESTS TO ESTIMATE THE PRESENCE, DIRECTION AND MAGNITUDE OF PHORIAS
Main subjective tests
  • Von Graefe test
  • Maddox rod test
  • Modified Thorington test.
All these tests have their drawbacks—they are subjective and require the control of accommodation.
 
FIXATION DISPARITY TEST
The possible small deviation which may exist without diplopia is termed the disparity of fixation.
Disparity fixation tests are designed to evaluate binocular vision and are the method of choice for prismatic correction. The main tests are:
  • Mallet's unit test
  • Vectographic test
  • Boris card test
  • Bernell Lantern test
  • Sheedy's diasporameter test.
 
EVALUATION OF POSITIVE AND NEGATIVE FUSIONAL VERGENCE
Positive or negative fusional vergence may be estimated as follows:
  • Smooth vergence testing—to assess fusional vergence amplitude and recovery at both distant and near. The test estimates blur, break and recovery at distance and near, base-in and base-out.
  • Step vergence testing—to evaluate the amplitude of fusional vergence outside the horopter using a prism bar. This method is objective since loss of binocularity may be observed. It only estimates break and recovery using base-in and base-out at near and distance.
  • Jump vergence testing—to measure the dynamics of the fusional vergence system and the ability to respond over a period of time, in which rapid and repetitive vergence changes are made. It is a measure of resistance and it is this characteristic which is clinically assessed.
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MEASUREMENT OF THE NEAR POINT OF CONVERGENCE
Measurement of the near point of convergence is indispensable for the study of convergence insufficiency caused by:
  • Anatomical factors
  • Developmental factors
  • Deterioration in the patient's general state
  • Lack of use of accommodative convergence
  • Strabismus
  • Non-use of one eye
  • Vertical heterophoria
  • Convergence paralysis.
Two types of tests are used for its estimation.
 
CONVERGENCE JUMP TEST
The patient is requested to fix his/her sight on a small object at some 50 cm and then on a second object at 15 cm. The patient's eyes converge from the distant to the close object. Anomalous responses include:
  • Versional movements of both eyes
  • Slow or dubious convergence
  • Lack of movement.
A further test consists of slowly moving an object towards the eyes along the nasal line from a distance of 50 cm until the patient sees double or the examiner notices that the eye has stopped converging. Since elderly subjects have a near convergence point closer to the eyes than the near point of accommodation, they will see a blurred image before it becomes double.
 
EXTERNAL OPHTHALMOLOGICAL EXAMINATION
The following should be checked for in a general examination of the patient.
  • Compensatory head positions: tilting right, left, up or down
  • Strabismus
  • Exophthalmos and endophthalmos
  • Epicanthus and telecanthus
  • Anatomical asymmetry, malformations or signs of trauma
  • Ptosis or other palpebral anomalies
  • Signs of previous strabismus surgery.
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RETINOSCOPY AND REFRACTION
In binocular vision anomalies, it is of utmost importance to correct the refractive error. In many cases of heterophoria, no further treatment is required and in the case of accommodative strabismus it may be the main treatment. Thus, it is essential that the total refractive error is precisely determined.
Each eye should receive adequate correction such that a sharp retinal image is obtained. This correction should be balanced so that there is no need for either eye to accommodate.
This equilibrium may be subjectively achieved using
  • The balance in infinity or separator method
  • A polaroid vectographic method (Grolman, 1966)
  • An equalizing technique involving alternate occlusion
  • A “fogging” method.
 
MEASUREMENT AND EVALUATION OF DEVIATION
The first factor to be evaluated in heterophoria, is whether or not it is compensated by correction of near and distant vision.
In strabismus, the deviation angle of near and distant vision is determined with the corresponding refractive prescription and its effect on this angle evaluated.
In long-time strabismus, sensory adaptations aimed at alleviating diplopia and confusion may have developed. It is appropriate to evaluate.
  • Retinal correspondence using Bagolini striated lenses It is determined by placing a filter bar in front of the deviated eye until diplopia or suppression occurs.
  • Suppression It is determined by placing the filter bar in front of the eye which does not deviate until diplopia occurs.
When it is possible to induce physiological diplopia, this indicates a good prognosis.
 
SENSORY STATE
 
WORTH'S FOUR DOT TEST
This subjective test is highly precise for the evaluation of the presence and size of the suppression scotoma which is estimated by moving 4 points away from the patient. As the lantern is moved away from the patient, the fixation point tends towards a smaller angle. At 40 cm, the angle is approximately 6° (peripheral scotoma) at 1 m, the angle is around 1.5° and at 6 m the angle is 1°, indicating foveal scotoma.13
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Fig. 8: Titmus stereo test
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Fig. 9: TNO stereo test
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Fig. 10: Lang stereo test
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Red-green glasses are worn and the patient is asked how many points he or she sees. If the answer is 4 points, the lantern is placed at 1 m. If 4 points may be seen at 40 cm, and 2 or 3 points at 1 m, there is minor suppression scotoma. If 2 or 3 points are seen even at 40 cm, suppression scotoma is greater.
As the size of scotoma increases, the level of stereopsis diminishes.
 
ESTIMATION OF THE LEVEL OF SUPPRESSION
Level of suppression is measured using Worth test and suppression is considered to be more intense if present when the light is diminished. A small, intense suppression scotoma is more difficult to treat than a larger, less intense scotoma.
 
STEREOPSIS
Stereopsis allows simple, in-depth perception. The horizontal disparities of images which stimulate both retinas are responsible for the sense of stereopsis. Vertical disparities do not appear to be of major influence.
From an essentially psychophysical perspective, it has been maintained that local contours of peripheral images are the main informative elements for stereoscopic perception. The sensation of an eventual change in brilliance in each pair of coinciding contours should be the same in each retina.
 
EVALUATION OF STEREOPSIS
Evaluation of stereopsis is performed subjectively by estimation of total and contour (local) stereopsis.
Local or contour stereopsis: Two similar figures displaced sideways are used. The Titmus stereo test and the Wirt's stereo test are examples of this type of card. One of the disadvantages of this type of stereopsis cards is that patients without stereopsis may be capable of guessing the correct answer using monocular clues.
Global stereopsis: Global cards with random points and no monocular clues. It is thus difficult to guess the answer.
Another important difference between contour and global cards is their value in the detection of tropias.
The random point stereogram with a disparity of 660 seconds of arc is effective for the detection of a constant strabismus. However, using contour stereopsis cards, a constant strabismus may occasionally present a stereopsis of up to 70 seconds of arc.
Contour cards may be used to detect peripheral stereopsis. Any value above 60 seconds of arc is considered peripheral stereopsis. Thus, either type of stereoscopic test is valid.15
A patient with normal binocular function should be capable of attaining 20 seconds of stereopsis using contour stimuli and appreciate stereopsis with thick random point cards.
 
ACCOMMODATION
This is the distance from the farthest point (remote point) to the nearest point (near point) in diopters, or the ocular capacity to focus at different distances. It should be measured with correction for far sight.
The most common exploratory method involves the use of a card which is slowly moved towards the eye until the patient cannot maintain a sharp image. This card is mounted on a ruler from which the distance in diopters may be read.
In the young patient with a very close near point, a negative lens of −4.00 is placed in front such that the accommodative range is displaced towards the center of the 1,00 mark. The value of this sphere is then added to the measurement.
The amplitude of accommodation diminishes with age from 10 to 65 years. It is the minimum value of dispersion of amplitude which is of clinical significance in normal subjects of any age group.
 
PUPILLARY REFLEXES
The presence of anomalies in pupillary reflexes may aid in the diagnosis of binocular problems arising from neurological disorders. It is, therefore, necessary to examine the response of the pupils to light and to near vision.
The pupillary light reflex is determined by projecting light in one eye and observing the contraction of the pupil. At the same time, contraction may be noted a pupillary in the other eye. This process is repeated in the opposite eye.
The pupillary near reflex is tested by requesting the patient to look at a distant object and then a further object placed at some 25 cm from the eyes. Pupillary constriction accompanying accommodation and convergence are observed.
 
EYE MOVEMENTS
There are four possible movements of the eyes. These occur simultaneously although they are subject to neurological control. Saccadic, persecution and vergence movements are provoked by visual stimuli while postural movements are independent of vision.16
Saccadic movements are the fastest that the oculomotor system may achieve. Their function is to direct a glance from one object to another within the visual field as rapidly as possible. These movements are performed by both eyes to the same degree and in the same direction. The aim is to position the image of a visual stimulus on the fovea. The cortical center of saccadic movements is probably the contralateral frontal lobe.
Persecution or following movements are those aimed at maintaining the image of an object which has stimulated us on the fovea, whose speed is no greater than 45° second. Above this velocity, saccadic movements appear. Persecution movements are fairly vulnerable and may be abolished by drugs, asthenopia, lack of attention and diffuse cerebral lesions. Cortical centers for persecution movements are in the ipsilateral parieto-occipital region.
Vergence movements are slow movements of the eyes in the same direction and in the inverse direction, aimed at establishing relative position to enable images of objects located at different distances from the subject to impress upon the corresponding regions of the retina, thus achieving sensory fusion.
Postural movements are those comprised of reflex rather than optical mechanisms and are coordinated by the vestibular apparatus and by tonic cervical reflexes. These movements are of short latency and their speed is 300° second.
 
BINOCULAR VISION ANOMALIES
There are three types of anomalies.
 
BINOCULAR ANOMALIES
  • False convergence insufficiency
  • Divergence insufficiency
  • Convergence insufficiency
  • Fusional vergence dysfunction
  • Exophoria and endophoria
  • Vertical phorias
  • Convergence excess
  • Divergence excess
 
ACCOMMODATIVE ANOMALIES
  • Accommodative insufficiency
  • Accommodative excess
  • Accommodative inflexibility
 
OCULOMOTOR ANOMALIES
Oculomotor anomalies can occur.17
 
BINOCULAR ANOMALIES
 
CONVERGENCE INSUFFICIENCY
Defining factors are:
  • Exophoria at near
  • Orthophoria at distance
  • Remote near point of convergence
  • Low CA/A (convergence accommodation/accommodation) ratio
  • Reduced positive fusional vergence at near.
Main symptoms appear during reading or other near vision tasks and are on the increase since the wide use of computers. These include asthenopia (ocular fatigue), blurred vision, drowsiness, double vision, difficulty in concentrating, sensation of ocular oppression and of movement of letters while reading. Children reject reading.
 
Treatment
  • Removal of the etiological factors which might lead to decompensation (general health of the patient, work conditions).
  • Prescription of near vision glasses in convergence insufficiency with accommodation insufficiency in adolescent patients. Base-in prisms and correction of myopic defects in children.
  • Orthoptic treatment—pencil-nose type exercises, physiological diplopia exercises, autoperforming of the convergence jump test by the patient and computerized orthoptic tests. Adequate convergence is normally achieved at 3 to 6 weeks.
 
FALSE CONVERGENCE INSUFFICIENCY
False convergence insufficiency should be distinguished from real convergence insufficiency.
Patients present with asthenopia, blurred vision, and tension in the neck, and symptoms of general fatigue.
Key factors for a differential diagnosis are:
  • Orthophoria at far
  • Exophoria at near
  • Low CA/A ratio
  • Low base-out fusional vergences a near.
Treatment is orthoptic and involves the use of base-out prisms to stimulate accommodation.18
 
DIVERGENCE INSUFFICIENCY
Slight distance and near endophoria with normal versions and reduced divergence at far.
Possible causes are:
  • Uncorrected hypermetropia
  • Lack of tone of internal recti muscles
  • Anatomical factors
  • Change in emotional or neurotic state
  • Use of stimulants
  • Anoxia
  • Pathological alterations of the central nervous system.
Symptoms include: far vision fatigue, blurred vision, intermittent diplopia at distance, ocular pressure end-of-day nausea, sensitivity to light, difficulty in far-near focussing, and car and train sickness and vertigo.
 
Diagnosis
  • Greater far endophoria than near
  • A reduced CA/A ratio
  • Reduced negative fusional vergences at distance.
It may be considered a mild disorder of binocular vision.
It is important to base the differential diagnosis on the excess of convergence, the basic endophoria, paralysis of a cranial nerve and paralysis of divergence.
 
Treatment
Eliminating the causes of decompensation by improving visional conditions at work. Since the most common cause of this decompensation is uncorrected hypermetropia, correction of all the hypermetropia in children and adolescents with cycloplegic prescription and the constant use of this correction both for distance and near vision normally resolves the symptoms and the endophoria.
If this is not effective, orthoptics may be used and the patient is taught to appreciate physiological diplopia and to perform exercises which increase the negative fusional reserve and positive relative accommodation.
Prisms are only necessary in a minority of cases with the power of the prism being that which compensates the endophoria. The prism should be of the minimum power that leads to a smooth, rapid recovery in the cover test.
 
CONVERGENCE EXCESS
Convergence excess is one of the most common nonstrabismic binocular vision problems.19
It includes:
  • Greater near endophoria than distance
  • High CA/A ratio
  • Greater frequency of deviation at near than at distance
  • Reduced smooth negative fusional vergences at near
  • Reduced jump negative fusional vergence.
The main symptom is cefalalgia and ocular tension while reading, inability to concentrate on reading, occasional double vision and blurred vision.
The causes are: an excessive accommodative effort due to uncorrected hypermetropia, an accommodation spasm or pseudomyopia. It may also appear in episodes of hysteria, psychological stress and anxiety.
An incipient presbyopia can give rise to an excess of convergence due to the large effort made to accommodate.
In most cases, a change in work habits is sufficient to resolve the symptoms. Correction of the hypermetropia using cycloplegic refraction for near and distance is a treatment option. At first, the patient sees blurred at distance although the image becomes sharper as the latent hypermetropia is manifest. This process can take from 1 hour to several days.
In some cases, bifocals will be prescribed to abolish the endophoria in near vision. These should be reviewed each 3 to 6 months to reduce the near addiction until abolished.
In incipient presbytia, in which there are symptoms of convergence excess, spectacles for near vision will be prescribed.
If following refractive correction, symptoms persist, orthoptic exercises will be required to develop the positive relative accommodation.
Prisms are not indicated.
 
DIVERGENCE EXCESS
Divergence excess appears as an exophoria of great magnitude in far vision and in some cases, as a divergent strabismus. It normally occurs in women and is of unknown etiology.
Main characteristics are:
  • High CA/A ratio
  • Normal positive fusional vergence at distance and near
  • No significant refractive error
  • Concomitant deviation
  • Suppression at distance.
The most common symptom is the deviation of one eye, photophobia and the winking or occlusion of one eye in bright sunlight.20
 
Treatment
Refractive correction is of no great help. On occasion, the use of sunglasses proves useful.
Orthoptic treatments of choice include those which treat the suppression, develop base-out prism vergences, develop the relative negative accommodation and those which stimulate a correct appreciation of the physiological diplopia. The use of prisms does not give good results since near vision is altered.
 
BASIC EXOPHORIA
Principal signs are:
  • Remote near point of convergence
  • Same far exophoria than near
  • Normal CA/A ratio
  • Reduced direct and indirect tests of positive and negative fusional vergence at distance and near.
Symptoms normally arise in near vision tasks and include cefalalgia and ocular tension, distance and near blurred vision, distance and near intermittent diplopia, drowsiness, difficulty in concentrating, sensation of ocular oppression and movement of letters while reading.
Most frequent etiological factor are:
  • Anatomical factors which lead to the normal position of anatomical rest, i.e. divergence
  • Hypertonic abductor muscles
  • Myopia
  • Age (elderly patients commonly present decompensated exophoria in near vision)
  • Patients with very high hypermetropia who are incapable of compensating their refractive error through accommodation
  • Small degrees of hypermetropia in incipient presbyopia.
Refractive treatment may contribute to compensation of the exophoria both in cases of myopia and in those of absolute hypermetropia. In patients in whom correction of the hypermetropia provokes decompensation of the exophoria, partial correction is prescribed.
The most appropriate correction is that which manages to compensate the exophoria and eliminate its symptoms. In patients with presbytia, the prescription should be as low as is compatible with adequate vision.
Orthoptic treatment is performed in patients under 20 years of age and consists of exercises which develop base-out prism vergences and negative relative accommodation, and those which achieve correct appreciation of the physiological diplopia or eliminate the suppression.21
Treatment with prisms is the most appropriate, particularly in adults. The power of the prism is that which ensures compensation of the exophoria. The best measure of prismatic power is subjective.
 
BASIC ESOPHORIA
Basic esophoria emerges as a decompensated esophoria of approximately the same value at distance than at near. The CA/A ratio is normal and it most commonly occurs in hypermetropia. Both direct and indirect negative fusional vergence tests are reduced.
Symptoms include ocular fatigue in distance and near work, cefalalgias, end-of-day ocular tension and intermittent blurred vision at near and distance.
Its etiology may be considered the same as that of divergence insufficiency and convergence excess. The indicated treatment for both is the same as for basic esophoria and the condition is consequently also known as mixed esophoria.
 
HYPERPHORIAS
Hyperphorias are latent upward deviations of one eye which become manifest deviations as the eyes dissociate.
Symptoms may be ocular, visual or referred. Ocular or asthenopic symptoms in vertical phorias are usually burning sensation, car-sickness, ocular tension, headache. Visual symptoms include difficulty in reading. Referred symptoms are nausea, vertigo, vomiting and nervousness.
Diagnostic signs are tilting the head and changing the astigmatic axis of refraction from distance to near.
Primary hyperphoria is mainly due to small defects of the eyes, orbits and muscle insertion points. Diagnosis involves the cover test, the balance in infinity test and tests of fixation disparity.
In most cases, correction of the refractive error is sufficient. Orthoptic treatment is rarely successful.
The majority of primary hyperphorias may be alleviated by means of small power vertical prisms. The lowest power prism which levels the letters in the balance in infinity test should be prescribed.
 
ACCOMMODATIVE ANOMALIES
 
ACCOMMODATIVE INSUFFICIENCY
Accommodative insufficiency involves a difficulty in stimulating accommodation. The main characteristics is an accommodative amplitude below the lower limit. When we talk about accommodative insufficiency we 22refer to a condition which affects prepresbyopes, given that the symptoms of presbyopia are identical to those of this condition.
Three subclassifications have been described.
  • Poorly sustained accommodation in which accommodative amplitude is normal at first but deteriorates with time.
  • Accommodation paralysis This is extremely rare and associated with several organic causes such as diabetes, saturnism, infections, glaucoma, trauma, etc.
  • Unequal accommodation whereby the accommodative dysfunction is only unilateral. Functional amblyopia is an example.
Accommodative insufficiency represents 84% of all accommodative abnormalities. Symptoms generally affect reading or other long duration near vision activities and include blurred vision, headache, ocular tension, reading problems, fatigue and drowsiness, reduced comprehension, sensation of tightness around the eyes, movement of letters.
Both direct and indirect results of measurements of accommodative stimulation are reduced.
Differential diagnosis of accommodative insufficiency should be performed with pseudoconvergence insufficiency, basic exophoria, divergence excess, accommodative excess and accommodative inflexibility.
Treatment consists of correction of the ametropia under cycloplegia.
Glasses with plus sphere correction leads to benefits, especially when the cause is organic, as a temporary solution while the cause is being treated.
 
ACCOMMODATIVE EXCESS
Accommodative excess is a difficulty in relaxing accommodation. It is also known as ciliary spasm, accommodative spasm, pseudomyopia.
Most of its symptoms are related to reading and other near work and are practically the same as those of accommodative insufficiency with the additional photophobia and blurred vision also at distance. Further, symptoms vary throughout the day, being worse at the end of the day.
Differential diagnosis should be performed with convergence excess, basic endophoria, accommodative insufficiency and accommodative inflexibility. Principal non-functional causes are cholinergic drugs, morphine and digitalis. In adults, encephalitis, and in children influenza, encephalitis and meningitis.
Treatment involves correction of the ametropia. As refractive errors of small magnitude are corrected, symptoms are immediately alleviated.
Glasses with positive sphere are not beneficial (differential diagnosis with accommodative insufficiency).23
 
ACCOMMODATIVE INFLEXIBILITY
Accommodative inflexibility is the difficulty the patient has in changing the accommodative response level. Amplitude is normal, but the patient is unable to make use of it rapidly or over long periods of time.
The main symptoms is difficulty in focussing from distance to near and vice versa. It is also associated with intermittent blurred vision, difficulty in reading attention and asthenopia at near.
Treatment consists of precise correction of the ametropia.
The differential diagnosis needs to be performed with convergence excess, basic endophoria, accommodative insufficiency and accommodative excess.
 
OCULOMOTOR ANOMALIES
In oculomotor dysfunction, the three areas of oculomotor function are simultaneously affected.
Main symptoms become apparent while reading, with excessive head movements, loss of place when reading, omission of words, jumping of lines, slow reading speed, poor comprehension, difficulty in copying from the board, etc.
It may be functional or secondary to anomalies of the centers of supranuclear control due to neurological causes.
Treatment consists of correcting the ametropia.