Ophthalmology
Question 73 of 97
A 43 year old woman presents to the Emergency Department complaining of 3 days of visual disturbance in the left eye. On examination you note that a torch shone into the left eye does not elicit constriction of either the right or left pupils. When a torch is shone into the right eye both pupils constrict. Damage to which nerve is responsible for this abnormal examination finding?
Answer:
Optic nerve damage on the left (e.g. transection of left optic nerve, CN II, somewhere between retina and optic chiasma, therefore damaging the left afferent limb, leaving the rest of the pupillary light reflex neural pathway on both sides intact) will have the following clinical findings:- The left direct reflex is lost. When the left eye is stimulated by light, neither pupils constrict. Afferent signals from the left eye cannot pass through the transected left optic nerve to reach the intact efferent limb on the left.
- The right consensual reflex is lost. When left eye is stimulated by light, afferent signals from the left eye cannot pass through the transected left optic nerve to reach the intact efferent limb on the right.
- The right direct reflex is intact. Direct light reflex of right pupil involves the right optic nerve and right oculomotor nerve, which are both intact.
- The left consensual reflex is intact. Consensual light reflex of left pupil involves the right optic nerve and left oculomotor nerve, which are both undamaged.
Cranial Nerve Palsy
Neurology / Ophthalmology
Last Updated: 18th August 2022
Cranial nerve II: Optic nerve
| Cranial Nerve | Optic Nerve (CN II) |
|---|---|
| Key anatomy |
|
| Function |
|
| Assessment |
|
| Clinical effects of injury |
|
| Causes of injury |
|
Cranial nerve III: Oculomotor nerve
| Cranial Nerve | Oculomotor Nerve (CN III) |
|---|---|
| Key anatomy |
|
| Function |
|
| Assessment |
|
| Clinical effects of injury |
|
| Causes of injury |
|
Cranial nerve IV: Trochlear nerve
| Cranial Nerve | Trochlear Nerve (CN IV) |
|---|---|
| Key anatomy |
|
| Function |
|
| Assessment |
|
| Clinical effects of injury |
|
| Causes of injury |
|
Cranial nerve VI: Abducens nerve
| Cranial Nerve | Abducens nerve (CN VI) |
|---|---|
| Key anatomy |
|
| Function |
|
| Assessment |
|
| Clinical effects of injury |
|
| Causes of injury |
|
Report A Problem
Is there something wrong with this question? Let us know and we’ll fix it as soon as possible.
Loading Form...
- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
